Spatial analysis of propagation thresholds from meteorological to hydrological droughts in the São Francisco river catchment, Brazil

Effective water management requires a deeper understanding of the spatiotemporal dynamics of thresholds that trigger the propagation from meteorological to hydrological droughts. In this sense, this study resorts to a probabilistic approach for assessing the likelihood of occurrence of a hydrological drought at distinct levels (moderate, severe, and extreme) conditioned to the durations and severities of meteorological droughts. The aim is to investigate how climate conditions and catchment characteristics influence these propagation thresholds. Therefore, critical thresholds were estimated for 50 sub-basins in the Alto São Francisco River Basin, Brazil. The duration thresholds, whose medians were 3.61, 5.58, and 10.67 months for moderate, severe, and extreme events, respectively, were not too different across the study region, for all levels, and no clear spatial patterns could be found for this statistic. The severity thresholds, on the other hand, were more structured in space, with medians 4,13, 6.81, and 10.09 for the referred levels, but much more dispersed. Additionally, we analyzed the correlations among the propagation thresholds and mean annual precipitation, baseflow index, and land use characteristics of the sub-basins, but no significant relationships were identified. Our results highlighted the difficulties in describing the spatial variability of the propagation thresholds, due to the complex interactions of climate, storage, and human intervention. Despite these limitations, the proposed approach proved able to capture the joint variations of drought statistics and might be useful for water resources management, promoting better decision-making and the development of appropriate mitigation strategies.