Evaluation of the Impact of Land Water Supply on the Distribution of Plant Productivity

Land water supply is a key component of the hydrological cycle. It influences plant growth and ecosystem productivity over land. The spatial correspondence between plant productivity and land water supply reflects how the hydrological cycle shapes land cover distribution and determines plant growth conditions. Evaluating such relationship using observations is essential to constrain Earth system models that couple terrestrial hydrology to the global carbon cycle. Previous works mostly relied on site-level measurements of mean annual precipitation and aboveground net primary productivity and found tight logistic plant-water relations over large climate gradients. In this study, we evaluate the capacity of various satellite-based water supply metrics to capture such plant-water relations. We use the SMOS and SMAP surface and root-zone soil moisture (SM) estimates, and GRACE/GRACE-FO total water storage (TWS) solutions to quantify water supply covering different soil depths. We use satellite-based solar-induced fluorescence measurements as a proxy for plant productivity. Initial results show that both SM and TWS estimates capture water limitation in dry land and saturated plant-water relations in wet regions, but compared with precipitation they show significantly different explanatory powers on the distribution of plant productivity. Similar analysis using atmospheric moisture demand as represented by vapor pressure deficit shows transition from energy to water limitation from cold to warm regions. These relationships are further evaluated against land cover distribution. The results are diagnostically compared with CMIP-6 model simulations for model improvement.