Investigation of the effect of climate change on evapotranspiration rate in different hydrological regions of Bangladesh

Abstract

Climate change may have ramification on agricultural production which is a key economic sector in Bangladesh and one of the main users of fresh water resources. The water requirement in agriculture depends on evapotranspiration rate of the specific area. The study areas include Barisal, Comilla, Jessore, Mymensingh, Rajshahi and Sylhet which are the representatives of six hydrological regions namely, South-Central, South-East, South-West, North-Central, North-West and North-East, respectively. In this study the evapotranspiration rate (ET0) was calculated for four time periods: observed base line (1961-90, i.e., 30 years historical data of the study areas) and three future projections 2006-2035 (represented as 2020), 2036-2065 (represented as 2050) and 2056-2085 (represented as 2070). The data for the latter three periods were collected from PRECIS model. To compute the ET0 value CROPWAT 8.0 software which is a decision support tool developed by the Land and Water Development Division of FAO was used. The results of the analysis reveal that the average minimum and maximum temperate will be increased by 1.11 0C, 2.45 0C, 3.54 0C and 0.95 0C, 2.39 0C and 3.68 0C by the year 2020, 2050 and 2070, respectively. The relative humidity will be decreased about 0.7%, 3.44% and 5.79%. Most of the time period wind speed shows an increasing trend. Sunshine hour and radiation both show an increasing trend among all the observing stations. The maximum radiation will be 21.09 MJm-2day-1 by the year 2070 at Sylhet. The overall evapotranspiration rate will be increased by about 7.15%, 12.33 and 20.64% by 2020, 2050 and 2070, respectively. The ET0 will be the highest at Jessore by the year 2070 about 5.14 mm/day. The annual rainfall will be increased about 14.04%, 15.61% and 18.94% by the year 2020, 2050 and 2070. The maximum rainfall will be observed at north-eastern region where as less amount of rainfall will be observed at north-western region of the country. Crop water requirement for rice will be increased at different seasons. At Sylhet, by the year 2070 maximum water will be required on dry season for Boro rice cultivation. Jessore will be the highest water required place on Kharif-I and Kharif-II season for cultivation of T. Aus and T. Aman, respectively. The irrigation demand for Boro rice cultivation will be reduced from the preset demand at different observing stations by the year 2020 and 2070. But it will be increased by the year 2070 about 15.26%, 18.91% and 19.14% at Barisal, Comilla and Jessore, respectively.