Abstract
Climate change is one of the most important global environmental challenges facing humanity with implications for food production, natural ecosystem and water supply. Agriculture plays an important role in Bangladesh's economy. Long-term climatic variability influences crop production and crop water demand. The vulnerability and risk of crop production due to climate change and climate variability can be minimized if recent and future climate change can be adequately evaluated and predicted. Agricultural decision makers, scientists and farmers can respond by adapting to any increased risks or take advantage of any positive impacts that may result from climate change. So, the purpose of this study is to analyze the long-term trend of agro-climatic parameters and reference crop evapotranspiration and to identify any change in agro-climatic parameters and reference crop evapotranspiration due to climate change for sustainable water resources management and crop suitability in irrigated agriculture of Bangladesh. Dhaka and Mymensingh districts of North Central Hydrological Region of Bangladesh were selected as the study area. Daily and monthly reference crop evapotranspiration determining parameters and reference crop evapotranspiration were computed by FAO Penman-Monteith method. The trend of agro-climatic parameters, reference crop evapotranspiration determining parameters and reference crop evapotranspiration (1976-2005) were detected and estimated by MAKESENS trend model. Correlation analysis and rate of change of each reference crop evapotranspiration determining parameters were performed for identifying the causes of variability of reference crop evapotranspiration. Actual crop evapotranspiration of different varieties of rice was calculated using crop coefficient and reference crop evapotranpiration values. The trend of rice water demand was also detected and estimated by MAKESENS trend model. Agro-climatic parameters for different varieties of rice crop in different seasons in different years (2010, 2020, 2030 and 2035) were predicted based on trend analysis results and evaluated. The study revealed that agro-climatic parameters of Dhaka and Mymensingh districts were changing and were not consistent both temporally and regionally. Reference crop evapotranspiration decreased/ decreased significantly in all decades and months except second decade of April and May, first decade of June, third decade of July and August in Dhaka district and second decade of May, third decade of July and first decade of September in Mymensingh district. Single or different combinations of reference crop evapotranspiration determining parameters were responsible for decreasing significantly decreasing rate of reference crop evapotranspiration. Decreasing/ significantly decreasing rate of net radiation and wind speed and decreasing/ significantly decreasing rate of net radiation, saturation vapour pressure deficit and wind speed played an important role for decreasing/significantly decreasing rate of reference crop evapotranspiration in Dhaka and Mymensingh districts. Rice water demand varied in different growing stages and total growing season. Rice water demand decreased/significantly decreased due to decreasing rate of crop coefficient and reference crop evapotranspiration at different growing stages in three growing seasons. All agro-climatic parameters except rainfall, relative humidity at harvest and ratio of growing season sunshine duration to photo-period were predicted as suitable to moderately suitable for different varieties of rice cultivation in different seasons. Predicted mean rainfall would vary from suitable to marginally suitable in Kharif-I and Kharif-II seasons which indicated the need for supplemental irrigation for rice cultivation. Predicted mean rainfall would be actually unsuitable but potentially suitable in Rabi season which indicated that rice cannot be cultivated as rainfed rice in Rabi season. Ratio of growing season sunshine duration to photo-period would be marginally suitable in Kharif-I and Kharif-II seasons and moderately suitable in Rabi season. Ratio of growing season sunshine duration to photo-period gradually decreased year after year and would be detrimental for rice productivity. The results revealed that climate change occurred during the study period in Dhaka and Mymensingh districts thus affecting the sustainable water resources management and crop suitability in North Central Hydrological Region of Bangladesh.