Climate of Bangladesh: Temperature and Rainfall Changes, and Impact on Agriculture and Groundwater—A GIS-Based Analysis

Abstract

Climate change has become a subject of great interest to the scientific community, since it has major impacts on the physical and human environment on the global, regional, and local scales. The climate of Bangladesh is changing, and its vital agricultural sector and groundwater resources will face the greatest impacts. Rising temperatures, high variability in rainfall, and seasonal shortages of rain will affect the local water balance and will be harmful for agriculture, as will the consequences of climate change such as floods, droughts, cyclones, tidal surges, and soil salinity changes. Therefore, country-level information about climate variability and changes, particularly temperature and rainfall changes, is needed. It is widely recognized that policy makers need reliable and well-synthesized information about climate change and its impacts in order to formulate sustainable management policies for resources and the environment.

This chapter illustrates and analyzes the decadal trends and changing patterns of temperature and rainfall in Bangladesh, using the available historical data and geographic information systems (GIS) and maps for the period of 1971–2010. The decadal mean, mean minimum, and mean maximum temperatures, and the decadal average, premonsoon, and postmonsoon rainfall are assessed and analyzed. The short-term (2011–2020) predictions for temperature and rainfall, using an autoregressive integrated moving average (ARIMA) time series analysis model, are also evaluated and analyzed spatially. Moreover, the impacts of temperature and rainfall changes on agriculture and groundwater resources are discussed.

There was an increasing trend in the mean (0.19 °C decade⁻¹), mean minimum (0.17 °C decade⁻¹), and mean maximum (0.21 °C decade⁻¹) temperatures in Bangladesh during 1971–2010, and these temperatures (mean, mean minimum, and mean maximum) predominantly increased over the three decades of 1981–2010. The decade of 2001–2010 was the warmest decade in Bangladesh, and the maximum temperature increased faster than the minimum temperature. The northwest and northeast of the country are more susceptible to a rising minimum temperature, while the southeast and central southern parts are more vulnerable to a rising maximum temperature. It was predicted that warming would continue predominantly in these parts of the country in 2011–2020. The mean temperature of the country would increase by about 0.18 °C, in comparison with 2001–2010, indicating about 0.76 °C warmer temperatures in the decade of 2011–2020 than in 1971–1980.

Though the decadal average rainfall showed an increasing trend at 76 mm decade⁻¹ during 1971–2010, there was a general trend toward decreasing rainfall in the pre- and postmonsoon seasons, in which rainfall declined by 8 and 4 mm decade⁻¹, respectively. The pre- and postmonsoon rainfall in Bangladesh declined sharply during the two decades of 1991–2010. However, the monsoon rainfall increased by 57 mm decade⁻¹. The model-predicted rainfall showed that during 2011–2020, the average and monsoon rainfall would increase by 119 and 21 mm, respectively, in comparison with 1971–1980. Declines in pre- and postmonsoon rainfall of 5 and 9 mm, respectively, were observed during this decade in comparison with 1971–1980. Greater decreases (of 30–252 mm) in premonsoon rainfall were noted in the western, southwestern, southern and, to some extent, northwestern parts of the country, and the decreases (of 100–289 mm) in rainfall would continue in these parts in 2011–2020, indicating areas vulnerable to decreases in premonsoon rainfall. Greater decreases (of 18–75 mm) in postmonsoon rainfall were noted in the southern, southeastern, eastern, and northwestern parts of the country, and it was anticipated that the decline (of 10–111 mm) in the rainfall in these areas would persist in 2011–2020. Moreover, the rainfall projections for 2011–2020 indicated that the monsoon rainfall would also decrease in the southwestern, central, and northwestern parts of the country, and greater decreases (of 200–221 mm) in the monsoon rainfall were projected for Rajshahi, Bogra, Dhaka, Faridpur, and Khulna in comparison with 1971–1980.

Since Bangladesh is basically an agrarian country, the expected temperature and rainfall changes would be harmful for its agriculture, because the drought situation would be prolonged and the use of groundwater for irrigation would increase in the country. In particular, because of the increases in the minimum and maximum temperatures and the decreases in seasonal rainfall, the environmental suitability for wheat, boro rice, and other crops grown in the pre- and postmonsoon seasons would be reduced and overextraction of groundwater during the dry season would create geo-environmental problems such as increasing saltwater intrusion and lowering of the water table, thus the country might face worsening of food security in the near future. Hence, agricultural practices, harvesting of surface water, and optimum use of groundwater need to be incorporated into mitigation policies and programs to combat the effects of future climate change.