Changes in connectivity and hydrological efficiency following wildland fires in Sierra Madre Oriental, Mexico

Fire modifies soil surface, and hence soil hydrological properties change after wildland fires. High fire severity causes partial or total removal of vegetation, reduction of soil aggregate stability and increased water repellency, which are associated with high runoff and erosion. The spatial connection among these runoff sources is an important factor to consider when evaluating fire-induced changes on hillslope and catchment hydrology, as fire generates connected areas of bare soil, which may increase hydrological connectivity and hence post-fire runoff and erosion. The aim of this study was to quantify changes in hydrological connectivity and efficiency in two burned areas in central Mexico. By integrating rainfall simulation and spatial analysis, an index of connectivity (IC) and the lateral hydrological efficiency index (LHEI) were computed based on land/cover use, fire severity and topography within 287 burned sub-basins. Post-fire IC and LHEI were compared with the pre-fire scenario, and the relationship between LHEI and the proportion of burned area was assessed at the sub-basin level. Thresholds of the burned area per fire severity needed to increase LHEI were determined by a classification tree. The index of connectivity and LHEI were higher after wildland fires. The burned area was positively related with LHEI, and at least 43.3% of area burned with high severity is sufficient to produce the highest LHEI. The results are evidence of the effect of fire on hydrological connectivity and efficiency which adds to the understanding of fire-hydrology relations and can be used for integrated catchment management, ecological restoration and risk assessment.