Amplified contrasts in evapotranspiration between wet and dry regions caused by compound drought-hot events

Evapotranspiration (ET) plays a crucial role in the terrestrial water, energy, and carbon budgets and is affected by different biotic and abiotic factors. Particularly, ET is significantly influenced by climate extremes, such as droughts and hot extremes, in the context of climate change. However, the response of ET to the concurrent droughts and hot extremes (CDHEs) remains largely elusive. Here, we leveraged long-term reanalysis data to compare the response of ET to individual droughts and CDHEs, and pinned down underlying drivers causing the difference. Results show negative anomalies of ET in the southwest North America, Argentina, eastern Brazil, southern/eastern Africa, central Asia, and Australia, and positive ET anomalies in northern South America, central Africa, southeast China, and southeast Asia under individual droughts and CDHEs compared with the entire warm season. We found stronger negative ET anomalies (-24.61 %) for relatively arid regions and stronger positive ET anomalies (39.69 %) for humid regions under CDHEs compared with those under individual droughts. This "less for less and more for more" paradigm for the ET response arises under CDHEs, which is associated with even lower precipitation, enhanced radiation, higher temperature, and increased vapor pressure deficit, compared to droughts operating alone. Findings from this study underscore the imperative of understanding ET anomalies by factoring in compounding drought-hot stresses in a warmer climate, and provide useful implications for water resource management, ecosystem conservation, and climate change adaptation strategies.