Analysis of the impact of the South-to-North water diversion project on water balance and land subsidence in Beijing, China between 2007 and 2020

Abstract

After operating the middle route of South-to-North Water Diversion Project (SNWDP), the total water transfer to Beijing has exceeded 5.0 km3, bringing significant changes to the water use structure of Beijing. This article compiles historic data from 2007 to 2020 to analyze changes in water circulation, groundwater level, climate factors and subsidence patterns in Beijing following implementation of the middle SNWDP. It is found that the main current pressure on Beijing's water supply has come from improved living standards, the gradual popularization of water-using appliances, and a rapid development of the accommodation and catering industries. An InSAR time series approach was used to map subsidence in Beijing between 2007 and 2020 using satellite images from Sentinel-1A/B, Radarsat-2 and ALOS-1. Climate factors including precipitation and evapotranspiration were estimated using the Penman-Monteith-Leuning Evapotranspiration V2 (PML_V2) product. By compiling ground subsidence data for Beijing and corresponding climate data, the impact of the SNWDP and climate factors on groundwater levels and ground subsidence in Beijing were examined We identified three periods to characterize the changes of surface displacement after implementation of the SNWDP as a) the pre-effect stage, b) the effective stage, and c) the post-effective stage. The contribution of the SNWDP was apparent at the second stage, alleviating the problem of land subsidence to some extent. The ease of subsidence at different stages are accounted for 4%, 26.5%, and 41.7%, respectively, in terms of the mean velocity changes. Based on the result of some general circulation models. Precipitation in the Beijing region is expected to increase over the next decade, implying a greater likelihood of rapid groundwater recovery. However, although groundwater is expected to recover in the long run, climate extremes in the future could possibly challenge the success of SNWDP during certain dry periods.