Identification and observed changes in the rainy season onset and termination in Central Chile

Abstract

The onset and termination of the rainy season shape the planning and operation of water resources systems. Thus, we identify the onset and termination in Central Chile (32–40°S) from 1960 to 2021 based on the occurrence of frequent wet spells (consecutive days with rainfall ≥1 mm). The method yields a latitudinal gradient on both the onset and termination dates consistent with the latitudinal variation of annual precipitation. We report robust shortening trends for the rainy season north of 35°S over the last 30 years (up to 7 weeks per decade), primarily due to a delay in the onset date. Between 1990 and 2021, the number of wet spells exhibited a significant negative trend north of 35°S and a significant negative trend in the average precipitation per wet spell in 32–40°S. The changes in precipitation timing and the significant decline in precipitation observed in Central Chile are then affecting the current water infrastructure.