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Streamflow in semiarid areas, especially in North China, was rapidly decreasing, which made it important to analyze the characteristics and influencing factors of streamflow. Using the hydro-meteorological data series of 1961–2017 in the upper Yongding River Basin (UYRB) (including the Yang River Basin (YRB) and Sanggan River Basin (SRB)), spatio-temporal variation characteristics of air temperature, precipitation, and potential evapotranspiration (E0) were analyzed. The results showed that precipitation has no significant trend; the temperature showed a significant increase of 0.1–0.5 °C per decade; E0 showed a significant decrease of approximately −2 mm/10yr (in 18 stations); the estimated rates of streamflow change were −7 and −8 mm/10yr for SRB and YRB. As for spatial distribution, the YRB presented a higher E0 value than the SRB; the mountain areas had more precipitation than the plain areas. The change points of streamflow occurred in 1982 and 2003. Both the Budyko and the DMC methods were used to evaluate the impacts of climate change and human activities on the mean annual streamflow. In variation stage I (1983~2003), impacts of human activities account for 90.6% and 62.7% of the mean annual streamflow changes in YRB and SRB, respectively. In variation stage II (2004~2017), the percentages were 99.5% and 93.5%, respectively. It is also noted that the first change point in streamflow was indeed at the beginning of China's land reform, when the farmers could manage their reallocated lands and, therefore, there was an increase in agricultural water consumption. The second change point coincided with "Capital Water Resources Planning", including water conservation projects and irrigation district construction programs. In general, human activities were mainly responsible for the significant decline in the annual streamflow of UYRB. This paper will provide valuable results for water resources planning and give guidance on the construction of water conservation function areas and ecological environment support areas in the capital. [ABSTRACT FROM AUTHOR]

In frequency analysis of annual maximum flood series (AMFS), it is mechanism‐based and significant to incorporate the information of the underlying "ordinary" daily streamflow events for improving accuracy of flood risk estimation and appropriate management. In previous studies related to flood nonstationarity, the classical norming constants method (C‐NCM) has been used to derive statistical parameters of annual maximum flood distribution from daily streamflow distribution. However, C‐NCM does not flexibly consider the feasible range of the scale parameter of annual maximum flood distributions, which can result in the inability to provide sufficient and reliable models to fit AMFS. This paper aims to investigate the potential of two alternative norming constants methods in fitting annual maximum floods, namely the Hall's norming constants method (H‐NCM) and the Fisher and Tippetts' norming constants method (FT‐NCM) respectively. A comparative study of these three methods was carried out using hydrological streamflow series of 77 stations in the Yangtze and Yellow River basins, China. The results found that H‐NCM outperforms both C‐NCM and FT‐NCM for the stations with relatively low‐skewness coefficient of AMFS. Therefore, H‐NCM is recommended to prioritize for practical applications when considering daily streamflow rather than small samples of flood events. Furthermore, if the skewness coefficient exceeds Cs,Gumbel≈1.14, the overall modelling performance of these three methods is significantly deteriorated. This can provide some reference for the applicability of the norming constants method in flood frequency analysis. [ABSTRACT FROM AUTHOR]

Separating the individual effects of climate variability and human activities on streamflow is more important than just knowing their combined effects. In this paper, using a scenario-based hydrological simulation approach, the streamflow changes caused by climate variability and two different types of human activities (i.e. land-use change and large reservoirs operations) as well as the contribution rates of these three factors over 272 sub-basins in the Yangtze river basin were quantified and compared among 5 different periods (i.e. 1988–1992 (P1), 1993–1997 (P2), 1998–2002 (P3), 2003–2007 (P4) and 2008–2012 (P5)). Results demonstrate that, at the annual scale, climate variability played a leading role in the change in outflow of most sub-basins. With regard to the seasonal variations in discharge at Datong station, climate factors played a predominant role during P1-P2 and P2-P3. Since the Three Gorges Reservoir began operating in 2003, the discharge was enhanced by reservoirs in January-May and reduced by reservoirs in July-December. Reservoir and climate factors codetermined seasonal streamflow change during P3-P4 and P4-P5. Land-use change made the smallest contribution to seasonal discharge fluctuations. This study can support decision-making in regional water resources planning and management. [ABSTRACT FROM AUTHOR]

Climate change and land use/cover change (LUCC) are two major factors that alter hydrological processes. The upper reaches of the Tarim River, situated in the northwest region of China, experience a dry and less rainy climate and are significantly influenced by human activities. This study comprehensively assessed the impacts of individual and combined climate changes and LUCCs on streamflow. Three general circulation models (GCMs) were utilized to predict future climate changes under three shared socioeconomic pathways (SSP119, SSP245, and SSP585). Cellular Automata–Markov (CA–Markov) was employed to predict future LUCC under three scenarios (i.e., ecological protection, historical trend, and farmland development). Streamflow for the period 2021–2050 was simulated using the calibrated MIKE SHE model with multiple scenarios. The results showed that from 2021 to 2050, increments in both average annual precipitation and average annual temperature under the three SSPs were predicted to lead to an increased streamflow. In comparison to the conditions observed in 2000, under three LUCC scenarios for 2030, the grassland area decreased by 1.04% to 1.21%, while the farmland area increased by 1.97% to 2.26%, resulting in reduced streamflow. The related changes analysis indicated that the variation in streamflow during winter is most significant, followed by spring. The study predicted that climate change would increase streamflow, while LUCC would decrease it. Due to the greater impact of LUCC, considering the combined effect of both factors, runoff would decrease. The contribution analysis indicated that climate change contributed between −7.16% and −18.66%, while LUCC contributed between 107.16% and 118.66%. [ABSTRACT FROM AUTHOR]

A better understanding of the effects of climate change and land use/cover change (LUCC) on streamflow promotes the long-term water planning and management in the arid regions of northwestern China. In this paper, the Soil and Water Assessment Tool (SWAT) and a separation approach were used to evaluate and separate the effects of climate change and LUCC on streamflow in the Xiying River basin. The SWAT model was calibrated by the hydro-meteorological data from 1980-1989 to obtain the optimum parameters, which were validated by the subsequent application to the period between 1990-2008. Moreover, streamflow under several scenarios with different climate change and land use conditions in 1990-2008 and 2010-2069 were further investigated. Results indicate that, in the period of 1990-2008, the streamflow was dominated by climate change (i.e., changes in precipitation and temperature), which led to a 102.8% increase in the mean annual streamflow, whereas LUCC produced a decrease of 2.8%. Furthermore, in the future period of 2010-2039, the mean annual streamflow will decrease by 5.4% and 4.5% compared with the data of 1961-1990 under scenarios A2 and B2, respectively, while it will decrease by 21.2% and 16.9% in the period of 2040-2069, respectively. [ABSTRACT FROM AUTHOR]

This paper applied a HIMS (hydroinformatic modeling system) model to simulate streamflow in the Luanhe River Basin. This model was compared with SIMHYD and XAJ models for eight sub-basins of the Luanhe River. The results showed HIMS model performed better than SIMHYD and XAJ models, in these areas. We then investigated the streamflow response to climate changes in the different sub-basins. Twenty hypothetical climate change scenarios (perturbed temperatures and precipitation) were used to test the sensitivity of HIMS model simulated annual and mean monthly streamflow. Our results demonstrated that: (i) the annual streamflow was positively related to precipitation, and there was a negative relationship between streamflow and temperature for all the eight sub-basins; (ii) in all sub-basins, the relationship of annual streamflow change to precipitation change was highly non-linear, but the relationship of annual streamflow change with temperature change was approximately linear; (iii) the annual streamflow response to precipitation change was more sensitive when increasing than decreasing; (iv) the annual streamflow response to climate change was more sensitive in the Xingzhouhe River sub-basin, followed by the Wuliehe River sub-basin, and the Sahe River sub-basin was least sensitive; (iv) there were few differences in inner-streamflow response to climate change in the Laoniuhe, Yimatuhe, and Yixunhe Rivers. But for other rivers, when the temperature changed, larger streamflow differences happened in winter and summer; when the precipitation decreased or was unchanged, the larger differences happened in winter months, and when the precipitation increased, larger differences happened in winter and summer. [ABSTRACT FROM AUTHOR]

Zhu, F.; Huang, W.; Cai, Y.; Teng, F.; Wang, B., and Zhou, Q., 2014. Development of a river hydrodynamic model for studying surface-ground water interactions affected by climate change in Heihe River, China. Over the past 50 years, glacier area in Qilian Mountain of the Heihe River basin has decreased by 29.6%, mainly resulting from the climate change. Understanding the interactions of surface and ground water interaction will be very helpful for studying climate-change impact on Hehei River basin. This paper presents the development of one-dimensional river hydrodynamic model for surface and ground water interactions (RHM-SG). Surface-water flow is described by the modified one-dimensional Saint Venant equations, which is solved by Preissmann scheme. The flow exchange between surface and ground water is described by Darcy's equation. Five model validation tests include uniform flow over sloping bed, one flood process, and river flow with interactions of ground water. Model tests demonstrate that the model compares well with analytic solution, and reasonably characterize the interaction between river flow and ground water. The model has also been tested in the application to the middle reach of the Heihe River. By including surface-ground water interactions, the accuracy of model predicted flow substantially improves. The correlation coefficient increases from 0.89 to 0.98, and the root-mean-square reduces from 21.16 m3/s to 8.49 m3/s, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the main reasons for the transformation of wetland ecosystems in the Delta of the Ili River in the period of 1979-2014. The study results are shown based on the analysis of multi-temporal satellite data Landsat, dynamics of hydrological regime of the river Ili, climate conditions and features of economic activities of the local community, as well as fieldwork in the study region. Analysis of area changes of main types of hydromorphic and semi-hydromorphic ecosystems of Delta river Ili in high and medium on water discharge in the following (1979, 1993, 2000, 2010, and 2015) years. Increasing water consumption in China and in Kazakhstan part of the Ili-Balkhash basin due to the development of the agrarian and municipal sectors of economy especially in China, significantly exceed increasing flow of Ili River, caused by regional warming in the catchment part of Ili River Basin. The global warming has intensified the degradation of glaciers in mountain catchment areas of Ili River, this in the near future threatens with a decline in river flow and as a consequence lead to the deterioration of delta ecosystems and the desiccation of lake Balkhash similarly to the ecological disaster of the Aral Sea. Analysis of long-term (from 1970 to 2013) climatic data from three meteorological stations demonstrated a trend of the regional increase of average annual air temperature by 1.4 °C and decreasing of average annual precipitation by 10 mm. These factors also contribute to the transformation process of hydromorphic ecosystems. [ABSTRACT FROM AUTHOR]

As global warming produces dramatic climate changes, water management is facing increasingly serious challenges. Given to the process of climate change and its complex effects on watershed hydrology, this paper investigates the spatial and temporal variation characteristics of major climatic factors (i.e., precipitation and temperature) over the upper Yangtze River basin (UYRB), China. The statistical analyses are based on annual and seasonal scales during 1951–2020 with a recorded period of seven decades. The Mann–Kendall nonparametric test and R/S analysis are used to record the temporal trends (past and future) of climate variables; the Pettitt test, standard normal homogeneity test and Buishand test are used to detect the homogeneity in climate series. The sensitivities of the streamflow to climatic parameters are assessed at the watershed scale, especially considering the Three Gorges Dam's (TGD) effect on changing runoff. The results of the study indicate that the annual precipitation of 29 out of 34 series indicate homogeneity, while 31 out of 34 annual mean temperature series show heterogeneity, with jump points around 1997 in the mean temperature of 20 sites. Detectable changes in precipitation were not observed during 1951–2020; however, the temperature increased significantly in the whole basin on annual and seasonal scales, except for several stations in the eastern part. The magnitude of increase in air temperature in high altitudes (Tibet Plateau) is higher than that in low altitudes (Sichuan Plain) over the last seven decades, and future temperatures continue to sharply increase in high altitudes. The TGD plays an important role in explaining the seasonal variations in streamflow at Yichang station, with streamflow experiencing a sharp increase in winter and spring (dry season) and a decrease in summer and autumn (rainy season) compared to the pre-TGD period. The streamflow variation at an annual scale is mainly regulated by climate fluctuation (variation in precipitation). During the last seven decades, increasing air temperature and decreases in rainfall and runoff signify reduced water resources availability, and the climate tends to be warmer and drier over the basin. The sensitivity of the streamflow to watershed precipitation is higher than that to temperature, with variation in annual rainfall explaining 71% of annual runoff variability. [ABSTRACT FROM AUTHOR]

The article explores the comment on an report on the impact of climatic change and human activities on streamflow in China's Hutuo River Basin. The reports' authors presented responses to various issues raised in the comment, which includes an expansion on the short statement on the changing rate in comparison with the precipitation in the Hutuo River Basin, the claim that climate variability and human activities are nonindependent and the uncertainty issue related to hydrological simulation.

Hydrological processes in most semiarid regions on Earth have been changing under the impacts of climate change, human activities, or combinations of the two. This paper first presents a trend analysis of the spatiotemporal changes in water resources and then diagnoses their underlying atmospheric and socio-economic causes over 10 catchments in the Laoha basin, a typical semiarid zone of northeast China. The impacts of climate variability and human activities on streamflow change were quantitatively evaluated by the VIC (Variable Infiltration Capacity) model. First, results indicate that six out of the 10 studied catch-ments have statistically significant downward trends in annual streamflow; however, there is no significant change of annual precipitation for all catchments. Two abrupt changes of annual streamflow at 1979 and 1998 are identified for the four largest catchments. Second, the Laoha basin generally experienced three evident dry-wet pattern switches during the past 50 years. Furthermore, this basin is currently suffering from unprecedented water shortages. Large-scale climate variability has affected the local natural hy-drologie system. Third, quantitative evaluation shows human activities were the main driving factors for the streamflow reduction with contributions of approximately 90% for the whole basin. A significant in-crease in irrigated area, which inevitably resulted in tremendous agricultural water consumption, is the foremost culprit contributing to the dramatic runoff reduction, especially at midstream and downstream of the Laoha basin. This study is expected to enable policymakers and stakeholders to make well-informed, short-term practice decisions and better plan long-term water resource and ecoenvironment management strategies. [ABSTRACT FROM AUTHOR]

Climate change may significantly affect the hydrological cycle and water resource management, especially in arid and semi-arid regions. In this paper, output from the Providing Regional Climates for Impacts Studies (PRECIS) regional climate model were used in conjunction with the Soil and Water Assessment Tool (SWAT) to analyse the effects of climate change on streamflow of the Xiying and Zamu rivers in the Shiyang River basin, an important arid region in northwest China. After SWAT model calibration and validation, streamflow in the Shiyang River Basin was simulated using the PRECIS climate model data for greenhouse gas emission scenarios A2 (high emission rate) and B2 (low emission rate) developed by Intergovernmental Panel on Climate Change. Monthly streamflow and hydrological extremes were compared for present-day years (1961-1990), the 2020s (2011-2040), 2050s (2041-2070) and 2080s (2071-2100). The results show that mean monthly streamflow in Shiyang River Basin generally increased in the 2020s, 2050s and 2080s between 0.7-6.1% at the Zamu gauging station and 0.1-4.8% at the Xiying gauging station. The monthly minimum streamflow increased persistently, but the maximum monthly streamflows increased in the 2020s and slightly decreased in the 2050s and 2080s. This study provides valuable information for guiding future water resource management in the Shiyang River Basin and other arid and semi-arid regions in China. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Extreme weather exerts a huge impact on human beings and it is of vital importance to study the regular pattern of meteorological and hydrological factors. In this paper, a selection of seven extreme indices is used to analyze the trend of precipitation extremes of 18 meteorological stations located in Zhejiang Province, east China using the Mann-Kendall test. Then the precipitation trends in the plum season (from May to July) and typhoon season (from August to October) are studied separately. The results show that the precipitation trend varies from east to west. There is a positive trend in the east and a negative one in the west. The largest part of Zhejiang Province shows a positive trend in heavy precipitation and the most significant upward trend is detected in Dinghai with 3.4 mm/year for precipitation on very wet days. Although the upward trend of extreme precipitation is not prevailing, the range of increase in specific areas is apparent, like Dinghai with 1.3 mm/year. Precipitation intensity exhibits an upward trend in most areas and a typical upward trend can be found in Dachendao, Tianmushan, and Yuhuan with 0.04, 0.02, and 0.05 mm/year respectively. Precipitation intensity in both plum and typhoon seasons has increased too, especially for the coastal stations. [ABSTRACT FROM AUTHOR]

This study calibrated and downscaled data from four scenarios in the Coupled Model Intercomparison Project Phase 6 (CMIP6) to drive the distributed hydrological model soil and water assessment tool (SWAT). Hereafter, this study systematically quantified the changes in streamflow under future climatic conditions in the middle-upper reaches of the Weihe River Basin. The results show that, compared with the base period (1991–2000), the low-emission SSP1-2.6 scenarios resulted in future streamflow reductions to values less than those recorded in the baseline period. Furthermore, the same is true for medium and high-emission SSP3-7.0 scenarios. Under the SSP1-2.6 emission scenarios, streamflow in the 2030s, 2040s, 2050s and 2060s will be reduced by 40%, 50%, 31%, and 38%, respectively. Under the SSP3-7.0 emission 12 scenarios, streamflow will decrease by 44%, 20%, 34%, and 7% in the 2023s, 2040s, 2050s and 2060s, separately. These results supply support for water resource management and water use in the Kuan-chung Plain in the future climate change. [ABSTRACT FROM AUTHOR]

Climatic variability and the quantification of climate change impacts on hydrological parameters are persistently uncertain. Remote sensing aids valuable information to streamflow estimations and hydrological parameter projections. However, few studies have been implemented using remote sensing and CMIP6 data embedded with hydrological modeling. This research studied how changing climate influences the hydro-climatic parameters based on the earth system models that participated in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). GRACE evapotranspiration data were forced into the Soil and Water Assessment Tool (SWAT) to project hydrologic responses to future climatic conditions in the Hongshui River basin (HRB) model. A novel approach based on climate elasticity was utilized to determine the extent to which climate variability affects stream flow. CMIP6 SSPs (shared socio-economic pathways) for the second half of the 20th century (1960–2020) and 21st century (2021–2100) projected precipitation (5–16%) for the whole Hongshui River basin (HRB). The ensemble of GCMs projected an increase of 2 °C in mean temperature. The stream flow is projected to increase by 4.2% under SSP-1.26, 6.2% under SSP-2.45, 8.45% under SSP-3.70, and 9.5% under SSP-5.85, based on the average changes throughout the various long-term future scenarios. We used the climate elasticity method and found that climate change contributes 11% to streamflow variability in the Hongshui River basin (HRB). Despite the uncertainty in projected hydrological variables, most members of the modeling ensemble present encouraging findings for future methods of water resource management. [ABSTRACT FROM AUTHOR]

With global climate change and increasingly extreme weather conditions, the water quality of the Lijiang River Basin (LRB) is facing huge threats. At present, there is still a lack of systematic research on water quality indicators and the influence of indirect factors such as meteorological factors on it in the LRB. Therefore, this study is based on the meteorological, hydrological, and water quality data of the LRB from 2012 to 2018, using the Mann–Kendall test, Morlet wavelet method, Spearman's rank correlation coefficient, sensitivity, and contribution rate to quantitative analysis of the relationship between climate conditions and water quality indicators. The results show that the change trends of these hydrological and climatic conditions have almost no significant sudden change; precipitation and streamflow are decreasing each year; the streamflow trend exhibits time hysteresis; precipitation has a stronger influence downstream than on the local area; water quality indicators of both stations exhibited a change period of around 18 to 20 months, with the exception of pH. Water quality indicators are insensitive to precipitation and streamflow, and sensitive to humidity and wind speed; DO was negatively correlated with climate indicators apart from wind speed; almost all water quality indicators in Yangshuo are highly sensitive to air temperature, and the contribution rate of air temperature to ORP and TP reached 4.81% and 3.56%, respectively; sunshine duration has a positive impact on reducing NH4-N and TP. The difference between Yangshuo and Guilin is mostly due to the input of external sources on both sides of the Lijiang River, which results in variations in climate conditions sensitivities. [ABSTRACT FROM AUTHOR]

It is now common knowledge that many water resources stresses relate to access to water within a basin. Yi River Basin, a typical river basin characterized by intensive agricultural processes, significant population growth, and water management, has been undergoing grave water problems. In this paper, the long-term trend of precipitation and streamflow in Yi River Basin, from 1964 to 2010, was investigated via Mann-Kendall test. The change point occurred in the year 1965 dividing the long-term series into two periods. Climate elasticity method and linear regression method were implemented to quantify the impact of precipitation and human activities on runoff and presented basically consistent results of the percentage change in an annual runoff for the postchange period. The results reveal that the decline of annual runoff in postchange period is mainly attributed to precipitation variability of 53.66–58.25% and human activities of 46.34–41.74%, as estimated by climate elasticity method and linear regression method, respectively. This study detected the changes in the precipitation-streamflow relationship and investigated the possible causes in the Yi River, which will be helpful for providing a reference for the management of regional water resources. [ABSTRACT FROM AUTHOR]

Hydrological nonstationarity has brought great challenges to the reliable application of conceptual hydrological models with time-invariant parameters. To cope with this, approaches have been proposed to consider time-varying model parameters, which can evolve in accordance with climate and watershed conditions. However, the temporal transferability of the time-varying parameter was rarely investigated. This paper aims to investigate the predictive ability and robustness of a hydrological model with time-varying parameter under changing environments. The conceptual hydrological model GR4J (Génie Rural à 4 paramètres Journalier) with only four parameters was chosen and the sensitive parameters were treated as functions of several external covariates that represent the variation of climate and watershed conditions. The investigation was carried out in Weihe Basin and Tuojiang Basin of Western China in the period from 1981 to 2010. Several sub-periods with different climate and watershed conditions were set up to test the temporal parameter transferability of the original GR4J model and the GR4J model with time-varying parameters. The results showed that the performance of streamflow simulation was improved when applying the time-varying parameters. Furthermore, in a series of split-sample tests, the GR4J model with time-varying parameters outperformed the original GR4J model by improving the model robustness. Further studies focus on more diversified model structures and watersheds conditions are necessary to verify the superiority of applying time-varying parameters. [ABSTRACT FROM AUTHOR]

In this paper, the Mann–Kendall test and F-test were combined to analyze the annual and seasonal streamflow variations and aberrance points for the twin rivers from 1963 to 2011. The Tennant method was subsequently used to evaluate the ecological flow assurance and deficit. Finally, the Double Mass Curve method was applied to identifying the human activities affecting the streamflow variations. The results were as follows: (1) Three similar stages of the streamflow variations were found for the twin rivers: fluctuations before 1980, the tiny downward trends from the 1980s to the 1990s, and the notably downward trends in the 2000s. (2) The seasonal streamflow also decreased continuously and dramatically, especially in summer, by 80.9% for the Chaohe River and 86.0% for the Baihe River. (3) During the spawning season, 83.3% and 73.1% of streamflow was not at the appropriate level for the Chaohe and Baihe Rivers, respectively, which indicated that the ecological environment was not optimal for the reproduction and breeding of aquatic organisms. While in other periods, the ecological flow assurance was better than that in spawning seasons for the Chaohe and Baihe Rivers, respectively. This indicated that the streamflow regimes of the twin rivers were not always optimal and conducive to the development of the aquatic ecosystem. (4) The streamflow variations of the twin rivers were influenced by increasingly intensive human activities such as changes of land use and land cover, and excessive exploitation and utilization of water resources. These influences were cumulative and showed a gradually increasing tendency. This research is helpful for understanding the streamflow regime and for forecasting of the regional extreme climate, such as drought and floods, and can provide a basis for decision making and formulating adaptive ecological security countermeasures in response to climate changes and human activities. [ABSTRACT FROM AUTHOR]

Afforestation to control soil erosion has been implemented throughout China over the past few decades. The long‐term hydrological effects, such as total water yield and baseflow, of this large‐scale anthropogenic activity remain unclear. Using six decades of hydrologic observations and remote sensing data, we explore the hydrological responses to forest expansion in four basins with contrasting climates across China. No significant change in runoff was found for the period 1970–2012 for the cold and dry Hailar River Basin in northeastern China. However, both forest expansion and reduced precipitation contributed to the runoff reduction after afforestation since the late 1990s. Similarly, afforestation and drying climate since the mid‐1990s induced a significant decrease in runoff for the Weihe River Basin in semi‐arid northwestern China. In contrast, the two wet basins in the humid southern China, Ganjiang River Basin and Dongjiang River Basin, showed insignificant changes in total runoff during their study periods. However, the baseflow in the winter dry seasons in these two watersheds significantly increased since the 1950s. Our results highlight the long‐term variable effects of forest expansion and local climatic variability on basin hydrology in different climatic regions. This study suggests that landuse change in the humid study watersheds did not cause dramatic change in river flow and that region‐specific afforestation policy should be considered to deal with forestation‐water quantity trade‐off. Conclusions from this study can help improve decision‐making for ecological restoration policies and water resource management in China and other countries where intensive afforestation efforts are taking place. Key Points: Both precipitation and afforestation explained reduction in runoff for dry basinsForest recovery did not result in significant changes in total runoff for two wet basinsDry season baseflow in two wet basins had an upward trend [ABSTRACT FROM AUTHOR]

Under the influence of climate change, the hydrological processes of glaciers have undergone significant changes, a fact which is seriously affecting agricultural production in the downstream region of the Tianshan Mountains, China. In order to explore the intrinsic relationship between climate change and hydrological elements, we proposed an "evaluation-driving-prediction" system to study it. First, we constructed a glacier-enhanced soil and water assessment tool model (GE-SWAT) and used a two-stage calibration method to optimize the model parameters. Next, a scenario analysis was used to evaluate the driving factors of historical runoff changes. Finally, we projected future runoff changes using bias-corrected regional climate model (RCM) outputs. The results of the case study on the Jinghe River Basin in the Tianshan Mountains show that from 1963 to 2016, total runoff increased by 13.3%, 17.7% of which was due to increasing precipitation and 1.8% of which was negated by rising temperatures. The glacier runoff increased by 14.5%, mainly due to the rising temperatures. A 3.4% reduction in snowmelt was caused by a lower snowfall/precipitation ratio, which significantly reduced the snowfall from June to August. The RCM projection indicated that the warming and humidification phenomenon in the study area will continue at least through to the mid-21st century. A consistent increase in glacier runoff and total runoff is projected, but the contribution rate of the glacier runoff will have little to no change under the RCP4.5 and RCP8.5 emission scenarios. Our research demonstrates the simulation performance of the GE-SWAT model in a basin with moderate glacier cover. This method is shown to be efficient in quantifying the impact of climate change on glacier hydrological processes and predicting future streamflow changes, providing a good research reference for similar regions. [ABSTRACT FROM AUTHOR]

Projecting future changes of streamflow in the Jinsha River Basin (JRB) is important for the planning and management of the west route of South-to-North Water Transfer Project (SNWTP). This paper presented an analysis of the implications of CMIP5 climate models on the future streamflow in the JRB, using SWAT model. Results show that: (1) In the JRB, a 10% precipitation decrease might result in a streamflow increase of 15 to 18% and a 1 °C increase in temperature might results in a 2 to 5% decrease in streamflow; (2) GFDL-ESM2M and NORESM1-M showed considerable skill in representing the observed precipitation and temperature, which can be chosen to analyze the changes in streamflow in the future; (3) The precipitation and temperature were projected to increase by 0.8 to 5.0% and 1.31 to 1.87 °C. The streamflow was projected to decrease by 4.1 to 14.3% in the upper JRB. It was excepted to change by −4.6 to 8.1% in the middle and lower JRB (MLJRB). The changes of low streamflow in the MLJRB were −5.8 to 7.4%. Therefore, the potential impact of climate on streamflow will have little effect on the planning and management of the west route of SNWTP. [ABSTRACT FROM AUTHOR]

In recent years, the stationary assumption of hydroclimatic variables as well as their temporal and spatial dependence structure have been challenged due to anthropogenic and climate changes. This study developed a stepwise and dynamic C-vine copula–based conditional model (SDCVC) to incorporate the nonstationarity into a monthly streamflow prediction, which depicted the predictor–predictand association on the basis of monthly streamflow and rainfall series of upstream and downstream stations in the Yangtze River basin of China. The model consists of (1) nonstationary modeling of the margins and nonstationary temporal and spatial dependence structure by the generalized additive models with location, scale, and shape (GAMLSS) and C-vine copula incorporating climate-related indexes as covariates during training time frames; and (2) a four-dimensional C-vine copula–based conditional quantile function to generate the simulated series during validation time frames. Three kinds of nonstationary models corresponding to different degrees were investigated to show the impact of nonstationarity on the streamflow forecasting. The proposed SDCVC model considering highest degree of nonstationarity outperformed the other two nonstationary models in terms of the performance metrics, because the SDCVC model not only described the dynamic change of time-varying connections between parameter and the large-scale climate forcings, but the stepwise strategy, by selecting the optimum time horizon, helped increase forecasting accuracy. Furthermore, the SDCVC model is superior, to some extent, to classical data-driven approaches [support vector regression (SVR) and adaptive-network-based fuzzy inference system (ANFIS)] in terms of the performance metrics. [ABSTRACT FROM AUTHOR]

Hydrological processes depend directly on climate conditions [e.g., precipitation, potential evapotranspiration ( PE)] based on the water balance. This paper examines streamflow datasets at four hydrological stations and meteorological observations at 79 weather stations to reveal the streamflow changes and underlying drivers in four typical watersheds (Meigang, Saitang, Gaosha, and Xiashan) within Poyang Lake Basin from 1961 to 2000. Most of the less than 90th percentile of daily streamflow in each watershed increases significantly at different rates. As an important indicator of the seasonal changes in the streamflow, CT (the timing of the mass center of the streamflow) in each watershed shows a negligible change. The annual streamflow in each watershed increases at different rates, with a statistically significant trend (at the 5 % level) of 9.87 and 7.72 mm year, respectively, in Meigang and Gaosha watersheds. Given the existence of interactions between precipitation and PE, the original climate elasticity of streamflow can not reflect the relationship of streamflow with precipitation and PE effectively. We modify this method and find the modified climate elasticity to be more accurate and reasonable using the correlation analysis. The analyses from the modified climate elasticity in the four watersheds show that a 10 % increase (decrease) in precipitation will increase (decrease) the annual streamflow by 14.1-16.3 %, while a 10 % increase (decrease) in PE will decrease (increase) the annual streamflow by −10.2 to −2.1 %. In addition, the modified climate elasticity is applied to estimate the contribution of annual precipitation and PE to the increasing annual streamflow in each watershed over the past 40 years. Our result suggests that the percentage attribution of the increasing precipitation is more than 59 % and the decreasing in PE is less than 41 %, indicating that the increasing precipitation is the major driving factor for the annual streamflow increase for each watershed. [ABSTRACT FROM AUTHOR]

Summary: In this paper we proposed: (1) an algorithm of glacier melt, sublimation/evaporation, accumulation, mass balance and retreat; (2) a dynamic Hydrological Response Unit approach for incorporating the algorithm into the Soil and Water Assessment Tool (SWAT) model; and (3) simulated the transient glacier retreat and its impacts on streamflow at basin scale. Application of the enhanced SWAT model in the Manas River Basin (MRB) in the Tianshan Mountains in northwest China, shows that the approach is viable as evidenced by a Nash–Sutcliff efficiency of 0.65 and a percent bias of −3.7% for daily streamflow and water balance, respectively. The results indicate that the glacier area decreased by 11% during the simulation period from 1961 to 1999, which is within the range of records from other glaciers. On average, glacier melt contributed 25% to streamflow, although glacier area accounts for only 14% of the catchment drainage area in the MRB. Glacier melt was positively correlated to temperature change (R 2 =0.70, statistical significance P <0.001) and negatively correlated to precipitation (R 2 =0.20, statistical significance P <0.005). The results indicate that glacier melt was more sensitive to temperature change than to precipitation change, implying that modeling the effects of climate change with increasing temperatures and decreasing precipitation should be further studied. [ABSTRACT FROM AUTHOR]

Abstract: Global climate change has tremendously altered the spatial and temporal distributions of precipitation. The Streamflow of the Yellow River decreased in the past decades, both because of human consumption and climate variations. This paper analyzed the trends of natural and observed streamflow of the Lijin hydrological station, as well as the precipitation and air temperature of the whole Yellow River Basin. There was an obvious change in the natural streamflow in 1991 when analyzed by the Mann-Kendall (M-K) method. Precipitation decreased in the whole Yellow River Basin. 22 Meteorological stations have slight increases, while the other 67 stations measured declines, in which 47 of the Meteorological stations’ decrements were over 5%. There was a descent of temperature for only 2 stations, while the temperature rose for the other 87 stations. The average temperature increment was 0.82°C and the highest was 1.91°C in Tsinghai Center station. The quantitative Streamflow-precipitation-temperature relations plot was drawn by Geostatistical Analyst module of ArcGIS 9.3. The streamflow have various responses to the different extents of precipitation and air temperature. In the past four decades, precipitation elasticity to streamflow was 1.95, and the elasticity index may give a general relationship between precipitation and streamflow. However, it varies with different scenarios. [Copyright &y& Elsevier]

Abstract: Long monthly streamflow series of three control hydrological stations of the Pearl River basin were analyzed by using the scanning t-test and the scanning F-test. Possible implications of the changing properties of streamflow variations for the water resource management of the Pearl River Delta are also discussed. The results indicated that: 1) more complicated changes were observed in terms of the second center moment when compared to the first original moment. More significant abrupt changes of the second center moment imply more sensitive response of streamflow stability to climate changes and human activities; 2) abrupt behaviors of the first (second) center moment of the streamflow variations tend to be more sensitive to climate changes and/or human activities in the larger river basin when compared to those in the smaller river basin. These phenomena are attributed to buffering functions of more storage space of longer river channel, and more complicated and longer runoff yield and concentration processes in the river basin of larger drainage area; 3) annual minimum streamflow of the Pearl River basin tends to be increasing. This will be helpful for better human mitigation of the salinity intrusion in dry seasons across the Pearl River Delta. Annual maximum streamflow, when compared to annual minimum streamflow, shows larger-magnitude variability reflected by larger standard deviation, implying unfavorable conditions for flood mitigation in the Pearl River Delta. The results of this paper are of scientific and practical merits for water resource management and sound human mitigation to water hazards across the Pearl River Delta, and also are a good case study for similar researches in other river deltas in the world under the changing environment. [ABSTRACT FROM AUTHOR]

Summary: Miyun Reservoir is the main raw water source for Beijing’s domestic water supply. Flow discharge to Miyun Reservoir decreased drastically over a 50-year period, from 1956 to 2005, and had seriously affected Beijing’s water supply. Climate variability and human activity had been identified as the two main reasons for the decrease in flow. Here, climate variability refers to changes in precipitation and temperature. Impact of human activity includes direct withdrawal of water (referred to as “direct abstraction” in this paper) from the river (primary) or groundwater and indirect impact due to man-made changes in land use and vegetation in the upstream of the reservoir. According to the historical record, “direct abstraction” from the upstream of the reservoir has increased significantly since 1984. The study period was split into two sub-periods, from 1956 to 1983 and from 1984 to 2005. Based on the historical record, annual runoff in the upstream catchment of Miyun Reservoir (i.e., inflow into the reservoir) had decreased from 90.3mm to 41.8mm for the two sub-periods, a decrease of 48.5mm. Over the same period, average annual “direct abstraction” increased from 2.2mm to 13.4mm, an increase of 11.2mm. The latter accounted for 23% (11.2mm/48.5mm) of the decrease in inflow into the reservoir. This study utilised: (1) a distributed hydrological model (geomorphology-based hydrological model, or GBHM) and (2) a climate elasticity model to conduct a quantitative assessment of the impact of climate variability and the indirect impact of human activity on the inflow into the reservoir. Simulation results of GBHM and the climate elasticity model showed that climate impact was accountable for about 55% and 51% of the decrease in reservoir inflow, respectively. The indirect impact of human activity (mainly man-made land use and vegetation changes) accounted for 18% of the decrease in reservoir inflow. [Copyright &y& Elsevier]

Streamflow series of five hydrological stations were analyzed with aim to indicate variability of water resources in the Tarim River basin. Besides, impacts of climate changes on water resources were investigated by analyzing daily precipitation and temperature data of 23 meteorological stations covering 1960–2005. Some interesting and important results were obtained: (1) the study region is characterized by increasing temperature, however, only temperature in autumn is in significant increasing trend; (2) precipitation changes present different properties. Generally, increasing precipitation can be detected. However, only the precipitation in the Tienshan mountain area is in significant increasing trend. Annual streamflow of major rivers of the Tarim River basin are not in significant trends, except that of the Akesu River which is in significantly increasing trend. Due to the geomorphologic properties of the Tienshan mountain area, precipitation in this area demonstrates significant increasing trend and which in turn leads to increasing streamflow of the Akesu River. Due to the fact that the sources of streamflow of the rivers in the Tarim River basin are precipitation and melting glacial, both increasing precipitation and accelerating melting ice has the potential to cause increasing streamflow. These results are of practical and scientific merits in basin-scale water resource management in the arid regions in China under the changing environment. [ABSTRACT FROM AUTHOR]

Abstract: The nonparametric Mann–Kendall test was used to detect the trends of major hydroclimatic variables in the Tarim River Basin, the largest inland river basin in China for the period of 1960–2007. Results showed that both mean annual air temperature and precipitation experienced an increasing trend, while annual streamflow demonstrated a mixed trend of decreasing and increasing: The mountainous region upstream showed an increasing trend and the region downstream exhibited a decreasing trend. Impacts of the increased air temperature on streamflow have shown different characteristics depending on location and seasons: it has positive effect on the runoff at mountainous region due to snowmelt and glacier-melt in spring, but negative effect on the runoff at plain area due to the increase of actual evaporation in summer. In addition, human activity contributed to the declining of streamflow in the arid plain oases at downstream of the Tarim River Basin. The results obtained in this paper can be used as a reference for the planning and management of water resources to maintain the health of the river system. [Copyright &y& Elsevier]

Climate change has affected the dynamics of the water cycle and its consequent effects on water resources in many regions. The Buyuan River, the largest tributary of the Upper Mekong River, is one of the regions with the strongest climate change in the Mekong River Basin, and its cross‐border impact on water resources has received increasing attention. However, few studies have focused on the runoff responses to future climate change in the Buyuan River Basin (BRB). In this study, the MIKE SHE model was applied to estimate the runoff of the BRB, based on climate‐change scenarios from the Beijing Climate Center Climate System Model (BCC‐CSM1‐1) under two Representative Concentration Pathways (RCPs). The simulations predicted a slight decrease in the mean annual runoff of the BRB under the RCP4.5 and RCP8.5 scenarios (2020–2049) compared with the reference period (1959–2012), with an increase in the magnitude of inter‐annual variation, leading to increased deficit and surplus during dry and wet years. The simulations predicted the earlier maximum monthly runoff and a more evenly distributed annual distribution of the runoff under RCP4.5 and RCP8.5 scenarios as compared to the reference period. The arrival of the flood season in the BRB was advanced by a month under future climate‐change scenarios. The results showed that the average annual runoff of the BRB does not change significantly under future climate‐change scenarios. However, there are obvious changes in the inter‐annual and intra‐annual distribution of the runoff. [ABSTRACT FROM AUTHOR]

The Yalong River basin (YRB), originating from the Tibetan Plateau, is critical for China's western development and electricity transmission. Climate change would affect the streamflow and potentially impact the hydropower in the YRB. In this study, the Automated Statistical Downscaling technique and the hydrological model SWAT were used to reproduce the observed precipitation, temperature and streamflow and predict them in the future. More importantly, the Bayesian Model Averaging (BMA) method was used to appraise the performance of four different Global Climate Models (GCMs) in simulating historical streamflow (1984–1997), and to quantify the uncertainties in future projections (2021–2100) under three Representative Concentration Pathways (RCPs) in the YRB. It was found that (i) the SWAT hydrological model has good applicability in the YRB; (ii) the BMA method can capture the historical streamflow reasonably better than individual GCM projections, providing a scientific reference for the future water resources planning and utilization in the YRB. [ABSTRACT FROM AUTHOR]

In this study, three representative concentration pathways (RCPs) and 15 general circulation models of the Coupled Model Intercomparison Project Phase 5 were used to assess the behaviour of precipitation (P) and surface air temperature (SAT) over part of the Songhua River Basin. The Water Evaluation and Planning (WEAP) model linked with SAT and P was used for monthly simulation of streamflow to assess the influence of land use/land cover and climate change on the streamflow. The results suggest that, under RCP2.6, RCP4.5 and RCP8.5, the SAT over the study area may increase in the 21st century by 1.12, 2.44 and 5.82°C, respectively. Moreover, by the middle of the 21st century, streamflow in the basin may have decreased by 19%. The decrease in streamflow may be due to changed land use conditions and water withdrawal, having critical implications for management and future planning of water resources in the basin. [ABSTRACT FROM AUTHOR]

Hydrological models are widely applied for simulating complex watershed processes and directly linking meteorological, topographical, land-use, and geological conditions. In this study, the Soil and Water Assessment Tool (SWAT) was calibrated at two monitoring stations, which improved model performance and increased the reliability of flow predictions in the Upper Xijiang River Basin. This study evaluated the potential impacts of climate change on the streamflow and water yield of the Upper Xijiang River Basin using Arc-SWAT. The model was calibrated (1991–1997) and validated (1998–2001) using the Sequential Uncertainty Fitting Algorithm (SUFI-2). Model calibration and validation suggest a good match between the measured and simulated monthly streamflow, indicating the applicability of the model for future daily streamflow predictions. Large negative changes of low flows are projected under future climate scenarios, exhibiting a 10% and 30% decrease in water yield over the watershed on a monthly scale. Overall, findings generally indicated that winter flows are expected to be affected the most, with a maximum impact during the January–April period, followed by the wet monsoon season in the May–September period. Water balance components of the Upper Xijiang River Basin are expected to change significantly due to the projected climate change that, in turn, will seriously affect the water resources and streamflow patterns in the future. Thus, critical problems, such as ground water shortages, drops in agricultural crop yield, and increases in domestic water demand are expected at the Xijiang River Basin. [ABSTRACT FROM AUTHOR]

Projections of streamflow, particularly of extreme flows under climate change, are essential for future water resources management and the development of adaptation strategies to floods and droughts. However, these projections are subject to uncertainties originating from different sources. In this study, we explored the possible changes in future streamflow, particularly for high and low flows, under climate change in the Qu River basin, eastern China. ANOVA (analysis of variance) was employed to quantify the contribution of different uncertainty sources from RCPs (representative concentration pathways), GCMs (global climate models) and internal climate variability, using an ensemble of 4 RCP scenarios, 9 GCMs and 1000 simulated realizations of each model–scenario combination by SDRM-MCREM (a stochastic daily rainfall model coupling a Markov chain model with a rainfall event model). The results show that annual mean flow and high flows are projected to increase and that low flows will probably decrease in 2041–2070 (2050s) and 2071–2100 (2080s) relative to the historical period of 1971–2000, suggesting a higher risk of floods and droughts in the future in the Qu River basin, especially for the late 21st century. Uncertainty in mean flows is mostly attributed to GCM uncertainty. For high flows and low flows, internal climate variability and GCM uncertainty are two major uncertainty sources for the 2050s and 2080s, while for the 2080s, the effect of RCP uncertainty becomes more pronounced, particularly for low flows. The findings in this study can help water managers to become more knowledgeable about and get a better understanding of streamflow projections and support decision making regarding adaptations to a changing climate under uncertainty in the Qu River basin. [ABSTRACT FROM AUTHOR]

Zhao, Y.; Zou, X.; Liu, Q., and Chen, Y., 2019. Impacts of climate variability and human activities on streamflow in the Wanquan River Basin along the east coast of Hainan Island, southern China. Journal of Coastal Research, 35(2), 410–419. Coconut Creek (Florida), ISSN 0749-0208. The influences of climate change and human activities on streamflow change have received significant attention recently. In this study, daily data from seven precipitation gauges and one hydrological station are analyzed to assess the impacts of climate variability and human activities on streamflow over the past 54 years in the Wanquan River Basin (WRB). The Mann-Kendall test and Morlet wavelet method were employed to analyze the streamflow series, and the relative effects of climate change and human activities were empirically determined based on a coupled water and energy budget analysis. The results show that annual streamflow exhibited a statistically insignificant decreasing trend throughout the entire basin at an annual rate of –0.015 × 108 m3/y. Meteorological factors, such as temperature, exhibited significant increases throughout the entire basin. A decreasing trend in precipitation and an increasing trend in potential evapotranspiration were identified in the upstream region, whereas the opposite trends were observed in the downstream region. Moreover, an abrupt change in streamflow at Jiaji station occurred in 1974, exhibiting periodicities of 2 to 4 and 8 to 11 years at a 95% confidence level during the periods of 1965–80 and 1970–75, respectively. Regarding the catchment-averaged water balance, a quantitative analysis revealed that climate change resulted in an increase in streamflow from the 1970s to the 2000s throughout the entire basin, and streamflow increased by 146%, 259%, 473%, and 128% in the 1970s, the 1980s, the 1990s, and 2000–13 relative to streamflow in the 1960s. However, human activities may have decreased streamflow (–46%, –159%, –373%, and –28% in the 1970s, the 1980s, the 1990s, and 2000–13, respectively). Therefore, the relative effect of climate change was greater than that of human activities. Further research is needed to clarify the mechanisms associated with the anthropogenic effects on runoff changes. [ABSTRACT FROM AUTHOR]

Human activities, as well as climate variability, have had increasing impacts on natural hydrological systems, particularly streamflow. However, quantitative assessments of these impacts are lacking on large scales. In this study, we use the simulations from six global hydrological models driven by three meteorological forcings to investigate direct human impact (DHI) and climate impact on streamflow in China. Results show that, in the sub-periods of 1971–1990 and 1991–2010, one-fifth to one-third of mean annual streamflow (MAF) was reduced due to DHI in northern basins, and much smaller (<4 %) MAF was reduced in southern basins. From 1971–1990 to 1991–2010, total MAF changes range from -13 % to 10 % across basins wherein the relative contributions of DHI change and climate variability show distinct spatial patterns. DHI change caused decreases in MAF in 70 % of river segments, but climate variability dominated the total MAF changes in 88 % of river segments of China. In most northern basins, climate variability results in changes of -9 % to 18 % in MAF, while DHI change results in decreases of 2 % to 8 % in MAF. In contrast with the climate variability that may increase or decrease streamflow, DHI change almost always contributes to decreases in MAF over time, with water withdrawals supposedly being the major impact on streamflow. This quantitative assessment can be a reference for attribution of streamflow changes at large scales, despite remaining uncertainty. We highlight the significant DHI in northern basins and the necessity to modulate DHI through improved water management towards a better adaptation to future climate change. [ABSTRACT FROM AUTHOR]

Baseflow availability and its contribution to streamflow are critical for planning and management of catchment hydrology and ecology. This study uses a digital filtering technique, statistical methods, and hydrological projection to investigate historical and future baseflow characteristics with respect to climate and land use impacts, exemplified by the large Poyang Lake catchment (China). Digital filtering results show that annual baseflow varied between 25 × 108 and 820 × 108 m3/year for the catchment rivers during 1953–2014. The results reveal that on average 62% of the long‐term streamflow in the catchment is derived from baseflow contribution. Statistics show a generally increasing trend in the annual baseflow and baseflow index (BFI) for most of the rivers over the past 60 years, with the major frequencies varying between 5 and 20 years. Although the trends in baseflow and BFI are attributable to the combined effects of climate and land use change across the catchment, baseflow variations are expected to be more sensitive to climate than land use changes. In general, precipitation plays a dominant role in controlling baseflow and can be used as an indication of the variations in baseflow at the subcatchment scale. Hydrological projection shows that annual baseflow and BFI are likely to increase by up to 31% and 13% during 2018–2035, respectively, based on historical baseflow trends. Our results indicate that management approaches for the catchment that consider groundwater and surface water as a joint resource will be needed to effectively manage the current and future river regime, its water resources, and water quality. [ABSTRACT FROM AUTHOR]

Understanding the dominant causes of streamflow alteration and effects of the current water diversion scheme is beneficial for sustainable management of water resources in an arid area. This study presents a quantitative attribution of the run‐off changes between headstreams and mainstream from 1960 to 2015 using the Choudhury–Yang equation and evaluates the effects of 18 times of ecological water conveyance in the lower reaches of the Tarim River Basin (TRB). Our results suggest that climate change was the primary determinant of increase of the streamflow in the headstreams from 2000 to 2015. While in the mainstream, human activities played a dominant role in deduction in the streamflow with the contribution of 54.8–355.6%. Eighteen episodes of ecological water conveyance have a positive effect on rising groundwater level and are highly related to seed falling time of Shrub and Perennial herbaceous and Annual herbaceous except for Arbor. It indicates that restoring the long‐term drying of the lower reaches through continuous water conveyance is feasible, although the existing programme has not restored the entire riparian system. Our study suggests that it is necessary to adopt an integrated approach for water resources allocation rather than relying on a single tributary contribution in the TRB. [ABSTRACT FROM AUTHOR]

Land use is the main factor that influences catchment hydrologic processes, and a better understanding of its effect is important for future land use planning and water resource management. By applying the Soil and Water Assessment Tool (SWAT), we assessed the effects of land use changes on major hydrologic processes (evapotranspiration (ET), discharge, river) on a large plain irrigation district, the Hetao Irrigation District (HID), China. The results indicated that SWAT was a useful tool for simulating the effects of land use changes on regional hydrologic processes. Human activities were the main factors that directly influenced land use in the HID. Land use changes had important impacts on the hydrologic processes of the HID. During 1995-2010, the land use changed greatly in the HID, leading to the changes in ET and discharge. The peak value of ET coincided with the exuberant crop growth period in the maximized sown crop area. In 1995s, wheat maximized the sown area and ET peaked in June; when sunflower and corn maximized the sown area in 2010s, ET peaked in July and August. The increased ET reduced discharge in the same period in the HID. Land use change affected the period and quantity of water diversion in the irrigation district. The quantity of water diverted in 1995 was greater than that in 2010, indicating that land use change significantly impacted the water quantity of the river, which was the water source of the irrigation district. This study will be a reference for future land use planning and water resource management in the irrigation district. [ABSTRACT FROM AUTHOR]

A slight variation in the magnitude of stream flow can have a substantial influence on the development of water resources. The Songhua River Basin (SRB) serves as a major grain commodity basin and is located in the northeastern region of China. Recent studies have identified a gradual decrease in stream flows, which presents a serious risk to water resources of the region. It is therefore necessary to assess the variation in stream flow and to predict the future of stream flows and droughts to make a comprehensive plan for agricultural irrigation. The simulation of monthly stream flows and the investigation of the influence of climate on the stream flow in the SRB were performed by utilizing the Integrated Water Evaluation and Planning (WEAP) tool coupled with observed precipitation data, as well as the Asian Precipitation-Highly-Resolved Observational Data Integration towards Evaluation of Water Resources (APHRODITE’s Water Resources) precipitation product. The Nash-Sutcliffe coefficient (NSC) was used to assess the WEAP efficiency. During the time of calibration, NSC was obtained as 0.90 and 0.67 using observed and APHRODITE precipitation data, respectively. The results indicate that WEAP can be used effectively in the SRB. The application of the model suggested a maximum decline in stream flow, reaching 24% until the end of 21st century under future climate change scenarios. The drought indices (standardized drought index and percent of normal index) demonstrated that chances of severe to extreme drought events are highest in 2059, 2060 and 2085, while in the remaining time period mild to moderate drought events may occur in the entire study area. The drought duration, severity and intensity for the period of 2011-2099 under all scenarios, [(A1B: 12, − 1.55, − 0.12), (A2: 12, − 1.41, − 0.09), (max. wetting and warming conditions: 12, − 1.37, − 0.11) and (min. wetting and warming conditions: 12, − 1.69, − 0.19)], respectively. [ABSTRACT FROM AUTHOR]

Under the impacts of climate variability and human activities, there is violent fluctuation for streamflow in the large basins in China. Therefore, it is crucial to separate the impacts of climate variability and human activities on streamflow fluctuation for better water resources planning and management. In this study, the Three Rivers Headwater Region (TRHR) was chosen as the study area. Long-term hydrological data for the TRHR were collected in order to investigate the changes in annual runoff during the period of 1956-2012. The nonparametric Mann-Kendall test, moving t test, Pettitt test, Mann-Kendall-Sneyers test, and the cumulative anomaly curve were used to identify trends and change points in the hydro-meteorological variables. Change point in runoff was identified in the three basins, which respectively occurred around the years 1989 and 1993, dividing the long-term runoff series into a natural period and a human-induced period. Then, the hydrologic sensitivity analysis method was employed to evaluate the effects of climate variability and human activities on mean annual runoff for the human-induced period based on precipitation and potential evapotranspiration. In the human-induced period, climate variability was the main factor that increased (reduced) runoff in LRB and YARB (YRB) with contribution of more than 90 %, while the increasing (decreasing) percentage due to human activities only accounted for less than 10 %, showing that runoff in the TRHR is more sensitive to climate variability than human activities. The intra-annual distribution of runoff shifted gradually from a double peak pattern to a single peak pattern, which was mainly influenced by atmospheric circulation in the summer and autumn. The inter-annual variation in runoff was jointly controlled by the East Asian monsoon, the westerly, and Tibetan Plateau monsoons. [ABSTRACT FROM AUTHOR]

The streamflow and water level complexity of the Poyang Lake basin has been investigated over multiple time-scales using daily observations of the water level and streamflow spanning from 1954 through 2013. The composite multiscale sample entropy was applied to measure the complexity and the Mann-Kendall algorithm was applied to detect the temporal changes in the complexity. The results show that the streamflow and water level complexity increases as the time-scale increases. The sample entropy of the streamflow increases when the time-scale increases from a daily to a seasonal scale, also the sample entropy of the water level increases when the time-scale increases from a daily to a monthly scale. The water outflows of Poyang Lake, which is impacted mainly by the inflow processes, lake regulation, and the streamflow processes of the Yangtze River, is more complex than the water inflows. The streamflow and water level complexity over most of the time-scales, between the daily and monthly scales, is dominated by the increasing trend. This indicates the enhanced randomness, disorderliness, and irregularity of the streamflows and water levels. This investigation can help provide a better understanding to the hydrological features of large freshwater lakes. Ongoing research will be made to analyze and understand the mechanisms of the streamflow and water level complexity changes within the context of climate change and anthropogenic activities. [ABSTRACT FROM AUTHOR]

The assessment of water resource responses to climate change is required in water resource planning and management, protecting environmental quality, and managing watersheds. This study modeled surface runoff and baseflow responses to variations in precipitation (0%, ±10%, and ±20%) and temperature (0 °C, ±1 °C, and ±2 °C) in 25 types of scenarios in the LanheWatershed (1140 km2), which possesses the typical hydrological and meteorological characteristics of the Loess Plateau in China. The study is based on the Soil and Water Assessment Tool (SWAT), which was calibrated and validated using the coefficient of determination (R2), Nash-Suttcliffe (Ens), and Percent bias (PBIAS), using the observed streamflow of Shangjingyou Station, a unique gauging station in the study area. The model was calibrated with daily streamflow, from 1967 to 1996, and then validated from 1997 to 2011. R2, Ens, and PBIAS were 0.95 and 0.84, 0.78 and 0.72, and 0.6% and -9.1% in annual and monthly calibration periods, 0.90 and 0.78, 0.74 and 0.67, and 22.1% and 18.8% in annual and monthly validation periods, and the overall performance ratings was ?satisfactory?. The assessment indicates that surface runoff is likely to be more affected than baseflow when altering temperatures and precipitation, and the noticeable changes of surface and baseflow are from June to September and October to November, respectively. Results also indicate that surface runoff and baseflow are very sensitive to the projected reduction in temperature, rather than to an increase of temperature, while precipitation is a constant. In turn, when the temperature is a constant, the surface runoff is sensitive to the projected increase in precipitation and the baseflow is sensitive to the decrease in precipitation. [ABSTRACT FROM AUTHOR]

Understanding the oasis ecosystem responses to upstream regulation is a challenge for catchment management in the context of ecological restoration. This empirical study aimed to understand how oasis ecosystems, including water, natural vegetation and cultivated land, responded to the implementation of the Ecological Water Diversion Project (EWDP) in the Heihe River in China. The annual Landsat images from 1987 to 2015 were firstly used to characterize the spatial extent, frequency index and fractional coverage (for vegetation only) of these three oasis ecosystems and their relationships with hydrological (river discharge) and climatic variables (regional temperature and precipitation) were explored with linear regression models. The results show that river regulation of the middle reaches identified by the discharge allocation to the downstream basin experiences three stages, namely decreasing inflow (1987-1999), increasing inflow (2000-2007) and relative stable inflow (2008-2015). Both the current and previous years' combined inflow determines the surface area of the terminal lake (R² = 0.841). Temperature has the most significant role in determining broad vegetation distribution, whereas hydrological variables had a significant effect only in near-riverchannel regions. Agricultural development since the execution of the EWDP might have curtailed further vegetation recovery. These findings are important for the catchment managers' decisions about future water allocation plans. [ABSTRACT FROM AUTHOR]

A growing number of studies on streamflow projection in the context of global climate change have been widely reported in past years. However, current knowledge on the role of different hydrological models to estimate future climate impact on flood in the Tibet Plateau is still limited so far. In this work, a group of hydrological models in conjunction with statistical downscaling outputs (SDSM and ANN) from the HadCM3 GCM model are used to evaluate the impacts of climate change on floods in the 21st century over the headwater catchment of Yellow River, the Tibet Plateau. The influence of different hydrological models on flood projection and quantile estimation are addressed. The results show that: (1) three hydrological models generate acceptable results of flood magnitude and frequency at Tangnaihai station during the past 50 years; (2) quite similar projections for future floods are obtained by means of different hydrological models, decreasing flood magnitude corresponding to the 2-, 5-, 10- and 50-year return periods is found under most scenarios in the 21st century. Meanwhile, flood frequency is likely to reduce in response to climate change; (3) the uncertainty in projected flood quantile by three different hydrological models increases with recurrence interval in term of relative length of confidence interval (RL). Besides, RL for flood quantile in future climate scenarios is likely to become larger than the baseline period. The results are valuable to improve our current knowledge of climate impact research in the alpine regions. [ABSTRACT FROM AUTHOR]

Water resources are very important for grain production in China. In this study, we investigate the changes in streamflow and grain production in China from 1956 to 2008. Since the 1980s, the increase of total grain production was mainly contributed by northern China where significantly decreasing precipitation and available water resources were observed. From 1985 to 2008, northern China accounted for 92.9 % of the national total grain production growth. Consequently, the main grain production area has shifted from the south to the north. However, the shift was mismatching the spatial distributions and temporal changes in precipitation and available water resources in China. During 1956 through 2008, precipitation decreased in the main grain production areas of the northern China by 1.23-1.27 mm per year. During the same period, observed streamflows in the five major rivers in northern China decreased by 13.4-92.4 %. Current grain production in northern China is dependent on overexploitation of groundwater. From 1987 to 2000, the average groundwater table declined 10.8 m with a maximum decrease of 34.8 m in North China Plain. Furthermore, the impacts of climate change and projected industrial development exacerbate the uncertainty of grain supply by northern China in the future. This study also indicated the potential of southern China for a more important role in ensuring sustainable food security of China, with increasing precipitation and streamflows observed in the Yangtze River and Pearl River basins. [ABSTRACT FROM AUTHOR]

Six global climate models (GCMs) from Coupled Model Intercomparison Project Phase 5 under three Respectively Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5) were used to assess the impact of climate change on streamflow for the Huangnizhuang catchment (HNZ) in China. Change factor method was used for bias correction between GCM outputs and observations and the SWAT model was used to simulate the hydrological processes. The results indicated that the SWAT model performed well in the study catchment with a monthly Nash-Sutcliffe efficiency (NS) of 0.93 and 0.91 and daily NS of 0.63 and 0.68 for calibration and validation periods respectively. Their corresponding relative errors were −2.2 and 8.9, and −2.6 and 8.5 % respectively. The ensemble of multi-GCMs projected an increase of precipitation in the middle and end of twenty-first century over the HNZ, ranging from −2.4 to 9 %. However, streamflow is likely to decline in the future, ranging −6.9 to 0.8 %, mainly due to an increase of evapotranspiration in a warming world, as air temperature shows steadily increases for all the GCMs and RCPs. Average monthly streamflow from six GCMs are likely to increase in August and September but decline from October to June. The associated uncertainties of the reported results were also discussed. It includes, but is not limit to, different GCMs, emissions scenarios, downscaling techniques as well as hydrological simulations. The results of this study can inform planning of long-term basin water management strategies taking into account global change scenarios. [ABSTRACT FROM AUTHOR]

This study investigated land-use and land-cover change (LUCC) and hydrological responses under consistent climate change scenarios (A1B and B1) in the Heihe River Basin (HRB), a typical arid inland river basin in northwest China. LUCC was first projected using the Dynamic Conversion of Land-Use and its Effects (Dyna-CLUE) model. Two cases (Case 1 and Case 2) were then established to quantify the hydrological responses to single climate change and the combined responses to climate change and LUCC with the Soil and Water Assessment Tool (SWAT). The results of LUCC modeling under the A1B and B1 scenarios present distinct regional characteristics and also indicate that the projected future land-use patterns are not appreciably different than the actual map for the year 2000. In Case 1, which only considers the impacts of single climate change, overall, the streamflow at the outlet of the upper HRB is projected to decline, whereas at the outlet of the middle HRB to increase, under both climate change scenarios. Meanwhile, the frequency of occurrence of hydrological extremes is expect to increase under both scenarios. In Case 2, which considers the combined impacts of climate change and LUCC, the changes in streamflow and frequency of hydrological extremes are found to be remarkably consistent with those in Case 1. The results imply that climate change rather than LUCC are primarily responsible for the hydrological variations. The role of LUCC varies with regions in the context of climate change dominated hydrological responses. [ABSTRACT FROM AUTHOR]

Water resources are contingent on the combined effects of climate change and watershed characteristics. An analytical model devised from the Budyko framework was used to investigate the partitioning of precipitation ( P) into actual evapotranspiration ( E) and streamflow ( Q) parameters for the Yellow River Basin (YRB), a water-limited basin, to estimate the response of E and Q to P and potential evapotranspiration ( E). Although a steady state was assumed, the analytical model, incorporating an adjustable parameter characteristic of catchment conditions ( ω), can be run to analyze the sensitivity of catchment characteristics on water resources. The theory predicts that Q and E are more sensitive to P than to E. For example, a 10 % increase in P will result in a 22.8 % increase in Q, while a 10 % increase in E will decrease Q by 13.2 %. The model shows that, to some extent, water balance is governed by changing catchment characteristics (such as changes in vegetation on annual scales). These findings indicate that additional elucidative data can be drawn from the Budyko framework when taking into account catchment characteristics. Furthermore, the model can analyze the response of water resources to climate change on different temporal and spatial scales. [ABSTRACT FROM AUTHOR]