Effects of Water Diversion Project on groundwater system and land subsidence in Beijing, China

South-to-North Water Diversion Project Central Route (SNWDP-CR) is one of the largest human engineering projects aimed at redistributing water resources, receiving a worldwide attention. It conveys water from southern China to the Beijing Plain northward through a 1300-km long canal system and operated since December 2014. Before this date, water supply to Beijing was mainly provided by means of aquifer over-exploitation, causing a significant lowering of the piezometric levels and a huge land subsidence. After 3 years of SNWDP-CR activity, it results of general interest to investigate if the implemented managed aquifer recharge and the supposedly reduced aquifer exploitation have been already accompanied by a piezometric recovery and a decrease of the subsidence rates. This is evaluated for the first time in this contribution, by integrating and statistically analyzing a large dataset consisting of hydrogeologic information, piezometric records, and land subsidence measurements carried out by Persistent Scatterer Interferometry and levelling. The results show that a small (~3 m) to large (~10 m) raise of the piezometric levels has been recorded in the central portion of the north Beijing plain with a certain decrease (up to 10 mm/yr) of the subsidence rates. Conversely, piezometric drawdown and land subsidence has continued to increase in the remaining parts of the study area. Managed aquifer recharge (MAR) carried out through infiltration ponds has produced a positive feedback, but at a local scale only. Therefore, it will be necessary to wait a longer period to assess whether the SNWDP-CR will be able to mitigate the hydrogeological hazards connected to groundwater overuse or only to counterbalance in part the growing water demand of the Chinese capital.