GRACE/GRACE-FO observed terrestrial water storage influencing global grassland growth

Land water supply for plant growth directly links the water and carbon cycles. The abundance or shortage of water storage influences plant water consumption strategies and have important implications for ecosystem drought resistance and resilience, especially for the grassland ecosystem where water is the primary factor limiting plant production. However, plant-accessible water is rarely quantified due to the lack of regional to global scale observations of deeper water storage, and the influence of deeper water supply on plant-water relation remains unknown. In this study, we evaluate the capacity of GRACE/GRACE-FO total terrestrial water storage (TWS) estimates to capture plant-accessible water supply at depth. We use ESA CCI surface soil moisture (SM) estimates to represent shallow water storage and MODIS EVI as a proxy for grassland productivity. We calculate the inter-annual correspondence of EVI against both TWS and SM over 24 GRACE mascons covering the majority of the global grassland areas. Our results show that complementary to SM measurements, TWS provides unique information about deeper water storage limiting grassland growth. We find that the seasonal change of TWS constrains plant-accessible water storage and leads to different plant-water relations in the grassland regions across the globe.