Rainfall Trends and Multi-Scale Variability in the Water-Receiving Area of the Zhejiang East Water Diversion Project: A 62-Year Analysis

Using daily rainfall observations from 1961 to 2022 (62 years) across 15 typical sub-regions within the water-receiving area of the Zhejiang East Water Diversion Project, this study systematically examines the spatiotemporal distribution, long-term trends, multi-scale variability, and inter-regional correlations of rainfall. An integrated framework was employed, including the Mann–Kendall (MK) trend test, Sen’s slope estimator, Hurst exponent analysis, and multi-scale sliding window analysis. Spatially, the multi-year average daily rainfall ranges from 3.47 mm to 5.68 mm, following a distinct “high in the center, low in the west” pattern, with the Yuyao Plain Mazhu Midstream Area identified as the regional rainfall maximum. In the raw Mann–Kendall test all 15 sub-regions exhibit increasing trends, of which 14 remain statistically significant (p < 0.05) after trend-free pre-whitening; Sen’s slopes follow a “coastal > riverine > hilly” gradient. Hurst exponents greater than 0.5 suggest persistent behavior in the rainfall series, although attribution to external forcing or separation from low-frequency climate variability requires additional analysis. Multi-scale sliding window analysis reveals strong scale dependence: the amplitude of trend fluctuations decreases by approximately 90% from ±16 mm at the 3-month scale to ±1.7 mm at the 12-month scale, while inter-regional correlation coefficients increase from 0.83 to 0.87. Notably, the Yuyao Plain Mazhu Midstream Area displays a unique “increase-then-decrease” correlation pattern, reflecting its distinctive hydro-geographic conditions. These findings provide a scientific basis for climate-adaptive scheduling of water diversion projects, supporting water security, urban resilience, and climate action.