Presenter
Prof. Di Long, State Key Laboratory of Hydroscience and Engineering, Tsinghua University
Co-author(s)
Prof. Yang Cai, Information Center，the Ministry of Water Resources
Dr. Yingjie Cui, State Key Laboratory of Hydroscience and Engineering, Tsinghua University
Dr. Yanhong Cui, State Key Laboratory of Hydroscience and Engineering, Tsinghua University
Dr. Chen Li, State Key Laboratory of Hydroscience and Engineering, Tsinghua University
Sub-theme
1. Water-Human-Economy(Agriculture, Industry, City...)-Ecology Nexus under a Changing Environment
Topic
1-4. Water security challenges in key regions
Body
The South-to-North Water Diversion and reductions in groundwater withdrawals have substantially changed water supply and use structure and profoundly influenced groundwater storage (GWS) in the Haihe River Basin (HRB). Reliable monitoring of regional GWS changes serves as a basis for water security and strategic groundwater reserves. Traditional approaches of calculating GWS changes over large areas using in-situ groundwater level measurements and specific yield/storage coefficients may be subject to large uncertainties due to large spatiotemporal variability in those variables and parameters. Here we compare different methods of processing GRACE signals and use four GRACE products to estimate changes in total water storage (TWS) and GWS in the HRB from 2003 to 2022. Impact of changes in TWS on evapotranspiration (ET) estimates across the basin is quantified. Results show that the coefficient of determination of GWS changes in the North China Plain (defined as the plain areas of the HRB in this study) retrieved from GRACE JPL Mascons data is highest relative to ground monitoring data. Over the past two decades GWS in the HRB generally shows a downward trend at three distinct stages, and declining rates from 2003 to 2011, 2012 to 2015 and 2016 to 2020 are estimated to be -2.39±0.13 km3/yr, -7.55±0.53 km3/yr, -3.73±0.26 km3/yr by GRACE JPL Mascons data. Although GWS has been largely recovered by ~ 16 km3 in a single year of 2021 due to higher than normal precipitation up to 830 mm/yr (mean annual precipitation is ~ 520 mm/yr for the past two decades) across the HRB and policy on restrictions of groundwater abstractions, the increase in GWS from the early nine months in 2022 has ceased. This means that there is still a long way to go for GWS recovery and comprehensive treatment of groundwater overexploitation in the North China Plain, given the historical depletion of GWS up to 180 km3 estimated by the Ministry of Water Resources of China. The multi-year average ET (521 mm/yr) without considering changes in TWS differs by up to 10 mm (3.2 km3/yr) from the multi-year average ET (530 mm/yr) considering changes in TWS. The maximum difference in annual ET with and without considering changes in TWS is about 80 mm/yr (25 km3/yr, 2014). The findings from this study provide the latest understanding of changes in TWS and GWS in the HRB over the past two decades.