Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya

Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 10⁶ m³ year^?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd.     

Climate change and runoff response based on isotope analysis in an arid mountain watershed of the western Kunlun Mountains

Climate change and runoff response were assessed for the Tizinafu River basin in the western Kunlun Mountains, China, based on isotope analysis. We examined climate change in the past 50 years using meteorological data from 1957 to 2010. Results of the Mann-Kendall non-parametric technique test indicated that temperature in the entire basin and precipitation in the mountains exhibited significant increasing trends. Climate change also led to significant increasing trends in autumn and winter runoff but not in spring runoff. By using 122 isotope samples, we investigated the variations of isotopes in different water sources and analysed the contributions of different water sources based on isotope hydrograph separation. The results show that meltwater, groundwater and rainfall contribute 17%, 40% and 43% of the annual streamflow, respectively. Isotope analysis was also used to explain the difference in seasonal runoff responses to climate change. As the Tizinafu is a precipitation-dependent river, future climate change in precipitation is a major concern for water resource management.

EDITOR A. Castellarin; ASSOCIATE EDITOR S. Huang     

Quantitative assessment of the impact of climate variability and human activities on runoff changes: a case study in four catchments of the Haihe River basin,China

Quantitative evaluation of the effect of climate variability and human activities on runoff is of great importance for water resources planning and management in terms of maintaining the ecosystem integrity and sustaining the society development. In this paper, hydro‐climatic data from four catchments (i.e. Luanhe River catchment, Chaohe River catchment, Hutuo River catchment and Zhanghe River catchment) in the Haihe River basin from 1957 to 2000 were used to quantitatively attribute the hydrological response (i.e. runoff) to climate change and human activities separately. To separate the attributes, the temporal trends of annual precipitation, potential evapotranspiration (PET) and runoff during 1957–2000 were first explored by the Mann–Kendall test. Despite that only Hutuo River catchment was dominated by a significant negative trend in annual precipitation, all four catchments presented significant negative trend in annual runoff varying from ?0.859 (Chaohe River) to ?1.996 mm a^?1 (Zhanghe River). Change points in 1977 and 1979 are detected by precipitation–runoff double cumulative curves method and Pettitt's test for Zhanghe River and the other three rivers, respectively, and are adopted to divide data set into two study periods as the pre‐change period and post‐change period. Three methods including hydrological model method, hydrological sensitivity analysis method and climate elasticity method were calibrated with the hydro‐climatic data during the pre‐change period. Then, hydrological runoff response to climate variability and human activities was quantitatively evaluated with the help of the three methods and based on the assumption that climate and human activities are the only drivers for streamflow and are independent of each other. Similar estimates of anthropogenic and climatic effects on runoff for catchments considered can be obtained from the three methods. We found that human activities were the main driving factors for the decline in annual runoff in Luanhe River catchment, Chaohe River catchment and Zhanghe River catchment, accounting for over 50% of runoff reduction. However, climate variability should be responsible for the decrease in annual runoff in the Hutuo River catchment. Copyright © 2012 John Wiley & Sons, Ltd.     

Hydrological Response of Runoff to Climate Change of Typical Tributaries in Ebinur Lake Basin of Xinjiang

In recent years, the natural hydrology behaviors were greatly influenced by climate change. The relation between runoff and climate change are always the core of scientific hydrological study in arid region. This paper presents a multi-variate time series controlled auto-regressive (CAR) model based on hydrological and climatic data of typical tributaries Jinghe River in Ebinur Lake Basin of Xinjiang covering the period from 1957 to 2012. The aim is to study the climate change and its effects on runoff of the Jinghe River, Northwest China. The results showed the following: the runoff of the Jinghe River was unevenly distributed and has obvious seasonal changes throughout the year. It was concentrated in summer and has along dry season with less runoff. The monthly maximum river runoff was from June to September and accounted for 74% of annual runoff. The river runoff increased since the 1980s till the 1990s; in the 21st century there was a trend of decreasing. The oscillatory period of annual runoff series in the Jinghe River Basin was 21a and 13a, and these periods were more obvious, followed by 32a and 9a. The oscillation with a time scale of 21a and 13a was a fulltimed domain. The MRE is 6.54%, the MAE is 0.84 × 10⁸ m³, and the RMSE is 0.039. The CAR model passed the F-test and residual test, and the change trend of calculated and measured values of annual runoff is consistence, which means that the model was reasonable.     

Assessing the effect of climate change on mean annual runoff in the Songhua River basin,China

Influences of climatic change on the components of global hydrological cycle, including runoff and evapotranspiration are significant in the mid‐ and high‐latitude basins. In this paper, the effect of climatic change on annual runoff is evaluated in a large basin—Songhua River basin which is located in the northeast of China. A method based on Budyko‐type equation is applied to separate the contributions of climatic factors to changes in annual runoff from 1960 to 2008, which are computed by multiplying their partial derivatives by the slopes of trends in climate factors. Furthermore, annual runoff changes are predicted under IPCC SRES A2 and B2 scenarios with projections from five GCMs. The results showed that contribution of annual precipitation to annual runoff change was more significant than that of annual potential evapotranspiration in the Songhua River basin; and the factors contributing to annual potential evapotranspiration change were ranked as temperature, wind speed, vapour pressure, and sunshine duration. In the 2020s, 2050s, and 2080s, changes in annual runoff estimated with the GCM projections exhibited noticeable difference and ranged from ? 8·4 to ? 16·8 mm a^?1 (?5·77 to ? 11·53% of mean annual runoff). Copyright © 2011 John Wiley & Sons, Ltd.     

Plausible impact of global climate change on water resources in the Tarim River Basin

Combining the temperature and precipitation data from 77 climatological stations and the climatic and hydrological change data from three headstreams of the Tarim River: Hotan, Yarkant, and Aksu in the study area, the plausible association between climate change and the variability of water resources in the Tarim River Basin in recent years was investigated, the long-term trend of the hydrological time series including temperature, precipitation, and stream-flow was detected, and the possible association between the El Nino/Southern Oscillation (ENSO) and these three kinds of time series was tested. The results obtained in this study show that during the past years, the temperature experienced a significant monotonic increase at the speed of 5%, nearly 1℃rise; the precipitation showed a significant decrease in the 1970s, and a significant increase in the 1980s and 1990s, the average annual precipitation was increased with the magnitude of 6.8 mm per decade. A step change occurred in both temperature and     

Long‐term trend of precipitation and runoff in Korean river basins

The spatial and temporal variations of precipitation and runoff for 139 basins in South Korea were investigated for 34 years (1968–2001). The Precipitation‐Runoff Modelling System (PRMS) was selected for the assessment of basin hydrologic response to varying climates and physiology. A non‐parametric Mann–Kendall's test and regression analysis are used to detect trends in annual, seasonal, and monthly precipitation and runoff, while Moran's I is adapted to determine the degree of spatial dependence in runoff trend among the basins. The results indicated that the long‐term trends in annual precipitation and runoff were increased in northern regions and decreased in south‐western regions of the study area during the study period. The non‐parametric Mann–Kendall test showed that spring streamflow was decreasing, while summer streamflow was increasing. April precipitation decreased between 15% and 74% for basins located in south‐western part of the Korean peninsula. June precipitation increased between 18% and 180% for the majority of the basins. Trends in seasonal and monthly streamflow show similar patterns compared to trends in precipitation. Decreases in spring runoff are associated with decreases in spring precipitation which, accompanied by rising temperatures, are responsible for reducing soil moisture. The regional patterns of precipitation and runoff changes show a strong to moderate positive spatial autocorrelation, suggesting that there is a high potential for severe spring drought and summer flooding in some parts of Korea if these trends continue in the future. Copyright © 2008 John Wiley & Sons, Ltd.     

Trend and change-point analyses of streamflow and sediment discharge in the Yellow River during 1950–2005

Abstract

The objectives of this work are: (a) to statistically test and quantify the decreasing trends of streamflow and sediment discharge of the Yellow River in China during 1950–2005, (b) to identify change points or transition years of the decreasing trends, and (c) to diagnose whether the decreasing trends were caused by precipitation changes or human intervention, or both. The results show that significant decreasing trends in annual streamflow and sediment discharge have existed since the late 1950s at three stations located in the upper, middle, and lower reaches of the Yellow River (P?=?0.01). Change-point analyses further revealed that transition years existed and that rapid decline in streamflow and sediment discharge began in 1985 in most parts of the basin (P?=?0.05). Adoption of conservation measures in the 1980s and 1990s corroborates the identified transition years. Double-mass curves of precipitation vs streamflow (sediment) for the periods before and after the transition years show remarkable decreases in proportionality of streamflow (sediment) generation. All percentiles of streamflow and sediment discharge after the transition years showed rapid reduction. In the absence of significantly decreasing precipitation trends, it is concluded that the decreasing trends were very likely caused by human intervention. Relative to the period before the transition, human intervention during 1985–2005 reduced cumulative streamflow by 13.5, 14.3 and 24.6% and cumulative sediment discharge by 29.0, 24.8 and 26.5%, at Toudaoguai, Huayuankou and Lijin, respectively, showing the quantitative conservation effect in the basin.

Citation Gao, P., Zhang, X.-C., Mu, X.-M., Wang, F., Li, R. & Zhang, X. (2010) Trend and change-point analyses of streamflow and sediment discharge in the Yellow River during 1950–2005. Hydrol. Sci. J. 55(2), 275–285.     

Modeling the effects of climate change projections on streamflow in the Nooksack River basin,Northwest Washington

The Nooksack River has its headwaters in the North Cascade Mountains and drains an approximately 2000 km² watershed in northwestern Washington State. The timing and magnitude of streamflow in a snowpack‐dominated drainage basin such as the Nooksack River basin are strongly influenced by temperature and precipitation. Projections of future climate made by general circulation models (GCMs) indicate increases in temperature and variable changes in precipitation for the Nooksack River basin. Understanding the response of the river to climate change is crucial for regional water resources planning because municipalities, tribes, and industry depend on the river for water use and for fish habitat. We combine three different climate scenarios downscaled from GCMs and the Distributed‐Hydrology‐Soil‐Vegetation Model to simulate future changes to timing and magnitude of streamflow in the higher elevations of the Nooksack River. Simulations of future streamflow and snowpack in the basin project a range of magnitudes, which reflects the variable meteorological changes indicated by the three GCM scenarios and the local natural variability employed in the modeling. Simulation results project increased winter flows, decreased summer flows, decreased snowpack, and a shift in timing of the spring melt peak and maximum snow water equivalent. These results are consistent with previous regional studies, but the magnitude of increased winter flows and total annual runoff is higher. Increases in temperature dominate snowpack declines and changes to spring and summer streamflow, whereas a combination of increases in temperature and precipitation control increased winter streamflow. Copyright © 2013 John Wiley & Sons, Ltd.     

The nonlinear hydro-climatic process in the Yarkand River, northwestern China

Based on the hydrologic and meteorological data in the Yarkand River Basin during 1957–2008, the nonlinear hydro-climatic process was analyzed by a comprehensive method, including the Mann–Kendall trend test, wavelet analysis, wavelet regression analysis and correlation dimension. The main findings are as following: (1) The annual runoff, annual average temperature and annual precipitation showed an increasing trend during the period of 1957–2008, and the average increase extent in runoff, temperature and precipitation was 2.234 × 10⁸ m³/10 year, 0.223 °C/10 year, and 4.453 mm/10 year, respectively. (2) The nonlinear pattern of runoff, temperature and precipitation was scale-dependent with time. In other words, the annual runoff, annual average temperature and annual precipitation at five time scales resulted in five patterns of nonlinear variations respectively. (3) Although annual runoff, annual average temperature and annual precipitation presented nonlinear variations at different time scales, the runoff has a linear correlation with the temperature and precipitation. (4) The hydro-climatic process of the Yarkand River is chaotic dynamic system, in which the correlation dimension of annual runoff, annual average temperature and annual precipitation is 3.2118, 2.999 and 2.992 respectively. None of the correlation dimensions is an integer, and it indicates that the hydro-climatic process has the fractal characteristics.     

Long‐term streamflow trends in the middle reaches of the Yellow River Basin: detecting drivers of change

The catchments in the Loess Plateau, in China's middle reaches of the Yellow River Basin, experienced unprecedented land use changes in the last 50 years as a result of large‐scale soil conservation measure to control soil erosion. The climate of the region also exhibited some levels of change with decreased precipitation and increased temperature. This study combined the time‐trend analysis method with a sensitivity‐based approach and found that annual streamflow in the Loess Plateau decreased significantly since the 1950s and surface runoff trends appear to dominate the streamflow trends in most of the catchments. Annual baseflow exhibited mostly downward trends, but significant upward trends were also observed in 3 out of 38 gauging stations. Mean annual streamflow during 1979?2010 decreased by up to 65% across the catchments compared with the period of 1957?1978, indicating significant changes in the hydrological regime of the Loess Plateau. It is estimated that 70% of the streamflow reduction can be attributed to land use change, while the remaining 30% is associated with climate variability. Land use change because of the soil conservation measures and reduction in precipitation are the key drivers for the observed streamflow trends. These findings are consistent with results of previous studies for the region and appear to be reasonable given the accelerated level of the soil conservation measures implemented since the late 1970s. Changes in sea surface temperature in the Pacific Ocean, as indicated by variations in El Niño–Southern Oscillation and phase shifts of the Pacific Decadal Oscillation, appear to have also affected the annual streamflow trends. The framework described in this study shows promising results for quantifying the effects of land use change and climate variability on mean annual streamflow of catchments within the Loess Plateau. Copyright © 2015 John Wiley & Sons, Ltd.     

近60年来白洋淀流域河川径流演变及湿地生态响应

白洋淀是雄安新区的核心生态功能区,近几十年来面临水源不足、湿地萎缩等生态环境问题.选取白洋淀流域上游王快、西大洋及拒马河3个子流域开展河川径流演变研究,结合1969年以来18期白洋淀湿地遥感影像,揭示白洋淀流域河川径流驱动湿地演变的过程机制.结果表明：近60年来白洋淀流域山区径流量呈持续衰减趋势,从P1阶段（1961—1979年）至P3阶段（1997—2019年）,典型子流域年径流系数均值由0.29降至0.12,山区年径流总量由30.84×10⁸ m³/a降至11.37×10⁸ m³/a,降幅达63.1%,梯田修建、地下水开采等人类活动是导致径流衰减的主要原因;不同子流域产流和基流减少对径流衰减的贡献率存在差异,以变质岩为主的王快子流域径流衰减的主要原因是地表产流减少,碳酸盐岩分布较广的拒马河子流域径流衰减的主要原因是基流减少;白洋淀湿地面积变化受控于地表水位波动,近60年来白洋淀湿地退化的直接原因是入淀流量减少,根本原因是人类活动影响导致的山区径流衰减.     

Comparative streamflow characteristics in urbanizing basins in the Portland Metropolitan Area,Oregon, USA

This study investigates changes in streamflow characteristics for urbanizing watersheds in the Portland Metropolitan Area of Oregon for the period from 1951 to 2000. The objective of this study was to assess how mean annual runoff ratio, mean seasonal runoff ratio, annual peak runoff ratio, changes in streamflow in response to storm amount, the fraction of time that the daily mean flow exceeds the annual mean flow, 3‐day recession constants, and dry/wet flow ratio vary among watersheds with different degrees of urban development. There were no statistically significant changes in annual runoff ratio and annual peak runoff ratio for the mixed land‐use watershed (Tualatin River watershed) and the urban watershed (Johnson Creek watershed) during the entire study period. The Tualatin River watershed, where most of the urban development occurred in a lower part of the watershed, showed a statistically significant increase in annual peak runoff ratio during the 1976 and 2000 period. The Upper Tualatin River watershed illustrated a significant decrease in annual peak runoff ratio for the entire study period. With significant differences in seasonal runoff ratio, only Johnson Creek exhibited a significant increase in both wet and dry season runoff ratios. Streamflow during storm events declined rapidly in the urban watershed, with a high 3‐day recession constant. At an event storm scale, streamflow in Fanno Creek, which is the most urbanized watershed, responded quickly to precipitation input. The fraction of time that the daily mean flow exceeded the annual mean flow and dry/wet flow ratio are all lower in Johnson Creek. This suggests a shorter duration of storm runoff and lower baseflow in the urbanized watershed when compared to the mixed land use watershed. The findings of this study demonstrate the importance of spatial and temporal scale, climate variability, and basin physiographic characteristics in detecting the hydrologic effects of urbanization in the Pacific Northwest of the USA. Copyright © 2006 John Wiley & Sons, Ltd.     

A remote sensing contribution to hydrologic modelling in arid and inaccessible watersheds,Pishin Lora basin,Pakistan

The lack of adequate field measurements often hampers the construction and calibration of rainfall‐runoff models over many of the world's watersheds. We adopted methodologies that rely heavily on readily available remote sensing datasets as viable alternatives for assessing, managing, and modelling of such remote and inadequately gauged regions. The Soil and Water Assessment Tool was selected for continuous (1998–2005) rainfall‐runoff modelling of one such area, the northeast part of the Pishin Lora basin (NEPL). Input to the model included satellite‐based Tropical Rainfall Measuring Mission precipitation data, and modelled runoff was calibrated against satellite‐based observations, the latter included: (i) monthly estimates of the water volumes impounded by the Khushdil Khan (latitude 30°40′N, longitude 67°40′E), and the Kara Lora (latitude 30°34′N, longitude 66°52′E) reservoirs, and (ii) inferred wet versus dry conditions in streams across the NEPL. Calibrations were also conducted against observed flow reported from the Burj Aziz Khan station at the NEPL outlet (latitude 30°20′N; longitude 66°35′E). Model simulations indicate that (i) average annual precipitation (1998–2005), runoff and recharge in the NEPL are 1300 × 10⁶ m³, 148 × 10⁶ m³, and 361 × 10⁶ m³, respectively; (ii) within the NEPL watershed, precipitation and runoff are high for the northeast (precipitation: 194 mm/year; runoff: 38 × 10⁶ m³/year) and northwest (134 mm/year; 26 × 10⁶ m³/year) basins compared to the southern basin (124 mm/year; 8 × 10⁶ m³/year); and (3) construction of delay action dams in the northeast and northwest basins could increase recharge from 361 × 10⁶ m³/year up to 432 × 10⁶ m³/year and achieve sustainable extraction. The adopted methodologies are not a substitute for traditional approaches, but they could provide first‐order estimates for rainfall, runoff, and recharge in the arid and semi‐arid parts of the world that are inaccessible and/or lack adequate coverage with field data. Copyright © 2011 John Wiley & Sons, Ltd.     

Trend,periodicity and abrupt change in streamflow of the East River,the Pearl River basin

The East River in the Pearl River basin, China, plays a vital role in the water supply for mega‐cities within and in the vicinity of the Pearl River Delta. Knowledge of statistical variability of streamflow is therefore important for water resources management in the basin. This study analyzed streamflow from four hydrological stations on the East River for a period of 1951–2009, using ensemble empirical mode decomposition (EEMD), continuous wavelet transform (CWT) technique, scanning t and F tests. Results indicated increasing/decreasing streamflow in the East River basin before/after the 1980s. After the early 1970s, the high/low flow components were decreasing/increasing. CWT‐based analysis demonstrates a significant impact of water reservoirs on the periodicity of streamflow. Scanning t and F test indicates that significantly abrupt changes in streamflow are largely influenced by both water reservoirs construction and precipitation changes. Thus, changes of streamflow, which are reflected by variations of trend, periodicity and abrupt change, are due to both water reservoir construction and precipitation changes. Further, the changes of volume of streamflow in the East River are in good agreement with precipitation changes. Copyright © 2012 John Wiley & Sons, Ltd.     

Temporal trends of hydro‐climatic variables and runoff response to climatic variability and vegetation changes in the Yiluo River basin,China

The Yiluo River is the largest tributary for the middle and lower reaches of the Yellow River below Sanmenxia Dam. Changes of the hydrological processes in the Yiluo River basin, influenced by the climatic variability and human activities, can directly affect ecological integrity in the lower reach of the Yellow River. Understanding the impact of the climatic variability and human activities on the hydrological processes in the Yiluo River basin is especially important to maintain the ecosystem integrity and sustain the society development in the lower reach of the Yellow River basin. In this study, the temporal trends of annual precipitation, air temperature, reference evapotranspiration (ET₀) and runoff during 1961–2000 in the Yiluo River basin were explored by the Mann‐Kendall method (M‐K method), Yamamoto method and linear fitted model. The impacts of the climatic variability and vegetation changes on the annual runoff were discussed by the empirical model and simple water balance model and their contribution to change of annual runoff have been estimated. Results indicated that (i) significant upwards trend for air temperature and significant downwards trend both for precipitation and ET₀ were detected by the M‐K method at 95% confidence level. And the consistent trends were obtained by the linear fitted model; (ii) the abrupt change started from 1987 detected by the M‐K method and Yamamoto method, and so the annual runoff during 1961–2000 was divided into two periods: baseline period (1961–1986) and changeable period (1987–2000); and (iii) the vegetation changes were the main cause for change of annual runoff from baseline period to changeable period, and climatic variability contributed a little to the change of annual runoff of the Yiluo River. Copyright © 2009 John Wiley & Sons, Ltd.     

Runoff modifications due to the conversion of natural grasslands to forests in a large basin in Uruguay

Uruguay has encouraged the development of the forestry sector since 1989. As a member of the Montreal Process, the country has followed a set of criteria and indicators for the Sustainable Forest Management. The aim of this paper is to describe the studies carried out in a large basin of 2097 km², located in an area of humid subtropical climate and 1300 mm of long‐term mean annual rainfall, where the conversion of natural grasslands to forests increased up to 540 km² during the last 15 years. Using data from daily rainfall and streamflow, the study analyses the effects of afforestation on the runoff and water loss. The analysis comprises hydrographs resulting from comparable rainfall events and annual and seasonal streamflow and water loss behaviour, both before afforestation (1975–1993) and during the afforestation period (1994–2008). A statistically significant reduction of runoff volumes (33–43%) and peak flows (59–65%) were identified on storm hydrographs. The annual and seasonal streamflow also showed diminishing tendencies due to the forestry development, whereas the water loss increases. The annual streamflow decreased between 8·2 and 36·5% depending on the annual rainfall totals. The streamflow reduction was higher during spring and summer (25·2–38·4%) and smaller during autumn and winter (15–20·3%). The water loss is expected to increase by 98 mm for the long‐term mean annual rainfall. The resulting information is a valuable input for the Integrated Water Resources Management of the Negro river basin located downstream, where hydroelectric power, rice irrigation and forestry development are supported. Copyright © 2008 John Wiley & Sons, Ltd.     

城市化背景下年最大日径流演变及影响因素研究——以长江下游秦淮河流域为例

随着气候变化和人类活动的加剧,城市化地区水文过程受到较大影响,极端水文事件发生频率显著加大,探究城市化地区洪水演变和驱动机理对于防洪减灾具有重大意义。本文以长江下游快速城市化地区的秦淮河流域为例,分析了1987—2018年期间该流域年最大日径流的演变特征,构建多元线性回归模型和广义可加GAMLSS模型识别了关键驱动因子并量化其贡献作用。结果表明:(1)城市化背景下秦淮河流域年最大日径流呈现显著上升趋势,平均增长速率为14.77 m³/(s·a),并于2001年发生显著突变。(2)汛期降水量和不透水面率是年最大日径流变化的关键驱动因素,最优模型显示前者贡献率超过了70%,表明了降水改变的决定性作用,而不透水面率贡献率超过20%则表明了下垫面的改变对年最大日径流演变存在显著影响。(3)不透水面的增加对年最大日径流和汛期降水量响应关系的影响程度从突变前的6.7%增加到突变后的10.4%,快速城市化已显著改变了流域降水-径流响应过程。研究表明,随着城市发展秦淮河流域的年最大日径流受到人类活动显著影响,洪涝威胁日趋增大,研究结果可为城市化地区防洪减灾提供一定参考。     

Response of the hydrological regime of the Yellow River to the changing monsoon intensity and human activity

Abstract

In the past 50 years, influenced by global climate change, the East Asian summer monsoon intensity (SMI) changed significantly, leading to a response by the water cycle of the Yellow River basin. The variation in SMI has three stages: (1) 1951–1963, SMI increased; (2) 1963–1965, SMI declined sharply, a feature that may be regarded as an abrupt change; and (3) 1965–2000, SMI remained at low levels and showed a tendency to decline slowly. The decreased SMI led to a reduction in water vapour transfer from the ocean to the Yellow River basin, and thus precipitation decreased and the natural river runoff of the Yellow River also decreased. Due to the increase in population and therefore in irrigated land area, the ratio of net water diversion to natural river runoff increased continuously. Comparison of the ratio of net water diversion to natural river runoff before and after the abrupt change in SMI indicates some discontinuity in the response of the man-induced lateral branch of the water cycle to the abrupt change in SMI. The frequently occurring flow desiccation in the lower Yellow River can be regarded as a response of the water cycle system to the decreasing summer monsoon intensity and increasing population. When the ratio of net water diversion exceeded the ratio of natural runoff of the low-flow season to the annual total natural runoff, flow desiccation in the lower Yellow River would occur. When the ratio of net water diversion is 0.3 larger than the ratio of the natural runoff of the low-flow season to the annual total natural runoff, an abrupt increase in the number of flow desiccation events is likely to occur.     

Impact of climatic change on streamflow in the upper reaches of the Minjiang River,China

Abstract

Characteristics of hydroclimatic change in the upper reaches of the Minjiang River are analysed using data collected over the past 50 years. The effect of autocorrelation of time series on trend analysis is removed by adopting a pre-whitening technique. Long-term hydrometeorological trend and abrupt changes are analysed by the Mann-Kendall test. The results were validated by the linear trend and Spearman methods. Correlations between runoff change with air temperature and with precipitation were studied with the Pearson method. The results clearly show that average air temperature in the upper reaches of the river is increasing, and precipitation decreasing, with differences in spatio-temporal distribution. Runoff change has a clear positive correlation with precipitation. Meteorological change, especially in precipitation, is the key governing influence of runoff volume. The annual runoff decrease, especially the decrease of inflow in spring and autumn and earlier appearance and longer duration of the low-flow season, will impact greatly on irrigation and municipal water supply. Therefore, relevant measures and further study are necessary.

Editor Z.W. Kundzewicz; Associate editor Q. Zhang

Citation Huang, X.R., Zhao, J.W., Li, W.H., and Jiang, H.X., 2013. Impact of climatic change on streamflow in the upper reaches of the Minjiang River, China. Hydrological Sciences Journal, 59 (1), 154–164.