Rainfall Trends and Multi-scale Variability in the Water-receiving Area of the Zhejiang East Water Diversion Project.

Authors

ZENG Tian-li¹, ZUO Xiao-xia¹, YANG Yu¹, DAI Huan¹, WU Mu-hong², ZHONG Lü-bin², CHEN Shu-yang³

1. Zhejiang Design Institute of Water Conservancy and Hydroelectric Power Co., LTD., Hangzhou 310002, China
2. Qingyuan County Water Conservancy Bureau, Lishui, Zhejiang 323800, China
3. Zhejiang Yansi Information Technology Co., Ltd., Hangzhou, Zhejiang 310051, China

Abstract

This study systematically investigates the spatiotemporal distribution characteristics, long-term trends, multi-scale variability, and regional correlation of rainfall in 15 typical sub-regions of Eastern Zhejiang based on long-term daily rainfall observation data from 1961 to 2022 (62 years). Employing the Mann-Kendall (MK) trend test, Sen’s slope estimation, Hurst exponent analysis, and multi-scale sliding window analysis, this research provides comprehensive insights into rainfall dynamics within the influence area of the Eastern Zhejiang Water Diversion Project.

Regarding spatial distribution, daily average rainfall ranges from 3.47 mm to 5.68 mm, exhibiting a distinct “high-in-center, low-in-west, medium-in-east” spatial pattern. The central high-value area (Yuyao Plain Mazhu Midstream Area) reaches 5.68 mm, while the western low-value area (Nansha Plain Area) records only 3.47 mm.

In terms of long-term trends, Mann-Kendall tests reveal that all 15 sub-regions exhibit statistically significant upward trends (p<0.05). Sen’s slope estimates demonstrate spatial differentiation in trend magnitude following a “high-in-coastal, medium-in-river, low-in-hilly” pattern. Hurst exponent analysis (H > 0.5) confirms that the observed upward trends possess long-term persistence.

The multi-scale variability analysis through sliding window reveals pronounced scale dependence. At the 3-month scale, precipitation exhibits high instability with large trend fluctuations (±16 mm) and low correlation. At the 12-month scale, trends become more stable (±1.7 mm) with improved correlation, indicating that long-term patterns are controlled by large-scale climate factors.

With respect to regional correlation, inter-regional correlations strengthen with increasing time scale, rising from 0.83 (3-month) to 0.87 (12-month). Notably, the Yuyao Plain Mazhu Midstream Area displays a unique “increase-then-decrease” correlation pattern, reflecting its special hydro-geographic conditions.

For engineering implications, the post-2010 intensification of rainfall fluctuations necessitates optimized scheduling strategies for the Eastern Zhejiang Water Diversion Project to enhance flood control and supply security under changing climate conditions.

Keywords

Eastern Zhejiang Water Diversion Project; rainfall spatiotemporal distribution; Mann-Kendall test; Sen’s slope estimation; Hurst exponent; multi-scale analysis; scale dependence