A Modeling Framework to Investigate Impact of Increased Storm Variability on Self-Organized Vegetation Patterns in Drylands

Banded patterns of vegetation growth on gentle slopes can be found in certain dryland regions. The soil water and biomass dynamics act on a slow timescale, and infrequent rainstorms inject water into the system on a fast timescale. We model the slow subsystem as the time-evolution of a reaction-diffusion equation, and we treat the storms as instantaneous kicks of added water. The water is deposited inhomogeneously due to differences in the infiltration rate and downhill flow speed in areas with dense biomass versus bare soil. Specifically, biomass impedes the downhill flow of surface water and increases infiltration, which leads to the surface water left by a storm being concentrated in the soil near the uphill edge of a vegetation band. We explore the effect of storm variability by introducing randomness into the timing and the amount of water deposited by storms. We are particularly interested in how storm variability affects the resilience of the vegetation patterns compared to the idealized case of identical, regularly-timed storms, as this may give insight into potential risks of ecosystem collapse due to increased variability brought about by climate change.