Comparative Assessment of Ecosystem Resilience to Droughts in Two Large Scale River Basins in India

Both carbon and water cycles play an important role in the functioning of terrestrial ecosystems. The impact of hydroclimatic disturbances such as droughts is not limited to hydrology, but, due to the strong link between carbon and water cycle, these disturbances have a deep impact on terrestrial ecosystems and their functioning. Here, we assessed and compared the responses of terrestrial ecosystems to droughts in two large-scale river basins in India namely Brahmaputra (194, 413 km²) and Ganga (861,452 km²) river basins. The concept of resilience has been widely used to assess the response of the systems to such extreme conditions and thus refers to the ability of a system to withstand the external disturbance and maintain its normal functionality under the disturbance. This study utilized resilience approach to compare ecosystem response to droughts in two river basins. Ecosystem water use efficiency (WUE) relates the carbon and water cycles and thus was used in this study as an indicator of ecosystem functioning or its response to hydroclimatic disturbances. It is defined as the ratio of gross primary production (GPP) and evapotranspiration (ET). We assessed the ecosystem resilience through comparison of ecosystem WUE for the dry period and the mean ecosystem WUE. The GPP and ET dataset from Moderate Resolution Imaging Spectroradiometer (MODIS) were used in this study for the period from 2000 to 2014. A large spatial variation in ecosystem WUE was found in both river basins, which was consistent with the variation in land cover and climate type. In general, ecosystem WUE was higher for Brahmaputra basin compared to the Ganga basin, which can be attributed to the presence of forests. The resilience analysis revealed that the Brahmaputra basin was more resilient compared to Ganga basin. Further, the sub-basin level assessment indicated a large spatial variation in both ecosystem WUE and resilience with in both basins. The role to climatic factors such as precipitation, temperature and solar radiation in ecosystem WUE was also studied. This study is helpful for better ecosystem management and policy-making in these basins.