Time lag effect of precipitation on groundwater level based on wavelet analysis in the People’s Victory Canal irrigation area, China

The People's Victory Canal irrigation area is an important agricultural irrigation region in the North China Plain, where groundwater resources play a crucial role in both agricultural production and the ecological environment. However, in recent years, the increasing depth of the groundwater, influenced by climate change and human activities, has posed significant challenges to the sustainable use of water resources in the region. Therefore, exploring the lag effect and its trends between precipitation and groundwater depth is essential for the scientific management of groundwater resources and optimizing water allocation. This study is based on the monthly average precipitation and groundwater depth data from the Xiazhuang in the People's Victory Canal irrigation area from 1993 to 2021. It uses methods such as continuous wavelet transform, cross-wavelet transform, and cross-correlation analysis to systematically analyze the lag effect and its changing patterns of groundwater table depth in response to precipitation at different time scales. The study finds that during the research period, precipitation generally showed a downward trend, while the groundwater table depth continuously increased and experienced a sudden change in 1999, after which it rose significantly. Before 2000, there was a strong correlation between precipitation and groundwater depth, with a noticeable response of groundwater depth to changes in precipitation, and the lag time was about 58.97 days. However, after 2000, this relationship gradually weakened, especially in years other than those with abundant rainfall, where the influence of precipitation on groundwater depth decreased significantly, and the lag time increased to 6 to 8 months. The study shows that before 2000, abundant precipitation led to a shallower groundwater, and the groundwater was more significantly influenced by precipitation. After 2000, reduced precipitation and the increased depth of the groundwater table weakened the response of groundwater to precipitation, thus enhancing the lag effect. This trend reflects a change in the mechanism of precipitation recharge to groundwater, which is likely closely related to intensified human activities, changes in the irrigation water extraction methods, and over-extraction of groundwater. The findings of this study can provide a scientific basis for water resource management in the irrigation area, helping to formulate appropriate groundwater regulation measures and ensure the sustainable use of regional water resources.