Shardul Agrawala
Bangladesh Unnayan Parishad, Dhaka
Tomoko Ota
Bangladesh Unnayan Parishad, Dhaka
Ahsan Uddin Ahmed
Bangladesh Unnayan Parishad, Dhaka
Joel Smith
Stratus Consulting, Boulder, USA
Maarten van Aalst
Utrecht University, The Netherlands.
Climate change, Economic development, Planning, Assistance policies, Natural resource, Management
Risk Management in Agriculture
Climate change, Environment
Climate: baseline, scenarios, and key vulnerabilities- This section briefly reviews projections of temperature and precipitation change for Bangladesh from climate models, and then addresses the major risks from climate change that Bangladesh may face. The sectoral risk is presented in order of importance. This order is based on subjective judgments about the significance of climate change impacts (which is a function of severity and importance of the affected resource), timing of impacts (whether the impacts are likely to be significant or noticeable in first half of this century or not until the latter half), and certainty of impact (any uncertainties about the relationship with climate change or the nature of the climate change itself). Current climate: Bangladesh has a humid, warm, tropical climate. Its climate is influenced primarily by monsoon and partly by pre-monsoon and post-monsoon circulations. The southwest monsoon originates over the Indian Ocean and carries warm, moist, and unstable air. The monsoon has its onset during the first week of June and ends in the first week of October, with some inter-annual variability in dates. Besides monsoon, the easterly trade winds are also active, providing warm and relatively drier circulation. In Bangladesh, there are four prominent seasons, namely, winter (December to February), Pre-monsoon (March to May), Monsoon (June to early October), Post-monsoon (late October to November). The general characteristics of the seasons are as follows: * Winter is relatively cooler and drier, with the average temperature ranging from a minimum of 7.2 to 12.8°C to a maximum of 23.9 to 31.1°C. The minimum occasionally falls below 5oC in the north through frost is extremely rare. There is a south to the north thermal gradient in winter mean temperature: generally, the southern districts are 5oC warmer than the northern districts. * Pre-monsoon is hot with an average maximum of 36.7°C, predominantly in the west for up to 10 days, very high rate of evaporation, and erratic but occasional heavy rainfall from March to June. In some places, the temperature occasionally rises up to 40.6°C or more. The peak of the maximum temperatures are observed in April, the beginning of the pre-monsoon season. In the pre-monsoon season, the mean temperature gradient is oriented in the southwest to the northeast direction with the warmer zone in the southwest and the cooler zone in the northeast. * Monsoon is both hot and humid, brings heavy torrential rainfall throughout the season. About four-fifths of the mean annual rainfall occurring during the monsoon. The mean monsoon temperatures are higher in the western districts compared to that for the eastern districts. Warm conditions generally prevail throughout the season, although cooler days are also observed during and following heavy downpours. * Post-monsoon is a short-living season characterized by withdrawal of rainfall and gradual lowering of night-time minimum temperature. The mean annual rainfall is about 2300mm, but there exists a wide spatial and temporal distribution. Annual rainfall ranges from 1200mm in the extreme west to over 5000mm in the east and north-east (MPO, 1991). Temperature and precipitation: Changes in area-averaged temperature and precipitation over Bangladesh were assessed based upon over a dozen recent GCMs using a new version of MAGICC/SCENGEN. MAGICC/SCENGEN is briefly described in Box 1. First results for Bangladesh for 17 GCMs developed since 1995 were examined. Next, 11 of 17 models which best simulate current climate over Bangladesh were selected. The models were run with the IPCC B2 SRES scenario (Nakicenovic and Swart 2000)3. Sea level rise: Another critical variable that determines the vulnerability of Bangladesh to climate change impacts is the magnitude of sea-level rise. There is no specific regional scenario for net sea-level rise, in part because the Ganges-Brahmaputra delta is still active and the morphology is highly dynamic. Literature suggests that the coastal lands are receiving additional sediments due to tidal influence, while there are parts where land is subsiding due to tectonic activities (Huq et al. 1996). Since the landform is constituted by sediment decomposition, compaction of sediment may also play a role in defining net change in sea level along the coastal zone. Agriculture: With over 35% of Bangladeshis suffering from malnourishment (Lal et al., 2001), the threat of increased hunger from the reduction in agricultural production would suggest the inclusion of agriculture as one of the major vulnerabilities facing the country. Yet the IPCC (Lal et al., 2001) and other studies (e.g., Karim et al., 1996) show crop yields potentially increasing at a few degrees Celsius increase in temperature. Beyond that, particularly as the CO2 fertilization saturates, yields could decrease. For example, Karim et al. (1996) estimated that rice yields would increase for about a 1.5°C increase combined with higher CO2 levels.
COM/ENV/EPOC/DCD/DAC(2003)3/FINAL
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