HEGFES: a modelling framework for spatially explicit ecohydrological feedbacks

The Hydro-Eco-Geo-FEdback Simulator (HEGFES) is a multi-dimensional, multi-domain and multi-physics simulator developed to study environmental feedback processes at their relevant spatial scales. The objective of HEGFES is to allow a simple and accessible way to test multiple feedback interactions among surface and subsurface hydrodynamics, hydrological, morphological, vegetation and ecohydrological processes, at different levels of complexity and spatial resolutions. HEGFES aims to acknowledge and simulate emergent behaviours rising from the small-scale interactions and feedbacks between different environmental processess, which often manifest at larger spatiotemporal scales. In consequence, the model framework is designed to allow for spatially explicit simulations of sets of environmental processes. Despite the complexity that the goal entails, its design is modular, based on a discrete cellular-automata approach, although allowing for rigorous physically-based formulations for fluxes. Of particular importance is the modular and highly flexible formulation of feedback operators, which allow to modify properties, rates, and processes of one model component due to the states of other model components. The different model components have been validated agains available reference solutions. Herein, we present the model structure and philosophy, and illustrate its application and potential by studying the feedbacks leading to vegetation pattern formation in dryland ecosystems. In the context of such systems, our approach allows to relax some of the simplying assumptions, by explicitly computing the spatial redistribution of water over complex topography at event time scale all the way to decades or centuries.