Deep root vegetation adaptations to drought and their modulation of evapotranspiration (ET) in Africa

Soil moisture exerts a strong influence on the surface energy balance, boundary layer development, convection, and precipitation, particularly in climates with seasonal drought where ET is water-limited. Lacking precipitation and surficial water sources, vegetation develops deep roots to access subsurface moisture stores from past precipitation or groundwater, effectively coupling the atmosphere to these slowly varying water reservoirs. Here we focus on Africa and ask how vegetation deep rooting systems over seasonally dry climates like those in the savannas modulate land surface fluxes, particularly during the transition from dry to wet seasons. We use the Noah-MP model with a newly implemented deep rooting scheme coupled to the MMF groundwater scheme and perform off-line simulations over Africa, comparing results with the default version with 2m soil columns and fixed roots depending on vegetation class- an approach still used by most land surface models. Atmospheric forcing is from ERA5.

Our results reveal that vegetation has a greater influence on ET fluxes across much of the African continent than most models assume, which can have implications for our current understanding of soil moisture-precipitation interaction in this well known hot-spot for land-atmosphere coupling.