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The arid endorheic basin of northwest China is characterized by rich land resources, water shortage, and a fragile ecological environment. The establishment of a credible coupling model of groundwater and surface water based on multi-source observation data is an effective means to study the change in basin water cycles and the sustainable utilization of water resources in the past and future. Based on the latest understanding of hydrogeological conditions, hydrology and water resource utilization data in the middle reaches of the Heihe River Basin (HRB), this paper constructs an up-to-date coupling model of surface water and groundwater to study the water balance change of the basin. The water resources data series under historical replay and CMIP5 climate model prediction are constructed to predict future changes in water resources. The study shows that, under the joint influence of natural conditions and human activities, the average annual recharge of groundwater in the study area from 1990 to 2020 is 17.98 × 108 m3/a, the average annual discharge is 18.62 × 108 m3/a, and the difference between recharge and discharge is −0.64 × 108 m3/a. The total groundwater storage is −19.99 × 108 m3, of which the groundwater storage from 1990 to 2001 was −17.52 × 108 m3 and from 2002 to 2020 was −2.47 × 108 m3. Abundant water from 2002 to 2020 in the basin significantly improved the loss of groundwater storage. Under the prediction of historical reappearance and the CMIP5 CNRM-CM5 model RCP4.5 and RCP8.5 pathways, the groundwater level of the Heihe River–Liyuanhe River inclined plain falls first because the HRB has just experienced a wet season and then rises according to future climate change. The groundwater level of the inclined plain east of the Heihe River and Yanchi basin decreases continuously because of the change in water cycle caused by human activities. The erosion accumulation plain is located in the groundwater discharge zone, and the water level is basically stable. Under the conditions of water resource development and utilization, the runoff of Zhengyixia hydrological station cannot meet the requirements of the "97 Water Dividing Plan" of the State Council in most years in the future, and the ecological and production water in the lower reaches of HRB cannot be effectively guaranteed. With the implementation of water-saving irrigation under the RCP4.5 and RCP8.5 scenarios, the runoff of Zhengyixia can meet the "97 Water Diversion Plan". It is suggested to further improve the level of agricultural water savings in the middle reaches of the HRB and control the reasonable scale of cultivated land in order to reduce water consumption in the middle reaches of the HRB and implement sustainable utilization of water resources in the HRB. [ABSTRACT FROM AUTHOR]

Surface water and groundwater interactions play an important role in hydrological cycle in a wetland ecosystem. Understanding its mechanism and interaction magnitude imposes significant effects in wetland protection and management. In this study, a heat tracer method was taken in the Baiyangdian wetland as a case and temperature time-series data were collected for surface water and wetland sediment of 0.2 m, 0.6 m and 1 m respectively in 3 monitor sites. Then, a one-dimensional vertical steady heat transport model was applied to estimate surface water inflows to groundwater. The results showed that the leakage rates were 0.04-0.29 mm/d and had a spatial and temporal variation. In the same monitor site, the leakage rate was higher in winter than it in summer. A total leakage amount for the Baiyangdian wetland was evaluated as 8.61 million m3/d. The surface water leakage resulting from the model was subject to several uncertainties including sediments inhomogeneity and the impact of non-ideal conditions. Despite the uncertainties of the model, when correctly applied, heat tracer method is able to provide detailed information on the spatial and temporal distribution of surface water leakage.

Water level dynamics of Wetlands are influenced by both climate change and human activities. Understanding the influence characteristics is important for the management of wetland water resources and ecology. Based on the water level dynamic and precipitation of the Baiyangdian Wetland, and the NPI index, the paper analyzes the response characteristics of the water level dynamic to the precipitation, and the teleconnections between the water level dynamic and the NPI by adopting method of wavelet analysis. Results show that climate change plays an important role on the response of the water level dynamic to the precipitation and also to the NPI, and human activities can significantly change the response characteristics. The response time lags of the water level dynamics to the NPI is longer than that of the water level dynamics to the precipitations, which indicates that the wetland precipitation might be partially influenced by the NPI. The knowledge of the response characteristics obtained in the paper is beneficial for water conservancy and control of the wetland, and is favorable for the sustainable development of its eco-environment.