  We develop a model for investigating the impact of rainstorm variability on
the formation of banded vegetation patterns in dryland ecosystems. Water input,
during rare rainstorms, is modeled as an instantaneous kick to the soil water.
The redistribution, from surface water to soil moisture, accounts for the
impact of vegetation on infiltration rate and downslope overland flow speed.
These two positive feedbacks between water and biomass distributions act on the
fast timescales of rain storms. During dry periods, a classic
reaction-diffusion framework is used for the slow processes associated with
soil water and biomass. This pulsed precipitation model predicts that the
preferred spacing of the vegetation bands is determined by the characteristic
distance that a storm pulse of water travels overland before infiltrating into
the soil. In this way, the vegetation pattern is determined by the fast
ecohydrological processes and may be attuned with its dryland precipitation
pattern. We demonstrate how this modeling framework, suited for stochastic rain
inputs, can be used to investigate possible collapse of a dryland
pattern-forming ecosystem under different precipitation patterns with identical
low annual mean. Model simulations suggest, for instance, that shorter rainy
seasons and greater variability in storm depth may both hasten ecosystem
collapse.
