Does groundwater enhance evaporative cooling?

Abstract:

Evaporation is a key process in land-climate interactions, not only because it directly regulates the hydrological cycle, but also because it contributes to the Earth’s energy balance. Due to its feedbacks on large-scale water processes and its impact on the dynamics of the atmosphere, it has been considered as a driver of droughts and heatwaves^1-3. While evaporation from ocean surfaces is likely to increase with rising temperatures, it is unclear whether evapotranspiration from land surfaces could similarly increase, due to possible limitations imposed by soil moisture and vegetation physiology⁴.
Observations suggest that groundwater (hereafter GW) has an important role in hydrological budgets and soil moisture variability in many regions, supplying moisture for evapotranspiration during dry seasons^{5, 6}. Although modeling studies suggest that GW is often close enough to the surface to interact with the atmosphere^{7, 8}, the soil water storage is often underestimated by land surface models. This is most likely due to neglecting the lateral movement of water from topographically higher altitudes to valley bottoms and its convergence close to the land surface, as well as the upward movement of water in the capillary fringe.
The focus of this study is to understand where and when GW may significantly enhance the availability of soil water for evapotranspiration. We also quantified the potential contribution of GW to evapotranspiration in the areas where GW is a major supply. We used the global network of eddy covariance observations⁹ (FLUXNET) along with global modeled GW depth¹⁰ and GLEAM ET model estimates¹¹ to address the current gap in modelling ET due to neglecting GW supply.
Having identified areas where GW is tightly coupled with the atmosphere through evaporation processes, the study provides the basis to examine the “air conditioning effect” of GW and test the idea if GW enhances evaporation to the extent that leads to a cooler temperatures and wetter climates.