Abstract
AbstractIt is well accepted that summer precipitation can be altered by soil moisture condition. Coupled land surface – atmospheric models have been routinely used to quantify soil moisture – precipitation feedback processes. However, most of the land surface models (LSMs) assume a vertical soil water transport and neglect lateral terrestrial water flow at the surface and in the subsurface, which potentially reduces the realism of the simulated soil moisture – precipitation feedback. In this study, the contribution of lateral terrestrial water flow to summer precipitation is assessed in two different climatic regions, Europe and West Africa, for the period June–September 2008. A version of the coupled atmospheric‐hydrological model WRF‐Hydro with an option to tag and trace land surface evaporation in the modelled atmosphere, named WRF‐Hydro‐tag, is employed. An ensemble of 30 simulations with terrestrial routing and 30 simulations without terrestrial routing is generated with random realizations of turbulent energy with the stochastic kinetic energy backscatter scheme, for both Europe and West Africa. The ensemble size allows to extract random noise from continental‐scale averaged modelled precipitation. It is found that lateral terrestrial water flow increases the relative contribution of land surface evaporation to precipitation by 3.6% in Europe and 5.6% in West Africa, which enhances a positive soil moisture – precipitation feedback and generates more uncertainty in modelled precipitation, as diagnosed by a slight increase in normalized ensemble spread. This study demonstrates the small but non‐negligible contribution of lateral terrestrial water flow to precipitation at continental scale.
Highlights
The interaction between soil moisture and climate has been a subject of debate in the scientific community for several decades (e.g., Seneviratne et al, 2010), as a better knowledge of the state of the land surface can potentially improve climate model skills (e.g., Berg et al, 2016; Dirmeyer et al, 2009; Zhou et al, 2019)
In West Africa, a relative increase in land precipitation recycling by up to 10% is found north of 12N, which suggests an enhanced sensitivity of monsoonal squall lines to lateral terrestrial water flow
This study provides the first model evaluation of the contribution of lateral terrestrial water flow to precipitation at continental scale for Europe and West Africa
Summary
The interaction between soil moisture and climate has been a subject of debate in the scientific community for several decades (e.g., Seneviratne et al, 2010), as a better knowledge of the state of the land surface can potentially improve climate model skills (e.g., Berg et al, 2016; Dirmeyer et al, 2009; Zhou et al, 2019). At global scale the positive feedback process is expected to dominate, and the global negative trend in soil moisture is expected to reduce the overall land precipitation (Berg et al, 2016; Zhou et al, 2019)
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