Climate change impact on the Sundarbans

Nandan Mukherjee Center for Climate Change and Environmental Research (C3ER) BRAC University • Part of GBM delta, spanning Physical setting about 350 km in width in Southern Bangladesh and the state of West Bengal in India • Within this geographical area, forests cover nearly 10,000 sq km, of which about 6,000 sq km are in Bangladesh: • Total land area is 4,143 km² • Water area of 1,874 km² • Home to a large human population: 4.5 million in India, 7.5 million in Bangladesh (Source: WWF, 2010) The Sundarbans appears deep green Agricultural lands are lighter green Towns appear as tan Streams are blue Sundarbans: The Eco-region is both Unique and Uniquely Fragile!

Unique because: • Most extensive mangrove forests exposed to freshwater and seawater mix. • Most significant strongholds of the Royal Bengal Tiger, an endangered species. • The flora of the Sundarbans, the mangrove, presents a natural buffer, a bulwark against coastal erosion and seawater ingress into one of the most densely populated regions of the world. Sundarbans: The Eco-region is both Unique and Uniquely Fragile! Sundarbans' fragility stems from its uniqueness. • Fragility due to rich ecological diversity, unique biota comprising : – 334 species of plants, 49 species of mammals, 400 species of fish, 320 species of birds, 53 species of reptiles, 11 amphibian species – Numerous invertebrates, phytoplankton, fungi, bacteria, zooplankton, benthic invertebrates, mollusks. • Human induced climate change threatens the delicate balance between land, air, and sea (WWF, 2010) • Temperature is showing an increasing trend, as well as precipitation • Variability in the climatic parameters has been increased OBSERVED EVIDENCES OF CLIMATE CHANGE Trend in Temperature Trend in Rainfall Variability in Temperature

• Annual count of summer days (>25°C) is increasing (J,S,K) • Monthly maximum value of daily minimum temperature is increasing (S) • Monthly minimum value of daily minimum temperature is decreasing (K) • Percentage of cool night and days are decreasing (J) • Percentage of warm days and warm spell duration is increasing (J) • Cold spell duration is decreasing (J) • Diurnal temperature variability (range) is increasing (J) Variability in Rainfall • Annual total wet-day precipitation is increasing (J,K) • Number of heavy (>10 mm) precipitation days increasing (J,K) • Number of very heavy precipitation (>20 mm) days increasing (J,S) • Annual count of days when Rainfall>5mm is increasing (K) • Consecutive dry days are decreasing (K) Relationship between climate change and hydro-meterology GHG increases Storm surge

Increases in Snow and ice melt Salinity intrusion radiative forcings

Backwater effect Increases in Sea level rise by tidal flow temperature

Changes in Changes in precipitation and drought ET

Changes in soil Changes in river Changes in runoff Changes in flood moisture flow

Changes in soil groundwater •Increased occurrence of storm surge in the Bay of Bengal •Increased tidal flooding and permanent inundation •Increase in salinity, and change in water quality

EFFECTS OF CLIMATE CHANGE Tropical Cyclone : some facts

Although science is not conclusive, IWTC (2006) noted that: • If projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase • Some increase in cyclone peak wind speed and rainfall will occur if climate continues to warm • Model studies and theory project a 3-5% increase in wind speed per degree Celsius increase of sea surface temperature.

Cyclone Sidr-It was never anticipated before

Source:http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2007/11/071115_sidr_mimic_anim.gif Composite Track of Cyclones in Bay of Bengal

1961-1990 2071-2100

(Unnikrishnan, 2009) Frequency Distribution of Cyclones in Bay of Bengal

1961-1990

2070-2100 Damage done by SIDR: A Preliminary Assessment • Cyclone Sidr struck Bangladesh with winds of over 220 km/h (150mph) and a tidal surge of > 6m • The authorities confirmed at least 2,3001 deaths. • An estimated one million families are thought to have been affected. Forest affected areas in the Sundarbans NDVI, Satellite Aqua, 20th November 2007 Resolution is 250 m

Affected area is 21% Of total Sundarbans area

Forest Area Affected by cyclone SIDR Damage done by SIDR: A Preliminary Assessment Effects on Fauna: • 40 species of mammals, • 400 species of birds and • More than 200 species of fishes fell victim to the calamity. SEA LEVEL RISE AND TIDAL FLOODING Historic WL rise in Sundarbans and adjacent area Coastal flooding

Year 2030 Year 2050

Sundarbans and Coastal District

Slide 22 Flood/ Inundation Analysis DECREASING FRESH WATER INFLOW AND SALINITY INTRUSION Situation of Gorai

• After the construction of Farakka, dry seasonal flow in the Gorai River has reduced drastically. • Mean dry seasonal flow decreased 72% and it has increase by 23% after the GWT • Mean 1-day low flow has been decreased from 146 cumec to to 51 cumec Line of equal salinity (5 ppt) for different sea level rise in dry season

0 SLR 32 cm SLR 88 cm SLR in base condition with SLR 32 cm with SLR 88 cm

Condition Salinity (ppt)

0-1 ppt 1-5 ppt 5-10 ppt 10-15 ppt 15-20 ppt 20-25 ppt > 25 ppt

Base condition 10.8% 16.2% 19.1% 20.9% 15.9% 12.6% 4.5%

SLR 32 cm 9.2% 17.8% 18.0% 18.6% 15.6% 15.7% 5.0% SLR 88 cm 4.0% 21.0% 17.8% 15.6% 14.9% 17.9% 8.8% Salinity distribution in different scenario EFFECT OF CLIMATE CHANGE ON BIODIVERSITY Changing Pattern in Distribution of Sundri and Gewa from 1992 to 2001

29 Changing Pattern in Distribution of Goran and Gewa from 1992 to 2001

30 Plant Type – Sundari – Health Index Under Different SLR Scenarios

Suitability of Sundri in SLR Base scenario Suitability of Sundri in SLR 32 cm scenario Suitability of Sundri in SLR 88 cm scenario

Very Good Good Poor Very Good Good Poor Very Good Good Poor 100 100 100

80 80 80

60 60 60

40 40 40 20 20 Percentage of Suitability 20 Percentage of Suitability

Percentage of Suitability 0 0 Block_A Block_B Block_C 0 Block_A Block_B Block_C Block_A Block_B Block_C Block in Sundarban Block in Sundarban Block in Sundarban

31 Impact on tigers

Medium Sea level High tiger tiger Low tiger rise (cm) abundance abundance abundance Total tiger (baseline is habitat habitat habitat habitat year 2000) (km2) (km2) (km2) (km2) 0 574 1,445 2,155 4,175 4 574 1,442 2,153 4,169 8 551 1,352 2,117 4,021 12 527 1,229 1,941 3,697 16 458 1,011 1,477 2,946 20 309 622 840 1,771 24 142 236 296 674 28 37 74 48 159 Impact on tigers

No SLR 28 cm SLR HOW TO SAVE THE SUNDARBANS: A TECHNICAL SOLUTION Importance of Ganges-Gorai System

• Due to a drastic fall in the flow of the Gorai River, at least seven of the 15 rivers dependent on it, are now nearly dead while eight others are flowing timidly. • The Gorai River normally has about 15 per cent of the Padma River’s annual flow volume. To keep the Gorai River bankful about 5 000 cum/sec flow will be required (BWDB 2000). • So a minimum flow of about 2 000 cum/sec in the Gorai River and 13 334 cum/sec in the Ganges River, is necessary for fresh water inflows to the Sundarbans. Proposed Ganges Barrage

Diversion flows down the Gorai River during the dry season could be made at 4 500 cum/s How to combat the situation

• Integrated coastal and marine management • Monitoring the impact of climate change on coral reef, Royal Bengal Tiger, crocodiles and Sundari tree • Coastal vulnerability and risk assessment • Economic valuation of Sundarbans' resources • Afforestation and reforestation by salt tolerant species How to combat the situation

• Facilitating natural regeneration and natural succession of native tree species • Creating public awareness through mass media • Initiating community based coastal forestation • Protecting existing mangroves against encroachment and cutting • Establishing mechanisms to harness benefit from Global Carbon Market Thanks

Lets save the Sundarbans and the Tigers