Evaporative Stress Index (ESI), also sometimes referred as Evaporative Stress Ratio (ESR), has been widely used as an indicator of vegetation evaporative stress, and is often used to track forest and agriculture droughts. Lower the stress, higher is the value of ESI or ESR. The goal of this study is to assess the suitability of these indices for tracking vegetation evaporative stress. As the dynamics of water loss from vegetation through transpiration (T) can be different than that of evapotranspiration (ET) from the ecosystem, it is hypothesized that ESI or ESR may not be sufficiently representative of the vegetation evaporative stress. Using eddy covariance flux tower data of 518 site years, distributed across 49-sites and 9 land covers globally, our findings reveal underestimation of vegetation evaporative stress by ESI during periods of high vapor pressure deficit (VPD) and overestimation during dry, low-VPD periods. The results highlight the need to improve representativeness of ESI for monitoring vegetation evaporative stress. Notably, this may entail accurate estimation of ecosystem T in systems lacking in-situ data, a challenge that warrants further attention.

中文翻译：

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生态系统层面的蒸发应力指数是否能代表植被的蒸发应力？


蒸发应力指数（ESI），有时也称为蒸发应力比（ESR），已被广泛用作植被蒸发应力的指标，并且通常用于跟踪森林和农业干旱。应力越低，ESI或ESR的值越高。本研究的目的是评估这些指数追踪植被蒸发应力的适用性。由于植被通过蒸腾 (T) 损失的动态可能与生态系统蒸散 (ET) 的动态不同，因此假设 ESI 或 ESR 可能不足以代表植被蒸发应力。使用分布在全球 49 个站点和 9 个土地覆盖的 518 个站点年份的涡流协方差通量塔数据，我们的研究结果揭示了 ESI 在高蒸气压赤字 (VPD) 期间低估了植被蒸发应力，而在干燥、低 VPD 期间高估了植被蒸发应力期间。结果强调需要提高 ESI 监测植被蒸发胁迫的代表性。值得注意的是，这可能需要在缺乏现场数据的系统中准确估计生态系统 T，这是一个值得进一步关注的挑战。