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- Title
Incorporating Plant Access to Groundwater in Existing Global, Satellite‐Based Evaporation Estimates.
- Authors
Hulsman, P.; Keune, J.; Koppa, A.; Schellekens, J.; Miralles, D. G.
- Abstract
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. Plain Language Summary: Groundwater can be a crucial source of water for plants: plants that have access to groundwater through their root system are more likely to survive periods of rainfall scarcity. However, many (satellite‐based) models neglect this water source and assume plants only depend on the unsaturated‐zone soil moisture. This assumption results in underestimated evaporation values during dry conditions, when groundwater may become the main (or even the only) source of water. In this study, we propose a new approach to improve evaporation estimates under water‐stressed conditions by incorporating groundwater in an existing global, satellite‐based evaporation model, and we assess the impact of groundwater on evaporation globally. The impact of this modification on the model's accuracy and on the resulting evaporation is evaluated. Representing groundwater increases the evaporation globally by 2.5 mm year−1 (0.5%) with much higher increases in certain regions. Key Points: Plant access to groundwater is often ignored in global evaporation estimates, yet it can be crucial during dry conditionsA new, conceptual approach to incorporate groundwater‐sourced evaporation in existing global, satellite‐based models is presentedConsidering groundwater affects the dynamics of evaporation in 22% of the continental surface and increases global land evaporation by 0.5%
- Subjects
GROUNDWATER; WATER table; GROUNDWATER flow; PLANT-water relationships; SOIL moisture; RAINFALL; HYDROELECTRIC power plants
- Publication
Water Resources Research, 2023, Vol 59, Issue 8, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2022WR033731