Vegetation patterns and soil-atmosphere water fluxes in drylands

Local soil water-vegetation feedbacks play an essential role in vegetation pattern formation in drylands. However, the impact of spatial vegetation patterning on atmosphere-soil water fluxes, and thus on vegetation-climate interactions, is still unknown, even though this issue is crucial to determine how much detail is needed in representing vegetation-atmosphere dynamics in climate models. In this work, we explore whether evapotranspiration fluxes depend only on bulk vegetation characteristics, such as biomass density or vegetated fraction, or rather they depend also on the spatial vegetation pattern dynamics. To address this point, we introduce a new explicit-space model for vegetation dynamics in water-limited ecosystems, which includes two soil layers and is able to correctly represent evapotranspiration in the presence of intermittent rainfall conditions. The model dynamics display spatial self-organization of vegetation with multiple stable states, and the model outcomes reveal that transpiration fluxes in the days following a rainfall event depend on the type of vegetation pattern. The difference in transpiration per unit mass between spots and stripes is about 10%. The results of the simulations also indicate that fluxes from fixed vegetation (representing e.g., cultivated areas) can be very different from those above dynamically evolving vegetation, even when the two vegetation types cover the same fraction of space and have the same biomass density.