Effects of climate change on T. Aman cultivation in Bangladesh

Abstract

In this study, trends of changes in temperature and precipitation patterns in wet season (June to November) in Bangladesh has been assessed through analysis of data on temperature and precipitation for the period 1976-2005 for 34 meteorological stations all over the country. The climate trends were assessed in terms of changes in maximum and minimum temperatures and changes in precipitation patterns. Analysis of monthly average maximum temperatures show increasing trend for all months of wet season. On the other hand, minimum temperatures show increasing trend for all months except November. Monthly average maximum temperatures of each of the months (June to November) increased by 0.38 to 1.06 °C during the 30 years period from 1976-2005. Similarly, monthly average minimum temperatures of each of the months from (June to October) increased by 0.22 to 0.60 °C during the same period. The magnitudes of increase in monthly average maximum and minimum temperatures during the 30-years period from 1976 to 2005 are quite significant. Number of hot days (i.e., day with average temperature exceeding 29.3 0c) show sharp increasing trend for most of the stations from June to August, while decreasing trend was observed during September- October. Total rainfall during monsoon showed increasing trend at 30 out of 34 weather stations, while total rainfall during Post-monsoon period shows increasing trend at 32 out of 34 weather stations. These observations are particularly significant in the context of Bangladesh where agriculture is heavily dependent on temperature and rainfall patterns. Effects of climate change on yield of two varieties of T. aman rice have been assessed using DSSAT (v4) modeling system. The yield of BRII and BRn T. aman varieties for the years 2008, 2030, 2050 and 2070 have been simulated for 12 selected locations in Bangladesh, which are selected from the major rice growing areas in different regions of Bangladesh. Available data on soil and typical crop management practice for T. aman rice were used in the simulations. The weather data required for this model (daily maximum and minimum temperatures, daily solar radiation and daily precipitation) were generated for the selected years and for the selected locations using the regional climate change model PRECIS. The model predicted average reduction of BRII yields in the future (i.e., 2030, 2050 and 2070) for most of the 12 selected locations in comparison to predicted yield in 2008. For BRll, average yield reductions are 12.5% for the year 2030, 11.9% for 2050 and 7.3% for 2070. Predicted reductions in yield of BR22 were relatively less pronounced compared to BRII. Changes in monthly average maximum and minimum temperatures have been found to be primarily responsible for reduction in T. aman rice yield. The impacts of incoming solar radiation and carbon dioxide concentration on T. aman rice are not as significant compared to the impacts of temperature. Variations in rainfall pattern (deficit or excessive rainfall) over the growing period on T. aman rice have also been found to be affect yield. Model results also suggest that climate change may make rice yield more vulnerable to transplanting date, predicting significant change in yield as transplanting date is varied from beginning to end of July. Increasing temperature and solar radiation have been predicted to shorten the duration of physiological maturity of T. aman rice. DSSAT modeling system could be a useful tool for assessing possible impacts of climate change and management practices on different varieties of rice and other crops.