Response of River Flow Regime to Various Climate Change Scenarios in Ganges-Brahmaputra- Meghna Basin

Abstract

The potential climatic variability over Ganges-Brahmaputra-Meghna (GBM) basin like alterations in precipitation and temperature are expected to have a significant impact on the natural flow regime of its rivers. The Lower Meghna River, being a major drainage outlet of the basin, is likely to be affected by such variability and hence its response to climate can be studied through the use of plausible scenarios of climate change. In this study, an artificial neural network (ANN) model, based on future climate projections of HadCM3 GCM, was constructed to examine the potential changes in the river flow regime assuming that climate tend to change as per the SRES scenarios A1B, A2 and B1. The results showed a trend of increasing monsoon flows for these scenarios during the periods of 2020s, 2050s and 2080s with a projected shift in the seasonal distribution of flows. Examining the monthly projected flows for different scenarios and comparing with the observed condition, it was found that the peak flow may increase 4.5 – 39.1% in monsoon and the dry period low flows may drop by 4.1 – 26.9% indicating high seasonality as a result of climate change. Due to seasonal variation of precipitation and temperature, i.e., excess precipitation in monsoon and lack of precipitation along with higher temperature in the dry season, the flood peaks are likely to shift towards earlier months and the rate of change of flows during the rising and recession of flooding would be much higher compared to current state of the river. These results also indicate the exacerbation of flooding potential in the central part of Bangladesh due to the largest increase of peak flows during monsoon.