  In the Monte desert, increasing population density, changing land rights and
infrastructure may encourage livestock activity, with unknown consequences on
ecosystems. Factors that influence livestock settlement distribution may affect
ecosystem degradation. We hypothesize that surface and groundwater availability
influence livestock settlements distribution. We evaluated this hypothesis with
a Monte Carlo based model to simulate Settlement Dynamics in Drylands (SeDD),
which calculates probabilities on a gridded region based on six environmental
factors: groundwater depth, vegetation type, proximity to rivers, paved roads,
old river beds, and existing settlements. A parameter sweep, including millions
of simulations, was run with combinations of parameters related to these
factors. The sets of parameter values that minimized the residuals between
simulations and observations indicated the relative importance of each factors
on settlement distribution. Distances to rivers and old river beds were
critical to explain the current distribution of settlements, while vegetation,
paved roads, and water table depths were not important. Spatial distribution of
simulated vegetation, which included degradation around livestock settlements,
generally agreed with remotely sensed vegetation classes. The model could be a
useful tool to evaluate the effects of land use changes (water provision, river
flows), on settlement distribution and vegetation degradation in arid
environments.
