Biophysical impacts of Earth greening modulate average and extreme water availability

Surface water availability (WA), defined as precipitation minus evapotranspiration, is affected by changes in vegetation structure. These biophysical impacts can alter the distribution of water availability, shifting both its average and extreme values, while the divergence is not yet quantified. Using long-term remote sensing observations, our analysis reveals that increases in leaf area index (LAI) lead to a widespread decline in average water availability, with a global reduction of -2.11 mm/month m² m^-2. Additionally, we show that in humid regions, extreme water availability—represented by the 15th and 85th percentiles of water availability from 2001 to 2020—exhibits stronger sensitivity to LAI variations than average water availability. Overall, the fraction of variance in low water availability explained by greening is minimal (-2.7%), followed by average water availability (6.8%), while high water availability exhibits the largest fraction (-23.6%).