Enhanced impact of droughts on ecosystem functioning despite unchanged resilience under climate change

Climate extremes, such as droughts associated with low soil water availability, significantly impact plant carbon uptake by reducing net primary productivity (NPP). NPP is crucial for regulating atmospheric CO₂ and maintaining the carbon balance of an ecosystem. Given the increased frequency and intensity of droughts under climate change, it is important to assess the shifts in the ecosystem functioning to ecological droughts. Using the outputs from 6 Earth System Models, we analysed impacts of droughts on NPP over 21^st century in India. We tested two hypotheses: first, that there will be an intensified reduction in NPP due to the increased frequency and intensity of droughts, and second, that there will be a decreased ecosystem resilience (greater NPP reduction per drought event) under warming climate. In this study, we used a multi-dimensional resilience index (MDRI) to quantify the response of ecosystems to droughts, which jointly considers the resistance and recovery time after the disturbance. Our results show a significant increase in extreme and moderate droughts over 21^st century, while mild droughts remained stable. The NPP reduction during extreme droughts is projected to be three times greater under the SSP2-4.5 scenario and six times greater under the SSP5-8.5 scenario compared with the baseline scenario. Due to longer recovery times and moderate resistance, the Western Ghats and lower Himalayan ecosystems exhibited low to moderate resilience. In contrast, high resistance and shorter recovery times resulted in very high resilience for the Northeastern regions. We found an increasing trend in the resistance, probably benefitting from carbon fertilisation, and decreasing trend in recovery rate, probably related to warming. Our findings do not support the second hypothesis, as we found no significant changes in ecosystem resilience due to trade-offs between resistance and recovery. This understanding can inform conservation strategies to mitigate the adverse effects of climate extremes on ecosystems that should be accounted in design of mitigation and adaptation plans.