洞庭湖生态水位及其保障研究

湖泊生态水位是维持湖泊生态系统健康的重要因素.基于洞庭湖城陵矶、杨柳潭、南咀3个水文站1959-2016年日平均水位序列进行分析,采用Mann-Kendall法、累积距平法和滑动T检验法综合确定洞庭湖水位变异时间节点,结合生态水位年内展布法以及IHA-RVA法,计算分析湖泊最小和适宜生态水位,并且采用Tennant法进行合理验证,在此基础上对水文变异前、后湖泊生态水位保障度进行研究.研究结果表明:(1)洞庭湖城陵矶和杨柳潭水文站年均水位呈上升趋势,而且城陵矶站水位上升趋势显著,南咀站年均水位呈显著下降趋势.(2)洞庭湖3个典型水文站水位年际变化突变年份为2003年,突变年份基本上与三峡工程蓄水时间相符.(3)城陵矶、南咀和杨柳潭年均最小生态水位分别为21.41、28.95和27.84 m,分别占多年平均水位的86.3%、95.9%和95.7%,城陵矶、南咀和杨柳潭年均适宜生态水位分别为23.29、29.51和28.36 m,分别占多年平均水位的93.9%、97.8%和97.5%,生态水位计算结果考虑了天然湖泊水位年内丰枯变化,满足了湖泊生态目标需求.(4)洞庭湖最低生态水位保障程度较高,基本能达到80%以上,但适宜生态水位保障程度相对较低,其中2003年以后洞庭湖10月和11月生态水位保障程度显著下降,与上游水利工程蓄水有关,建议在此期间采取调度措施适当增加洞庭湖水量,以保障湖泊生态系统的健康与生物多样性.     

Hydro-climatic trends in the Abay/Upper Blue Nile basin,Ethiopia

Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay/Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann–Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations.Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar – typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.5 °C/decade, 0.3 °C/decade in rainy season (June–September), 0.6 °C/decade in small rainy season (March–May), and 0.6 °C/decade in dry season (October–February). Other stations in the Abay/Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use/land cover change and climate variability on streamflow of Abay/Blue Nile basin and its tributaries needs to be understood better.     

Effects of climate change and human activities on runoff and sediment inputs of the largest freshwater lake in China,Poyang Lake

The nonparametric Mann-Kendall test and the Pettitt test were employed to examine the change trends and shifts of runoff and sediment input to Poyang Lake between 1961 and 2013. Water balance and linear regression models were used to evaluate the impacts of climate variability and human activities on the runoff and sediment discharge changes. The results showed that runoff inputs to the lake had insignificant temporal trends and change points, while sediment inputs had significant decreasing trends, with an abrupt change in 1989. Quantitative assessment demonstrated that human activities led to a small decrease (5.5%) in runoff inputs to the lake, and a dramatic (121.4%) decrease in sediment inputs to the lake between the reference period (before the change point) and the human-influenced period (after the change point). This work provides a useful reference for future policy makers in water resource utilization and environmental safety of the Poyang Lake basin.     

洞庭湖流域气候变化特征(1961-2003年)

以22个气象站1961-2003年的气象观测数据为基础,对洞庭湖流域的气温、降水和参照蒸散量进行趋势与突变分析．从1970年开始,洞庭湖流域经历了一个缓慢而稳定的增温过程,1990s发生突变进入快速增温时期;尤其是是在春、冬季节,这种突变式的增温特征非常显著;秋季持续而稳定增温,而夏季气温并无明显变化．进入1990s,洞庭湖流域降水有明显增多,尤其是夏季降水突变式增加;与此同时,夏季暴雨频率也突变式增大,但是暴雨强度并无明显变化．1900s迄今,参照蒸散量持续而稳定的减少,夏季减少量尤为显著．全球变暖的区域响应,驱动洞庭湖流域水循环速度加快,夏季降水增多,而蒸发能力减弱,这是1990s洞庭湖流域洪水频发的主要气候因子．     

Spatio-temporal variation and abrupt changes for major climate variables in the Taihu Basin, China

Long-term trend and abrupt changes of major climate variables in the Taihu Basin were investigated based on the mean, maximum and minimum air temperature, diurnal temperature range (DTR), precipitation, relative humidity and sunshine duration at six meteorological stations from 1954 to 2006. Results showed that the long-term trend for annual precipitation was not statistically significant during the past 53?years, but a wetter tendency was detected and the increasing centre for annual precipitation was located in the southeast of the study area. Mean air temperature has increased by 1.43°C, similar trends were also identified for maximum and minimum air temperature, which have increased by 1.06 and 1.54°C, respectively, while DTR exhibited a slight decreasing trend with a rate of about ?0.09°C/(10?year). The annual mean relative humidity and sunshine duration exhibited a decreasing trend, with Kendall slope values of ?0.99%/10?year and ?7.797?h/10?year, respectively. Examination of long-range dependence showed that all climate variables exhibited strong persistence at annual scale except minimum air temperature. Detection of abrupt changes using nonparametric Mann–Kendall and Pettitt methods showed different results. Abrupt changes occurred in the 1980s and 2000s for annual precipitation using the nonparametric Mann–Kendall method, while no abrupt changes were detected using the Pettitt method. Abrupt changes of temperature and relative humidity took place in the early 1990s using the nonparametric Mann–Kendall method, which occurred in the late and mid 1980s using the Pettitt method, while abrupt changes of sunshine duration and DTR detected by two methods occurred in the similar period. The result will be helpful for local flood control and drought relief in urban planning and construction under future global climate change.     

Theoretical estimates for the influence of Lake Victoria on flows in the upper White Nile

Abstract

A theoretical model is described for estimating the impacts of changes in Lake Victoria levels on river flows, lake levels and swamp areas in the upper White Nile basin. The basis of the model is to represent the main river channel by a series of interconnected lakes and swamps, whose water balances are described by differential equations relating outflows to levels, areas and the net basin supply at each point. Closed form solutions are obtained for two situations: (a) a long-term change in the mean level of Lake Victoria, and (b) a return to equilibrium levels following an initial disturbance in Lake Victoria levels. A simple model for the net basin supply to Lake Victoria is also used to relate these changes in levels to changes in climate and runoff in the basin. The results illustrate the extreme sensitivity of White Nile flows to changes in Lake Victoria levels and outflows, and in particular to variations in the direct rainfall on the lake surface. Estimates are also presented for the various time scales and time delays which affect the White Nile system.     

Trends in hydrological and climatic variables affected by four variations of the Mann-Kendall approach in Urmia Lake basin,Iran

ABSTRACT

The trends in hydrological and climatic time series data of Urmia Lake basin in Iran were examined using the four different versions of the Mann-Kendall (MK) approach: (i) the original MK test; (ii) the MK test considering the effect of lag-1 autocorrelation; (iii) the MK test considering the effect of all autocorrelation or sample size; and (iv) the MK test considering the Hurst coefficient. Identification of hydrological and climatic data trends was carried out at monthly and annual time scales for 25 temperature, 35 precipitation and 35 streamflow gauging stations selected from the Urmia Lake basin. Mann-Kendall and Pearson tests were also applied to explore the relationships between temperature, precipitation and streamflow trends. The results show statistically significant upward and downward trends in the annual and monthly hydrological and climatic variables. The upward trends in temperature, unlike streamflow, are much more pronounced than the downward trends, but for precipitation the behaviour of trend is different on monthly and annual time scales. Furthermore, the trend results were affected by the different approaches. Specifically, the number of stations showing trends in hydrological and climatic variables decreased significantly (up to 50%) when the fourth test was considered instead of the first and the absolute value of the Z statistic for most of the time series was reduced. The results of correlations between streamflow and climatic variables showed that the streamflow in Urmia Lake basin is more sensitive to changes in temperature than those of precipitation. The observed decreases in streamflow and increases in temperature in the Urmia Lake basin in recent decades may thus have serious implications for water resources management under the warming climate with the expected population growth and increased freshwater consumption in this region.

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

Spatial and temporal variations in rainfall erosivity during 1960–2005 in the Yangtze River basin

Water resources and soil erosion are the most important environmental concerns in the Yangtze River basin, where soil erosion and sediment yield are closely related to rainfall erosivity. The present study explores the spatial and temporal changing patterns of the rainfall erosivity in the Yangtze River basin of China during 1960–2005 at annual, seasonal and monthly scales. The Mann–Kendall test is employed to detect the trends during 1960–2005, and the T test is applied to investigate possible changes between 1991–2005 and 1960–1990. Meanwhile the Rescaled Range Analysis is used for exploring future trend of rainfall erosivity. Moreover the continuous wavelet transform technique is using studying the periodicity of the rainfall erosivity. The results show that: (1) The Yangtze River basin is an area characterized by uneven spatial distribution of rainfall erosivity in China, with the annual average rainfall erosivity range from 131.21 to 16842 MJ mm ha^?1 h^?1. (2) Although the directions of trends in annual rainfall erosivity at most stations are upward, only 22 stations have significant trends at the 90 % confidence level, and these stations are mainly located in the Jinshajiang River basin and Boyang Lake basin. Winter and summer are the seasons showing strong upward trends. For the monthly series, significant increasing trends are mainly found during January, June and July. (3) Generally speaking, the results detected by the T test are quite consistent with those detected by the Mann–Kendall test. (4) The rainfall erosivity of Yangtze River basin during winter and summer will maintain a detected significant increasing trend in the near future, which may bring greater risks to soil erosion. (5) The annual and seasonal erosivity of Yangtze River basin all have one significant periodicity of 2–4 years.     

Assessing the impact of climate variability and human activities on streamflow from the Wuding River basin in China

Located in the Loess Plateau of China, the Wuding River basin (30 261 km²) contributes significantly to the total sediment yield in the Yellow River. To reduce sediment yield from the catchment, large-scale soil conservation measures have been implemented in the last four decades. These included building terraces and sediment-trapping dams and changing land cover by planting trees and improving pastures. It is important to assess the impact of these measures on the hydrology of the catchment and to provide a scientific basis for future soil conservation planning. The non-parametric Mann–Kendall–Sneyers rank test was employed to detect trends and changes in annual streamflow for the period of 1961 to 1997. Two methods were used to assess the impact of climate variability on mean annual streamflow. The first is based on a framework describing the sensitivity of annual streamflow to precipitation and potential evaporation, and the second relies on relationships between annual streamflow and precipitation. The two methods produced consistent results. A significant downward trend was found for annual streamflow, and an abrupt change occurred in 1972. The reduction in annual streamflow between 1972 and 1997 was 42% compared with the baseline period (1961–1971). Flood-season streamflow showed an even greater reduction of 49%. The streamflow regime of the catchment showed a relative reduction of 31% for most percentile flows, except for low flows, which showed a 57% reduction. The soil conservation measures reduced streamflow variability, leading to more uniform streamflow. It was estimated that the soil conservation measures account for 87% of the total reduction in mean annual streamflow in the period of 1972 to 1997, and the reduction due to changes in precipitation and potential evaporation was 13%. Copyright © 2007 John Wiley & Sons, Ltd.     

Proglacial sediment trapping in recently formed Silt Lake,upper Lillooet Valley,Coast Mountains,British Columbia

The sedimentology of proglacial Silt Lake was assessed by lake sediment coring and monitoring of lacustrine processes during a late‐summer period of high glacier melt to characterize sediment delivery from the heavily glacierized catchment and investigate the sediment trapping dynamics of this upland lake. A complete varve chronology was established for a distal basin of the lake which was exposed by Lillooet Glacier retreat between 1947 and 1962. The varve record showed decreasing sedimentation rates in the basin while the glacier retreated, and as the lake became free of ice contact in the early 1970s. Although recession has continued over recent decades, and glacier proximity to the lake has, therefore, continued decreasing, lacustrine sedimentation rates are now accelerating due to changing basin morphometry caused by delta progradation. Over shorter time scales, lake sedimentation patterns respond to changing runoff conditions, including late‐summer glacier melt intensity, intra‐annual flooding events, diumal runoff fluctuations, and within‐lake turbidity currents. Turbidity currents included quasi‐regular flows during high diurnal discharges and an episodic flushing of temporarily stored sediment from the sandur or delta at a time of low stage. Suspended sediment yield to Silt Lake is estimated to exceed 10³ Mg km^?2 a^?1, a magnitude that surpasses previous local and regional yield estimates for the glacierized headwaters of the Lillooet River valley. Since Silt Lake currently traps a significant prooportion of that upland sediment supply, and the trapping efficiency of the basin has been variable at decadal time scales, the formation and continued development of Lilt Lake has likely had a significant influence on downstream sediment delivery. Lacustrine sediment‐based proxies of long‐term hydroclimatic variability being developed in glacially distal settings should include provisions for dynamic sediment trapping effects in upstream water bodies that often form in the active proglacial environment. Copyright © 2008 John Wiley & Sons, Ltd.     

鄱阳湖水面蒸发量的计算与变化趋势分析(1955-2004年)

利用器测折算法与气候模式法,分别计算鄱阳湖周围康山、棠荫、都昌、星子、湖口5站的单站水面蒸发量,以5站两种方法计算值的平均值代表鄱阳湖大湖面的水面蒸发量,求得鄱阳湖1955-2004年各月的水面蒸发量和蒸发水量,结果为：多年平均年蒸发量1081．2 mm．年蒸发水量27．06×10~8 m~3．对年、月水面蒸发量在近50年来的变化趋势进行了分析,表明除5月份外,其他各月蒸发量和年蒸发量均呈逐渐减少趋势,年蒸发量平均每年减小2．79 mm,年蒸发水量平均减少0．05×10~8 m~3,对湖区水资源持续利用和湖泊环境将产生明显影响．对水面蒸发量递减原因进行了初步探讨．     

Evaluation of temperature trends over India / Evaluation de tendances de température en Inde

Abstract

Abstract The impact of climate change is projected to have different effects within and between countries. Information about such change is required at global, regional and basin scales for a variety of purposes. An investigation was carried out to identify trends in temperature time series of 125 stations distributed over the whole of India. The non-parametric Mann-Kendall test was applied to detect monotonic trends in annual average and seasonal temperatures. Three variables related to temperature, viz. mean, mean maximum and mean minimum, were considered for analysis on both an annual and a seasonal basis. Each year was divided into four principal seasons, viz. winter, pre-monsoon, monsoon and post-monsoon. The percentages of significant trends obtained for each parameter in the different seasons are presented. Temperature anomalies are plotted, and it is observed that annual mean temperature, mean maximum temperature and mean minimum temperature have increased at the rate of 0.42, 0.92 and 0.09°C (100 year)^-1, respectively. On a regional basis, stations of southern and western India show a rising trend of 1.06 and 0.36°C (100 year)^-1, respectively, while stations of the north Indian plains show a falling trend of –0.38°C (100 year)^-1. The seasonal mean temperature has increased by 0.94°C (100 year)^-1 for the post-monsoon season and by 1.1°C (100 year)^-1 for the winter season.     

Trends in extreme temperature indices in the Poyang Lake Basin,China

Based on daily maximum and minimum temperature records at 78 meteorological stations in the Basin of China’s largest fresh water lake (Poyang Lake Basin), the temporal and spatial variability of 11 extreme temperature indices are investigated for the period 1959–2010. The analysis indicates that the annual mean of daily minimum temperature (T_min) has increased significantly, while no significant trends were observed in the annual mean of daily maximum temperature (T_max), resulting in a significant decrease in the diurnal temperature range. Trends and percentages of stations with significant trends in T_min-related indices are generally stronger and higher than those in T_max-related indices; however, no significant trends can be found in T_max-related indices (TXMean, TX90p, TXx and TX10p) at both seasonal and annual time scale. Low correlations with Global-SST ENSO index are also detected in T_max-related indices. Significant positive relationships can be found in T_min-related indices (TNMean, TNx, TNn and TN90p), however, the most significant negative coefficient was also found in cold nights (TN10p) with the Global-SST ENSO index. Singular value decomposition (SVD) correlating extreme temperatures over the Poyang Lake Basin and the North Pacific SST indicates the East China Sea, Western Pacific and Bering Sea to be stronger linked with T_min than T_max with the first mode (SVD-1) explaining 90 and 94 % of annual T_max and T_min respectively.     

太湖的降水效应

本文分析了太湖湖区降水的时空分布特征;估算和讨论了太湖的降水效应;揭示了太湖的降水效应不太显著;太湖湖区降水量的变化是该湖水位变化的决定性因素之一。     

Estimate of sediment inflow into Vistonis Lake, Greece

In the present study, the mean annual sediment inflow into Vistonis Lake (Thrace, northeastern Greece) was calculated. The sediment quantity originates mainly from the basins of Kossynthos, Kompsatos and Travos (Aspropotamos) Rivers. The whole basin area (mountainous part) contributing to the lake amounts to about 845 km². The above mean annual sediment quantity was compared with the mean annual sediment accumulation in the lake. The latter quantity was estimated from the mean annual decrease of the lake water volume for a period of 22 years, which was determined by means of older and newer topographic maps (isobath contours). For the calculation of the mean annual sediment yield at the outlets of the three above mentioned basins, a mathematical model consisting of three submodels was used: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The comparison of the computational results by means of the mathematical model with the estimation results by means of the topographic maps is satisfactory and encouraging.     

Spatial and temporal characteristics of changes in precipitation during 1957�C2007 in the Haihe River basin, China

The present study explores the spatial and temporal changing patterns of the precipitation in the Haihe River basin of North China during 1957–2007 at annual, seasonal and monthly scales. The Mann–Kendall and Sen’s T tests are employed to detect the trends, and the segmented regression is applied to investigate possible change points. Meanwhile, Sen’s slope estimator is computed to represent the magnitudes of the temporal trends. The regional precipitation trends are also discussed based on the regional index series of four sub-basins in the basin. Serial correlation of the precipitation series is checked prior to the application of the statistical test to ensure the validity of trend detection. Moreover, moisture flux variations based on the NCEP/NCAR reanalysis dataset are investigated to further reveal the possible causes behind the changes in precipitation. The results show that: (1) Although the directions of annual precipitation trends at all stations are downward, only seven stations have significant trends at the 90% confidence level, and these stations are mainly located in the western and southeastern Haihe River basin. (2) Summer is the only season showing a strong downward trend. For the monthly series, significant decreasing trends are mainly found during July, August and November, while significant increasing trends are mostly observed during May and December. In comparison with the annual series, more intensive changes can be found in the monthly series, which may indicate a shift in the precipitation regime. (3) Most shifts from increasing trends to decreasing trends occurred in May–June, July, August and December series, while opposed shifts mainly occurred in November. Summer is the only season displaying strong shift trends and the change points mostly emerged during the late 1970s to early 1980s. (4) An obvious decrease in moisture flux is observed after 1980 in comparison with the observations before 1980. The results of similar changing patterns between monthly moisture budget and precipitation confirmed that large-scale atmospheric circulation may be responsible for the shift in the annual cycle of precipitation in the Haihe River basin. These findings are expected to contribute to providing more accurate results of regional changing precipitation patterns and understanding the underlying linkages between climate change and alterations of hydrological cycles in the Haihe River basin.     

应用MODIS数据监测千岛湖流域植被覆盖动态(2001-2013年)

流域植被覆盖状况对于水源地生态环境保护具有重要的指示作用.当前的水质目标管理不仅要着眼于湖库水质参数控制,更应该从整个流域的角度维系生态平衡.在此背景下,依托长时间序列MODIS遥感数据对千岛湖流域2001-2013年植被覆盖状况进行监测,采用最小二乘法趋势分析和Mann-Kendall显著性检验方法分析了千岛湖流域植被的空间分布特征、时间变化特征与长期变化趋势.研究表明该方法能够有效地监测流域植被覆盖的时空动态变化:1)从空间分布上来看,千岛湖流域植被覆盖状况整体较好,但同时也发现受人为干扰较大的地域如河、湖附近的城镇建设用地、农业用地以及园地,其NDVI值明显低于自然林地;2)从时间变化特征上看,2001-2013年千岛湖流域植被年际NDVI在0.69~0.73之间波动,且近年来有增长趋势,年内季节性NDVI动态分析表明高时间分辨率的MODIS数据能够用来区分常绿植被与落叶植被的物候特征,以分析不同植被类型对流域氮、磷流失的风险差异;3)从变化趋势上看,2001-2013年植被覆盖状况改善的区域远大于退化的区域,其中改善区域约占流域面积的55.90%,呈现出一定退化状态的区域约占29.60%(严重退化区域仅占3.97%),而相对稳定不变区域约占14.51%.经与气温与降水等气候因子进行相关性分析表明,植被NDVI与气温呈显著正相关,而降水则不敏感,说明气温是研究区植被生长的主导气候因子.同时发现,人类活动对局部植被变化影响较大.研究结果可为流域水资源与生态环境保护提供空间数据支撑.     

1988-2018年滇池氮磷比的时空演变特征与原因解析

氮、磷浓度是制约湖泊营养状态和生产力水平的重要环境因子,而氮磷化学计量比是湖泊生态系统的主要指标,因此,判识氮磷比变化趋势及其驱动力对湖泊生态恢复具有重要意义.研究基于19882018年连续观测数据,分析了滇池氮磷浓度和氮磷摩尔比(简称氮磷比)的时空分布演变特征;采用多元线性回归模型分别对滇池草海和外海氮磷比驱动效应进行定量解析,筛选出影响湖体氮磷比变化的潜在驱动因子.结果表明:①19882018年滇池氮磷比呈现显著的线性上升趋势,其中草海和外海氮磷比分别上升1.3和0.7 a^-1.②草海和外海分别在2008年和2004年发生了氮磷比上升突变,突变前上升归因于总氮浓度快速增加,突变后则是由于总磷浓度下降较快.③滇池的氮磷浓度变化主要是受流域氮磷输入负荷、跨流域调水、流域氮磷削减、风速和水位的综合影响,但受控因子在不同区域可能存在差异.④气温是滇池氮磷比变化的主要驱动因子,流域人为氮磷输入差异是滇池氮磷比变化的次要驱动因子.     

1950s以来鄱阳湖流域降水变化趋势及其持续性特征

以鄱阳湖流域1950s至2005年10个台站的日降水量为基础,采用距平分析、Mann-Kendall非参数检验对鄱阳湖流域1950s以来的年、季降水特征和变化趋势进行分析,并以此为基础,结合Hurat指数,从3年、5年、10年三个时间尺度上分析该流域未来降水的变化趋势.结果表明,鄱阳湖流域年内降水分配不均,年际变化较为...