Change of the Baseflow and It′s Impacting Factors in the Source Regions of Yellow River
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The purpose of this study is to identify and assess the change of baseflow and climatic impacting factors in the source regions of the Yellow River,based on the analyses of long hydrological time series(1956-2000) from four subbasins of the source regions of the Yellow River and the whole source regions of the Yellow River.Kalinin baseflow separation technique has been improved based on the characteristics of climate and streamflow of the study regions,then applied to estimate baseflow.Statistical method is adopted in order to investigate the effect of climate factors on baseflow.Annual mean baseflow in the source regions of the Yellow River is 13.246 billion m3,accounting for more than 60% of the total runoff of the area interested.Annual baseflow is in direct proportion to annual precipitation.The sharp rise in temperature in the 1990s decreased baseflow significantly.The impacts of climate factors on baseflow are different in different subcatchment.In subbasin above Huangheyan Hydrologic Station,which is relative cold and arid with annul mean temperature of-3.84 °C and the water area accounted for 7.95% of the subbasin,both temperature and precipitation nearly had no direct impacts on baseflow on annual time scale.The increasing temperature thaws frozen soil more rapid,thus lowers the groundwater table and lake water level,hence decreases water supply of baseflow from groundwater and lake water.In subbasin between Huangheyan and Jimai Hydrologic Station baseflow is influenced both by precipitation and temperature but the response rate of baseflow to precipitation is more rapid than temperature.In subbasin between Jimai and Maqu Hydrologic Stations precipitation and temperature area two key factors impacting baseflow,but the effect of precipitation is more pronounced than temperature,while in subbasin between Maqu and Tangnag Hydrologic Station precipitation is the only climate factor affecting baseflow in short term.The factors inducing serious decrease of baseflow in the 1990s are also investigated into.Keywords:
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Base flow
Groundwater discharge
Depression-focused recharge
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The Wuding River Basin,which is one of the biggest catchments in the Loess Plateau,is dry and lack of water resources.In this paper,recharge-discharge relationship in the basin has been investigated using the daily streamflow records since the 1950s.It was estimated that the annual recharge of the basin varied from 11.38 mm to 15.69 mm.For different sub-catchments the ratio between recharge and precipitation ranged in 2.9%-4.7%,while the ratio between recharge and baseflow was 73.5%-86.8%.Baseflow is highly correlated with recharge.Spatially,the loess area has the largest recharge and recharge-precipitation ratio and the headwater area has the largest recharge-baseflow ratio,while the sandy area has the smallest.Temporally,groundwater recharge has decreased significantly,which consequently resulted at the significant reduction of baseflow.However,the decrease rate of baseflow is larger than recharge indicating the impacts of human activities like groundwater withdrawing.
Base flow
Depression-focused recharge
Loess plateau
Groundwater discharge
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Base flow
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Climate change has effects on hydrological change in multiple aspects, particularly in the headwaters of the Yellow River (HWYR), which is widely covered by climate-sensitive frozen ground. In this study, the annual runoff was partitioned into four runoff compositions: winter baseflow, snowmelt runoff, rainy season runoff, and recession flow. In addition, the effects of global warming, precipitation change, and frozen ground degradation were considered in long-term variation analyses of the runoff compositions. The moving t-test was employed to detect change points of the hydrometeorological data series from 1961 to 2013, and flow duration curves were used to analyze daily runoff regime change in different periods. It was found that the abrupt change points of cold season runoff, such as recession flow, winter baseflow, and snowmelt runoff, are different from that of the rainy season runoff. The increase in winter baseflow and decrease in snowmelt runoff at the end of 1990s was closely related to global warming. In the 21st century, winter baseflow presented a larger relative increase compared to rainy season runoff. The correlation analyses indicate that winter baseflow and snowmelt runoff are mainly controlled by water-resource-related factors, such as rainy season runoff and the accumulated precipitation in cold season. To analyze the global warming impacts, two runoff coefficients—winter baseflow discharge rate (Rw) and direct snowmelt runoff coefficients (Rs)—were proposed, and their correlation with freezing–thawing indices were analyzed. The increase of Rw is related to the increase in the air temperature thawing index (DDT), but Rs is mainly controlled by the air temperature freezing index (DDF). Meanwhile, the direct snowmelt runoff coefficient (Rs) is significantly and positively correlated to DDF and has decreased at a rate of 0.0011/year since 1980. Under global warming, the direct snowmelt runoff (runoff increment between March to May) of the HWYR could decrease continuously in the future due to the decrease of accumulative snow in cold season and frozen ground degradation. This study provides a better understanding of the long-term runoff characteristic changes in the HWYR.
Snowmelt
Base flow
Wet season
Water year
Hydrometeorology
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Abstract Baseflow is essential for stream ecosystems and human water uses, particularly in areas with Mediterranean climates. Yet the factors controlling the temporal and spatial variability of baseflow and its sources are poorly understood. Measurements of oxygen and hydrogen isotopic composition (δ 18 O and δ 2 H) were used to evaluate controls on baseflow in the stream network of a 64‐km 2 catchment in western Oregon. A total of 607 water samples were collected to contrast baseflow in a year of near average precipitation (2016) to a year with low winter snowpack and subsequent summer drought conditions (2015). Spatial autocorrelation structures and relationships between surface water isotopic signatures and geologic and topographic metrics throughout the network were determined using Spatial Stream Network models. Isotope values varied widely in space and between years, indicating disparate baseflow water sources. During average flow conditions, the spatial variation in δ 18 O was primarily related to elevation, reflecting the influence of prior precipitation and input of water from snowmelt at higher elevation. In contrast, during drought conditions, the spatial variation in δ 18 O was also related to terrain slope and roughness—proxies for local water storage in deep‐seated earthflows and other Quaternary deposits. A prominent spring‐fed tributary with high unit baseflow discharge illustrated the importance of subsurface water storage in porous volcanic bedrock. As drought increases in a warming climate, baseflow in mountain catchments may become more dependent on storage in geologic and geomorphic features.
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Snowmelt
Snowpack
Bedrock
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The Chapman-Maxwell method (the CM filter) with recession constant calculated from Automatic Baseflow Identification Technique (ABIT) was used to separate baseflow from daily runoff at the Taonan hydrological station in Taoer River basin．Time series-based rainfall-runoff events were separated to explore runoff event response to precipitation． Annual precipitation, runoff and baseflow were found to show decreasing trends, with abrupt decreases detected in all three．Baseflow was found to maintain continued runoff process, with a total number of 72 events being identified from daily series of streamflow．A strong correlation of the volume of precipitation (Ptot) to maximum runoff (Qmax) and maximum baseflow (QBmax) was observed．Runoff event response to precipitation showed marked threshold characteristics, being affected by soil moisture content and watershed water storage．Runoff process was found to be affected by climate change and human disturbance, therefore linking dynamic hydrological changes to ecological indexes was helpful to protect river ecology．These data will help to understand runoff generation and hydrological connectivity, and provide certain theoretical and practical references to maintain river ecosystem health．
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Runoff regeneration processes are one of the key processes in the water cycles. Runoff can be separated into direct runoff and baseflow according to the response rate to precipitation.The baseflow is generally defined as the part of river runoff come from groundwater storage and other delayed water, while the direct runoff is defined as the part of river runoff direct response to precipitation. Based on this theory, the impact of climate factors on runoff is analyzed by investigating the conversion rate of precipitation to total runoff, baseflow and direct runoff. In the sources regions of the Yellow river, runoff coefficient was in positive relation with precipitation and in negative relation with air temperature; runoff increased with the precipitation. In the 1990s the sharp decrease of precipitation and increase of temperature contributed to the decrease of runoff. Impacts of climate on runoff were different in different subbasin in the source regions of the Yellow river. In subbasins above Jimai hydrologic station with mean annual temperature below -3.0 ℃, temperature was the key factors affecting runoff. With the increase of temperature runoff will decrease. In subbasin between Jimai hydrologic station and Maqu, runoff and baseflow both increased with the increase of precipitation, and decreased with the increase of temperature. In subbasin between Maqu and Tangnaihai hydrologic stations, precipitation was the vital climate factor affecting runoff(including baseflow and direct flow and total runoff), only direct flow are slightly influenced by temperature.
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This paper analyzes the long term (1965～1998) data of the monthly temperature and precipitation observed by 26 meteorological stations upstream from Lanzhou Hydrological Station in the Yellow River watershed and the monthly data of streamflow of the Yellow River, measured by 5 hydrological stations, so as to examine the streamflow regime and its change in the upper reaches of the Yellow River in recent 40 years. The results show that the climatic warming occurs universally in the upper reaches of the Yellow River, especially in winter, which has resulted in the temperature increase and shrinkage of frozen earth, sharp increase of evaporation, and the change of streamflow in the watershed; the precipitation in the watershed has been obviously reduced. The natural inflow from the upper reaches of the Yellow River is significantly reduced, especially since 1990. Viewing from the seasonal change of streamflow in the watershed, the streamflow is obviously increased in spring (from April to June) because of the increase of precipitation and the snowmelt runoff in this season; the streamflow is reduced in autumn and winter due to the decrease of precipitation in these seasons. It is considered that the streamflow change of the Yellow River is mainly affected by human activities, such as the streamflow regulation by reservoirs.
Snowmelt
Flood forecasting
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Based on the data observed in Kaqun Hydrological Station and Tashikuergan Meteorological Station from 1961 to 2006,the characteristics of climate change and the response of runoff to climate change at headwater of the Yarkant River were analyzed.It was found that the mean annua1 temperature was rising,and annual precipitation was increasing.After verifying the series of precipitation and temperature,the variation of precipitation and temperature are increasing,only the temperature changed more obviously than the precipitation.Temperature were the main factors which resulted in runoff changing.The correlation coefficient of temperature and runoff was the largest,being 0.81.The correlation coefficient between annual precipitation and runoff was-0.57.When precipitation was in the same circumstances,the runoff increased with temperature rising;when temperature was in the same circumstances,the runoff is decreased with precipitation increasing.
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