Variations in plant strategy to water stress across the globe based on microwave vegetation optical depth

Droughts are one of the most costly natural hazards across the globe and are projected to intensify in frequency and severity in a warming climate. The severity of droughts in one ecosystem largely depends on the plant strategy responding to droughts. Plants usually employ a range of strategies, such as regulating stomatal conductance, changing plant structure, accessing deeper soil moisture through deep roots, utilizing internal water storage, to moderate water stress. However, where and when these strategies are deployed are still poorly understood. Further, incorrect parameterization of plant water stress leads to erroneous seasonal and interannual dryness and drought prediction in main earth system models. Therefore, the efforts to examine the plant strategy to water stress across different climate zones and plant function types are warranted. Based on daily microwave vegetation optical depth (VOD) product from ASMR-E during 2002-2011, we estimate 1) a global effective plant rooting depth from VOD and 2) physiological regulation of water stress. By combining the VOD-derived variations in soil and leaf water content and the estimated rooting depth, we aim to disentangle where and when the plant physiology and roots dominate the response to water stress for further introduction into the NOAH land model. Our results suggest the great potential of the microwave VOD product in monitoring ecosystem responses to droughts and facilitating research on mechanisms of plant strategies. Findings in this work will open a new avenue of improving drought prediction in earth system models by incorporating the explicit plant water stress strategies.