Threshold of climate extremes that impact vegetation productivity over the Tibetan Plateau

Vegetation growth is adversely impacted by multiple climate extremes related to the water and thermal stress over the Tibetan Plateau (TP). However, it remains unknown at which stress level these climate extremes can trigger the abrupt shifts of vegetation response to climate extremes and result in the maximum vegetation response across TP. To fill this knowledge gap, we combined the hydrometeorological data and the satellite-derived vegetation index to detect two critical thresholds that determine the response of vegetation productivity to droughts, high-temperature extremes, and low-temperature extremes, respectively, during 2001–2018. Our results show that the response of vegetation productivity to droughts rapidly increases once crossing −1.41±0.6 standard deviation (σ) below the normal conditions of soil moisture. When crossing −2.98σ±0.9σ, vegetation productivity is maximum damaged by droughts. High-temperature extremes, which have the two thresholds of 1.34σ ±0.4σ and 2.31σ±0.4σ over TP, are suggested to trigger the strong response of vegetation productivity at a milder stress level than low-temperature extremes (two thresholds: −1.44σ±0.5σ and −2.53σ±0.8σ). Moreover, we found the compounded effects of soil moisture deficit in reducing the threshold values of both high- and low-temperature extremes. Based on the derived thresholds of climate extremes that impact vegetation productivity, Earth System Models project that southwestern TP and part of the northeastern TP will become the hotspots with a high exposure risk to climate extremes by 2100. This study deciphers the high-impact extreme climates using two important thresholds across TP, which advances the understanding of the vegetation response to different climate extremes and provides a paradigm for assessing the impacts of climate extremes on regional ecosystems.