Abstract
Based on the daily precipitation data during 1960–2016 at 72 stations and the daily streamflow data during 1956–2016 at 7 hydrological stations in the Huai River Basin (HRB), China, eco-surplus and eco-deficit under influences of abrupt streamflow behaviors were analyzed using Flow Duration Curve (FDC). The relations between indicators of hydrological alteration (IHA) and ecological indicators (Shannon Index, SI) were quantified, investigating impacts of altered hydrological processes on the evaluations of the ecological instream flow. Besides, we also quantified fractional contributions of climatic indices to nonstationary ecological instream flow using the Generalized Additive Models for Location Scale and Shape (GAMLSS) framework. While the possible impact of human activities on ecological instream flow will be revealed based on land use changes data. The results indicated that: (1) FDC is subject to general decrease due to hydrological alterations, and most streamflow components are lower than 25% FDC. We found increased eco-deficit and decreased eco-surplus due to altered hydrological processes. The FDC of the streamflow in the main stream of the HRB is lower than that along the tributaries of the HRB. Eco-surplus (eco-deficit) changes are in good line with precipitation anomaly changes during the Spring, Autumn and Winter periods. However, the hydrological alterations due to hydrological regulations by the reservoirs are the primary cause behind the mismatch between ecological instream flow and precipitation anomalies during summer; (2) Annual and seasonal eco-surplus (eco-deficit) is decreasing (increasing) and that during winter season is an exception. Although higher eco-surplus in winter than in other seasons, the eco-surplus is decreasing persistently and the 21st century witnessed the lowest eco-surplus along the main stream of the HRB. Meanwhile, the Shannon index indicated decreased ecological diversity across the HRB; (3) The ecological instream flow is highly sensitive to The Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Niño 3.4 Sea Surface Temperature Index (Nino3.4). Meanwhile, the ecological instream flow along the mainstream of the HRB is highly sensitive to climate indices. While the ecological instream flow by GAMLSS model has better fitting performance in describing the extreme values and local trends.
Highlights
Variations of ecological instream flow are closely related to variability and availability of water resources and are related to the diversity of the river ecological system and river health [1]
The change of the Flow Duration Curve (FDC) curve can be used to illustrate the change of ecological instream flow (Figure 4)
The results showed that the biodiversity indices were significantly correlated with the ecological instream flow, Indicator of Hydrological Alterations (IHA)-Shannon Index (SI)
Summary
Variations of ecological instream flow are closely related to variability and availability of water resources and are related to the diversity of the river ecological system and river health [1]. Human activities e.g., building water conservancy projects, industrial and irrigation demand water have caused the river hydrological variation and environmental degradation, which have affected natural hydrological variation. The quantity and quality of water required for protection of water resources and ecosystems are required [2,3,4]. Alterations of river discharge have normally occurred in a great number of rivers caused by climate change and human activities, usually through the construction of DAMS. Intensified human activities, such as changing land use and the building of water reservoirs, have significantly altered natural streamflow regimes for the past six decades [8]
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