Global patterns of water storage in the rooting zones of vegetation

Abstract

The rooting-zone water-storage capacity—the amount of water accessible to plants—controls the sensitivity of land–atmosphere exchange of water and carbon during dry periods. How the rooting-zone water-storage capacity varies spatially is largely unknown and not directly observable. Here we estimate rooting-zone water-storage capacity globally from the relationship between remotely sensed vegetation activity, measured by combining evapotranspiration, sun-induced fluorescence and radiation estimates, and the cumulative water deficit calculated from daily time series of precipitation and evapotranspiration. Our findings indicate plant-available water stores that exceed the storage capacity of 2-m-deep soils across 37% of Earth’s vegetated surface. We find that biome-level variations of rooting-zone water-storage capacities correlate with observed rooting-zone depth distributions and reflect the influence of hydroclimate, as measured by the magnitude of annual cumulative water-deficit extremes. Smaller-scale variations are linked to topography and land use. Our findings document large spatial variations in the effective root-zone water-storage capacity and illustrate a tight link among the climatology of water deficits, rooting depth of vegetation and its sensitivity to water stress.

Forest productivity recovery or collapse? Model‐data integration insights on drought‐induced tipping points

“…We first augment pre‐drought PAW to 2250 mm which is equal to 100% soil moisture in this study and should be seen as a theoretical maximum. A maximum PAW of 2250 mm is reasonable given that other studies have reported 1200 mm PAW in southern Sierra Nevada mid‐montane forests (Stocker et al, 2023) and 2017 was a particularly wet year with 1703 mm annual precipitation. We assume that the rooting depth maximum for the site is 4.5 m given that there is weathered bedrock–hard bedrock boundary at 4.5 m and that porosity for the study area is 0.5.…”

Four ways to define the growing season

“…Models use daily precipitation and potential evapotranspiration in combination with plant available soil moisture storage capacity (e.g., Churkina et al, 1999), and by solving the water balance equation, a moisture driven season can be defined (‘bucket model’: Paulsen & Körner, 2014; SVAT model: Meusburger et al, 2022). A novel satellite‐based approach is using estimates of actual evapotranspiration (ET) from a combination of surface temperature and net radiation (in essence by solving the Bowen‐ratio equation for latent heat flux) and infer the size of the remaining water stores from time series of precipitation and ET (Stocker et al, 2023).…”

A multi‐satellite framework to rapidly evaluate extreme biosphere cascades: The Western US 2021 drought and heatwave

“…Indeed, in the pixels where TWS Granger‐causes GPP, we find that previously estimated maximum rooting depths (Fan et al, 2017) are deeper by .55 m than in pixels where the causality is not detected ( p < .05 based on student's t ‐test of means). Additionally, several recent studies confirm plant water use of deeper soil stores across the Western United States, especially along the west coast (Kannenberg et al, 2023; McCormick et al, 2021; Miguez‐Macho & Fan, 2021; Stocker et al, 2023). As a result, despite similar rainfall deficits between 2020 and 2021, maintained TWS in 2020 resulted in smaller negative GPP anomalies throughout 2020; if TWS anomalies in 2020 were set to those in 2021, the negative GPP anomalies in 2020 would have at least doubled (Figure 7b).…”

“…Additionally, several recent studies confirm plant water use of deeper soil stores across the Western United States, especially along the west coast (Kannenberg et al, 2023;McCormick et al, 2021;Miguez-Macho & Fan, 2021;Stocker et al, 2023). As a result, despite similar rainfall deficits between 2020 and 2021, maintained TWS in 2020 resulted in smaller negative GPP anomalies throughout 2020;…”