Incorporating Plant Access to Groundwater in Existing Global, Satellite-Based Evaporation Estimates

Groundwater is an important water source for evaporation, especially during dry conditions. Despite this recognition, plant access to groundwater is often neglected in global evaporation models. This study proposes a new, conceptual approach to incorporate plant access to groundwater in existing global evaporation models, and analyses the groundwater contribution to evaporation globally. To this end, the Global Land Evaporation Amsterdam Model (GLEAM) is used. The new GLEAM-Hydro model relies on the linear reservoir assumption for modeling groundwater flow, and introduces a transpiration partitioning approach to estimate groundwater contributions. Model estimates are validated globally against field observations of evaporation, soil moisture, discharge and groundwater level for the time period 2015-2021, and compared to a regional groundwater model. Representing groundwater access influences evaporation in 22% of the continental surface. Globally averaged, evaporation increases by 2.5 mm year(-1) (0.5% of terrestrial evaporation), but locally, evaporation can increase up to 245.2 mm year(-1) (149.7%). The groundwater contribution to transpiration is highest for tall vegetation under dry conditions due to more frequent groundwater access. The temporal dynamics of the simulated evaporation improve across 75% of the stations where groundwater is a relevant water source. The skill of the model for variables such as soil moisture and runoff remains similar to GLEAM v3. The proposed approach enables a more realistic process representation of evaporation under water-limited conditions in satellite-data driven models such as GLEAM, and sets the ground to assimilate satellite gravimetry data in the future.

Automated summary

This study proposes a new approach to incorporate plant access to groundwater in global evaporation models and analyzes the contribution of groundwater to evaporation globally. The proposed approach improves the representation of evaporation under water-limited conditions and has the potential to assimilate satellite gravimetry data in the future.