Water Constraint is Limiting Global Gross Primary Productivity

 

We use a light use efficiency model (LUE)  to describe gross primary productivity (GPP) from 1982 to 2016 using the GIMMS-3g FPAR record and NASA MERRA-2 reanalysis, and explore how GPP trends and anomalies can be explained using annual changes in temperature and hydrology. The GPP model uses optimum LUE (LUE_opt) inferred from the global FLUXNET network and extrapolated using solar induced chlorophyll fluorescence observations. We find that increasing trends in GPP at mid to high latitudes over the 35-year study period are due to reduced cold temperature of plant growth constraints. Our results suggest a persistent and increasing negative carbon-climate feedback at mid to high latitudes. We also find an increasing atmospheric vapor pressure deficit trends over the tropics, which represents an emerging positive climate feedback that results in a negative trend in GPP after the early 2000s. We expect that further warming, increasing water constraints, and disturbance events will significantly reduce global ecosystem productivity.