Spatial analysis of daily rainfall concentration in Paraíba State, Brazil

Recent studies indicate a reduction of total rainfall and an increase of extreme rainfall events in the Brazilian Northeast region. It is crucial to understand the concentration of daily rainfall for environmental planning and land management. This study performs the analysis of the daily rainfall concentration for the Paraíba State in the period between 1970 and 2019, using data from 26 rainfall stations across the State. Additionally, to the total annual precipitation (PP), the following concentration indicators were applied: frequency of days with precipitation up to 20mm (R20MM), maximum daily rainfall (Rx1Day), maximum rainfall over 5 days (Rx5Day), frequency of days with precipitation in the 10th (P10), 90th (P90), 95th (P95), and 99th (P99) percentiles, number of rainy days (NRD), and the Concentration Index (CI), which estimates the contribution of daily rainfall to the annual total. The Mann-Kendall test and Sen's slope were applied to identify possible trends in the time series and its magnitude. Spatially, the highest concentration values were observed in the Litoral and Brejo regions, decreasing towards the State hinterland. Temporally, most indicators displayed negative trends, suggesting reductions in both annual rainfall totals and rainfall on isolated days or groups of days. However, the CI showed predominantly an upward trend, indicating increased rainfall concentration. P10 values also exhibited an increase tendency, suggesting that days with the lowest rainfall amounts are becoming more frequent.