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Understanding the impact of climate change on runoff and its extremes is of great significance for water resource assessment and adaptation strategies, especially in water-scarce regions. This study aims to analyze the impact of future climate change on runoff and its extremes in the upper reaches of the Heihe River basin in northwest China. The projected runoff was derived using the Soil Water Assessment Tool with climate data from the CSIRO-MK-3-6-0 model under the scenario of RCP4.5, and a frequency analysis of runoff was performed by generalized extreme value distribution. The results indicate that, compared with the baseline period of 1961 to 2000, the minimum and maximum temperatures in the period 2031 to 2070 were predicted to increase by 2.5 °C on average. The precipitation in most months was also predicted to increase, with an average rise of 16.5%. The multi-year average runoff was projected to increase by 8%. The annual mean and extreme flows were also expected to rise under future climate change at different return periods, and the low flow was expected to increase the most. [ABSTRACT FROM AUTHOR]

High flow events (including both the high flow pulses and floods) exert many critical ecological functions in riverine ecosystems and their elimination will lead to severe ecological degradation. However, common hydropower operations are only required to legally maintain the minimum environmental flows (e-flows). The extra release of high flow events will result in revenue loss of hydropower producers. In this research, we propose an approach to assessing the eco-compensation standard which is necessary to compensate the loss of hydropower producers and promote the release of high flows to downstream rivers. The scenario tree approach is adopted for the generation of possible scenarios of flows and electricity prices to deal with the uncertainties of the two factors in deregulated electricity markets. A stochastic linear programming method is proposed to determine the maximum mean annual revenues under two e-flow provision scenarios, i.e., only sustaining the minimum e-flows (scenario 1) and sustaining both the minimum e-flows and a specified number of high flow events (scenario 2). The revenue difference under the two e-flow scenarios is set as the eco-compensation standard. A case study in the Wangkuai reservoir, China, demonstrates that the eco-compensation standard is obviously influenced by the installed hydropower generation capacity (IHGC) and the number of high flow events planned to be released. Moreover, the greatest standards may be not corresponding to a very large IHGC. [ABSTRACT FROM AUTHOR]

Abstract: Baojixia water diversion works have direct impacts on river hydrology, primarily resulting in the changes of the magnitude, frequency of low and high flows, ultimately generating a new hydrologic regime differing significantly from the natural flow regime. Streamflow and precipitation data from 1944 to 2008 at Linjiacun station are analyzed in this study. In order to evaluate hydrologic alteration before and after water diversion, the Range of Variability Approach (RVA) is used in this paper, and hydrologic data was divided into two periods: before and after 1972, when Baojixia diversion works brought to service in the Wei River. It is supposed that the hydrologic time series before 1972 represents the hydrologic regime for the pre-impact period, and that after 1972 for the post-impact period. The Chi-square test is used to analyze the hydrologic alteration of monthly flows, which is classified as low, middle and high hydrologic alterations. Flow Duration Curve (FDC) representing the relationship between the magnitude and frequency of streamflow was used to investigate flow characteristics from low flow to high flow. FDC is categorized as three parts on the basis of magnitude of streamflow: high flow (below 10% of exceedance frequency), low flow (over 90% of exceedance frequency) and constant flow (from 10% to 90% of exceedance frequency). The results show that the magnitude of monthly flow decreased obviously in the post-impact period, especially in dry seasons. The degree of hydrologic alteration is high. The shape of FDC in the post-impact period is different from that in the pre-impact period. There is an obvious trend for FDC in the pre-impact period, while there is no obvious regularity between magnitude of streamflow and exceedance probability in the post-impact period. According to the analysis on the data of water diversion, water withdrawn accounted for about 80 percent of natural runoff in dry seasons. This may be the reason why the alteration of monthly flow in dry seasons is highest. In summary, monthly streamflow after 1972 changed greatly because of water diversion. This analysis makes one to understand hydrologic regime well, and will be helpful for the management of water resources in the Wei River basin. [Copyright &y& Elsevier]

Long-term variations in reservoir water chemistry could provide essential data in making sustainable water quality management decisions. Here, we analyzed the spatiotemporal variabilities of nutrients, sestonic chlorophyll-a (CHL-a), nutrient enrichment, dominant algal species, and overall chemical water health of the third-largest drinking water reservoir in South Korea during 2000-2020. Our results distinctly explained the strong influence of monsoon rainfall on spatial and annual water chemistry variations. We observed a consistent increase in the chemical oxygen demand alluding to organic matter pollutants, while a steady declining trend in the sestonic CHL-a. The long-term total phosphorus (TP) level showed a steady reduction from the riverine zone to the lacustrine area. However, a higher total coliform bacteria (TCB) was observed at the water intake tower sites. TP displayed a strong link to algal CHL-a and ambient nitrogen phosphorus ratios, suggesting a robust phosphorus-limitation state. The severe phosphorus-limitation was also corroborated by the findings of trophic state index deviation. The high and low flow dynamics exhibited the strong influence of intensive rainfall carrying many nutrients and sediments and flushing out the sestonic CHL-a. Successive eutrophic conditions prevailed along with dominating blue-green algae species (Microcystis and Anabaena). We observed a strong positive correlation (r = 0.62) between water temperature and CHL-a and between total suspended solids and TP (r = 0.65). The multi-metric water pollution index characterized the overall water quality as 'good' at all the study sites. In conclusion, the long-term spatiotemporal variabilities of the ecological functions based on the nutrient-CHL-a empirical models are regulated mainly by the intensive monsoon precipitation. The drinking water could become hazardous under the recurrent eutrophication events and chemical degradations due to uncontrolled and untreated inflow of sewage and wastewater treatment plant effluents. Therefore, we strongly advocate stringent criteria to mitigate phosphorus and organic pollutant influx for sustainable management of Daecheong Reservoir.