The Collapse Points of Increasing Trend of Vegetation Rain-Use Efficiency under Droughts

The vegetation rain-use efficiency (RUE) represents the ability of an ecosystem to use rainfall and is an important descriptor of ecological functions of terrestrial system. Although studies have been conducted to investigate the impact of droughts on vegetation, we still lack critical understanding of how exactly RUE responds to droughts of different time scales and intensities. Here, we present evidence for a rapid response in RUE, and collapse points of RUE increase trend during droughts by using multi-source meteorological data and satellite-derived vegetation indices. The highest correlation was found consistently between RUE and computed drought index at time scale of 1 month for all biome types and climate regimes. We further discovered that RUE increased significantly with amplification of drought intensity to a maximum RUE, especially for semi-arid and arid biomes. As drought is prolonged, RUE increased till a tipping point was reached across all biomes and climatic conditions, indicating that the long-term droughts weaken the sensitivities of RUE to drought and threaten the resilience of ecosystem. This study comprehensively provides a satellite-based evaluation of RUE response to different drought features. We envisage that the findings would contribute to the development of drought early warning from an ecological perspective and to provide the sustainable environmental management.