SENSITIVITY OF WATER RESOURCES OF BANGLADESH

TO CLIMATE VARIABILITY AND CHANGE

AHSAN UDDIN AHMED

HeadWater and Environment Division

Bangladesh Unnayan Parishad (BUP)

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

In terms of per capita mean annual availability of water resources, Bangladesh ranks high.

But there is a great influence of climate variability, in relation to both temporal and spatial distribution of water resources.

Such variabilities determine availability and use-potential of water, which in turn characterize agro-ecological diversity of the country.

The location of the country in its regional setup adds an element of vulnerability by giving rise climatic extremes.

The regional aspects of water management put additional difficulties towards adaptation to climate variability and change.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

Bangladesh is a low-lying delta.

The eastern-Himalayan rivers (GBM) drain over the landmass of Bangladesh.

The country occupies only about 7% of the combined catchment area, while it has to drain over 92% of the GBM flows.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

The climate of the country is strongly influenced by monsoon.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

About 80% of all rainfall occurs between June and mid-October.

Such a high seasonal rainfall variability results in “too much water” in monsoon, and “too little water” in the dry season.

Peak monsoon brings flood and flood situation is accentuated by poor conveyance capacity, and high backwater effect at confluences.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

Usual floods VS Unusual floods

There has been an increase in frequency for high intensity floods

Severe floods occurred in 1987, 1988 and 1998

During the deluge of 1998 about 68% of the landmass of the country was under water for about 70 days!

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

In the post-monsoon to pre-monsoon period, rainfall diminishes while temperature increases.

Low rainfall runoff reduces river flows, consequently salinity penetrates along the coastal rivers.

A combination of increased temperature and reduced rainfall results in an increase in evapo-transpiration, which is detrimental for crop growth.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

How climate variability will change under climate change regime?

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

-60

-40

-20

0

20

40

60

80

100

1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080

Year

Mo

nso

on

Rai

nfa

ll C

han

ge

(%)

ECHAM4

HadCM3

CSIRO

CCSR

CCC

NCAR

GFDL

A-O Coupled GCM projections of monsoon rainfall (IS92a).

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

0

1

2

3

4

5

6

7

8

9

10

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months

Rain

fall

(m

m/d

ay)

Observed

CTL

GHG (2041-60)

Under climate change scenarios, mean monthly rainfall will show significant changes over normal (i.e., current variability).

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

Number of rainy days in Bangladesh will increase by about 20 days.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

Conclusions

Water resources and hydrology of Bangladesh are highly sensitive to current climate variability.

Within Bangladesh, climate variability has two major dimensions: temporal and spatial. Both are highly significant.

There are various elements of vulnerability associated to current climate variability.

Under climate change, observed climate variability will only increase causing extreme climate conditions.

Floods, droughts and salinity ingress will occur more frequently and with higher intensity.

The country has to implement adaptation measures in order to reduce its current vulnerability to climate variability and change.

AIACC Regional Workshop: Asia Sensitivity of Water Resources of Bangladesh

Thank you so much