Padrões climáticos regionais de precipitação e temperatura no clima futuro na bacia hidrográfica do rio São Francisco

Abstract

Studies on climate change, especially at the watershed scale, require better spatial resolutions than those of Global Circulation Models (GCMs). One way to address this limitation is through downscaling, which refers to techniques for scaling down or regionalizing. This regionalization, based on physical or statistical approaches, is applied to the output variables of GCMs so that they provide a better signal of climate at the spatial scale of interest. The objective of this research was to evaluate changes in climate patterns through statistical regionalization applied to the Model for Interdisciplinary Research on Climate (MIROC), versions 5 and 6, in the São Francisco Watershed (SFW). This watershed is essential for supplying water to rural and urban areas in the Brazilian Northeast, especially in its semiarid region. To assess regional climate changes, the Bias Correction Constructed Analogs with Quantile Mapping Reordering (BCCAQ) statistical reduction method was applied to the daily precipitation, maximum temperature, and minimum temperature variables of MIROC5 and MIROC6. Regionalizations for historical climate were compared with original MIROC outputs using measures of mean error (ME), root mean square error (RMSE), standard deviation ratio (rSD), coefficient of determination (R²), and percentage bias relative to the mean of observations (PBIAS), as well as spatial distribution and time series. The results indicate that regionalization reduces systematic bias for maximum and minimum temperatures, with small corrections to both maximum and minimum values in both calibration and validation periods. Regarding precipitation, BCCAQ satisfactorily corrected the annual precipitation cycle but overestimated in the headwaters region of the river, the Upper São Francisco (USF). Regionalization measures showed absolutely lower ME, RMSE, rSD, and PIBIAS in all sub-regions of the basin. In the study for future scenarios, maximum and minimum temperatures increase throughout the basin and sub-regions, mainly in SSP5-8.5 and RCP 8.5 scenarios, with a slight decrease in precipitation in the USF and Middle SFW regions.