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Groundwater exploitations in semi‐arid regions result in significant declines of groundwater levels and streamflow and even trigger seasonal streamflow drying up, which may bring adverse impacts on riparian ecosystems. It is critical to explore future streamflow changes caused by variable climate scenarios and groundwater exploitation intensities; however, a comprehensive assessment of the streamflow drying up frequency remains lacking. Furthermore, the thresholds of controlling factors beyond which streamflow drying up occurs have rarely been explored. Here we develop an integrated surface water‐groundwater model for the Taoer River Basin (TRB), a typical semi‐arid watershed in northeast China. We apply the model to multiple future scenarios to reveal the frequency of potential streamflow drying up and explore the thresholds of controlling factors of streamflow drying up based on a decision tree method. We find that the groundwater level in the lower region of the TRB (LTRB) is hard to recover to the riverbed elevation and the streamflow drying up frequency is still high unless the groundwater exploitation is reduced by 50%. However, this leads to a competition between the ecological and economic objectives. Our results also show that the streamflow drying up frequency in the LTRB is very sensitive to the upstream water inflow that can be regulated through the reservoir operation or inter‐basin water diversion, indicating the importance of a basin scale strategic management. The findings of this paper can help policy makers sustainably exploit water resources in semi‐arid regions. [ABSTRACT FROM AUTHOR]

In recent decades, the frequency and severity of inland river seawater intrusion has increased in the Pearl River Estuary (PRE) of China. Based on time series of water salinity data, river discharges, tides, and wind records for the period 2003–2015, this study aims to examine the regular pattern and underlying mechanisms of the seawater intrusion in the Modaomen channel of the PRE. Toward this end, the autocorrelation and spectral analysis are used to quantify the periodicity of runoff, tide, and water salinity and to infer the regular patterns of seawater intrusion. The Pearson correlation and the LMG metric are used to examine the effects of influencing factors on seawater intrusion. Results indicate that seawater intrusion in the Modaomen channel has distinct annual (369 days) and half-monthly (14.8 days) cycles, corresponding well with annual and half-monthly tidal cycles. Spatially, the frequency, severity, and periodicity of seawater intrusion decrease with increased landward distance away from the channel mouth. The prevention of seawater intrusion by incoming river flow becomes more remarkable as freshwater flows downstream. Shifts in wind speed and direction can strengthen or weaken seawater intrusion, depending on if wind is in the opposite or same direction of river flow. Further analysis using the LMG metric suggests that river discharge plays a dominant role in governing seawater intrusion. Overall, river discharges, tides, and wind are three major forces triggering the inland river seawater intrusion and account for, respectively, 46%, 15%, and 15% of the variation of water salinity in the Modaomen channel. The study is featured in not only identifying the major factors in driving seawater intrusion but also quantifying their relative contribution. Thus, the findings are important for water resources manager to predict and manage inland river seawater intrusion in the PRE of China. [ABSTRACT FROM AUTHOR]

A better understanding of how streamflow interacts with climate change and human activities would contribute to the efficiency and effectiveness of water resources management. Specifically, quantifying the climate and human contributions has widely been used when attributing streamflow changes. However, only a few previous studies compared the results derived by different methods that are currently available, and even fewer studies have ever had a close look at the uncertainties induced by various estimations of evapotranspiration. This research first examined the streamflow changes for 12 catchments on the Loess Plateau in China during the period of 1961–2018 with Mann–Kendall test and relevant statistical measurements. Then, 8 Budyko-based climate elasticity methods, each with 13 estimations of evapotranspiration, were used to quantifying human and climate contributions to streamflow change in the study area (i.e., 104 pairs of values for human and climate contributions for one catchment). The results showed that significant declining trends could be found in 11 of the 12 catchments studied. In terms of contribution rates, human activity has been shown as the major contributor to the streamflow decrease (60–90%) compared to climate change (10–50%). By comparing the contribution results derived by possible combinations of attribution method and evapotranspiration estimation, the variability due to different Budyko-based methods being used seems to be related to geographical location and climate. Although the spatial pattern of variability due to different estimations of evapotranspiration is not obvious, it is necessary to consider the uncertainties induced when launching contribution analysis over specific regions. [ABSTRACT FROM AUTHOR]