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We developed an open source Monte Carlo based model to simulate Settlement Dynamics in Drylands (SeDD). The model assigns partial probabilities to each pixel within a grid region, based on several factors that can influence the establishment and subsistence of settlements: groundwater depth, vegetation type, proximity to rivers, paved roads, old river beds, and existing settlements. Partial probabilities are considered to be independent from each other, and therefore multiplied to calculate an overall probability for each pixel. Settlements are assigned by maximum probabilities or randomly, according to pre-established threshold probability values. We also modeled the gradual reduction of vegetation caused by a new settlement in neighboring pixels, decreasing the probabilities related to vegetation type. The final distribution of settlements is given by an average over multiple Monte Carlo simulations. The model is computationally efficient and could be used to rapidly explore different scenarios of settlement dynamics and vegetation degradation in arid environments, and other environmental factors that can be added to the framework without performing changes in the source code. (C) 2016 Elsevier B.V. All rights reserved.