Climatic vulnerability, impacts and coastal adaptation Climatic vulnerability implies the degree of sensitivity and adaptive capacity of social and ecological system. Particular climate induced extreme weather events; saline water intrusion; changes in coastal morphology; and sea level rise have manifested the key vulnerabilities to social, physical, financial and human sectors in coastal area. The intense and recurrent forms of extreme events cyclones and associated storm surges and tidal flooding reflect the clear evidences of climate change induced threats along different coastal zones. Bangladesh has experienced 159 cyclones (including 48 severe cyclonic storms, 43 cyclonic storms, 68 tropical depressions) over the period from 1877 to 2009 (Hossain et al. 2012). The estimation indicates that a severe cyclone has the highest possibility to hit Bangladesh in every 3 years. Bangladesh has observed increased temperature each year with annual average 0.125 °C/year which almost equals the rate of global warming (Sarwar 2005). Increase of global temperature and particular sea surface temperature over 27o c is conducive for further development of cyclones and associated storm surges as well as sea level rise in Bangladesh. Soil and water salinity is a chronic threat in coastal areas which has got multi-fetched dimensions with climate changes. Changes in annual precipitation rate coupled with tidal inundation and flooding and sea level rise are significant factors for increasing salinity level in soil and fresh water of the coastal zones. Drawing on periodical observations, salinity intrusion is highly predicted to increasing and shifting in new areas due to 1 cm and 30 cm of sea level rise (Hossain et al. 2012). Based on 30 cm rise in sea level indicates shifting saline front (2 dS/m) in dry season from 30 km to 50 km north in most of Khulna, Jessore, Barisal, Patuakhali and Noakhali (greater) districts and parts of Faridpur and Comilla districts. With a 1 m rise in sea level, the saline water front will move far north on the northeastern side of Bangladesh. Most of Jessore, Faridpur, Comilla and part of Dhaka (greater) districts will be affected by saline surface water intrusion. Land erosion is recognized as another threat in coastal and flood plain areas though enough evidences for relation to climate changes are limited. Land erosion is estimated approximately 3,199 ha/year in the Meghna river estuary (Islam 2006). Particular high monsoonal wind waves and currents, high river discharge currents, strong tidal forces and storm surges are some observed causes for increasing land erosion. Despite that land erosion is accompanied by accretion of river estuaries the geo-morphological process shapes large scale coastal land formation. The river networks of the GBM carries large volume of sediment deposition to the Bay of Bengal which are then reworked and redistributed by wave and tide to form newly accreted lands locally termed as Chars (Iftekhar 2006). The river system deposits that sediment through tidal action during monsoon and accelerates erosion and form new extensive lands in the rivers. Among the sediments, two thirds are discharged into the Bay of Bengal, whilst the rest contributes to the formation of new Char land. Whilst there is an annual net gain of land in coastal ecosystems, the erosion of land is increasing threats to coastal areas because of displacement of human settlement and accordingly gradual loss of livelihoods.
Key impacts and adaptation Climate change induced shocks have severe impacts on livelihoods of coastal community. The impacts on livelihood due to climate change depend on the nature and severity of the physical impacts relating to agriculture, water availability and quality, disaster-proneness, hospitability of the physical environment due to rising temperature and changing water regimes to pathogenic activity and coastal inundation (Hossain et al. 2012). The coastal zone of Bangladesh in enriched with natural resources where mainly agriculture and fisheries and mangroves offer the major livelihood sources. Salinity impacts any kind of agricultural cultivation in coastal areas. Almost 50 % of the coastal arable lands are affected with salinity in terms of changing seasons, less crop variety and eventually lower productivity of lands. Out of 2.85 million ha of coastal cultivable land in Bangladesh about 1.0 million ha of arable land are affected by varying degrees of salinity and most of these lands remain fallow in dry season (Karim et al. 1990). Of the 1.0 million ha of saline area, 0.38 million ha are in Khulna, 0.22 million ha in Patuakhali, 0.11 million ha in Chittagong and the rest are in Barisal and Noakhali regions. Agriculture crop cultivation is lower in coastal areas compared to other parts of the country. Different seasonality effects on salinity, tidal flooding and water logging reduce the soil and land quality for intensive crop cultivation. While three seasons were followed in traditional agriculture of Bangladesh, salinity stress and sudden weather shocks reduced cropping season and diversity of land uses. Depending on monsoon rainfall and land suitability Transplanted Aman (T Aman) is cultivated as only single crop in coastal area. Due to lack of fresh water, any further crops in dry season are extremely limited. To some extent, salt-tolerant rice variety and pulses has been used with limited fresh water as winter agricultural cultivation. Nevertheless, high level of tide and cyclonic wind with storm surges and sea level rise aggravate the salinity stress in crop production. The higher likelihood of lower crop productivity indicates that lower adaptive capacity of the marginalized farmer communities.
Fisheries are important livelihood sources of large coastal population which has also been affected with climatic threats from sea level rise induced salinity and flooding and increasing frequency and damage intensity of cyclones. Open sea and river fishing is affected with sea level rise due to change the location of the river estuary, fish habitat and breeding ground. Extreme tidal inundation with storm surges and sea level rise is affecting freshwater fish ponds due to salinity ingress. Though particular level of salt is favorable for shrimp farming in large coastal areas, raised inundation height affect hatcheries and ponds through sudden flooding. Economic loss in shrimp farming was estimated to be the largest due to storm surges and tidal flooding affected shrimp fields. Natural and plantation mangroves in coastal belt are exposed to climatic risks, mainly sea level rise, salinity intrusion and severe weather events. The Sundarbans have the highest likelihood to be affected severely with sea level rise from 10 cm to 1 m. Loss of Sundarbans will reduce the subsistence livelihood sources of almost 10 million people who are involved with fisheries, wood collection and honey collection (Islam and Haque 2004). The intensity of climate changerelated impacts from sea level rise and saline intrusion is slowly degrading the functional capacity of the mangroves to regenerate and continue generating ecosystem services. Cyclonic shocks caused severe damages of both Sundarbans and planted mangroves through species loss and creating large gaps, loss of shelter habitat and species migration capacity. The combined impacts of these stresses are reducing species diversity and lower roles to harbor grounds for associated flora and fauna at ecosystem level to adapt. Large scale protection of the mangroves and promoting diversity at ecosystem level are increasingly crucial for ecological adaptation as well securing the mitigation efforts. Climate change affects different sectors depending on sensitivity to particular shocks, but coastal people has largely vulnerable in terms of weak livelihood assets and adaptive capacity. Losses in crops, livestock, fisheries, commerce, industry or wage employment lead less alternative resources to adapt to shocks. The most vulnerable groups are landless, marginalized farmers with very little land and no other sustainable source of income are possessing lower adaptive capacity. Coastal adaptation is closely related to adjustment through physical and natural measures as well as enhancing economic and human capacity. Adaptation measures require climate resilient infrastructure to avoid excess water logging and ensure freshwater storage and irrigation; promotion of the salt tolerant and fast growing rice variety; diversification of land uses; and enabling marketing in coastal areas. Integrated land use technique with agricultural crops and fish cultivation can be viable adaptation means to diversify livelihoods and addressing salinity risks in food production.