Rainfall and streamflow extreme events in the Sao Francisco hydrographic region

Extreme rainfall and streamflow events are becoming increasingly more relevant to discussions concerning potential climate changes on planet earth. In most cases, impacts related to the occurrence of such phenomena can be amplified due to the lack of planning and structure. In this context, the main objective of the study is to estimate the period and level of return of intense rainfall events in homogeneous subregions of the Sao Francisco hydrographic region, as well as to define which of these subregions are most vulnerable to the recurrence of these episodes. We used rainfall data from 105 rain gauges and streamflow data from 103 stream gauges comprising the years from 1988 to 2017. Through cluster analysis, four homogeneous rainfall subregions were defined and validated by the silhouette index, capable of identifying misallocated stations in the clustering process. A generalized Pareto distribution from the extreme value theory was used to calculate the period and level of return of intense rainfall events in each subregion. We then related the retrieved estimates with information about the drainage network, streamflow, land use and occupation, and socioeconomic and demographic factors in the watershed region. Results indicated the existence of subregions vulnerable to hydrological and geological processes intensified due to human activity and the recurrence of hydrometeorological phenomena. The scenarios found for the recurrence of intense rainfall events indicated the severity to which some subregions may be subjected, moreover, they reinforce the need for the development of public policies for the prevention and minimization of impacts.