Abstract
Atmospheric moisture recycling effectively increases the amount of usable water over land as the water can undergo multiple precipitation–evapotranspiration cycles. Differences in land cover and climate regulate the evapotranspiration flux. Forests can have deep roots that access groundwater facilitating transpiration throughout the dry season independent of precipitation. This stable transpiration buffers the forest against precipitation variability. However, it is not known whether the buffering effect, already modeled for tropical forests, is common to all forests globally. Here we apply a state‐of‐the‐art Lagrangian moisture tracking model (UTrack) to study whether forest land cover in the upwind precipitationshed can lead to a reduction in monthly precipitation variability downwind. We found a significant buffering effect of forests in the precipitation variability of 10 out of 14 biomes globally. On average, if 50% of precipitation originates from forest, then we find a reduction in the coefficient of variation of monthly precipitation of 60%. We also observed that a high fraction of precipitation from non‐forest land sources tends to have the opposite effect, that is, no buffering effect. The average variation of monthly precipitation was 69% higher in areas where 50% of precipitation originates from non‐forest land sources in the precipitationshed. Our results emphasize the importance of land cover composition in the precipitationshed to buffer precipitation variability downwind, in particular forest cover. Understanding the influence of land cover in a precipitationshed on atmospheric moisture transport is key for evaluating an area's water‐climate regulatory ecosystem services and may become increasingly important due to continued changes in land cover and climate change.
Highlights
Atmospheric moisture recycling is a highly important process in the hydrological cycle, as it effectively increases the available water within a catchment and at regional scales (van der Ent et al, 2010)
We investigated whether forests buffer against monthly precipitation variability across the globe and we find that, these contributions are fundamental to reduce precipitation variability downwind in 10 out of the 14 global terrestrial biomes we examined
We find that the buffering effect of forests was strongest for tropical biomes, that is, tropical moist forests, tropical savannas and mangroves
Summary
Atmospheric moisture recycling is a highly important process in the hydrological cycle, as it effectively increases the available water within a catchment and at regional scales (van der Ent et al, 2010) It is the process by which evaporated water is returned to the atmosphere where it can precipitate in situ or be carried downwind and precipitate out (Aragão, 2012). For vegetated land cover types, transpiration (Dekker et al, 2000) and leaf surface area increase interception evaporation (Vrugt et al, 2003) Short vegetation such as grasses and crops have a simple canopy structure and relatively shallow rooting depths, making transpiration strongly dependent on recent precipitation (O'Connor et al, 2019) while trees and forests have taller, more complex canopies that facilitate higher evapotranspiration. Such an understanding of these contributions of forest to atmospheriic moisture highlights the interdependency of downwind land cover types on water originating from forests elsewhere, a fundamental ecosystem service at local, regional and global scales
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