Quantifying the Relative Contribution of Climate and Human Impacts on Runoff Change Based on the Budyko Hypothesis and SVM Model

The Wei River Basin (WRB), the largest tributary of the Yellow River in China, has experienced a noticeable decrease in annual runoff during the last 50 years. Quantifying the relative contributions of climate change and human activities on runoff changes is thus important for local water resources management and sustainable water resources utilizations. In this study, the heuristic segmentation method was first adopted to detect the change points of annual runoff at Linjiacun and Huaxian stations which lies in the middle and lower reaches of the basin, respectively. Then, the Budyko hypothesis and SVM-based model were applied to attribute the detected runoff changes to climate change and human activities. Results showed that: (1) two change points were detected for the annual runoff at the Linjiacun station (1971 and 1993), and Huaxian station (1969 and 1993); (2) based on the Budyko hypothesis, the relative contributions of climate change and human activities to runoff changes at Linjiacun and Huaxian stations are 42.2 %, 57.8 % and 30.5 %, 69.8 %, respectively, whilst those based on the SVM-based model are 45.3 %, 54.7 % and 34.7 %, 65.3 %, respectively. The high consistence between the two approaches indicates that human activities are the dominate factor on historical runoff changes in the WRB.     

渭河中下游年径流量变化趋势及突变分析

以渭河中下游林家村、咸阳、临潼和华县等4个典型水文站资料为例,采用滑动平均法、累积距平和线性倾向估计法分析年径流量变化趋势;采用滑动t检验,有序聚类法和Mann-Kendall法分析年径流量的突变情况。结果表明:20世纪70年代以来,渭河流域径流量呈减少趋势,各站年径流量的变化趋势相似,各水文站径流量突变点发生在70年代初和90年代初。不同水文站突变情况存在差异,林家村突变点发生在1970年和1990年,咸阳站在1970年和1990—1992年之间,临潼站在1968年和1990—1994年之间,华县站在1968年和1990年。渭河流域径流量变化是气候变化和人类活动共同作用的结果,前者主要表现为降水和潜在蒸发量的变化,后者主要体现在流域内水利工程的建设。     

Impact of Climate Change on Water Resources in the Tarim River Basin

The plausible association between climate change and the variability of water resources in the Tarim River basin, west China is investigated in this study. The long-term trend of the hydrological time series including temperature, precipitation, and streamflow are detected by using both parametric and nonparametric techniques. The possible association between the El Niño/Southern Oscillation (ENSO) and these three kinds of time series are tested. This study enhances the knowledge of the climate change impact on water resources in the Tarim River basin. The conclusion obtained in this investigation shows that the temperature experienced a significant monotonic increase at the 5% level of significance during the past 50 yr, and precipitation also exhibited an upward tendency during the past several decades. A significant jump is also detected for both time series around 1986. This may be resulted from the possible impact of climate change, although the interior climate mechanism needs further investigation. Although precipitation and the streamflow from the headwater of the Tarim River exhibited significant increase, decreasing trend has been detected in the streamflow along the mainstream of the river. It implies that anthropogenic activities instead of the climate change dominated the streamflow cessation and the drying-up of the river. Results also showed that no significant association exists between the ENSO and the temperature, precipitation and streamflow in the study area. This conclusion shows that the water curtailment, river desiccation, and ecosystem deterioration in the Tarim River basin may be mainly resulted from the impact of human activities.     

渭河生态基流时空分异特征及保障率分析

以渭河为研究对象,依据渭河干流北道、林家村、魏家堡、咸阳、临潼、华县6个主要断面1971-2014年的水文实测资料,基于河流典型生态环境特征划分河流生态类型,并对其生态基流量进行优化计算,在此基础上揭示渭河生态基流时空分异特征及生态基流保障率。结果表明:选取北道、林家村、魏家堡、咸阳、临潼、华县断面枯水期的最小值作为相应断面的生态基流量推荐值,分别为5. 68、2. 51、11. 39、25. 33、77. 26和61. 86 m3/s;从时间变化看,各断面生态基流年内最大值均集中在汛期(7-9月),最小值集中在枯水期(12-次年3月)。除汛期外,各断面的生态基流月均值变化轨迹整体一致,各断面生态基流除8月与1、2、3、4、6、10、11、12月差异不显著(P>0. 05)外,其余各月两两之间差异均显著(P <0. 05);从空间分布来看,林家村断面1月生态基流量最小,华县断面8月生态基流量最大,体现出渭河上游生态基流量不足而下游河道泥沙淤积的生态环境特征;生态基流量总体上呈上游低下游高的特征,除魏家堡和华县断面月均生态基流量差异不显著(P> 0. 05)外,其余各断面之间差异均显著(P <0. 05)。     

Potential outcomes of multi-variable climate change on water resources in the Santa Basin,Peru

Water resources in the Santa Basin in the Peruvian Andes are increasingly under pressure from climate change and population increase. Impacts of temperature-driven glacier retreat on streamflow are better studied than those of precipitation changes, yet present and future water resources are mostly dependent on precipitation, which is more difficult to predict with climate models. This study combines a broad range of projections from climate models with a hydrological model (WaterWorld), showing a general trend towards an increase in water availability due to precipitation increases over the basin. However, high uncertainties in these projections necessitate basin-wide policies aimed at increased adaptability.     

Impacts of precipitation and temperature changes on annual streamflow in the Murray–Darling Basin

The relationship between the interannual changes in streamflow, precipitation and temperature of the Murray–Darling basin is investigated by using a two-parameter climate elasticity of streamflow approach. The non-linear relationship between streamflow and both precipitation and temperature indicates a greater streamflow sensitivity to precipitation than to temperature but a more significant impact of temperature change on streamflow than previously reported. The physical mechanisms producing high streamflow sensitivity to temperature change are not well understood, but may relate to concurrent changes in sub-annual precipitation characteristics such as seasonality, spatial distribution and intensity. Thus these characteristics need to be assessed and accounted for when attempting to project how streamflow, and hence water availability, may change in a future warmer world.     

Assessing the impact of human activities on hydrological and sediment changes (1953–2000) in nine major catchments of the Loess Plateau,China

The Range of Variability Approach (RVA) is employed to investigate the variability and spatial patterns of hydrological and sediment changes (1953–2000) induced by intensified human activities, i.e. the implementation of water and soil conservation measures, in nine major catchments of the Loess Plateau, China. Results indicate that: (1) streamflow and sediment load regimes were greatly changed by the implementation of conservation measures; (2) similar spatial patterns of high hydrological and sediment changes resulting from the intensive implementation of conservation measures are observed in most catchments of the middle Yellow River. However, slightly different behaviours of changes exist due to the unique complexity of hydrological and sediment processes in this region and (3) the impacts of various conservation measures on hydrological and sediment processes are closely associated with the extent and types of these measures. Engineering works have a quite immediate impact on streamflow and sediment regimes. Considerable vegetation controls are recognized as additional important driving forces for high hydrological and sediment alterations among various soil conservation measures. In vegetation controls, afforestation is the major factor causing the changes of runoff and sediment processes in these nine catchments. The results of the current study will be greatly beneficial to the regional water resources management and restoration of eco‐environmental system in the middle Yellow River basin characterized by intensified soil‐conservation measures under the changing environment. Copyright © 2009 John Wiley & Sons, Ltd.     

降水和人类活动对乌江上游径流变化的影响分析

径流量变化与气候和人类活动密切相关,其相互作用使得流域水循环发生变化,对气候变化和人类活动进行定量分析,可为流域调控水资源效率、协调农业发展等提供参考。以乌江上游为例,基于鸭池河水文站和流域内及周边共12个气象站,根据1960-2013年长时间序列实测径流与气象资料,利用Mann-Kendall法、累积距平法判断流域降水量和径流量的突变时间,用Morlet小波法对径流量进行周期变化分析,重点分析乌江上游流域降水与人类活动对径流量变化的贡献率。结果表明:1960-2013年间,径流量与降水量无显著增加趋势;径流量和降水量在此期间存在1986和2002年两个突变点,且突变特征和阶段特征同步;径流量与降水量的共振周期为18～19 a及19～20 a,流域径流量对降水量变化具有一定滞后作用,滞后时间为1～2 a;以1960-1986年为基准期,1987-2002年降水和人类活动对径流的贡献率分别为50.93%和49.70%,2003-2013年降水和人类活动对径流的贡献率分别为49.30%和50.70%。降水对径流变化的影响程度在降低,而人类活动对径流变化的作用在增大,因此,未来流域水资源管理应重视良性人类活动的构建与调控。     

Effects of land‐use change and climate variability on streamflow in the Woken River basin in Northeast China

In this study, the soil and water assessment tool, which is a widely used hydrological model, is applied to study the response of streamflow to land‐use changes and climate variability in the Woken River basin in northeastern China. This model is calibrated and verified based on sensitivity analysis to simulate the effects of land‐use change, climate variability, and extreme land‐use scenarios on streamflow. Simulations are performed to construct different scenarios for quantitative analysis. Compared with the base period, the land‐use change reduced the annual average streamflow and had little effect on the monthly streamflow. Climate variability increased the average annual streamflow and had a substantial effect on monthly streamflow. The effect of climate variability on streamflow was much greater than that of land‐use changes. Under the extreme land‐use scenarios, the annual average streamflow under the forestland scenario decreased, and the average annual streamflow under the grassland and agricultural land scenarios increased. Both the forestland and grassland scenarios exhibited lower monthly streamflow from March to August with especially large influences in June–August, which was when floods were more likely to occur. The agricultural land scenario exhibited the opposite trend. These results indicate that climate variability will obviously change streamflow and that natural disasters related to both high and heavy precipitation must be emphasised. Relevant departments can optimize the land‐use structure and spatial layout to mitigate the negative effects of climate variability.     

Effects of Land-Use and Climate Change on Hydrological Processes in the Upstream of Huai River, China

Land use/land cover and climate change can significantly alter water cycle at local and regional scales. Xixian Watershed, an important agricultural area in the upper reach of the Huaihe River, has undergone a dramatic change of cultivation style, and consequently substantial land use change, during the past three decades. A marked increase in temperature was also observed. A significant monotonic increasing trend of annual temperature was observed, while annual rainfall did not change significantly. To better support decision making and policy analysis relevant to land management under climate change, it is important to separate and quantify the effect of each factor on water availability. We used the Soil and Water Assessment Tool (SWAT), a physically based distributed hydrologic model, to assess the impact of Land use and climate changes separately. The SWAT model was calibrated and validated for monthly streamflow. Nash-Sutcliff efficiency (NSE), percentage bias (PBIAS), and coefficient of determination (R ²) were 0.90, 6.3 %, and 0.91 for calibration period and 0.91, 6.9 %, and 0.911 for validation period, respectively. To assess the separate effect of land use and climate change, we simulated streamflow under four scenarios with different combinations of two-period climate data and land use maps. The joint effect of land use and climate change increased surface flow, evapotranspiration, and streamflow. Climate variability increased the surface water and stream-flow and decreased actual evapotranspiration; and land use change played a counteractive role. Climate variability played a dominant role in this watershed. The differentiated impacts of land-use/climate variabilities on hydrological processes revealed that the unapparent change in stream-flow is implicitly because the effects of climate variability on hydrological processes were offset by the effects of land use change.     

Modeling Water Resources and River-Aquifer Interaction in the Júcar River Basin,Spain

The paper presents how to solve some practical problems of water planning in a medium/large river basin, such as: the water resources assessment and its spatial-temporal variability over the long-short term, the impact of human activities on the water cycle, due to groundwater pumping and water returns into aquifers, the river-aquifer interactions and the aquifer depletion. It is based on the use of a new monthly conceptual distributed water balance model -PATRICAL- that includes the surface water (SW), groundwater (GW) behavior and the river-aquifer interaction. The model is applied to the Júcar River Basin District (RBD) in Spain (43,000 km²), with more than 250 aquifers, including catchments with humid climates (Júcar RBD northern), semiarid and arid catchments (southern). The model has a small number of parameters and obtains a satisfactory performance in SW and GW behavior. It has been calibrated/validated using monthly streamflows and two additional elements not generally used in models for large river basins, GW levels and river-aquifer interactions. In the hydrological time series of the Júcar RBD headers a statistical change point in the year 1979/80 is detected. It is due to changes in precipitation patterns and represents a 40 % of reduction in streamflows in relation with the previous period. The impact of GW pumping in all aquifers is determined, the ‘Mancha Oriental’ aquifer produces a significant reduction in streamflows of the Júcar river –around 200–250 hm³/year. The GW level in the ‘Villena-Benejama’ aquifer -Vinalopo Valley- has declined more than 200 m in last 30 years.     

Streamflow Trends and Climate Variability Impacts in Poyang Lake Basin, China

Under the background of global warming, does the effect of the rising global surface temperature accelerate the hydrological cycle? To address this issue, we use the hydro-climatic data from five sub-basins in Poyang Lake basin in the southeast China over the past 50 years, to investigate the annual and seasonal trends of streamflow and the correlations between streamflow and climatic variables. The Theil–Sen Approach and the non-parametric Mann–Kendall test are applied to identify the trends in the annual and seasonal streamflow, precipitation and evapotranspiration series. It was found that annual and seasonal streamflow of all the stations had increasing trends except Lijiadu station in wet season. Only 37.5% hydro-stations in annual streamflow increased significantly, while most stations increased at 95% significance level in dry season. Trends in annual and seasonal precipitation during the whole period were generally not as significant as those in evapotranspiration. The correlations between streamflow and climate variables (precipitation and evapotranspiration) were detected by the Pearson’s test. The results showed that streamflow in the Poyang Lake basin are more sensitive to changes in precipitation than potential evapotranspiration.     

Hydrological Responses to Climate Change in Nenjiang River Basin,Northeastern China

Under the background of global climate change, hydrological responses to climate change were investigated in Northeastern China. This study analyses the trends of annual and seasonal temperature, precipitation and streamflow series in Nenjiang River Basin. Correlations between streamflow and meteorological variables were investigated, while parametric method and nonparametric tests were applied to determine the trends and correlations. Data collected from a series of monitoring stations showed significant increasing trends of annual and seasonal mean temperature versus time, whereas during the whole period the annual and seasonal precipitation in the basin did not exhibit similar trends although temporal and spatial variations were detected. Affected by the precipitation and temperature changes, significant trends of decreasing annual, spring and autumn streamflow were demonstrated; the decrease concentrating mainly on the mainstream and tributaries of the left bank. Correlation analyses revealed strong relationships between the streamflow and meteorological variables in Nenjiang River Basin, and the impacts of climate change on streamflow were complicated. Results from this study will help water resource managers for decision makings that address the consequences of climate change.     

Assessment of Contributions of Climatic Variation and Human Activities to Streamflow Changes in the Lancang River,China

The construction and operation of hydropower reservoirs on the Lancang River have drawn worldwide concern, because streamflow changes have occurred in this river since the introduction of dams. To address these concerns, it is necessary to quantitatively assess relative contributions of climatic variations and human activities to these changes. In this research, Mann-Kendall method was used to assess the trends in hydro-climatic data. The streamflow data were divided into a reference period (1956–1985) and a change period (1986–2008) based on hydropower reservoir construction timeline. The Back-Propagation Artificial Neural Network (BP-ANN) model was used to reconstruct natural streamflow. The contributions of climatic variations and human activities were investigated at the yearly, seasonal and monthly time scales. The results indicate that human activities exerted a slightly greater impact on flow changes than did climatic variations, at the yearly time scale (54.6 and 45.4 %, respectively). At the seasonal time scale, climatic variations made a greater contribution (65.8 %) during the wet season, while the contribution of human activities became the dominant factor during the dry season (85.3 %). At the monthly time scale, the contribution of climatic variations in January, June, August, and September was greater than that of human activities, while in the remaining eight months, human activities exerted a greater contribution than did climatic variation. The relative contributions of human activities and climatic variations (RCs) were also determined during the single- and cascade-dam periods; these did not always increase at the three time scales when dam system shifted from single-dam to cascade-dam.     

Development of a Demand Driven Hydro-climatic Model for Drought Planning

In recent years, droughts with increasing severity and frequency have been experienced around the world due to climate change effects. Water planning and management during droughts needs to deal with water demand variability, uncertainties in streamflow prediction, conflicts over water resources allocation, and the absence of necessary emergency schemes in drought situations. Reservoirs could play an important role in drought mitigation; therefore, development of an algorithm for operation of reservoirs in drought periods could help to mitigate the drought impacts by reducing the expected water shortages. For this purpose, the probable drought’s characteristics and their variations in response to factors such as climate change should be incorporated. This study aims at developing a contingency planning scheme for operation of reservoirs in drought periods using hedging rules with the objective of decreasing the maximum water deficit. The case study for evaluation of the performance of the proposed algorithm is the Sattarkhan reservoir in the Aharchay watershed, located in the northwestern part of Iran. The trend evaluations of the hydro-climatic variables show that the climate change has already affected streamflow in the region and has increased water scarcity and drought severity. To incorporate the climate change study in reservoir planning; streamflow should be simulated under climate change impacts. For this purpose, the climatic variables including temperature and precipitation in the future under climate change impacts are simulated using downscaled GCM (General Circulation Model) outputs to derive scenarios for possible future drought events. Then a hydrological model is developed to simulate the river streamflow, based on the downscaled data. The results show that the proposed methodology leads to less water deficit and decreases the drought damages in the study area.     

Hydrologic impacts of small‐scale instream diversions for frost and heat protection in the California wine country

Though many river studies have documented the impacts of large water projects on stream hydrology, few have described the effects of dispersed, small‐scale water projects on streamflow or aquatic ecosystems. We used streamflow and air temperature data collected in the northern California wine country to characterize the influence of small instream diversions on streamflow. On cold spring mornings when air temperatures approached 0°C, flow in streams draining catchments with upstream vineyards receded abruptly, by as much as 95% over hours, corresponding to times when water is used to protect grape buds from freezing; flow rose to near previous levels following periods of water need. Streams with no upstream vineyards showed no such changes in flow. Flow was also depressed in reaches below vineyards on hot summer days, when grape growers commonly use water for heat protection. Our results demonstrate that the changes in flow caused by dispersed small instream diversions may be brief in duration, requiring continuous short‐interval monitoring to adequately describe how such diversions affect the flow regime. Depending on the timing and abundance of such diversions in a drainage network, the changes in streamflow they cause may be an important limiting factor to valued biotic resources throughout the region. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of calibration data series length on performance and optimal parameters of hydrological model

In order to assess the effects of calibration data series length on the performance and optimal parameter values of a hydrological model in ungauged or data-limited catchments (data are non-continuous and fragmental in some catchments), we used non-continuous calibration periods for more independent streamflow data for SIMHYD (simple hydrology) model calibration. Nash-Sutcliffe efficiency and percentage water balance error were used as performance measures. The particle swarm optimization (PSO) method was used to calibrate the rainfall-runoff models. Different lengths of data series ranging from one year to ten years, randomly sampled, were used to study the impact of calibration data series length. Fifty-five relatively unimpaired catchments located all over Australia with daily precipitation, potential evapotranspiration, and streamflow data were tested to obtain more general conclusions. The results show that longer calibration data series do not necessarily result in better model performance. In general, eight years of data are sufficient to obtain steady estimates of model performance and parameters for the SIMHYD model. It is also shown that most humid catchments require fewer calibration data to obtain a good performance and stable parameter values. The model performs better in humid and semi-humid catchments than in arid catchments. Our results may have useful and interesting implications for the efficiency of using limited observation data for hydrological model calibration in different climates.     

Variable Streamflow Contributions in Nested Subwatersheds of a US Midwestern Urban Watershed

Quantification of runoff is critical to estimate and control water pollution in urban regions, but variation in impervious area and land-use type can complicate the quantification of runoff. We quantified the streamflow contributions of subwatersheds and the historical changes in streamflow in a flood prone urbanizing watershed in US Midwest to guide the establishment of a future pollution-control plan. Streamflow data from five nested hydrological stations enabled accurate estimations of streamflow contribution from five subwatersheds with variable impervious areas (from 0.5% to 26.6%). We corrected the impact of Missouri river backwatering at the most downstream station by comparing its streamflow with an upstream station using double-mass analysis combined with Bernaola-Galvan Heuristic Segmentation approach. We also compared the streamflow of the urbanizing watershed with seven surrounding rural watersheds to estimate the cumulative impact of urbanization on the streamflow regime. The two most urbanized subwatersheds contributed >365 mm streamflow in 2012 with 657 mm precipitation, which was more than fourfold greater than the two least urbanized subwatersheds. Runoff occurred almost exclusively over the most urbanized subwatersheds during the dry period. The frequent floods occurred and the same amount of precipitation produced ~100 mm more streamflow in 2008–2014 than 1967–1980 in the urbanizing watershed; such phenomena did not occur in surrounding rural watersheds. Our approaches provide comprehensive information for planning on runoff control and pollutant reduction in urban watersheds.     

Impacts of climatic variability on northward flowing rivers in North America,using a paired basin approach

Northward flowing rivers are the most vulnerable system to a general early warming trend in terms of flood risk. In a changing climate, how well we understand the variability of precipitation and streamflow and the correspondence between them determines the appropriateness and efficiency of river engineering activities, flood control structures, and water resource management policies. Using both time and frequency domain approaches, this study investigated variations and periodicities in precipitation and discharge of two neighboring northward flowing river basins, the Red River of the North (referred to hereafter as the Red River) basin and the Little Missouri River basin in North America. Additionally, this study also characterized whether the most dominant quasiperiodic climate variation El Niño Southern Oscillation (ENSO) affected regional precipitation and streamflow. Results indicated that the southern and central Red River basin experienced significant increases in precipitation and discharge, particularly in cold season, while the Little Missouri River basin had no statistically significant change in precipitation or discharge. The global atmospheric oscillation ENSO had little effects on the regional precipitation and streamflow increases in the Red River basin. Furthermore, strong spectral coherences and prominent annual/semi‐annual periodicities in precipitation and discharge were revealed, confirming how precipitation determines frequency peaks and primary oscillation cycles of discharges in both basins. By removing broad‐scale climatic driver, this study indicated that some local forcing is most likely responsible for the excessive water abundances in the Red River basin, among which agriculture land usages stand out to be the most promising driver.     

Modeling Climate Change Effects on Streams and Reservoirs with HSPF

This study deals with the effects of the expected climate change on the hydrology of watersheds and on water resources. HSPF (Hydrological Simulation Program—Fortran) has been used to model streamflow and reservoir volume as realizations of watershed response. Climate change scenarios have been prepared based on trends expected in western Turkey in the first half of the twenty-first century and a hypothetical watershed with different land uses has been simulated. Changes in streamflow due to landuse, soil type and climate change have been examined using flood frequency and low flow analysis. The simulations have revealed quantitatively the difference among the responses of watersheds with no vegetative cover and with forests or pasture to trends in temperature and precipitation. It has also been found that monthly variations are very important in predicting the future response of watersheds. Significant differences have been observed in streamflows and reservoir volumes on a monthly basis between scenarios, soil types and land uses. Though the effects of temperature and precipitation act to counterbalance their effects on a long-term scale, on a monthly basis they can act to reinforce their effects and create drought periods and floods.