Temporal Change Detection (2001-2008) Study of Sundarban ( Final Report ) Professor Sugata Hazra Kaberi Samanta , Anirban Mukhopadhyay & Anirban Akhand School of Oceanographic Studies Jadavpur University 2010 - 0 - Temporal Change Detection (2001- 2008) Study of Sundarban (Final Report) Professor Sugata Hazra Kaberi Samanta , Anirban Mukhopadhyay & Anirban Akhand School of Oceanographic Studies Jadavpur University March, 2010 - 1 - Summary The ‘Temporal Change Detection(2001-2008) study of Sundarban’ has been taken up by the School of Oceanographic Studies, Jadavpur University on October, 2009, as per the MOU executed between the WWF and Jadavpur University on 23rd. September 2009. Accordingly 75% of working expenses i.e. Rs. 3, 75,000/- has been received by the university on 28.10.2009. The work has been conducted as per schedule according to the following TOR: 1. Identification, mapping and classification of vulnerable islands using satellite imageries/data (time series analysis) 2. Identification and classification of embankments from satellite imageries/data and ground truthing 3. Land use and land cover status for the period between 2001 and 2008 and carrying out change detection exercise using satellite imagery/data generated earlier. 4. Estimation of temperature rise over land and sea; Assessment of rainfall and cyclone trend over the island system 5. Estimation of Sea Level Rise from existing data 6. Change in forest cover for the period between 2001 and 2008 and carrying out change detection exercise using satellite imagery /data generated earlier. The present report summarises the important findings of the above study. The supporting data and the maps have been appended to facilitate the understanding and analysis of sponsoring organisation. However , a comprehensive analysis will be appended with the final report. At the present level, the following conclusions can be drawn: 1. The shore line change detection study has been done using LISS III satellite images of January 2001 and January 2009 accompanied by field verification. It has been observed that the entire island system has suffered a net land loss of 44 Km2 within the study period with an average rate of erosion of 5.5 Km2 per year. This happens to be significantly higher than the rate approaching 4 Km2 as observed in the - 2 - previous decades. Ten sea facing most vulnerable island- clusters, namely Sagar, Ghoramara, Jambudwip, Namkhana, Mousuni, Dakhsin Surendranagar, Dhanchi,Dalhousi, Bulchery, and Bhangaduani have borne the major thrust of erosion and submergence . They together constitute the 68% of the lost land to the sea. The offshore islands like Jambudwip in the west or Bhanduani on the east demonstrate loss of 20 to 16% of their land area within 20001 to 2009. The results have been discussed in Chapter 1 2. The embankments have been mapped from the high resolution images in consultation with pre existing maps of the department of Irrigation and Waterways, Govt. of West Bengal , with limited field checks. Four different types of embankments can be recognized in the field. The total length of the embankments is found to be 3638 Km. The vulnerable portion of the embankments was found and mapped to be 416 k m , before Aila. In the post Aila situation , the vulnerable portion appears to be close to 1000 amongst which 305 Km is totally breached, 553 Km stretch is severely damaged while around 140 km is partially damaged. The findings have been discussed in Chapter II 3. In the study of land use change, it has been observed that there is a significant increase in the settlement area from1226 Km2 to 1666 Km2 while the available agricultural land reduced from 2149 Km2 to 1691 Km2. The change detection analysis clearly depicts the land conversation from agriculture land to settlement area with vegetation. , particularly in the S 24 parganas. In the north 24 parganas, the change detection analysis brings out a different picture . Here conversion of agriculture land to aquaculture is more conspicuous. This conversion , along with the growth rate of population implies increasing threat to the ecological sustainability and food security of the study area. While the Mudflats are reduced almost by 50% during the study period , there is a marginal increase in the aquaculture farms from 603 Km2 to 649 Km2. Both water bodies and swamp area have increased . This appears to be driven by sea level rise and coastal erosion. The details have been discussed in the Chapter III. - 3 - 4. For estimation of Temperature rise, rainfall and Cyclone pattern, it has been decided to access and extract daily information of Sea Surface temperature, Rainfall and Wind data set for the entire Bay of Bengal area from modern High resolution Ocean satellites (Aqua-Modis Level 3 , 11µ , Tropical Rainfall measuring Mission (TRMM) Microwave Imager , and AMSRE ). It is obvious that the temperature of the Sea Surface of the Bay of Bengal, hourly rainfall data per unit area of the Bay of Bengal and the Cyclone frequency and intensity over the northern Bay of Bengal are more representative climate Change indicator and drivers of the sea level change observed at Sagar Island at Sundarban. The initial observations are quite significant to understand the recent accelerated change of climatic pattern in the study area. During the period of observation (2003-2009)the SST showed a rising trend at the rate of 0.0453 oC/ year and reached the highest level in the last year under study This is . This is almost double of the rate observed (0.019 oC/ year ) during the period 1985-2000 (Hazra,2003, for a smaller space window). During the same period the monsoon rainfall has increased at the rate of 0.0041 mm/hr resulting in a marginal increase in the average annual rainfall in the Bay of Bengal area. However, the the total rainfall in the land area has not incresead during the study period. During the period 1999 to 2005, when there was a little downward trend in the SST, from several number of depressions formed, only three could be materialized into severe and super-cyclonic storms. Whereas in the next four years, with sharp rise of SST , seven such cyclonic storms have been generated from the in the northern bay of Bengal, which includes Mala, Sidr, Bijli and Aila impacting wide areas of Sundarban 5. The Tide guage data of Sagar Island observatory indicated a rise in the Relative Mean Sea Level (RMSL) at the rate of 17.8 mm/ year during the present decade. This is significantly higher than the rate of 3.14mm/year as observed during the previous decade.. The mean tide level of Sundarban seems to vary in close correlation with the SST and Rainfall in the Bay of Bengal. However, beside these two main factors, subsidence, siltation and other local causes may be responsible for the exceptionally high rate of relative sea level rise in Sundarban during the - 4 - present decade. Normalising with the data from previous decade the composite average rate of SLR in Sagar island appears to be 8.63 mm/year 6. Forest cover change mapping indicates some serious impact of Climate Change and sea level rise. In most of the islands, dense forest seems to have grown, thanks to the sustained efforts of forest plantation. However the reduction of forest area from 2168.9 Km2 to 2132. Km2 is mainly due to two reasons , erosion and submergence and secondly, the conversion to saline blanks / salt pans, which has grown from 38.74 Km2 to 74.796 Km2 within this 8 years time span. However some re- colonisation by salt tolerant mangrove species can be observed in some islands The increase is water area within the islands also points to a slow gradual invasion of the sea. - 5 - Chapter I Erosion- Accretion of Indian Sundarban - 6 - Administrative Blocks in Indian Sundarbans: The Sundarban in the Indian part consists of 13 blocks in the South 24 Parganas and 6 blocks in the North 24 Parganas. The south 24 parganas consists of Sagar, Namkhana, Kakdwip, Patharpratima, Mathurapur I & II, Jaynagar I & II, Canning I & II, Basanti, Gosaba & Kultali. While the 6 blocks under North 24 parganas consists of Haroa, Hasnabad, Minakhan, Sandeshkhali I & II and Hingalganj. Plate. No. 1.1 - 7 - Plate. No. 1. 2 Coastal erosion and accretion measures changes in shoreline dynamics. Detailed monitoring of these changes is very important, to assess the impact of climate change and sea level rise. Information on shoreline changes can help to predict future changes and to prepare the adaptation policies for climate change. Coastal erosion is constantly reshaping the islands of Indian Sundarbans. With more or less constant sediment and water flow in the estuary within the time frame concerned, coastal erosion appears to be a product of change in sea level and tidal hydraulics. With continuing tidal and storm surges of higher intensity / height, sediments that were previously in equilibrium with the hydraulic system, are dislodged, eroded and are deposited within the channel/sub tidal areas. This results in progressive reduction of land area with shallowing. of channel floor/near- lsland bathymetry. The eroded material may be carried by tidal currents to the north and can be redeposited in the tide- sheltered’ sections of north and east. - 8 - Rate of coastal erosion in the Indian Sundarban have been measured to be about5.50 sq kms / year within the time frame of 2001 - 2009 and eventually it is most dominant in the south western edges of the individual islands. Erosion has affected both sandy beaches and mud flats. Even inlands with dense mangrove on the east (like Bhanga duani/Mayadwip, Dalhousi or Bulcherry) have been substantially eroded. Total land area of 6402.090 sq.kms of Indian Sundarbans in the year 2001 has been found to be reduced to 6358.048 sq.kms.