A Study on the Response of Precipitation to Climatic and Ecological Factors in the Middle and Lower Reaches of the Yellow River Based on Wavelet Analysis

Regional precipitation patterns are influenced by a combination of global climatic drivers and local environmental conditions. This study takes Henan Province, located in the middle and lower reaches of the Yellow River, as a case study. Using wavelet analysis, cross-wavelet transform (XWT), and wavelet coherence (WTC), we investigated the periodic relationships between summer (July) precipitation in Henan Province during 1983–2022 and four key factors: El Niño–Southern Oscillation (ENSO), East Asian Summer Monsoon (EASM), Western Pacific Subtropical High (WPSH), and Normalized Difference Vegetation Index (NDVI). The results indicate that (1) Precipitation shares a common periodic signal at approximately 3–6 years with all influencing factors, and additionally exhibits low-frequency co-variability at the 18–20-year timescale with ENSO, EASM, and WPSH; (2) ENSO, EASM, and WPSH are identified as the primary drivers of precipitation variability in the middle and lower reaches of the Yellow River; (3) In recent years, anomalous summer precipitation in this region has been closely linked to the periodic activities of ENSO, EASM, and WPSH.