Intensified Structural Overshoot Aggravates Drought Impacts on Dryland Ecosystems

A favorable environment can induce vegetation overgrowth to exceed the ecosystem carrying capacity, exacerbating water resource depletion and increasing the risk of lagged effects on vegetation degradation. This phenomenon is defined as structural overshoot, which can lead to large-scale forest mortality and grassland deterioration. However, the current understanding of structural overshoot remains incomplete due to the complex time-varying interactions between vegetation and climate. Here, we used a dynamic learning algorithm to decompose the contributions of vegetation and climate to drought occurrence, trace the connection between antecedent and concurrent vegetation dynamics, thus effectively capturing structural overshoot. This study focused on the climate-sensitive hotspot in Northwest China drylands, where significant vegetation greening induced by a warming and wetting climate was detected during 1982-2015, leading to soil moisture deficit and aggravating vegetation degradation risks during droughts. We found that during this period, structural overshoot induced approximately 34.6% of the drought events, and lagged effects accounted for 16.7% of the vegetation degradation for these overshoot drought events. The occurrence of overshoot droughts exhibited an increasing trend over time, which was primarily driven by vegetation overgrowth followed by precipitation variation. Although the severity of overshoot and non-overshoot droughts were generally comparable in spatial distribution, the impact of overshoot droughts is still becoming increasingly obvious. Our results indicate that the expected intensified overshoot droughts cannot be ignored and emphasize the necessity of sustainable agroecosystem management strategies. Structural overshoot droughts, defined as the vegetation growth that exceeds the ecosystem carrying capacity due to the favorable environments, have posed substantial threats to Northwest China drylands. Using a dynamic learning algorithm driven by satellite and reanalysis data, we conducted comprehensive assessments of the impact of structural overshoot on drought occurrence in the dryland ecosystem of Northwest China. Our results reveal that structural overshoot accounted for over one-third of drought events, and demonstrated increasing trends from 1982 to 2015. The frequency and impact of structural overshoot droughts are expected to increase in a warming climate, which highlights the importance of sustainable land use management. Structural overshoot accounted for over 1/3 drought events in Northwest China drylands during 1982-2015Nearly 20% vegetation declines were caused by vegetation lagged effects of overshoot droughtsStructural overshoot drought frequency increased due to vegetation overgrowth trailed by precipitation