Hidden Vulnerability: Extreme Drought Threatens Dryland Plant Communities Under Climate Change

Extreme heat and drought are becoming more frequent, altering the distribution and disturbance cycles of plant communities. These weather events have caused widespread mortality of woody plant species globally. We investigated the environmental conditions preceding multiple shrub mortality events in a widespread North American dryland (big sagebrush ecosystems) using field and remote sensing data, a process-based ecosystem water balance model, and historic weather data. We identified temperature and soil water conditions that were similar across sites preceding a mortality event. We used historic and future climate data with an ecosystem water balance model to investigate how the probabilities of these events have and will change relative to historic (1915-1980) frequencies under current conditions and future emissions scenarios. Our analysis showed that the frequency of these events is likely to increase and, in many areas, has already surpassed historical conditions. Last, we used 898 sites spread across big sagebrush ecosystems to understand the spatial variability of this increase in frequency of mortality-related conditions. While the frequency of extreme hot and dry conditions is projected to increase, there is substantial variability across the region. Our findings highlight substantial risks of weather-related mortality in regions previously projected to be relatively stable under climate change, suggesting that extreme events may represent an underappreciated dimension in modeling efforts.