Changing Flow Patterns In The Ganges And Brahmaputra Basins: Evidence Of Regional Climate Warming In The Eastern Himalayas?

The Ganges-Brahmaputra-Meghna basin region of South Asia is home to over 500 million people. Water is intricately linked with the overall development framework of this region. Concerns about region wide climate warming and early signs of glacial retreat have raised questions about the long-term flow availability of these rivers. In addition, possible seasonal shifts in the regional streamflow patterns may lead to major changes in environmental impacts and water management and usage practices. We compare precipitation, streamflow, and related atmospheric changes for the upper Brahmaputra and the Ganges basin regions at monthly, seasonal, annual and decadal scales. We find that a strong warming signal is evident in the recorded discharge of the two rivers with seasonal flow values for both basins showing a significant shift over the last decade. Increasing trends have been observed in the Brahmaputra and Ganges low flows over the last decade. Monthly flow in the dry season has risen significantly, while monsoon flow volumes have decreased. While there has been no change in precipitation patterns in the region, investigation using temperature Reanalysis data show that winter temperatures in the high altitude regions are increasingly warmer thereby causing abnormal patterns of snow accumulation and depletion. Our findings are corroborated by remotely sensed snow cover patterns in corresponding years. While these hydroclimatic changes may provide short-term relief for dry season water scarcity, long-term viability of the available runoff remain questionable. It is thus imperative to understand the shifting flow patterns and associated impacts on water needs in the region.