Tracing runoff components in the headwater area of Heihe River by isotopes and hydrochemistry

Since water resources of the Heihe River Basin are primarily in the form of surface runoff in the Qilian Mountains,identifying its sources and components is essential for researchers to understand water cycling and transformation in the basin.It will help to properly exploit water resources,and contribute to ecological environment construction.The paper uses the isotope data of hydrogen and oxygen in water and hydrochemistry data collected at a high altitude to trace the sources of surface runoff in Heihe River in rainy season and uses the three-component mixing model to estimate the contribution of each component to runoff.Results indicate that surface water consists of precipitation,melt water and groundwater,with precipitation being the primary component and contributing to 59%-64%of runoff.Melt water and groundwater account for 15%-25%and 12%-22%,respectively.Precipitation accounts for 60%,groundwater for 22%and glacial melt water for 18%of the outflow in the main stream of the Heihe River.The composition is of great significance for water cycling and conversion research as well as water resource evaluation and management.

Runoff components and the contributions of precipitation and temperature in a highly glacierized river basin in Central As

Understanding the main drivers of runoff components and contributions of precipitation and temperature have important implications for water-limited inland basins,where snow and glacier melt provide essential inputs to surface runoff.To quantify the impact of temperature and precipitation changes on river runoff in the Tarim River basin(TRB),the Hydrologiska Byrans Vattenbalansavdelning(HBV)-light model,which contains a glacier routine process,was applied to analyze the change in runoff composition.Runoff in the headstream parts of the TRB was more sensitive to temperature than to precipitation.In the TRB,overall,rainfall generated 41.22%of the total runoff,while snow and glacier meltwater generated 20.72%and 38.06%,respectively.These values indicate that temperature exerted more major effects on runoff than did precipitation.Runoff compositions were different in the various subbasins and may have been caused by different glacier coverages.The runoff volumes generated by rainfall,snowmelt,glacier melt was almost equal in the Aksu River subbasin.In the Yarkand and Hotan River subbasins,glacier meltwater was the main supplier of runoff,accounting for 46.72%and 58.73%,respectively.In the Kaidu-Kongque River subbasin,80.86%was fed by rainfall and 19.14%was fed by snowmelt.In the TRB,runoff generated by rainfall was the dominant component in spring,autumn,winter,while glacier melt runoff was the dominant component in summer.Runoff in the TRB significantly increased during 1961–2016;additionally,56.49%of the increase in runoff was contributed by temperature changes,and 43.51%was contributed by precipitation changes.In spring,the runoff increase in the TRB was mainly caused by the precipitation increase,opposite result in summer and autumn.Contribution of temperature was negative in winter.Our findings have important implications for water resource management in high mountainous regions and for similar river basins in which melting glaciers strongly impact the hydrological cycle.

Effects of forest cover type and ratio changes on runoff and its components

Changes in forest cover can affect not only the total runoff from a watershed,but also the runoff components(e.g.,surface runoff,interflow,groundwater flow).In this study,based on the WetSpa model simulation method and the recursive digital filtering(RDF)method,the Banchengzi watershed in the mountainous region of Beijing,China,was selected to investigate how changes in forest cover type and cover percentage affect total runoff,surface runoff,interflow,and groundwater flow through scenario settings.Our results show that the difference between the WetSpa model and the RDF method for separating runoff components is small,with only 4.7%and 0.4%difference between the calibration and validation periods.Total runoff in different forest types followed the order shrub forest>coniferous forest>mixed forest>broadleaf forest.Regarding runoff components,the proportions of baseflow(sum of interflow and groundwater flow)to total runoff were 61.1%and 60.8%for broadleaf and mixed forests,which was significantly higher than those of 53.0%and 43.1%for coniferous and shrub forests.However,the proportion of shrub forest baseflow was high in wet years,and that of broadleaf forest baseflow was high in normal and dry years.The proportions of interflow and groundwater flow from various forest cover types to total runoff continued to increase with increasing forest cover rate.Our results have important implications for the implementation of afforestation projects and forest conservation programs,contributing to water resource regulation and ecosystem protection in watersheds.

Effects of Spatial Information of Soil Physical Properties on Hydrological Modeling Based on a Distributed Hydrological Model

The spatial distribution of soil physical properties is essential for modeling and understanding hydrological processes. In this study, the different spatial information (the conventional soil types map-based spatial information (STMB) versus refined spatial information map (RSIM)) of soil physical properties, including field capacity, soil porosity and saturated hydraulic conductivity are used respectively as input data for Water Flow Model for Lake Catchment (WATLAC) to determine their effectiveness in simulating hydrological processes and to expound the effects on model performance in terms of estimating groundwater recharge, soil evaporation, runoff generation as well as partitioning of surface and subsurface water flow. The results show that: 1) the simulated stream flow hydrographs based on the STMB and RSIM soil data reproduce the observed hydrographs well. There is no significant increase in model accuracy as more precise soil physical properties information being used, but WATLAC model using the RSIM soil data could predict more runoff volume and reduce the relative runoff depth errors; 2) the groundwater recharges have a consistent trend for both cases, while the STMB soil data tend to produce higher groundwater recharges than the RSIM soil data. In addition, the spatial distribution of annual groundwater recharge is significantly affected by the spatial distribution of soil physical properties; 3) the soil evaporation simulated using the STMB and RSIM soil data are similar to each other, and the spatial distribution patterns are also insensitive to the spatial information of soil physical properties; and 4) although the different spatial information of soil physical properties does not cause apparent difference in overall stream flow, the partitioning of surface and subsurface water flow is distinct. The implications of this study are that the refined spatial information of soil physical properties does not necessarily contribute to a more accurate prediction of stream flow, and the selection of appropriate soil physical property data needs to consider the scale of watersheds and the level of accuracy required.

The response of sedimentary record to catchment changes induced by human activities in the western intertidal flat of Yalu River Estuary,China

The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores,along with the hydrologic data and human activities in the catchment.The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea,which could be divided into three stages as 1958–1970,1971–1990 and 1991–2009.Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes.There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010,i.e.,1940–1950,1951–1980,1981–1990 and 1991–2010.The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980,whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990.Despite the further reduction of the water and sediment input into the sea from 1990 to 2009,this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly,the significantly increased silt contents of the sensitive component.