Evidence of Geological Control on the Hydrological Response of Tropical Volcanic Catchments

The aim of this study is to assess the key drivers of runoff generation in permeable volcanic catchments, and notably the role of geology. Therefore, the hydrological response of 28 catchments located on the tropical volcanic Island of la Réunion, characterised by strong climatic forcing and geological contrasts, was studied. High‐frequency measurements (15‐min time step) of radar rainfall and discharge records over the 2014–2022 period were analyzed to develop a hydroclimatic database including 4591 storm‐flood events. At the annual scale, results show regional patterns in the rainfall‐runoff relationship, associated with the geological age and the local climate. Our results provide evidence of windward/leeward and geological effects on hydrological response at both the annual and flood event scales, with a significant correlation between the event‐scale runoff coefficient and annual rainfall. Combined with a statistical analysis of the data, including the application of a random forest algorithm, results suggest the importance of antecedent saturation conditions, preferentially occurring on the older and more weathered geology, while younger geology displayed a more episodic pattern. This study contributes to increasing our understanding of the hydrological behaviour of tropical volcanic catchments, by analysing the relative importance of climate and geology in controlling the catchments' hydrological response, which may help improve water management and flood prediction.