Climate Modeling, Drought Risk Assessment and Adapfation Strategies in the Western part of Bangladesh

Abstract

Climate change is the greatest environmental challenge facing the world today and meteorological extremes like drought have been a subject of global concern since long. Present study on climate modeling, drought risk assessment and adaptation strategies have been carried out in the western part of Bangladesh with the aims of assessing the agricultural drought risk to find out the sustainable adaptation measures in the context of global climate change. Daily rainfall data reduced in weekly form of 12 meteorological stations for the period 1960 to 2011 have been used in this study. Climate modeling has been performed by Mann-Kendall (MK) test statistics (trend detection), Sen's slope estimator (rate of change) and Autoregressive Integrated Moving Average (ARIMA) model (future prediction). Drought hazards have been characterized by Markov chain analysis and drought vulnerability explored using socio-economic indicators. Drought risk map has been developed by integrating drought hazard and vulnerability indices by Geographical Information System (GIS). Annual average temperature in the area is about 25.44°C. The lowest mean annual temperature experiences in the north-east and the highest in south­western part of the area. The spatial pattern of seasonal temperature is similar like annual temperature. Predicted annual mean temperatures by ARIMA model may vary from 24.47 to 25.97, 24.57 to 26.03, 24.69 to 26.03, 24.54 to 26.03 and 24.73 to 26.75°C in the area during the period 2012 to 2016 respectively and they are higher than the long term observed mean temperature. Though temperature is rising, the predicted spatial pattern will remain same in the future. The north-west of the area is more drought prone and less crops prospect area due to the low values of drought index (DI), probability of getting at least 8, 10 and 12 consecutive wet weeks is comparatively low, probability of at least 3 consecutive dry weeks is comparatively high and expected number of wet weeks lies between 7 to 9. The southern part is less drought prone and high crops prospect areas due to the high values of DI, probability of getting at least 8, 10 and 12 consecutive wet weeks is comparatively high, probability ofat least 3 consecutive dry weeks is comparatively low and expected number of wet weeks lies between 10 to 13. Decade and year wise analysis also indicate almost similar results. Annual occurrences and percentage of annual probability indicate that probability of extreme drought occurrence increases in recent decades in Dinajpur, lshwardi and Rajshahi areas, but frequency is decreasing i.e. drought event is becoming more frequent in these areas. In the study area, drought hazard index (OHi) ranges from 15 to 32. Spatial pattern of OHi indicates that northern districts like Panchagarh, Thakurgoan, Dinajpur, Nilphamari, Nawabganj, Naogaon, Rajshahi and Natore suffer from more extreme drought hazards in comparison to rest of the districts. Drought vulnerability index (DVI) indicates that the northern part of the area are exposed to high to very high drought vulnerable as higher percentage of illiterate people, higher dependence on agricultural practices and high percentage of irrigated to cultivable land. The southern part of the study area exposes moderate to low vulnerable as all the values of vulnerability indicators are comparatively low. Drought risk map has been prepared integrating DHI and DVI values and show agricultural drought poses high risk in northern districts and low in southern districts (coastal areas). It is also found that 21.63%, 26.54% and 29.68% of the study area are exposed to very high, high and moderate drought risk respectively. High DHI value due to high variability of rainfall and high DVI due to weak socio-economic conditions has made the northern part turn more drought vulnerable area than other parts. Hazard risk ranking based on frequency and severity of agricultural drought classes indicate even low risk areas also suffer from extreme agricultural drought due to uneven spatio­temporal nature of rainfall during cropping season. To minimize the adverse effect of drought, some adaptation strategies have been suggested based on study findings: socio-economic and physical factors should be included in management policy to make more effective planning. The drought mitigating hydrological adaptation measures should be taken after ranking risks, importance of sector and climate associated events, and effective drought forecasting and warning techniques need to be considered. Therefore, it is urgent to act on adaptation keeping in mind about climate features such as rainfall and temperature variability, possible impacts of climate change and risk ranking to make viable mitigation measures.