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Jfuas No.2 December 2013

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Trends of rainfall and Temperature in North Darfur State

Salih Ahmedai Abdalla, Faculty of Environmental Sciences and NaturalResources

University of Al-Fashir, Sudan

دافورا�معدالت شمال والية فى الحرارة درجات و مطار

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Abstract

Precipitation in arid and semi-arid zones results from convective

cloud mechanisms producing storms of short duration, relatively high

intensity and limited areas extent. The climate of Al- Fashir is semi-

desert (a typical Sahel). The mean annual rainfall for Al- Fashir

meteorological station for the period 1917-2012 (96 years) is 249.6

mm. The return period for p 67% is 197.2 mm or higher can be

expected in 2 years out of 3 years. The return period for p 33% is 285

mm or higher can be expected in 1 year out of 3 years. There was

considerable short-term variability in annual rainfall totals and

drought conditions are integral part of the climate in North Darfur

State.

In North Darfur State there was an increase of the annual

temperature since 1950 to2009 which is about 0.5 o C. Climate

change induced loss of livelihood in crop and pastoral and drives

farmers to fall back on more Intensive exploitation of forest resources


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with consequences for biodiversity. Studies reported that increasing

temperatures due to climate change will increase rainfall by 5-20%

from December to February, and decrease rainfall by 5-10% from

June to August by 2050. On regional variations it was concluded that

warming is likely to be greatest over the interior of the semi- arid

margins of the Sahara and central Southern Africa. Droughts have

become more common, especially in the tropics, since 1970.Droughts

are becoming longer and more severe and affecting wider area. This is

consistent with decreased precipitation in some areas and higher

temperatures causing drying conditions. Increasing sea surface

temperatures and loss of snow are direct contributors to drought.

1-Introduction

North Darfur State lies between latitudes 12º N and 20º N and

longitudes 21º 52′ E and 27º 54′ E. It had a population of 2.1 million

according to 2008 census. The state located on the southern edge of

the Sahara desert and falls within the Sahel zone. The boundaries of

the Sahel are demarcated by the 100 mm and 600 mm isohyets

average annual rainfall. The numerous definitions of the Sahel locate

it between10º N, with an average rainfall of 600 mm and 17º N, with

average 100 mm rainfall. The rainy season extends from May to

October with a peak in August. The dominant characteristic of this

region is that the rains fall in summer over a 2- 4 month period, with

extreme dryness during the rest of the year (Abdalla, 2008).

The landscapes consist of repeating patterns of sand dunes and

sandy loamy clay depressions separated by gentle slopes. The sand


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dunes have good infiltration but low water holding capacity. Due to

large pore spaces in the soil heavy showers of rain can rapidly

penetrate the depth. As a result losses through runoff and evaporation

are much lower on the loamy sand soils. This makes the dunes the

favored environment for cultivation and growing millet. Areas where

infiltration is less than rainfall, surface water gathers to form pools

which are used as watering places. In the depressions water can

infiltrate deeply contributing to the formation of groundwater. This

enable trees and herbaceous perennials to survive and provide browse

for livestock. Natural and manmade wells in such sites supply

drinking water for man and animals (Abdalla, 2008).

People practice rain-fed shifting cultivation on sandy and clay

soils. They cultivate sorghum, millet, sesame and groundnuts during

the rainy season and they keep livestock. Farmers practice a type of

rotating agriculture which left portion of the land as fallow. Rainwater

harvesting techniques were used for cultivation of crops. Land tenure

was held either by tribe or group. Agriculture is adversely affected by

low and erratic rainfall. Areas of low annual rainfall may receive

heavy thunder storms causing flood and erosion. Three months appear

to be of importance for crop growth and production. July rainfall

determines the beginning of the cultivation, the growing days and

production. When July is dry, the number of growing days is reduced

and growth is consequently limited. When August is wet, water can be

stored in the soil and used by plants for growth during September.

September rainfall can influence the plants maturation period. Apart


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from these three months, rainfall has little bearing on production; it

can trigger early germination and influence species composition. Late

rains in October can be disastrous causing the dry vegetation to rot.

Hundred years ago, the average temperature of the earth was

about 13.7 o C (56.5 o F); today, it is closer to14.4 o C (57.9 o F).

During the past 150 years, the earth has slowly become warmer,

mostly between the years 1910 and 1940. From 1940 to 1975, there

was a slight cooling trend beginning with the 1970s, the pace picked

up. Intergovernmental Panel on Climate Change (IPCC, 2007)

reported that the average global temperature increased more rapidly at

a rate of 0.2 oC (0.36 o F) per decade. The warmest years on record

are the most recent. Studies in East Africa suggest that increasing

temperatures due to climate change will increase rainfall by 5-20%

from December to February, and decrease rainfall by 5-10% from

June to August by 2050. It is reported that the average global

temperature has increased by 0.74 °C (1.3°F) over the past century

and the warmest years on record have occurred during the recent 12

years 1995-2006.The warming trend for the last 25 years is more than

double of the past century (IPCC,2007). The purpose of this paper was

to assess the significant trends of rainfall and temperature on the state.

Droughts have become more common, especially in the tropics,

since 1970. Droughts are becoming longer and more severe and

affecting wider area (Jerry, 2008).


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2-Data and methods

The study was carried out in Al-Fashir meteorological station

which was established in 1917 for the measurements of rainfall,

temperature, evaporation, radiation and other climatic parameters. The

data was collected for rainfall and temperature for the periods1917-

2012, 1959-2009; respectively. Al- Fashir town (Meteorological

Station) lies on latitude 13o 38′ N, longitude 25o20′ E with elevation

of 730 meter. The climate of the state is semi-desert (a typical Sahel).

In the Sahel zone three divisions are recognized. The sub-desert

rainfall is less than 200 mm, the typical Sahel 200-400 mm with a

rainy season of 2 to 2.5 months, and the Sahel of Sudanese border

400-600 mm with a growing season of 3 months. The main features of

the climate are the short rainy season, highly variable with

unpredicted droughts and 90% of the rainfall falls between July and

September (Tables I, 2, 3, 4 and Fig.1)


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Probability rainfall analysis is a graphical method to determine

the probability or frequency of occurrence of yearly or seasonal

rainfall. The probability of occurrence p (%) can be calculated from

the equation (FAO, 1991).� 1 � $� 2 ,�/+)%3 $45,�-)% 6&,,

Where: P = probability in % of observation of the rank m, m =

the rank of the observation, N = total number of observations used.

The above equation is recommended for N equal 10 to 100. From the

curve the probability of occurrence or exceedance of a rainfall value

of a specific magnitude can be obtained. Inversely, it is also possible

to obtain the magnitude of the rain corresponding to a given

probability (Fig4).The return period T can be derived once the

exceedance probability P (%) is known from the equations:� �&,,3� $��%

3- Results

3-1 Rainfall

The annual rainfall for AL-Fashir meteorological station for the

period 1917-2012 is 249.6 mm (Table 1, 2 and Fig 1). In the area

between latitudes 12o N- 15o N about 85% of the annual rainfall

occurs during July and September and over 60% of the total

precipitation occurs in July and August and most of the rains fall in

the form of heavy thunder storms of short duration. The long-term

annual rainfall for the periods1951-1980, 1961-1990, 1971-2000 were

263,212.6 and 193.4 mm, respectively (Table 2). The mean annual


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rainfall for the periods 1917-1946,1947-1976 and1977-2006 were

288.8, 274.9 and194.5 mm, respectively (Fig2). ILO(1997) reported

that the ten-yearly mean annual rainfall for the periods 1946-1955,

1956-1965, 1966-1975 and 1976-1985 were 327.1, 286.1, 224.9 and

161.8 mm, respectively(Fig3). .

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GFZ/GTZ (1988) reported that the mean annual rainfall showed

a decline of 51% since 1950’s(Table3).The figures indicate that the

proportion of seasonal rainfall expected in July, a critical month for

millet production has fallen from around 30% down to 17%. A

considerable proportion of annual rainfall can fall in one or two

storms and the period 1937-1986 (50 years) the isohyets moved about

200 km to the south. The average amount of annual rainfall became

considerably less. In 1985 almost 20% of annual rainfall occurred in

April and May, while in May 1989 about 21% of the year’s rain fell in

one 38.8 mm storm. Most of this rain would have been used up by

weeds before the millet could be planted. The average annual rainfall

for 1987 and 1988 almost the same but the difference in rainfall


13

distribution caused failure of the millet crop in1987 and very good

harvest in 1988.��

Table (1) was ranked in descending order and the rainfall

probability and return period were calculated to the following

equations. The mean annual rainfall for Al- Fashir meteorological

station for the period 1917-2012 (96 years) is 249.6 mm. The return

period for p 67% is 197.2 mm or higher can be expected in 2 years out

of 3 years. The return period for p 33% is 285 mm or higher can be

expected in 1 year out of 3 years. There was considerable short-term

variability in annual rainfall totals and drought conditions are integral

part of the climate in North Darfur State. Droughts have become more

common, especially in the tropics, since 1970.Droughts are becoming

longer and more severe and affecting wider area. This is consistent

with decreased precipitation in some areas and higher temperatures

causing drying conditions. Increasing sea surface temperatures and

loss of snow are direct contributors to drought.


14

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The mean annual temperature increases from north to south and

it is high throughout the year. The drop in temperature by summer

rains is greater than that caused by sun in winter. For the comparison

of the climatologically factors between the long –term 1951-1980

and1971-2000, in the former the wind speed and relative humidity

were higher where in the lateral the temperatures were high (Table

2).This indicated that the region became more arid (El Sheikh, 2009).

Solar radiation average over 200 watts / m2 in most places and in

Sahara 275 watt/m2. Evaporation exceeds 3300 mm / year and the wet


15

periods extend from the second week of June to the third week of

September. The hot dry winds reduce the effectiveness of rainfall by

evaporation from the soil surfaces. Potential evapotranspiration (ETP)

in the southern Sahel is 4.2 mm/day during the growing season and in

the north it is 5.2 mm/ day. During the cooling winter months

December to February evapotranspiration falls to over 3 mm/day

(ILO, 1997).There was an increasing of the annual temperatures since

1950 to2009 which about 0.5 oC (Table 4,5 andFig.4). IPCC (2007)

reported that the average global temperature has increased by 0.74 °C

(1.3°F) over the past century and the warmest years on record have

occurred during the recent 12 years 1995-2006.The warming trend for

the last 25 years is more than double of the past century.

Surface temperatures have been observed in East Africa for

more than 100 years and results indicate that since 1905, and even

recently, the trend of TM ax. is not significant and T Min results

suggest an accelerating temperature rise.

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4-Discussion

Al-Fashir meteorological station mean annual rainfall for the

period 1917-2012 is249.6 mm. The return period for 67% is 197.2 mm

or higher can be expected in 2 years out of 3years. The return period

for 33 % is 285 mm or higher can be expected in 1 year out of 3 years.

There was considerable short-term variability in annual rainfall totals

and the poor rains to drought conditions are integral part of the climate

in North Darfur and should not be considered as an expected event.

The normal rainfall for the following successive periods, 1941-

1970, 1961-1990 and1971-2000 shows declining trend. The

coefficient of variation of rainfall for the same periods shows a rising

trend. In the central part of the country, the coefficient of variation

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varies between 20 and 60%.The trend lines of the mean annual rainfall

indicate a long wet period during 1960-1970 and a relative dry period

during1971-2006. Comparison of the two mean annual normal rainfall

isohyets: namely, the 200 mm and the500 mm, for 1941-1970 and

1971-2000, shows remarkable shift in the rainfall belt in the Western

Sudan.

There was an increasing of the annual temperatures since 1950

to2009 which about 0.5 o C (Table 4, Fig.5). . Boko ( 2007). reported

that in the low latitudes of the tropics, many wet areas will get wetter

and dry areas, drier, aggravating drought and food tendencies. In

addition the frequency and magnitude of extreme weather events will

increase, creating more variability in water supplies that drive

agricultural and hydrological systems.

5-Conclusion

FAO (1994) defines food security as access by all people at all

times to the food needed for a healthy and active life. FAO (2008)

gives the four main components of food security as food availability,

food accessibility, food utilization and system stability which implies

affordability. The impact of climate change on Africa’s agricultural

systems related from increased intra- annual and inter-annual climate

variability followed by rapid depletion of Sub- Saharan Africa’s

natural resources and increasing of the soil erosion which further

threatens the sustainability of the peasant farmer (Padgham, 2009 ). In

arid and semi-arid climates the standard deviation ratio of maximum

to minimum annual amounts is greater. With mean annual rainfalls of


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200-300 mm the rainfall in 19 years out of 20 ranges from 40-200% of

the mean and for 100 mm/year from 30-350% of the mean(

FAO,1991). Warming in Africa may be higher than the global average

and that it may persist throughout all seasons. Further, annual mean

surface air temperatures are expected to increase between 3oC and

4oC by 2009, roughly1.5 times the average global temperatures rises

.On regional variations it was concluded that warming is likely to be

greatest over the interior of the semi- arid margins of the Sahara and

central Southern Africa. It was reported that in oceans rising water

temperatures may reduce the food supplies that fish in upper water

layers depend on, and increased carbon dioxide in the atmosphere will

increase the acidity of water bodies (IPCC, 2007).

African dry lands are affected by temperature increases for most

of Africa, while expected rainfall trends vary (Christensen et al.,

2007).There is a general consensus that climatic variability will

increase, leading to an increase in drought and floods and to grow

uncertainty about the onset of the rainy season. Annual rainfall

fluctuations affects the hydrological cycle, water resources, agriculture

and ecosystem performance and services.

Water is essential for all life and is used for food production,

drinking and domestic and industrial uses. It is also part of the large

ecosystem on which biodiversity depends. Precipitation, converted to

soil and groundwater and thus accessible to vegetation and people, is

the dominant pre-condition for biomass production and social

development in the dry lands. Lack of water is caused by low water


19

storage capacity, low infiltration, large inter-annual and annual

fluctuations of precipitation and high evaporation demand.

REFERENCES.1 Abdalla,S.A.(2008). Use of Controlled Spate Irrigation for the

Improvement of Sorghum Growth. and Productivity in NorthDarfur State.Ph.D.thesis, U of K.

2. Boko. M.,Niang, l.,Nyong, A.,Vogel, C.,Githeko, A.,Medany,M.,Osman-Elasha. B.,Tabo, R. and Yanda,P.2007.Africa:Climate change 2007: Impact, Adaptation andVulnerability. Contribution of Working Group 11 to theFourth Assessment Report of the Intergovernmental Panel onClimate Change.Parry, M L.,Canziani, O.F., Pahutikof, J P.,van der Linden, P. J, and Hanson, C. E., (Eds),CambridgeUniversity Press, Cambridge, UK, 433-467.

3. Conway, D. (2000). Some aspects of climate variability in theNorth East Ethiopian Highlands-Wollo and Tigray. Sinet:Ethiopian Journal of Science 2000, 23:139-6.Christy.J.R, et.al (2008). Surface temperature variations inEast Africa and possible causes.

4. Christensen, J. H., Hewitson, Busuioc, A., Chen, A., Gao, x.,Held, I., Jones, R., Kolli, R. K., Kwon, W. T., Lprise, R.,Magana Rueda, V., Mearns, l., Menendez, c. c., Raisanen,j., Rinke, A, Sarr, A., Whetton, p.( 2007).Regional climateprojections. In: Solomon, Qin, d., Manning, m, C hen, Z.,Marquis, M., Avery, K. B., Tignor, M., Miller, H. L.(Eds).Climate Change 2007: The Physical Science BasisContribution of Working Group 1 to the Fourth AssessmentReport on the International Panel on Climate Change.Cambridge University Press. Cambridge, United Kingdomand New York, NY, USA.


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5. El Sheikh, A .T.M. (2009). Darfur internally displaced people(IDP) Ground water Resources. Capacity, Depletion Risksand Contingency Planning (Cited).

6. FAO (1991).Water harvesting. A manual for the Designs andConstruction of Water Harvesting Schemes for PlantProduction. Rome, 1991.

7. FAO (1994).Special Programme for Food Security Food andAgricultural Organization of the United Nations, Rome.

8. FAO (2008).Challenges for Sustainable land Management (SLM)for food security in Africa.25th Regional Conference forAfrica, Nairbi Kenya, Information Paper 5. 15pp.

9. G FE / GTZ. (1988) Development potential of wadis areas inDarfur, Sudan.

10. IPCC (2007).Climate change 2007: Impact, Adaptation andvulnerability .Contribution of Working Group 11 to theFourth Assessment Report of the Intergovernmental anel onClimate Change. Cambridge University Press, Cambridge.UK

11. G FE / GTZ.(1988) Development potential of wadis areas inDarfur, Sudan.

12. ILO (1997). Report on the effect of the project components onthe environments. Darfur and Kordofan Districts.

13. Padgham, J. (2009). Agricultural development under a changingclimate: Opportunities and Challenges for adaptation.TheWorld Bank. Agriculture and development and EvironmentDepartment. Htt:// siteresources,Worldbank .org/INTARD/.Resources/ climatechangecombined. Pdf .Cited 01Dec 2009.

14. Jerry.S (2008).Global warming and climate change demystified(cited).

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