Documentary reconstruction of monsoon rainfall variability over western India, 1781-1860

George C.D. Adamson and David J. Nash

G.C.D. Adamson

School of Environment and Technology, University of Brighton,Lewes Road, Brighton BN2 4GJ, UKe-mail: g.adamson@brighton.ac.uk

D.J. Nash

School of Environment and Technology, University of Brighton,Lewes Road, Brighton BN2 4GJ, UK

and, School of Geography, Archaeology and Environmental Studies,University of the Witwatersrand, Private Bag 3, Wits 2050, South Africae-mail: d.j.nash@brighton.ac.uk

Abstract

Investigations into the climatic forcings that affect the long-term variability of the Indian summer

monsoon are constrained by a lack of reliable rainfall data prior to the late 19 th century. Extensive

qualitative and quantitative meteorological information for the pre-instrumental period exists within

historical documents, although these materials have been largely unexplored. This paper presents

the first reconstruction of monsoon variability using documentary sources, focussing on western

India for the period 1781-1860. Three separate reconstructions are generated, for (i) Mumbai, (ii)

Pune and (iii) the area of Gujarat bordering the Gulf of Khambat. A composite chronology is then

produced from the three reconstructions, termed the Western India Monsoon Rainfall

reconstruction (WIMR). The WIMR exhibits four periods of generally deficient monsoon rainfall

(1780-85, 1799-1806, 1830-1838 and 1845-1857) and three of above-normal rainfall (1788-1794,

1813-1828 and 1839-1844). The WIMR shows good correspondence with a dendroclimatic drought

reconstruction for Kerala, although agreement with the western Indian portion of the tree-ring

derived Monsoon Asia Drought Atlas is less strong. The reconstruction is used to examine the

long-term relationship between the El Nino-Southern Oscillation (ENSO) and monsoon rainfall over

western India. This exhibits peaks and troughs in correlation over time, suggesting a regular long-

term fluctuation. This may be an internal oscillation in the ENSO-monsoon system or may be

related to volcanic aerosol forcings. Further reconstructions of monsoon rainfall are necessary to

validate this. The study highlights uncertainties in existing published rainfall records for 1817-1846

for western India.

Keywords: Summer monsoon; documentary reconstruction; ENSO; western India

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1 Introduction

Unravelling the climatic forcings that drive variability in the Indian monsoon is of vital importance

given the fundamental role of monsoon rains in the economy of the subcontinent. Current thinking

holds that monsoon rainfall variability is affected by internal intraseasonal and interannual

fluctuations (Gadgil and Srinivasan 1990; Krishnan et al. 2000; Annamalai and Slingo 2001; Gadgil

2003), as well as teleconnections with tropical/subtropical atmospheric-ocean circulation patterns

such as the Indian Ocean Dipole (IOD) (Saji et al. 1999; Ashok et al. 2001; Ashok and Saji 2007)

and El Niño-Southern Oscillation (ENSO) (Cole et al. 2000; Krishnamurthy and Goswami 2000;

Fasullo and Webster 2002; Goswami and Xavier 2005; Krishna Kumar et al. 2006; Lim and Kim

2007). Understanding the exact nature of these relationships on interdecadal timescales is

important in order to enable robust long-term forecasting. However, this is constrained by an

absence of reliable meteorological information from the subcontinent before the late 19 th century.

For example, debate is currently ongoing as to the nature of the relationship between ENSO and

monsoon rainfall. Whilst some studies suggest a weakening in the ENSO-monsoon relationship

due to recent warming (Krishna Kumar et al. 1999; Kinter et al. 2002), others point towards longer-

term fluctuations, with periods of unusually strong coupling from c.1885-c.1910 and c.1965-c.1980

and weaker correlation during other periods (Torrence and Webster 1998; Maraun and Kurths

2005; Robinson et al. 2008). It is not possible to reconcile these arguments when dealing with a

dataset for India as a whole that goes back no further than 1871.

The first systematic rainfall observations in India started at Madras in 1813. However, by the

time meteorological records began to be collected at the Colaba Observatory in Bombay in 1843,

the number of rain gauges in India was only 11 and a national gauging network did not appear until

1871 (Sontakke et al. 2008). Regional rainfall reconstructions prior to 1871 (Sontakke et al. 2008)

rely on statistical inferences using this small network of gauges. Climatic reconstruction using

natural proxies is also problematic within peninsular India. Reconstructions using ice-cores are

feasible only within the Himalayan regions, and dendroclimatological investigations are challenging

due to a lack of clearly defined growth rings in the majority of indigenous species. Climatic

reconstruction using teak is being developed, but this research is still only in its infancy (see

Bhattacharyya and Yadav 1999; Ram 2011).

The reconstruction of historical rainfall levels in India is possible using documentary sources

(see Nash and Endfield 2002, 2008; Nash and Grab 2010; Nicholson et al. 2012). Europeans

resident during the late 18th and early 19th centuries, including representatives of the British East

India Company (EIC) and western missionary societies, recorded a wealth of climatic information

on a non-systematic basis. This ranged from detailed weather diaries to ad hoc climatic

observations in personal letters and commercial/government records, reflecting the fascination with

tropical climates exhibited by colonists (Grove 1997; Harrison 1999; Endfield and Nash 2002;

Adamson 2012). Much of this information survives within archives in the UK, India and USA, but,

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with few exceptions (e.g. Pant et al. 1993; Walsh et al. 1999; Adamson and Nash 2012), has been

unexplored as a climatic resource.

This study extends the climatic record for the subcontinent by synthesising meteorological

information contained within historical documents to produce a semi-quantitative reconstruction of

monsoon rainfall variability in western India (Figure 1) for the period 1781-1860. Western India has

been selected as the study area for two reasons. First, abundant historical English-language

sources are available, including newspapers, materials relating to the EIC and, from 1823,

extensive documentation written by missionaries. Second, rainfall levels in the meteorological

subdivisions of ‘Konkan and Goa’ and ‘Gujarat’ are highly correlated at interannual timescales with

Niño-3.4 sea surface temperature (SST) anomalies (correlation coefficient = ~0.45; Parthasarathy

et al. 1993), which are understood to be a driver of rainfall variability over India (Krishnamurthy and

Goswami 2000; Fasullo and Webster 2002; Krishna Kumar et al. 2006; Lim and Kim 2007).

In this paper, seasonal monsoon rainfall indices are derived using historical documentary

materials and calibrated against available instrumental rainfall data. Indices are generated for three

reconstruction areas: (i) Mumbai, (ii) Pune, and (iii) an area of southern Gujarat bordering the Gulf

of Khambat (hereafter referred to as the ‘Gulf of Khambat’). The three reconstructions are

combined to produce a composite chronology for the entire study area, termed the Western India

Monsoon Rainfall reconstruction (WIMR). The WIMR chronology is compared to two

dendroclimatic studies and a regional rainfall reconstruction based on statistical inferences from a

small network of rain gauges. We conclude with a consideration of the implications of our results

for the understanding of ENSO-monsoon dynamics over time.

2 Climatology of western India

The rainfall regime of western India is dominated by the southwest monsoon. Winter circulation in

the region is characterised by lower-tropospheric northeasterlies, producing a net continent-ocean

flow. Thermal insolation generates a lower-tropospheric heat low over the Thar Desert to the north

of the study area during March-May (Gadgil 2003), which, together with the migration of the

Tropical Convergence Zone, drives the monsoon (Gadgil and Srinivasan 1990; Srinivasan et al.

1993; Annamalai and Slingo 2001; Lawrence and Webster 2001). Monsoon onset occurs in

Mumbai on 10 June (1781-2011 mean; Adamson and Nash 2012) as the zone of maximum

convection migrates northwards from its winter position at 0°-5°N to its mean summer latitude of

20°N (Gadgil 2003). Rains may occur before this date, particularly in coastal regions, due to the

action of onset vortices formed over the Arabian Sea (Mooley and Shukla 1987).

The monsoon season generally lasts until late-September or mid-October. Rainfall in western

India is sourced predominantly from subtropical cyclones, which develop over the northeastern

Arabian Sea and are driven by a low-level westerly jet, the cross-equatorial Somali jet, which forms

in late May (Mohanty et al. 2005). Deflection of air over the Western Ghats causes conditional

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instability (Grossman and Durran 1984), resulting in an area of rainfall maximum located just off

the west coast (Krishnamurti et al. 1983). Mumbai lies within this maximum and receives around

2000mm rainfall per year, predominantly falling during the monsoon months (Bhowmik et al. 2008).

The Deccan region is situated in the rain shadow zone to the east of the Western Ghats and

receives significantly lower rainfall than adjoining coastal areas (Gunnell 1997). Precipitation is less

regular in the Deccan than in coastal regions, although this phenomenon is more marked to the

south of the study area (Gunnell 1997). Rainfall in northern parts of the study area originates from

depressions formed in the Bay of Bengal, which are transported across the subcontinent by the

upper easterlies (Gadgil 2003). These form twice a month on average and propagate in a westerly

direction, with a lifespan of approximately 5 days (Yoon and Chen 2005). Depressions are weak by

the time they reach the study area, resulting in low average rainfall in this region (~550mm per

year; GHCN 2010).

During the monsoon season, western India experiences ‘active’ periods of rainfall separated by

‘break’ periods of several days duration when little or no rainfall occurs. The timing and duration of

break periods is subject to the position of the zone of maximum convection. This zone is normally

located at a mean latitude of 25°N during the monsoon season, but periodically migrates

northwards to 30°N, bringing heavy rainfall to the southern Himalaya and reduced precipitation

over the remainder of the country (Krishnamurthy and Goswami 2000). Break periods are also

generally associated with the production of new zones of maximum convection at 5°N, which then

commence a northward propagation and lead to a return to active conditions (Gadgil 2003).

Easterly anomalies (Krishnamurthy and Shukla 2000), and a weakening in lower tropospheric

vorticity (Goswami et al. 2003), result in 75-85% departures from the long-term average rainfall

during break periods in the study region (Gadgil 2003). The region of the Western Ghats is the first

area to experience increased rainfall at the recommencement of active periods (Krishnan et al.

2000; Krishnamurthy and Shukla 2007).

3 Data sources

The locations of the main archives consulted for this study, together with the coding used to cite

individual sources in the text, are provided in Table 1. The archive consulted most extensively was

the India Office Records collection housed in the British Library, St Pancras, London, UK. This

archive contains the records of the EIC, which comprises of copies of correspondence and minutes

sent either as annual reports or synthesised into volumes relating to specific events. Three

volumes on drought conditions were particularly useful, covering droughts in 1812-13, 1823-25 and

1832-33. A travel diary by a Dr Anton Hove, entitled ‘Tours for Scientific and Economical Research

of Guzerat-Kattiawar and the Conkuns, in 1787-88’ (BL IOR/V/22/212 No. 16) was also consulted

in depth. The British Library at St Pancras additionally contains an extensive collection of Private

Papers, which includes letters, diaries, scrapbooks and personal business records from individuals

or families who were resident in India during the colonial period. All Private Papers containing

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materials relating to western India during the study period were consulted, comprising thirty

volumes.

The British Library Newspaper Collection, Colindale, London, was also consulted. This archive

contains microfilmed back-issues of English-language newspapers from Mumbai. The earliest

available newspaper was the Bombay Gazette, which has issues stored from August 1792,

although the holdings of this publication are incomplete. The primary newspapers used for this

study therefore were the Bombay Courier and Bombay Times. The Courier was published from

1793 until 1846. Meteorological information within the Courier was sparse during the last two years

of its publication, so from 1844 to 1860 the Times was used as the main newspaper source. For

years where meteorological information was lacking within these publications, or where issues

were missing, issues of the Bombay Gazette and later the Bombay Monthly Times and Bombay

Standard were consulted. The publication frequency of the various non-monthly newspapers

increased almost simultaneously, rising from weekly in 1793 to twice weekly in 1835, thrice weekly

from 1840 and daily from 1850. All newspapers followed generally the same format, with stories

often repeated in several publications. The quality of meteorological information and the

terminology adopted was therefore very similar between publications. From 1833, all newspapers

included identical fortnightly State of the Weather and the Crops reports (see Table 2).

A number of other collections of historical documents were explored in addition to materials held

in the British Library. These included the archives of three western missionary associations: the

Church Missionary Society, American Board of Commissioners for Foreign Missions and Scottish

Missionary Societies (Table 1). Documentation within these archives consists of reports and letters

from missionaries in the field to their respective central offices, together with some private

correspondence. The archives of the Government of Maharashtra, located at Elphinstone College,

Mumbai, India, were consulted for the records of the colonial Government of the Bombay

Presidency. These comprise predominantly of letters, minutes, official proclamations and circulars,

and petitions from the local population. Miscellaneous materials within the National Archives of

Scotland, and the archives of the Royal Society, London, and Aberdeen Medico-Chirurgical

Society were also analysed.

Some previously published materials, mainly scholarly articles published during the late 18th and

early-mid 19th centuries, were used as primary sources. These included two weather diaries that

appeared in the Transactions of the Royal Society (Banks 1790; Sykes 1835) and a weather diary

and famine report published in the first edition of the Transactions of the Literary Society of

Bombay (Carnac 1819; Nicholls 1819). A synthesis of information on famines in colonial western

India, the Report of Past Famines in the Bombay Presidency, was the only secondary source

utilised (Etheridge, 1868). This was originally collated from oral and written records, and was

published eight years after the end of the study period.

4 Methodology5

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4.1 Data collection and sorting

Information on climate or climate-dependent phenomena within each historical source was

recorded verbatim. This included direct references to climatic conditions, as well as reports of

droughts and floods. Reports of harvests yields were also recorded as a broad indicator of

seasonal rainfall levels, particularly those included within the State of the Weather and the Crops

sections of Mumbai newspapers from 1833 onwards (see Table 2). For each observation, the

author, place of publication, location referred to, date written, date (range) referred to, and recipient

(if applicable) were recorded in a central database. Information included within individual sources

ranged from general comments on the conditions during a season to daily weather accounts within

systematic or semi-systematic weather diaries. Instrumental temperature and pressure readings

were also sometimes included. Certain documents were used extensively for climatic

reconstruction due to the quality and quantity of information recorded (Table 2).

Recorded information was sorted into monthly blocks by location. Climatic reconstruction was

undertaken for three areas (Figure 1). The ‘Mumbai’ region comprises approximately the

contemporary area of Greater Mumbai, including the 19th century Bombay Island together with

Salsette and Colaba. The region of ‘Pune’ comprises the administrative district of Pune, including

the present day city. The ‘Gulf of Khambat’ region incorporates the administrative divisions of

Surat, Bharuch, Vadodara, Anand, Kheda, Ahmadabad and Bhavnagar that surround the Gulf.

Where no other data were available, information from the peninsular of Kathiawar was also used

for the Gulf of Khambat reconstruction. The number of datapoints (i.e. individual quotations) used

for monsoon reconstruction for each of the three areas, together with the number of sources from

which these quotations were derived, is summarised in Figure 2.

Quotations were used to produce summaries of rainfall conditions during the monsoon for each

of the reconstruction areas. Four ‘monthly’ summaries were created for the monsoon period:

May/June; July; August; and September/October (hereafter referred to as the ‘rainfall months’).

May and June were combined to allow for fluctuations in the date of monsoon onset, which

generally occurred during early-mid June but occasionally in late May (cf. Adamson and Nash

2012). Rainfall associated with cyclonic activity before the date of onset was not included.

September and October were combined to take into account variations in the end-monsoon date.

An example of a monthly summary table for the Mumbai reconstruction area during the monsoon

season of 1853 is provided in Table 3.

4.2 Generation of calibration tables

Calibration of the reconstruction was undertaken where reliable instrumental data overlapped with

the documentary record. For Mumbai, the Global Historical Climatology Network (GHCN) publishes

homogenous monthly instrumental data collected at the Colaba Observatory from 1847. Data

spanning the monsoon months only are also available from 1817; however, our archival

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explorations have revealed that these data may be unreliable. The data derive from a network of

rain gauges across Mumbai, published in newspapers; published monthly data are not always

derived from the same gauge and in some years are averages of several gauges. Furthermore, no

evidence exists as to the ways in which these data were collected or the instruments used. The

data are therefore likely to contain inhomogeneities. As a result, a 13-year calibration period was

selected for the Mumbai reconstruction, encompassing 1847-1859. For Pune, the GHCN publishes

homogenous instrumental rainfall data collected at the Poona Observatory from 1856. Five years

of rainfall data are also available from 1826-1830. These were collected as part of Colonel Henry

Sykes’ reports on the Statistic of the Deccan (BL MSS Eur K388) and can be assumed to be

reliable with a high degree of confidence. A 10-year calibration period was therefore selected for

the Pune reconstruction, comprising the years 1826-1830 and 1856-1860. No instrumental data

are available for the Gulf of Khambat during the study period so calibration was not possible for

this region.

Calibration was achieved by first assigning a 5-point monthly rainfall index value – ranging from

-2 (‘scanty rainfall’) to +2 (‘heavy rainfall’) – to each month within the two calibration areas. Indices

were assigned based on instrumental data, using categories adopted by the Indian Meteorological

Department (IMD) to describe rainfall variability at short intervals (Table 4). The boundaries of each

category were delimited by percentage deviations from a Long Period Average (LPA) of monthly

rainfall. The LPA was calculated using data from 1847-1950 for Mumbai and from 1826-1830 and

1856-1950 for Pune. This is different to the LPA currently used by the IMD – an average of the last

30 years – and was selected in order to (i) incorporate the calibration periods and (ii) avoid any

recent changes in the rainfall regime which may have occurred due to anthropogenic warming

(Robertson et al. 2001) or multidecadal fluctuations in rainfall intensity (Parthasarathy et al. 1987;

1994; Guhathakurta and Rajeevan 2008). These LPAs are used for all further analyses in this

paper.

Documentary information for rainfall months falling within each index class was analysed to

determine key descriptors and conditions associated with each category. For example, in Mumbai,

five rainfall months during the calibration period were classified as +1 (excess rain). Content

analysis of documentary material revealed that this particular rainfall class was associated

regularly with (i) the descriptor ‘seasonable rain’, (ii) slight crop damage due to flooding, and (iii)

periods of heavy rainfall interspersed with drier intervals. This information was used to generate

calibration tables detailing the predominant rainfall properties and descriptors associated with each

index category. The calibration table for Mumbai is presented in Table 5. The calibration table for

Pune was the same as for Mumbai, with the exception that ‘moderate/more or less’ was used

regularly by observers to refer to average rainfall, ‘satisfactory’ to above average rainfall, and

‘sufficient’ to excess rainfall. As no calibration was possible for the Gulf of Khambat, it was

assumed that descriptors for this reconstruction area had the same meaning as for Mumbai, since

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the climatic regime in southern Gujarat is more similar to that of Konkan than the western Deccan

Plateau (Gadgil and Joshi 1983; Gunnell 1997).

4.3 Classification of rainfall across the reconstruction period

Where meteorological descriptions within the documentary materials were of sufficient quantity and

quality, the calibration tables were used to classify rainfall months across the reconstruction period.

Full monthly reconstruction was possible from 1833 onwards. Prior to this date, some years had

either very few quotations, or quotations that were not sufficiently detailed to allow for classification

of rainfall intensity at the monthly scale. Coverage was particularly sparse prior to 1811.

The derived monthly classifications were used to generate seasonal classifications (May-

October), in order to represent rainfall variability during an entire monsoon. The IMD uses a 5-point

index scale to classify rainfall at the seasonal scale, referred to as the 5-Parameter Statistical

Ensemble Forecasting System (5-PSEFS; Table 6). Like the weekly/monthly rainfall descriptors

shown in Table 4, the 5-PSEFS ranks rainfall according to deviation from a LPA, although the

percentage brackets are narrower to reflect the lower variability of rainfall at the seasonal scale. In

order to maintain continuity with IMD terminology, a methodology was devised to convert monthly

indices to seasonal. Monthly rainfall data within the instrumental period (post-1847 for Mumbai,

post-1856 for Pune and post-1871 for the Gulf of Khambat) were first “degraded” into the 5 monthly

classes shown in Table 4. This was achieved by assigning descriptive rainfall classes for each

month according to the deviation of rainfall from the LPA for that month. Seasonal (MJJASO)

rainfall within the instrumental record was also degraded into the classifications used in the 5-

PSEFS. (Where this approach is used in this paper, the resulting monthly and seasonal rainfall

data are referred to as “degraded instrumental data”.)

Several methods were attempted to determine the optimal relationship between the monthly

and seasonal classes. The method that produced the highest correlations involved summing

monthly values and assigning a seasonal classification accordingly. Where the summed monthly

values were -1, 0 or +1, these classifications were assigned to the season overall; years with

summed values of ≥ +2 or ≤ -2 were assigned a category of +2 or -2 respectively. This approach

produced Pearson’s correlation coefficients of 0.79 for Mumbai and 0.85 for Pune (significant at

99%).

For some years, meteorological descriptions were insufficient in number and/or detail to allow

for reconstruction using the monthly calibration table. Quotations, however, often existed that

described conditions across the entire season. For example, only one quotation is available for the

monsoon at Pune in 1813. This is from Mountstuart Elphinstone, a reliable observer (Adamson

2012), and states that the rains were “the heaviest ever known here” (BL MSS Eur F88/370, 21

September 1813). Likewise, no contemporary reports are available for the Gulf of Khambat relating

to 1790. However, the Report of Past Famines in the Bombay Presidency mentions famine in five

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locations in southern Gujarat in 1790/91 due to lack of rain (Etheridge 1868). A second set of

calibration tables was therefore created in order to provide rainfall classifications for these years.

These were generated in the same way as the monthly calibration tables, but were compared

against degraded instrumental data for the whole monsoon season using the percentage

deviations listed in Table 6. The seasonal calibration table for Mumbai is provided in Table 7.

No documentary data were available for the period 1780-1786. Instrumental rainfall

measurements exist for this period within a weather diary presented to the Royal Society in 1790

(RSCHS MA.213). Seasonal monsoon indices were derived for 1781-1786 by degrading the data

using the percentage boundaries in Table 6. Rainfall measurements were taken only from the

onset of the monsoon (which varies in each year; Adamson and Nash 2012) until the withdrawal,

generally in mid-October. Furthermore, little information is provided on the design of the instrument

or on the methods and times of data collection. It is possible therefore that the instrumental data

may be unreliable. 1780 was excluded as the rain gauge was not set until 4 July 1780.

4.4 Derivation of composite Western India Monsoon Rainfall reconstruction

A composite reconstruction, the WIMR, was produced for the entire study area in order to

represent monsoon variability across western India. To achieve this, the seasonal monsoon indices

derived for each of the three reconstruction areas were assigned a representative percentage

rainfall value. The indices +1, 0 and -1 were assigned values equivalent to the mid-point of their

respective 5-PSEFS percentage ranges (Table 6), i.e. 107%, 100% and 93% respectively. Years

classified as +2 and -2 were assigned a value equivalent to the average percentage deviations

corresponding to these classes within instrumental records for the LPA. These were found to be

132% for the class +2, and 69% for the class -2. For the Gulf of Khambat, the LPA was taken as

1871-1950 (due to data availability) and the instrumental data used was an average of data for the

principal meteorological stations within the region (Surat, Vadodara, Bharuch, Kheda, Ahmedabad,

Bhavnagar and Rajkot).

For each year, an average of the three reconstruction areas was generated, weighted according

to mean MJJASO rainfall totals during the LPA (1797mm for Mumbai, 641mm for Pune and

811mm for the Gulf of Khambat; GHCN 2010). Categories for Mumbai were assigned a weighting

of 0.55, Pune 0.20, and the Gulf of Khambat 0.25. Where reconstruction had not been possible for

all three stations, the composite index was based on the available data only. The final result was

then re-assigned into one of the five seasonal rainfall classes based on the percentage deviations

specified for the 5-PSEFS.

4.5 Methodological process for selected years

The following section is designed to illustrate the methodological process. Years from each rainfall

category are presented to show how individual rainfall months were classified and combined to

form the three regional reconstructions and WIMR. The five selected years span the full 9

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reconstruction period and illustrate how variations in data quality and quantity were addressed.

Monthly and seasonal rainfall classifications for each of these years are presented in Table 8,

together with the associated WIMR category.

4.5.1 Deficient monsoon year: 1838

An example of a deficient (-2) monsoon year is 1838, when significantly below average rainfall

occurred in all three reconstruction areas. The months of May/June contained reports of a “want of

rain” at Surat and Bharuch and rainfall of an “unsatisfactory nature” in Kheda within the State of the

Weather and the Crops (BLNC MC 1112, 19 July 1838). Rainfall at the Gulf of Khambat was

therefore classified as scanty. A “favorable appearance” was reported at Pune and “very favorable

accounts” from Thane, resulting in a classification of normal in Mumbai and excess in Pune (BL

MC 1112, 19 July 1838). Mumbai and the Gulf of Khambat recorded scanty rainfall in July, with

deficient rain reported in Pune. The Bombay Courier reported in mid-July “we regret extremely to

learn that not a drop of rain has fallen at Rajkote” (BLNC MC 1112, 10 July 1838). In Surat it was

reported that “the rice was suffering very seriously” (BLNC MC 1112, 4 August 1838).

Documents indicate that rainfall increased slightly during August in Mumbai and the Gulf of

Khambat (normal in Mumbai, deficient in the Gulf of Khambat), although in Pune it was reported

that “rain was urgently required every where in the Principal and Sub-Divisions of this Zillah, and

gloomy apprehensions were entertained of the serious consequences of a drought” (BLNC MC

1112, 11 September 1838). Scanty rainfall was again reported in Mumbai and the Gulf of Khambat

in September and October, although “most abundant” rains were recorded in Pune in early October

(BL MC 1122, 5 October 1838), resulting in a classification of normal rain. On 3 October the

Bombay Gazette reported "there is every probability of an almost total failure of the crops of every

description, in consequence of the long continued drought" (BL MC 1122, 3 October 1838).

4.5.2 Below normal monsoon year: 1818

The year 1818 was classified as a below normal (-1), based on average rainfall at Mumbai and

deficient rainfall at Pune. Rainfall at Mumbai was variable throughout the season, with scanty

rainfall in May/June, deficient in July, heavy in August, and excess in September/October. On 4 th

July, the Bombay Courier stated that the rainfall in June “does not amount to one half of what fell in

June last year” (BLNC MC 1112, 4 July 1818). In early August, the Courier stated that the weather

had been “much too fine for this season of the year” (BLNC MC 1112, 1 August 1818). In early

September, however, the Courier reported “abundant” rains in Thane and flooding in Panvel (BL

MC 1112, 5 September 1818), resulting in a classification of excess rainfall for September/

October.

In the Pune district, no information is available for May/June, although in mid-July it was

reported in Karandi that no rain had yet fallen (BL MSS Eur F88/363, 11 July 1818), and in Shirur

no rain had been recorded by 1 August and “the cattle were dying for want of forage” (BLNC MC 10

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1112, 1 August 1818). This suggests deficient/scanty rainfall for May/June and July. Few reports

are available for August, although the Courier reported a fall of rain in “Deckan” which contributed

to a diminution in reported cases of cholera. No further rainfall was reported for

September/October, and a famine was recorded in late 1818 in Solapur, immediately to the east of

the Pune district (Etheridge 1868). This indicates overall deficient rainfall for the season at Pune.

No reports are available from the Gulf of Khambat.

4.5.3 Normal monsoon year: 1853

The 1853 monsoon season was classified as normal (0), based on heavy rainfall during the first

half of the monsoon season and deficient during the second, with a similar pattern repeated across

all reconstruction areas. An observer in Bombay noted on 20 June that “all the flat parts of the

island are under water” (BL MSS Eur Photo 431, 20 June 1853), and the Bombay Times reported

on the same day “we seldom remember a heavier fall of rain in June than we have had during the

past ten days” (BL SM 73, 20 June 1853). The State of the Weather and the Crops likewise

reported “heavy” and “excessive” rain in Gujarat, with reports of flooding and crop damage in

Ahmedabad, Surat and Kheda (BL SM 73, 19 July 1853). Rainfall in Pune towards the end of June

was categorised as “every where abundant, and in some places, excessive” (BL SM 73, 26 July

1853). Rainfall in May/June was therefore classified as heavy in all areas. Accounts from July also

indicate heavy rainfall, with “plentiful”, “heavy”, and “unceasing” rain reported in the Gulf of

Khambat (State of the Weather and the Crops reports; BL SM 73, 2 August 1853). Rainfall from 10

to 13 July in Pune was reported as being the heaviest remembered by “that most sapient of sages

the ‘oldest inhabitant’” (BL SM 73, 18 July 1853). “Seasonable” and “plentiful” rain was reported in

Thane and Colaba (BL SM 73, 19 August 1853), resulting in a classification of excess rain in

Mumbai, with rainfall classified as heavy over Pune and the Gulf of Khambat.

“Little rain” was reported in Pune in August (BL SM 73, 3 September 1853), with “partial” rain in

Thane and reports of subsequent crop damage (BL SM 73, 23 September 1853). Likewise

“deficient” rainfall was reported at Ahmedabad, with “fair” conditions over Kheda and reports of

crop damage due to drought (BL SM 73, 23 September 1853). Rainfall was therefore classified as

scanty in all regions in August. Similar accounts of very low or no rainfall were reported in the State

of the Weather and the Crops reports during September/October, with accounts of crop damage

across all three reconstruction areas (BL SM 73, 3 November 1853 and 9 November 1853). A

classification of scanty rainfall was therefore assigned for all regions during September/October.

4.5.4 Above normal monsoon year: 1793

Although few records are available, 1793 was classified as an above normal (+1) monsoon year.

Reconstruction for Mumbai was based predominantly on one quotation from the Bombay Courier,

which stated: "The late favourable Monsoon among its other benefits, must be attended with

peculiar advantage to the Speculative Cultivators of Salsette” (BLNC MC 1112, 19 October 1793).

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Two further articles within the Courier mention “favourable” weather (BLNC MC 1112, 27 July 1793

and 3 August 1793), and a letter dated 4 August mentions the recent “Rainy and Stormy” weather

(NLS MSS.19207, 4 August 1793). The reconstruction for Pune is based on only one quote, also

included within the Bombay Courier of 19 October. This article states “by intelligence from Poonah

of the 12th instant we learn that the cutting of the Grain has commenced there—that the Crops

have been very favourable” (BLNC MC 1112, 19 October 1793). This indicates elevated rainfall,

but not enough to damage crops (i.e. category +1).

4.5.5 Excess monsoon year: 1827

Overall, excess rainfall occurred in Mumbai and the Gulf of Khambat in 1827 and above average

rainfall in Pune, generating a WIMR category of +2. Only one report is available for Gujarat for

1827, from 13 October in the Bombay Courier. This states that “the monsoon has been one of the

heaviest, and at the same time one of the most agreeable, rainy seasons, that has occurred for

several years” (BLNC MC 1112, 13 October 1827). Rainfall for the season over the Gulf of

Khambat was therefore classified as excess. Reports for Mumbai indicate that rain in June fell with

“unusual severity” (BLNC MC 1112, 23 June 1827) (i.e. heavy rainfall), although later reports are

inconclusive with no indication of either below- or above-average rainfall. Reports for Pune also

mention heavy rainfall in early June. An observer in Pune recorded “Violent” rainfall in her diary of

10, 11 and 12 June 1827 (BL MSS Eur D888, 10/11/12 June 1827), and a report in the Bombay

Courier of 13 June reports “a considerable quantity of rain… in the Deccan” (BLNC MC 1112, 13

June 1827). Rainfall in July was, however, described as “only showers” (BL MSS Eur D888, 7

August 1827), and therefore classified as scanty. August likewise recorded only “scanty showers”

(BLNC MC 1112, 5 September 1827), although with more regular reports of rainfall (BL MSS Eur

D888) and was classified as deficient. Daily rain was recorded in early September (BL MSS Eur

D888, 16 September 1827), with “violent” rain on 26 September (BL MSS Eur D888, 16 September

1827) and “tremendous rain” on 7 October (BL MSS Eur D888, 16 September 1827). A

classification of heavy was therefore assigned for rainfall during September/October.

5 Results

5.1 Monsoon rainfall reconstructions for Mumbai, Pune and the Gulf of Khambat

Reconstructed seasonal monsoon indices for the Mumbai region are presented in Figure 3a.

Reconstruction was possible from 1781 onwards, with monthly rainfall indices generated for all but

seven years (1790, 1793, 1796, 1806, 1809, 1829, 1831); reconstruction for these years was

based on seasonal information. No reconstruction could be undertaken for a further six years

(1791, 1792, 1797, 1805, 1807, 1811) due to an absence of documentary meteorological

evidence. Three periods of below-average rainfall are evident from the reconstruction: 1781-1787,

1799-1806 and 1833-1840. Above-average rainfall occurred from 1788-1798 with a sustained

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period of above-average rainfall apparent from c.1813 to c.1830. A further period of above average

rainfall is evident from 1846 to 1854.

Figure 3a also displays instrumental rainfall data for Mumbai, which show a strong agreement

with the reconstructed monsoon rainfall indices (Kendall Tau correlation coefficient of 0.59,

significant at 99%). Degrading the instrumental data into the five rainfall categories allows for direct

comparison; this indicates a strong relationship ( coefficient of 0.64, significant at 99%). This is

comparable with coefficients calculated for other documentary series in Europe (cf. Brázdil et al.

2005). Only seven years between 1817 and 1846 exhibit differences of more than one class

between the reconstructed and degraded data – 1818, 1821, 1825, 1831, 1837, 1839, 1842. No

years indicate differences of more than two classes. This supports the adopted methodology (but

note the comments in section 4.2 regarding the homogeneity of the GHCN data).

For Pune, documentary evidence was available for reconstruction from 1792 onwards, with data

gaps from 1796-1802, 1806-1810 and 1820-1822. Reconstructions for 1792, 1793, 1805, 1811,

1813, 1823, 1831 and 1832 were reliant on seasonal descriptors. The reconstructed monsoon

index for the Pune region is presented in Figure 3b. Periods of predominantly below-normal rainfall

are evident from c.1824-1833 and c.1845-1858. A sustained period of above-normal rainfall is

evident from 1834-1844, with only one year of below-normal rainfall during this period (1838). It is

difficult to infer trends before 1823 due to gaps within the data.

The reconstructed monsoon rainfall indices for the Gulf of Khambat are presented in Figure 3c.

It was not possible to reconstruct rainfall for a number of years (1782-1785, 1789, 1791-1793,

1795-1801, 1806, 1808-1811, 1814-1815, 1817-1818, 1820, 1823 and 1826) due to a lack of

documentary evidence. Seasonal reconstructions only were undertaken for 13 years (1781, 1786,

1790, 1794, 1803, 1805, 1813, 1816, 1819, 1822, 1827, 1830, 1831 and 1832). Sparse data

before 1827 makes it difficult to infer trends. However, after this date, three periods of above-

normal (1834-1837, 1842-1844 and 1854-1859) and three of below-normal (1830-1833, 1838-1841

and 1846-1850) rainfall are evident.

The rainfall reconstructions for Mumbai, Pune and the Gulf of Khambat generally show strong

agreement, with the majority of years exhibiting differences of two classifications or less between

the three regions. Between Mumbai and Pune, 40 out of 51 years (88%) show differences of two

classifications or less. Between Mumbai and the Gulf of Khambat the figure is 45 of 50 (90%) and

between Pune and the Gulf of Khambat 39 of 44 (89%). This is comparable to figures within the

instrumental record: from 1871 (the first year for which instrumental rainfall data for the Gulf of

Khambat are available) to 1950, degrading instrumental data into the five seasonal rainfall classes

(Table 6) shows differences of greater than two categories on 18 occasions between Mumbai and

Pune (23%), 15 occasions between Mumbai and the Gulf of Khambat (19%) and 13 occasions

between Pune and the Gulf of Khambat (16%). Deviations of four categories (i.e. -2 to +2) occur on

six occasions during the reconstruction period: 1804 (between Mumbai and Gulf of Khambat),

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1826 (Mumbai and Pune), 1832 (Mumbai and Pune/Gulf of Khambat), 1835 (Mumbai and Gulf of

Khambat), 1840 (Pune and Gulf of Khambat) and 1851 (Mumbai and Pune). This phenomenon

also occurs on 16 occasions between 1871 and 1950.

Differences between Mumbai and Pune are likely to be related to the rain shadow effects of the

Western Ghats (Gunnel 1997), and it is significant to note that on all four occasions where four

classes separated rainfall in these regions the location experiencing the heavier rainfall was

Mumbai. Differences between the Gulf of Khambat and Mumbai/Pune are likely to be related to the

influence of northwesterly-moving depressions from the Bay of Bengal, which affect rainfall over

Gujarat but have little impact over western peninsular India (Gadgil 2003).

5.2 Western Indian Monsoon Rainfall reconstruction

The WIMR reconstruction, which combines the seasonal monsoon rainfall indices for Mumbai,

Pune and the Gulf of Khambat, is displayed in Figure 3d. The WIMR uses data from all three

reconstruction areas during 45 years of the study period (including every year from 1827-1860),

from two areas during 16 years, and from one area only in a further 18 years. No data were

available for 1791 and 1797. The record exhibits four periods of generally deficient monsoon

rainfall: 1780-85, 1799-1806, 1830-1838 and 1845-1857. Above-normal rainfall is evident for 1788-

1794, 1813-1828 and 1839-1844. Using power spectrum analysis, a periodicity is observed of

approximately 6-7 years, although this is not statistically significant.

In general, the number of quotes available for reconstruction increases throughout the

reconstruction period. Records are particularly sparse prior for the period 1781-1799 (with the

exception of 1787-1788 and 1794) and 1804-1811 (Figure 2). Regional reconstructions during

these periods were undertaken using mainly seasonal rather than monthly descriptors, and are

reliant occasionally on only a handful of quotes. Likewise, years during these periods often do not

contain data for all three regions, with some years displaying no data. The WIMR therefore will

necessarily be of lower reliability during these periods, although this is difficult to quantify. Years

where reconstruction was reliant on seasonal descriptors only are indicated on Figure 3.

During the compilation of the rainfall indices for Mumbai, Pune and the Gulf of Khambat, one

period was identified when primary and secondary sources present potentially conflicting climatic

signals. This coincides with the famine of 1790-1792 documented within the secondary source, the

Report on Past Famines in the Bombay Presidency (see Table 2). In this report, Etheridge (1868)

suggests that famine occurred in Pune, Satara and various parts of Gujarat during 1790-1791, and

in Pune and Satara in 1792-1793. Famine is also reported in Kheda and Pune in 1791-1792. One

contemporary record, taken from the reports of the Public Department of the colonial government,

confirms that the famine in Bombay in 1790 followed a severe drought. The record notes that

Bombay received “the smallest quantity of rain ever remembered” in 1790 leading to an “almost

total failure of the Crops of Grain” (BL IOR/F/4/428/10490, 24 December 1790). This year was

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therefore given an index value of -2. The famine reported in Pune and Satara during 1792

(Etheridge 1868) may not be entirely attributable to drought, as the only available contemporary

report for that year (BLNC MC 1122, 15 August 1792) states that elevated rainfall fell in August. As

a result, an index value of -1 was assigned. The information for 1791 is more ambiguous. There is

one account of drought conditions (Etheridge 1868: 95), but a documentary report for Vadodara

describes “a luxuriant crop of Cotton and Grain” (NLS MS.13695, 11 January 1804). Etheridge

(1868) notes that the famine of 1791 may have been due to a “bringing together of troops” (p. 95).

It is also possible that the report of drought conditions in 1791 was the result of a dating error.

Early (i.e. prior to English occupation) reports of famines were generally reliant on oral tradition,

creating potential issues with dating, particularly as some dates are stated using the Samvat

calendar which is itself geographically variable. To avoid potential error, no index value has been

assigned for 1791.

6 Comparison of monsoon rainfall reconstructions with other proxies

The following section compares the WIMR chronology presented in section 5 with other proxy-

based climatic reconstructions pertaining to western India. As noted in the introduction,

dendroclimatic reconstructions are sparse for peninsular India. However, Borgaonkar et al. (2010)

have derived a 523-year tree-ring record from teak using 64 cores from three sites in Kerala,

c.1000km from Mumbai. This record was used to generate a ring-width index from 1481 onwards,

which is statistically robust from 1748. The chief determinant of tree growth was found to be

moisture availability during the growing season, represented by the June-September (JJAS)

Palmer Drought Severity Index (PDSI) (Dai et al. 2004). Significant correlation was also found

between the reconstructed ring width chronology and All-India Monsoon Rainfall (AIMR)

(correlation coefficient = 0.32, rising to 0.52 on decadal timescales; Borgaonkar et al. 2010).

Borgaonkar et al. (2010) identify that whilst there is a statistically significant (>95%) relationship

between low growth years and low moisture availability, this relationship breaks down in years with

above normal rainfall. This renders the ring-width index a poor proxy for overall seasonal rainfall,

but a useful indicator of past drought years (Borgaonkar et al. 2010). A simple comparison can

therefore be made between teak low-growth years and WIMR (Table 9). Of the 16 low-growth

years presented by Borgaonkar et al. (2010), eight also exhibit reduced rainfall in the WIMR

chronology (including 1832 which exhibits deficient rainfall in Pune and Gujarat, but excess rainfall

in Mumbai). No reconstructed rainfall data are available for 1791 (section 5.1); however, as ring

width is dependent upon moisture in the previous and concurrent monsoon (Borgaonkar et al.

2010), this low-growth year may be related to the deficient monsoon of 1790. The deficient rainfall

years of 1801 and 1823 may have also contributed to low growth years in 1802 and 1823. Seven

years exhibiting low growth, however, display average or above-average rainfall in the WIMR, and

an additional nine years with deficient rainfall do not exhibit low teak growth. This suggests either

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uncertainty in the teak reconstruction or WIMR, or localised drought in either southern or western

India.

Agreement of the WIMR with the gridded Monsoon Asia Drought Atlas (MADA) of PDSI for the

East and South Asian monsoon region (Cook et al. 2010) is weaker. Ten years within the WIMR

display deficient rainfall within two or more regions: 1790, 1803, 1812, 1823, 1824, 1832, 1838,

1845, 1848 and 1855. Of these, only 1845 and 1855 are associated with drought within the MADA,

and then only for Gujarat but not the Deccan. The monsoon season of 1824 was deficient in

Gujarat but the MADA identifies positive PDSI values over western peninsular India. The years

1790 and 1832 display highly positive PDSI values across western India, indicating elevated

rainfall. Neutral PDSI values are displayed for 1803, 1812, 1823, 1838 and 1848.

These discrepancies between the WIMR and MADA classifications may be related to problems

within the methodology adopted in the documentary reconstruction. However, several previous

studies have highlighted the particular skill of documentary records in capturing extreme

meteorological conditions (cf. Bradley 1999; Brázdil et al. 2005; Jones et al. 2009), and it is likely

that reports of drought are reliable. For example, a report from the town of Porbandar on the

Kathiawar peninsular in September 1812, describes: “no rain has fallen here and of course now the

Season is too far advanced for us to expect any, the face of the Country is miserable, resembling a

sandy beach, more than anything else” (BL MSS Eur D666, 30 September 1812). A report to the

Literary Society of Bombay in April 1815 by the British Resident at Baroda (Vadodara) describes in

great detail a severe famine in Gujarat in 1812 and 1813, caused by “a failure of the rain” (Carnac,

1819). Six other quotations in 1812 indicate deficient rainfall in Gujarat, and famine in this region is

mentioned within the Report of Past Famines in the Bombay Presidency (Etheridge, 1868). It is

therefore highly unlikely that the PDSI of ~ +2 assigned to southern Gujarat within the MADA for

this year is correct. The disagreement may instead be reflective of the spatial coverage of tree-ring

records within the MADA, which is derived from a network of 327 tree-ring records of which only

four are from peninsular India (Cook et al. 2010). It is hoped that, as new tree-ring chronologies are

developed for the Indian subcontinent, more rigorous verification of the WIMR series against

dendroclimatic datasets will be possible.

Sontakke et al. (1993, 2008) and Sontakke and Singh (1996) used rain gauge data to produce

an extended JJAS rainfall record for India and for eight homogenous climate regions within India.

The study area crosses two of these homogenous regions, with Mumbai and Pune located within

the West Peninsular India (WPI) region and the Gulf of Khambat within the Northwest India (NWI)

region. No direct comparison can therefore be made between these studies and WIMR.

Correlations can, however, be drawn between the results presented in Sontakke et al. (2008) and

a composite of reconstructed rainfall at Mumbai and Pune (Figure 4). To enable this comparison,

an average of the instrumental rainfall data for Mumbai and Pune post-1860 was degraded into the

5-point classification system using the percentage boundaries presented in Table 6.

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For the instrumental period (1861-2000), the Kendall Tau coefficient between rainfall recorded

at the Colaba Observatory, Mumbai, and WPI rainfall (degraded into the 5-point classification

system) is 0.33. The correlation between Pune rainfall and WPI for the same period is 0.44, and

the correlation between WPI rainfall and the average of rainfall at Mumbai and Pune is 0.39. For

1817-1860 – the portion of the reconstruction period for which comparison with Sontakke et al.

(2008) is possible – these correlations decrease to = 0.19, 0.20 and 0.20 respectively, which are

not significant at the 95% level.

This apparent breakdown in correlation may represent an error in the methodology adopted for

this study. However, the poor correlations established for the reconstruction period could instead

arise due to uncertainties within early data used in Sontakke et al. (2008). During the early years of

the WPI reconstruction, Sontakke et al. (2008) rely on 1817-1846 published instrumental data for

Mumbai, available through the GHCN. As mentioned in section 4.2, there are uncertainties in these

data (which may be inhomogenous). We do not challenge the statistical methodology adopted by

Sontakke et al. (2008). However, due to the unreliable rainfall data from 1817-1846 we suggest

that the regional and national monsoon rainfall reconstructions presented by Sontakke et al. (2008)

for years prior to 1847 should be treated cautiously when analysing long-term trends.

7 Long-term relationship between ENSO and Western Indian Monsoon Rainfall

The extended rainfall record provided by the WIMR permits an examination of the long-term

dynamics of monsoon variability. The lack of proxy-derived reconstructions of the IOD prohibits

analysis of the relationship between this climate mode and monsoon rainfall on longer timescales.

Annual ENSO indices based on SLP and SST have been constructed for as far back as 1500

(Cole et al. 2000; Braganza et al. 2009; Li et al. 2011). However, these indices generally fail to

replicate correlations between AIMR and ENSO observed in modern instrumental series such as

Niño 3.4 (Parthasarathy et al. 1993). A number of documentary-derived ENSO chronologies are

also available, the most commonly cited being that produced by Quinn and Neal (1992) and

updated by Ortlieb (2000).

Gergis and Fowler (2009) developed a multi-proxy reconstruction of ENSO events dating back

to 1525. This utilised instrumental data, tree-ring reconstructions, coral records, ice-cores and

documentary records from several locations on the rim of the Pacific and Indian Oceans to

generate a quantified magnitude score for each El Niño and La Niña event, which was transposed

into a 5-point strength index using percentiles. The discrete ranked nature of the Gergis and

Fowler (2009) reconstruction, hereafter referred to as GFENSO, provides a suitable comparison

with the WIMR chronology. However, as Gergis and Fowler (2009) include a drought chronology

for India (Whetton and Rutherfurd 1994) as an El Niño proxy in their reconstruction, a slight

alteration to the GFENSO indices was necessary to avoid circularity. For years classified as El

Niño in GFENSO and by Ortlieb (2000), and as Indian drought years by Whetton and Rutherfurd

(1994), the GFENSO chronology was left unaltered. For years categorised as El Niño in GFENSO 17

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but not in Ortlieb (2000), the proxy relating to the Indian drought was removed from GFENSO and

the magnitude classification for that year adjusted using the methodology presented by the

authors. This discounted El Niño events identified by Gergis and Fowler (2009) in 1782, 1838 and

1860.

The modified GFENSO indices were combined into a single chronology, with extreme El Niño

years given a ranking of -5 and extreme La Niña years +5. Years exhibiting neither El Niño nor La

Niña conditions were ranked as zero. The validity of using this index was determined by correlating

the chronology with annual mean Niño-3.4 SST data for 1871-2002. This generates a Kendall Tau

coefficient of 0.46, significant at 99%. Correlation between AIMR and GFENSO produces a

coefficient of 0.26 (significant at 99%). This is lower than the coefficient of 0.40 calculated

between AIMR and annual mean Niño-3.4 SST. However, sliding correlation analysis between

GFENSO and degraded rainfall data during the instrumental period clearly isolates two periods of

strong coupling from c.1885-c.1910 and c.1965-c.1980 (Figure 5), which have been identified in

previous analyses of the long term relationship between Niño 3.4 SSTs and Indian monsoon

rainfall (Torrence and Webster 1998; Maraun and Kurths 2005). This suggests that GFENSO is

suitable for examining long-term changes in correlation between ENSO and monsoon rainfall, if not

the exact magnitude of the correlation.

The long-term relationship of ENSO with localised rainfall in western India was determined by

correlating GFENSO with the seasonal monsoon indices derived in this study for the three

separate reconstruction areas and for WIMR. As shown in Table 10, all areas produced generally

stationary correlations between the reconstruction and instrumental period. The correlation

between ENSO and WIMR also appears to retain stationarity. To examine this further, 21- and 31-

year sliding Pearson correlations between the modified GFENSO and WIMR were generated

(Figure 5), with monsoon rainfall indices prior to 1860 derived from the documentary reconstruction

and from 1860 using instrumental data.

As noted above, Figure 5 replicates the high correlations between levels of monsoon rainfall

and ENSO observed in previous studies (Torrence and Webster 1998; Maraun and Kurths 2005),

with peaks in correlation at c.1905 and c.1976. A further peak in correlation is noted between

c.1835 and c.1845. This is a potentially significant finding, particularly given current debates over

whether the apparent breakdown in the ENSO-monsoon relationship since 1976 is a product of

anthropogenic climate change or represents the downward arm of a longer-term fluctuation (cf.

Krishna Kumar et al. 1999; Gershunov et al. 2001; Kinter et al. 2002; Maraun and Kurths 2005;

Goswami and Xavier 2005; Xavier et al. 2007; Robinson et al. 2008). If the apparent periodicity of

approximately 75 years were a persistent feature, our results would support the latter

interpretation. Modelled variability in the ENSO-monsoon relationship over 1,000 years exhibits a

similar fluctuation (Kitoh 2007), suggesting an internal oscillation of the system.

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Maraun and Kurths (2005) proposed that the periods of coherence between ENSO and the

Indian monsoon centred on c.1905 and c.1976 may be related to volcanic activity. Both periods

commence with major volcanic events in Indonesia (Krakatau in 1883 and Mount Agung in 1963),

and occur during periods of high volcanic activity, associated with high mean stratospheric optical

aerosol depths (Bertrand et al. 1999). Maraun and Kurths (2005) suggested that volcanic activity

may increase the phase coupling between ENSO and the monsoon by increasing the variance of

ENSO and/or through global cooling due to the release of sulphate aerosols, rendering the

monsoon more sensitive to ENSO fluctuations.

The third period of strong ENSO-monsoon relationship indicated through our analysis (1815-

1856; Figure 5) also begins with a major Indonesian eruption (Tambora: 1815), and spans a period

of enhanced stratospheric aerosol depth associated with higher volcanic activity. In contrast, the

identified periods of poor ENSO-monsoon coupling (1866-1886 and 1936-1956) are both

associated with lower volcanic activity (Bertrand et al. 1999). Analysis of ENSO variance through

time exhibits similar peaks at c.1970, c.1900 and c.1820 (Fowler et al. 2012). Our results therefore

add further weight to the argument presented by Maraun and Kurths (2005). Whether the apparent

fluctuation in the ENSO-monsoon relationship is an internal oscillation or related to volcanic-

induced cooling has significant implication for forecasting, and we support the call by Maraun and

Kurths (2005) for model simulations of this effect.

8 Conclusions

This study has used English-language documentary records to derive a semi-quantitative

reconstruction of monsoon rainfall variability over western India for the period 1781-1860. This

represents an extension of 66 years on the existing homogenous instrumental record for the

region, which begins at the Colaba Observatory, Bombay, in 1847. Monsoon rainfall

reconstructions have been presented for Mumbai, Pune and the area of southern Gujarat

surrounding the Gulf of Khambat, and combined to produce a composite WIMR chronology for

western India as a whole. The WIMR exhibits four periods of generally below-normal (1780-85,

1799-1806, 1830-1838 and 1845-1857) and three of above-normal (1788-1794, 1813-1828 and

1839-1844) monsoon rainfall. Ten widespread droughts are evident, in 1790, 1803, 1812, 1824,

1833, 1838, 1845, 1847-48, 1850 and 1855.

The WIMR exhibits agreement with a tree-ring derived drought chronology for Kerala.

Agreement with the Monsoon Asia Drought Atlas is weaker, but this may be related to the paucity

of tree-ring data used to reconstruct conditions over India within the MADA. Our results suggest

that regional rainfall series derived by statistical inference from early instrumental rainfall data may

exhibit a degree of unreliability prior to 1847. This is due to the use of instrumental data for Mumbai

from 1817-1846 (currently available through the GHCN), which, our archival explorations reveal,

may be inhomogenous.

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Comparison between our rainfall reconstruction and ENSO indices suggests periods of

generally higher and lower correlation between ENSO and monsoon rainfall over western India,

with a periodicity of approximately 75 years. This may be related to either volcanic activity or an

internal oscillation in the ENSO-monsoon system. Future reconstructions of pre-instrumental

monsoon variability in India should be analysed to determine whether such periodicity is also

observed, as this may have implications for current debates regarding recent reductions in the

correlation between ENSO and monsoon rainfall.

Taken as a whole, this study demonstrates the considerable potential for historical

climatological studies of moisture variability in the tropics and subtropics, particularly for regions

with strongly seasonal rainfall regimes and rich, well-preserved archives of historical documents. It

is hoped that the results will enable further analysis of the long-term variability of monsoon rainfall

and associated climatic forcings for the Indian subcontinent.

Acknowledgements

GCDA was in receipt of a University of Brighton doctoral research scholarship whilst the archive-

based research for this paper was undertaken. The Dudley Stamp Memorial Fund (administered by

the Royal Geographical Society), the Royal Historical Society and the Indian National Trust for Arts

and Cultural Heritage (INTACH) UK Trust Grants provided funding to GCDA to support visits to the

Houghton Library, Harvard, USA and the Archives of the Government of Maharashtra, Mumbai,

India. Our thanks go to the two anonymous reviewers whose comments greatly improved this

paper.

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List of Figures

Figure 1: Map of India displaying the study area, principal locations noted in the text, plus

average onset dates for the southwest monsoon (1900-1941) across the subcontinent

(after IMD 1943). Mean monthly rainfall distribution patterns are also shown for

Mumbai, Pune, and the Gulf of Khambat (the latter calculated using data from Surat,

Vadodara, Bharuch, Kheda, Ahmedabad, Bhavnagar and Rajkot) (GHCN 2010).

Figure 2: Number of datapoints (i.e. quotations) used during the reconstruction of monsoon

rainfall variability in: (a) Mumbai; (b) Pune; (c) Gulf of Khambat. (d) Number of sources

available across all three reconstruction areas.

Figure 3: Reconstructed seasonal monsoon indices for the three regional reconstruction areas:

(a) Mumbai, including instrumental rainfall data taken from GHCN (2010); (b) Pune; (c)

Gulf of Khambat. Dark grey (pale grey) bars indicate years for which monthly (seasonal

only) reconstruction was possible. (d) The Western India Monsoon Rainfall

reconstruction. Indices for 1781-1786 for Mumbai are derived from instrumental data

published in the Philosophical Transactions of the Royal Society (RSCHS MA.213).

Figure 4: Composite monsoon rainfall reconstruction for Mumbai and Pune.

Figure 5: 21- and 31-year sliding correlations for the relationship between ENSO intensity (using

a modified version of the Gergis and Fowler [2009] historical El Niño and La Niña

series) and the Western India Monsoon Rainfall reconstruction.

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List of Tables

Table 1: Details and codes for archival collections consulted in the UK, USA and India.

Table 2: Key sources used for documentary reconstruction of monsoon intensity.

Table 3: Summary of descriptive rainfall conditions from documentary materials, together with

illustrative quotes for the monsoon season of 1853, Mumbai reconstruction area.

Table 4: Indian Meteorological Department terminology to describe localised rainfall at a weekly

or monthly timescale, used to generate monthly indices of monsoon strength. The final

category (in italics) is an addition for the purposes of this study.

Table 5: Calibration table of monthly indices of monsoon strength for Mumbai, describing

prevailing characteristics of each monsoon classification noted within documentary

archive material during the calibration period.

Table 6: Rainfall categories and percentage of long-period average as used in the IMD 5-

Parameter Statistical Ensemble Forecasting system.

Table 7: Calibration table of seasonal descriptors of monsoon strength for Mumbai, describing

prevailing characteristics of each monsoon classification noted within documentary

archive material during the calibration period.

Table 8: Regional monthly, seasonal and Western India Monsoon Rainfall (WIMR) rainfall

categories for 1838, 1818, 1853, 1793 and 1827. See section 4.5 for descriptions of

conditions. N.D. indicates no data.

Table 9: Kerala teak series low-growth years (Borgaonkar et al. 2010) with reconstructed

monsoon indices for the three reconstruction areas and Western India Monsoon

Rainfall (WIMR). Years in agreement are shaded. N.D. indicates no data.

Table 10: Correlations between the modified GFENSO index (Gergis and Fowler 2009; see text)

and reconstructed seasonal monsoon indices for the three study areas and the

combined Western India Monsoon Rainfall (WIMR) record. Correlations post-1860 are

calculated using degraded instrumental data.

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Table 1: Details and codes for archival collections consulted in the UK, USA and India.

Name of collection Archive Location Archive codeIndia Office Records British Library, St Pancras,

London, UKBL followed by catalogue number

India Office Private Papers British Library, St Pancras, London, UK

BL followed by catalogue number

British Library Newspaper Collections

British Library, Colindale, London, UK

BLNC followed by catalogue number

Church Missionary Society University of Birmingham Library, UK

UBL followed by catalogue number

American Board of Commissioners for Foreign Missions

Houghton Library, Harvard, USA HLH followed by catalogue number

Scottish Missionary Societies National Library of Scotland, Edinburgh, UK

NLS followed by catalogue number

National Library of Scotland Archives

National Library of Scotland, Edinburgh, UK

NLS followed by catalogue number

Archives of the Government of Maharashtra

Department of Archives, Government of Maharashtra, Mumbai, India

DAGM followed by catalogue number

Royal Society Archives Library of the History of Science, Royal Society, London, UK

RSA followed by catalogue number

Aberdeen Medico-Chirurgical Society

University of Aberdeen Library, UK (available online)

UAL followed by catalogue number

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Table 2: Key sources used for documentary reconstruction of monsoon intensity.

Name CodeDiary of the Rain at Bombay from 1780 to 1787 RSCHS MA.213 / Banks (1790)

8-year weather diary of rainfall, which forms the earliest available data for the study period. The diary comprises of an instrumental record of rainfall for the monsoon period, commencing at the onset (as prescribed by the author of the diary).

Tours for scientific and economical research, made in Guzerat-Kattiawar, and the Conkuns, in 1787-88 by Dr. Hove

BL IOR/V/22/212 No. 16

The book consists of a printed transcription of diaries kept by Dr. Anton Pantaleon Hove whilst on tour in northwest India. It records descriptive weather conditions almost daily, with sporadic temperature readings in Fahrenheit.

Case books of James McGrigor, 1799-1803 ABCMS 4/1/4/15-23

Contain weekly summaries of climatic conditions at Bombay, as well as information on sick and wounded soldiers. The case books are held at the library of the Aberdeen Medico-Chirurgical Society.

Weather diary of Jasper Nicholls, 1802-1805 BL MSS Eur F/172/2-9

Nicholls’ diaries contain several ad hoc weather observations and monthly ‘meteorological abstracts’, including temperature observations, general comments on the weather and days of ‘heavy’ and ‘light’ rains.

Diaries of Mountstuart Elphinstone and Lucretia West, 1811-1828

BL MSS Eur F88/278-374; BL MSS D888/1

Although not systematic weather diaries, the journals contain frequent references to climate, including occasional temperature readings in Fahrenheit. Together they comprise a near-daily record of meteorological conditions in Bombay during the 1820s.

Bombay Courier, Bombay Gazette, Bombay Times, Bombay Standard

BL MC 1112; BL MC 1122; BL SM 44; BL SM 72

Climatic information printed within the newspapers ranges from brief comments on the progress of the monsoon to detailed descriptions of weather conditions including temperature and pressure observations. Extreme weather events that had an impact upon human livelihoods, such as droughts, floods or storms were generally recorded, particularly within Bombay itself. Occasional weather diaries were also published, as well as sporadic rain gauge information.

State of the Weather and the Crops (Within newspapers)

From 1833, bi-weekly reports of the ‘State of the Weather and the Crops’ were generated for the monsoon season (June to October), drafted by the Government Collectors in each of the divisions of the Bombay Presidency. The reports contained descriptive comments on monsoon rainfall and the progress of the crops.

Reports of past famines in the Bombay Presidency Etheridge (1868)

This document published in 1868, and consists of collated reports of previous famines. Material has been used only where there is significant overlap between reports from different areas, and/or where contemporary reports are also available.

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Table 3: Summary of descriptive rainfall conditions from documentary materials, together with illustrative quotes for the monsoon season of 1853, Mumbai reconstruction area.

Monsoon Month

Description of conditions Illustrative Quotes

May/June First report of rain around 30 May. Occasional storms until two days of heavy rain on 13 and 14 June.Sunshine on 15, then succession of heavy showers.Heavy rain from 17 until at least 21 June. Flooding in Bombay. Reports of one of the heaviest falls in June remembered.‘Abundant’ rainfall in Thane and Colaba during the second half of June, with banks destroyed and crops flooded.

“We have had little rain and no thunder worth speaking of as yet, and we still wait for our opening easterly squall. But we have during the last four and twenty hours had a thick damp atmosphere with an almost constant drizzle.” Bombay Times, BLNC SM 73, 14 June 1853"We seldom remember a heavier fall of rain in June than we have had during the past ten days.” BLNC SM 73, 20 June 1853

July ‘Abundant’ rain reported across all regions in first half of July, with floods reported in some places. One area only described as ‘insufficient’.Very heavy rain until at least 20 July in Bombay (cleared by 25)‘Seasonable’ rain during late July, with a very few areas described as ‘deficient’.

"Heavy showers" Diary of Isabella Bremner, NLS MSS.19224, 8 July 1853"Since we came down from Matheran we have had constant rain 50 inches of water haven fallen in five weeks we are anxiously looking out for a break." Correspondence of F.P. Lester, BL MSS Eur Photo 431, 20 July 1853

August ‘Light’/’partial’ rain during first half of August, with some reports of damage to crops.Rainfall in the second half of the month described as ‘scanty’.

“COLABA-There had been a slight fall of rain in all the Talookas of the Colaba sub-collectorate… the crops had suffered in some instances from want of sufficient rain.” Substance of the Weather Reports for the fortnight ending 15 August, BLNC SM 73, 3 September 1853

September / October

Rainfall in first half of September ‘seasonable’/’good’ throughout the region. Crops revived.Little or no further rain in September or October anywhere; reports of significant damage to crops.

“TANNA-In the Sungam, Mahim and Bassein districts there was no rain at all, during this fortnight, and in others it was so slight and partial that no general benefit was experienced.” Substance of the Weather Reports for the fortnight ending 30 September, BLNC SM 73, 9 November 1853

Seasonal Summary

Very heavy rainfall during June. Up to mid-July rainfall described as some of heaviest ever known. Much less rainfall in August and September, leading to damage to the crops by October. Water drought reported in Bombay in May 1854.

29

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Table 4: Indian Meteorological Department terminology to describe localised rainfall at a weekly or monthly timescale, used to generate monthly indices of monsoon strength. The final category (in italics) is an addition for the purposes of this study.

IMD rainfall category

Percentage deviation from long-period average (LPA)

Reconstructed monthly rainfall class

Scanty < 40% -2

Deficient 40% - 80% -1

Normal 80% - 120% 0

Excess 120% - 160% 1

Heavy > 160% 2

30

944945946

947

Table 5: Calibration table of monthly indices of monsoon strength for Mumbai, describing prevailing characteristics of each monsoon classification noted within documentary archive material during the calibration period.

Rank Classification Characteristics Key Descriptors-2 Scanty Widespread drought reported for the entire or

majority of the month, with no reports of heavy rainfall. Reports of low rainfall unequalled in the recent past.Reports of damage to or failure of crops, with a large temporal and/or spatial extent.

Drought, scanty rainfall, fair, clear, deficient, insufficient, suspension of monsoon

-1 Deficient Generally reports of low rainfall, but balanced out with reports of moderate rainfall over the month, or short period of heavy rain.Intermissions of rain and bright conditions.No reports of flooding; reports of heavy rainfall are spatially or temporally limited.No reports of damage to crops, or reports are limited temporally and/or spatially.

Light, slight, partial, moderate, more or less rain

0 Normal Mixed reports, and not universal throughout the region.Either no widespread drought or flood, or roughly equal reports of droughts and floods.

Regular, sufficient, favourable, satisfactory

+1 Excess Periods of elevated rainfall, interspersed with dry periodsLocalised flooding or reports of crop damage due to moisture, but of limited spatial or temporal extent.

Seasonable, plentiful rain

+2 Heavy Reports of flooding with a large spatial and/or temporal extent, and damage to crops due to excessive moisture.Heavy rain or storms.Reports of heavy rainfall unequalled in the recent past.

Torrential, abundant, considerable, superabundant, continual rain, boisterous conditions

31

948949950

951

Table 6: Rainfall categories and percentage of long-period average as used in the IMD 5-Parameter Statistical Ensemble Forecasting system.

IMD rainfall category

Percentage deviation from long-period average

Reconstructed monthly rainfall class

Deficient < 90% -2

Below Normal 90% - 96% -1

Normal 96% - 104% 0

Above Normal 104% - 110% 1

Excess > 110% 2

32

952953

954

Table 7: Calibration table of seasonal descriptors of monsoon strength for Mumbai, describing prevailing characteristics of each monsoon classification noted within documentary archive material during the calibration period.

Rank

Classification Characteristics

-2 Deficient Widespread drought reported, either during the monsoon year or prior to the onset of the following monsoon season.Reports of damage to, or failure of crops towards the end of the monsoon season;Rainfall reported as deficient for at least 1½ months. (“Scanty”, “deficient”, “mild” or equivalent descriptors).

-1 Below Normal

Mixed reports, with no major reports of drought and famine, or localised droughts.Break periods evident within daily reports, or rainfall described as “showers”, “intermittent” or “light rain” where no daily reports are available.No reports of flooding; reports of heavy rainfall are spatially or temporally limited.Monsoon seasons where rainfall is described as very heavy towards the start, but with damage to crops due to drought reported at the end of the season, may be categorised within this class.

0 Normal Mixed reports, and not universal throughout the region.Either no widespread drought or flood, or roughly equal reports of droughts and floods.Description of an “average” monsoon season.

+1 Above Normal

Very heavy rain reported, but for a short period only (≤1 month).Localised flooding, but not widespread.Reports of low rainfall for one month maximum.Rainfall generally described as “sufficient” (or equivalent), with few reports of “excessive” or “copious” (or equivalent) rainfall.Abundant or above average harvest.

+2 Excess Reports of widespread flooding, and damage to crops due to too much rain.Repeated reports of “heavy” and “abundant” rainfall, or equivalent.Reports of continuous rainfall.

33

955956957

958

Table 8: Regional monthly, seasonal and Western India Monsoon Rainfall (WIMR) rainfall categories for 1838, 1818, 1853, 1793 and 1827. See section 4.5 for descriptions of conditions. N.D. indicates no data.

Year/Region “Monthly” rainfall classifications Seasonal classificationMay/Jun Jul Aug Sep/Oct

1838Mumbai 0 -2 0 -2 -2

Pune 1 -1 -2 0 -2

Gulf of Khambat -2 -2 -1 -2 -2

WIMR -2

1818Mumbai -1 -2 2 1 0

Pune -1 -2 1 -2 -2

WIMR -1

1853Mumbai 2 1 -2 -2 -1

Pune 2 2 -2 -2 0

Gulf of Khambat 2 2 -2 -2 0

WIMR 0

1793Mumbai N.D. N.D. N.D. N.D. 1

Pune N.D. N.D. N.D. N.D. 1

WIMR 1

1827Mumbai 2 0 0 0 2

Pune 2 -2 -1 2 1

Gulf of Khambat N.D. N.D. N.D. N.D. 2

WIMR 2

34

959960961962

963964

Table 9: Kerala teak series low-growth years (Borgaonkar et al. 2010) with reconstructed monsoon indices for the three reconstruction areas and Western India Monsoon Rainfall (WIMR). Years in agreement are shaded. N.D. indicates no data.

Low-growth year Mumbai Pune Gulf of Khambat WIMR1791 N.D. N.D. N.D. 1790: -2

1792: -11794 2 -1 -1 21802 -1 N.D. 1 1801: -2

1802: 01803 -2 -2 -2 -21812 -2 -2 -2 -21814 2 -1 N.D. 21818 0 -2 N.D. -11821 0 N.D. 1 01824 -2 -2 -2 1823: -2

1824: -21829 0 -2 0 -11832 2 -2 -2 01833 -1 0 -2 -21837 1 2 1 11838 -2 -2 -2 -21844 -1 2 2 11853 -1 0 0 0

35

965966967968

Table 10: Correlations between the modified GFENSO index (Gergis and Fowler 2009; see text) and reconstructed seasonal monsoon indices for the three study areas and the combined Western India Monsoon Rainfall (WIMR) record. Correlations post-1860 are calculated using degraded instrumental data.

Years Mumbai(1781-)

Pune(1811-)

Gulf of Khambat(1812-)

WIMR(1781-)

Reconstruction period (earliest stated-1860)

0.09 0.10 0.07 0.09

Instrumental period (1861-2002)

0.12* 0.08 0.14* 0.15**

All available years (1781-2002)

0.11* 0.09† 0.09† 0.13**

† = significant at 90% * = significant at 95%. ** = significant at 99%

36

969970971972973

974

975