Contribution of precipitation to terrestrial water storage recovery in the Haihe Basin based on GRACE data

Terrestrial water storage (TWS) in the Haihe Basin is vital to ecosystem function and socioeconomic development, but it is subject to disturbances from climate change and human activities. After more than a decade of operation of the South-to-North Water Diversion (SNWD) Project, groundwater levels in the basin have rebounded markedly; however, this recovery temporally coincides with recent frequent extreme rainfall events. Although recent studies largely attribute this recovery to the SNWD Project, the specific contribution of natural precipitation is yet quantitatively constrained. This study integrates multiple precipitation datasets with Gravity Recovery and Climate Experiment (GRACE) observations to quantify the precipitation-driven contribution to TWS change (TWSC) from 2004 to 2024, utilizing a precipitation-TWSC linear regression model. Results indicate the precipitation has increased by 113.5 mm (21.7%) in the late wet period (2016-2024). Therefore, regression analysis was conducted separately for the periods of 2004-2015 and 2016-2024. The segmented regression results reveal a significant shift in the intercept term (from -9.3 mm to -42.4 mm, indicating the TWSC under an average precipitation condition), while the precipitation-to-TWSC conversion rate slightly increased from 47% (95% confidence interval (CI): 11%-77%) to 56% (95% CI: 34%-74%). The trend of terrestrial water storage anomalies (TWSA) in the Haihe Basin increased from -5.99 Gt/yr for the period 2003-2015 to 2.52 Gt/yr for 2016-2024, a difference of 8.51 Gt/yr. At the water input end, the precipitation input increased by 33.42 Gt/yr between the two stages, but the cross-basin water diversion volume including the SNWD project increased by only 5.09 Gt/yr. The ratio of the precipitation increment to the cross-basin water diversion increment is 6.6:1. The data difference indicates the recent TWS recovery in the Haihe Basin is dominantly driven by precipitation increase. These findings provide quantitative data support for regional water resources management and climate adaptation strategies.