AN ANALYSIS OF THE FACTORS CONTROLLING FLOODING IN GUYANA IN

2005, 2006 & 2008

Presenter:Presenter:Garvin CummingsGarvin Cummings

Research SupervisorResearch Supervisor: : Dr. David Farrell, CIMHDr. David Farrell, CIMH

Presenter:Presenter:Garvin CummingsGarvin Cummings

Research SupervisorResearch Supervisor: : Dr. David Farrell, CIMHDr. David Farrell, CIMH

PRESENTATION OUTLINE

• AIM AND OBJECTIVES OF THE RESEARCH

• INTRODUCTION

FLOODING IN GUYANA

• IMPACTS OF THE 2005, 2006 & 2008 FLOODS

• RESEARCH METHODOLOGY

• ANALYSIS OF RAINFALL DATA

• RESULTS – RAINFALL DATA ANALYSIS

• RESULTS – GOVERNMENT INVESTMENTS

• CONCLUSION

AIM OF THE RESEARCH

The aim of the research was to analyze the rainfall patterns associated with three flood events in 2005, 2006 and 2008 in Guyana and evaluate whether structural and non-structural investments made by the Government of Guyana after the 2005 flood mitigated the impact of the 2006 and 2008 floods.

OBJECTIVES OF THE RESEARCH

The research sought to achieve the following objectives:

1. Analyze the rainfall patterns that influenced the 2005, 2006 and 2008 flood events; this included a comparison of the spatial and temporal rainfall variability that gave rise to the three flood events. In addition, this objective also included a

characterisation of the antecedent moisture conditions before each of the flood events

OBJECTIVES OF THE RESEARCH

2. Assess the structural and non-structural investments made by the Government of Guyana (GOG) and Non Governmental Organisations (NGOs) toward flood mitigation subsequent to the 2005 flood and evaluate how these investments influenced the impact of the 2006 and 2008 floods.

3. Investigate how land-use practices may have changed before and after the 2005 flood and how these may have influenced the impacts of

subsequent floods.

INTRODUCTION

In January, 2005; February 2006 and December 2008 Guyana suffered three (3) of its most catastrophic flood events.

These three events were particularly noticeable because they all caused significant damages and occurred in Guyana’s secondary rainfall season (mid-Nov to mid-Feb); rainfall amounts and intensities are generally expected to be less than the primary rainfall season (mid-Apr to mid-Jul).

INTRODUCTION

All three (3) flood events impacted primarily Guyana’s Coastal Plain:

10% of land space 90% of total population below mean sea level most fertile lands centre for agriculture (35% GDP), commerce, culture, education and communication prone to (fluvial, pluvial and coastal) flooding

Atlantic Ocean

Brazil

Venezuela

Surinam

INTRODUCTION

Flooding on the Coastal Plain is driven by:

Extreme rainfallProximity to the Atlantic Ocean and the EDWCIt’s below mean sea level and is subject to storm surges

All three of these factors contributed to the three flood events in some way

East Demerara Water Conservancy (EDWC)

RAINFALL EVENTS

2005 Months prior to January, 2005 were dry 87% of December, 2004 rain fell in the last 9 days In January:- the 2, 3, 4 & 5-day rainfall records were exceeded- 30 year avg. of 185.2 mm was exceeded with 1108.2 mm surpassing the Dec.,1942 record of 1022 mm There was a period of high tides during this time of heavy rainsEDWC overflowed its banks

RAINFALL EVENTS

2006 Rainfall began on November 30, 2005 The highest 1-day rainfall in Georgetown (147.6 mm) on Nov 30 All stations along the coast exceeded their 30-year average in Dec 22 consecutive rain-days in Dec New 5-day maxima rainfall of 300.5 mm – surpassed 1942 record of 299.9 mm In January, 2006 stations exceeded their 30-year average by 2 to 5 times

RAINFALL EVENTS

2008 Rain began in early December, 2008 On December 10 several stations recorded in excess of 50 mm with as much as 236.5 mm in one location. Georgetown recorded 89.9 mm in 2.5 hrs and 115.5 mm in 24 hrs – the 9th Most locations surpassed their 30-year average

Rainfall and Normals for Selected Stations December 2008

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Stations

Rain

fall

(mm

)

Monthly total

30-year average

SUMMARY OF FLOOD IMPACTS

2005 2006 2008Approx. 278,000 persons (37 % of country’s population )affected

Over 35,000 persons affected 2,000 to 3,0000 persons affected

34 deaths and water borne diseases

No deaths, but waterborne diseases

No deaths, but waterborne diseases

Losses of approx. US D 465.1 million /65% of GDP

Total losses estimated at USD 30.1 million /4.8% of GDP

Losses in excess of USD 5 million

In excess of USD 275 in losses suffered in the housing sector

Agriculture sector bore 74% of the losses

Approximately 190 sq. Km of rice affected and 32.5 sq. Km affected

Region 4 suffered 55% of the total losses

Region 5 suffered 79.2% of the total losses

Region 2 suffered the greatest losses

4 to 5ft of flood water on the ground for 4 to 5 weeks in some locations

1 to 3ft of flood water on the ground for 1 to 2 weeks in some locations

1to 2ft of flood water on the ground for 1 to 2 weeks in some locations

Source: ECLAC/Min of Agri

METHODOLOGY: Study Area

Source: ECLAC Source: Bureau of Statsistics

METHODOLOGY: Data Collection

1. Desk Study: Collection of reports and literature from which

secondary data on the 2005, 2006 & 2008 were retrieved

This included environmental background data, rainfall distribution, weather reports, social and economic impact assessments of the floods, previous work, newspaper articles

Sources included: the Ministries of Agriculture, Education, Health; Guyana Red Cross; Parliament Library, etc.

METHODOLOGY: Data Collection

Data collected included: Daily rainfall data for thirty-eight (38) locations in

the study area for the flood periods Historical data for the 38 locations were collected for

the computation of return periods Interview of senior government officials to ascertain: -

- the state of the drainage infrastructure prior to 2005 -- what investments were made after 2005 to reduce the impacts of future floods

- investments made into infrastructural development

METHODOLOGY: Data Analysis

Antecedent Moisture Condition: An analysis of the rainfall data for two (2) months prior

to the three flood events was done . The analysis included:

- comparison of rainfall amounts with the 30-year average- the number of rain days (greater than 1 mm in 24 hrs)- the number of wet days (greater than 5 mm in 24 hrs)

This analysis allowed for inferences on soil saturation levels and infiltration capacities immediately before the onset of the rainfall events that triggered the flooding.

METHODOLOGY: Data Analysis

Rainfall data analysis: Rainfall data for the three flood events for 38 stations

within the study area were analyzed to determine the return period of the rainfall event at each location. The analysis included:

- Simple Arithmetic Averaging to estimate missing data

- Statistical tests to remove outliers (Grubbs-Beck Test)

- Frequency Analysis/Gumbel plots to determine return periods for each flood event for the 38 locations

METHODOLOGY: Data Analysis

Rainfall duration: CIMH conducted a study in 2008 which showed that

floods in Guyana are not always intensity-driven, but are more volumetrically-driven.

The study showed that even though the 2005 flood was the most catastrophic for Guyana the 24 hour rainfall was rarely in excess of 25 years for any location

This research used 7-day maxima rainfall with a 4-day overlapping window for each location to ascertain the return period

RESULTS: Antecedent Moisture

Rainfall and Normals for Selected Coastal StationsNovember 2004

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Stations

Rain

fall

(mm

)

Monthly total

30-year average

Rainfall and Normals for Selected StationsDecember 2004

0

50

100

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Anna

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Onde

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Stations

Rain

fall (

mm

)

Monthly total

30-year average

BEFORE THE JANUARY 2005 FLOOD

RESULTS: Antecedent Moisture

BEFORE THE JANUARY 2006 FLOOD

Rainfall and Normals for Selected Coastal Stations November 2005

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350

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Stations

Rain

fall (

mm

)

Monthly total

30-year average

Rainfall and Normals for Selected Coastal Stations December 2005

0

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200

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700

800

Anna

Reg

ina

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Ond

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Stations

Rain

fall

(mm

)

Monthly rainfall

30-year average

RESULTS: Antecedent Moisture

BEFORE THE JANUARY 2008 FLOOD

Rainfall and Normals for Selected Coastal Stations November 2008

0

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100

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350

Anna

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ina

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ity

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Onde

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on

Stations

Rain

fall (

mm

)

Monthly total

30-year average

Rainfall and Normals for Selected Stations December 2008

0

200

400

600

800

1000

1200

1400

Anna

Reg

ina

Char

ity

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Stations

Rain

fall

(mm

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Monthly total

30-year average

RESULTS: Rain days

BEFORE THE FLOODS

RESULTS: Wet days

BEFORE THE FLOODS

RESULTS: Return Periods

In general, Return Periods for 7-day maxima rainfall across the Study Area in 2005 was in the extreme range with the greatest return periods being 2500 years in Leonora Back, Region 3 and 1097 years in Georgetown.

The Return Periods for 2006 and 2008 were noticeably less than 2005 for most locations.

RESULTS: Return Periods

REGION 4

Yr George-town

Tr (yrs) Ogle Front

Tr

(yrs)Ogle Back

Tr

(yrs)LBI

FrontTr

(yrs)Mon Repos Agri Stn

Tr

(yrs)

`05 658.1 1097† 595.4 344† 426.1 37 700.1 147† -  

`06 301.1 8 254.6 5 345.6 12 517.7 64† 229.4 8

`08 287.4 7 197.3 2 257 3 263.5 8 -  Yr Enmore

FrontTr (yrs) Cane

Grove Back

Tr

(yrs)Cane Grove Front

Tr

(yrs)Timehri Tr

(yrs)

`05 392 182† 412 25 387.3 24 326.8 47.5

`06 257 5 264.2 4 288.2 7 231.1 8

`08 407.5 306† 303 7 131 1 216.5 6

WATER LEVELS IN THE EDWC, 2005

WATER LEVELS IN THE EDWC, 2006

Average Water-level in the EDWC, 2005/2006

50

51

52

53

54

55

56

57

58

59

60

Date

Wate

r-l

evel

(ft-

GD

)

Average Water-level in the EDWC, 2008/2009

54.00

55.00

56.00

57.00

58.00

59.00

60.00

Date

Wate

r-le

vel

(ft-

GD

)WATER LEVELS IN THE EDWC, 2008

EMPTYING THE EDWC IN 2006 & 2008

POST 2005 INVESTMENTS

Annual Drainage & Irrigation Allocations

6168.5 6159.5

17033.5

13254

20447

14414

4000

7000

10000

13000

16000

19000

22000

2003 2004 2005 2006 2007 2008 2009

Years

US

D (

x1

00

0)

POST 2005 INVESTMENTSBE

FOR

E 2

005

AFT

ER 2

005

POST 2005 INVESTMENTS

BEFORE 2005

AFTER 2005

CONCLUSION

1. There were considerable spatial and temporal variation in the rainfall influencing the three flood events – the same general locations were not impacted by all three events

2. In 2005, the flood was triggered by a 7-8 day period of extreme rainfall

3. While the rainfall was extreme, it was also clear that the drainage infrastructure (including pumps and sluices) did not follow a strict maintenance schedule prior to 2005

4. In 2006 and 2008 there were instances of extreme rainfall, but it was distributed over a of 2-3 week period prior to the flood events

CONCLUSION

5. There were considerable investments directed toward improving the drainage system after the 2005 flood – approx. 100 million US dollars from 2005 to 2009

6. There was uncertainty in the effectiveness of the investments in mitigating the impacts of the 2006 and 2008 for the following reasons:

the extensive variability of rainfall over the three flood events made comparison difficult

the areas where significant investments were made after the 2005 flood did not receive rainfall of a similar magnitude in 2006 and 2008

CONCLUSION

the floods of 2006 and 2008 were caused primarily by the release of water from the EDWC and therefore it was difficult to ascertain the contribution of direct rainfall

7. Flood insurance was proposed as a further safeguard for the physical infrastructure and livelihoods in light of the projected impacts of climate change.

THANK YOU!