In the Brazilian semiarid region, characterized by erratic rainfall patterns, heavy precipitation events can disrupt soil structure, erode surface particles, and leach essential nutrients, thereby reducing land fertility and productivity. This study investigates the impacts of rainfall variability on rainfall erosivity, runoff, and soil erosion by employing climate indices to assess precipitation variability and the SWAT model to simulate hydrological responses in the Apodi-Mossor & oacute; River basin. To estimate soil erosion, the SWAT model was calibrated using hydro-meteorological data collected from 15 rainfall gauges and two runoff stations, covering the period from 1984 to 2018. Rainfall variability was assessed using the Mann-Kendall test, Sen's slope estimator, and seven precipitation indices: (a) maximum number of consecutive dry days in a year (CDD), (b) maximum precipitation in a single day (RX1DAY), (c) maximum precipitation over five consecutive days (RX5DAY), (d) number of days with precipitation > 10 mm/day (R10mm), (e) > 50 mm/day (R50mm), (f) > 100 mm/day (R100mm), and (g) total annual precipitation on days exceeding the 95th percentile (R95p). Rainfall erosivity was estimated using an equation adapted for the Brazilian semiarid region. Model performance was evaluated using the coefficient of determination (R-2), Nash-Sutcliffe efficiency (NSE), Kling-Gupta efficiency (KGE), and percent bias (Pbias). The findings reveal a decline in extreme precipitation events, suggesting a reduction in daily rainfall intensity on wet days, as indicated by trends in R95p values. Annual trend analyses showed that the greatest decreases in precipitation occurred at the Ant & ocirc;nio Martins (- 2.90 mm/year), Martins (- 2.38 mm/year), and Areia Branca (- 1.83 mm/year) stations, while Campo Grande (1.51 mm/year) and Alexandria (1.98 mm/year) exhibited the most significant increases. These variations highlight the complex spatiotemporal patterns of rainfall distribution and their influence on rainfall erosivity, surface runoff, and soil erosion in Brazil's semiarid region. This variability-likely driven by climate change and exacerbated by anthropogenic factors-has significant implications for agricultural productivity and water availability.