Abstract: Using daily precipitation observation data from 34 national meteorological stations in Chongqing from 1971 to 2024 , this study aims to explore the evolution characteristics of the rainy season onset dates in Chongqing. Methods such as correlation analysis , M-K test , and Morlet wavelet analysis are applied . The results show that : (1) The onset of rainy season in Chongqing spans a wide temporal range , with multi-year average onset dates ranging from late April to mid-May , demonstrating a progressive trend gradually from the central region to the western and northeastern regions . The inter-annual variation of the rainy season onset dates is also large , with the earliest onset across the city in 2002 and the latest in 2007 , so there is a difference of 29 days between the earliest and latest onset dates of rainy season . There are 12 years with later onset and 11 years with earlier onset of rainy season . (2) The variation of accumulated precipitation in April-May is closely related to the rainy season onset time . In most years with earlier (later) onset of rainy season , the accumulated precipitation in April-May is more (less) . (3) The inter-annual variability in the early 21st century and around the 2010s is more pronounced in the 10 - to 14-year cycle , the inter-annual variability in the late 1980s and early 1990s is more prominent in the 6 - to 8 - year cycle , and the inter-annual variability in the late 2010s exhibits a stronger signal in the 4-year cycle . In conclusion , the spatial distribution and inter-annual variation of the rainy season onset dates in Chongqing are both large , with a difference of up to 29 days between the earliest and latest onset dates . The inter-annual variability of the rainy season onset in Chongqing shows a certain periodic change .