ALBERT

Description: Glaciers are significant fresh water storage systems in western China and contribute substantially to the summertime runoff of many large rivers in the Tibetan Plateau. Under the scenario of climate change, discussions of glacier variability and melting contributions in alpine basins are important for understanding the runoff composition and ensuring that water resources are adequately managed and protected in the downstream areas. Based on the multi-source spatial data and long-term ground observation of climatic and hydrologic data, using the remote sensing interpretation, degree-day model, and ice volume method, we presented a comprehensive study of the glacier changes in number, area, and termini and their impacts on summertime runoff and water resource in the Tuotuo River basin, located in the source region of the Yangtze River. The results indicated that climate change, especially rising temperature, accelerated the glacier melting and consequently led to hydrological change. From 1969 to 2009, the glacier retreat showed an absolutely dominant tendency with 13 reduced glaciers and lost glacier area of 45.05 km 2 , accompanied by limited growing glaciers in the study area. Meanwhile, it indicated that annual glacial runoff was averagely 0.38×10 8 m 3 , accounting for 4.96 % of the total summertime runoff, followed by the supply from precipitation and snowmelt. The reliability of this magnitude was assessed by the classic volume method, which also showed that the water resources from glacier melting in the Tuotuo River basin increased by approximate 17.11×10 8 m 3 , accounting for about 3.77 % of the total runoff over the whole period of 1969 - 2009. Findings from this study will serve as a reference for future research about glacier hydrology in regions where observational data are deficient. Also it can help the planning of future water management strategies in the source region of the Yangtze River.

Description: Snow variability is an integrated indicator of climate change, and it has important impacts on runoff regimes and water availability in high-altitude catchments. Remote sensing techniques can make it possible to quantitatively detect the snow cover changes and associated hydrological effects in those poorly gauged regions. In this study, the spatial-temporal variations of snow cover and snow melting time in the Tuotuo River basin, which is the headwater of the Yangtze River, were evaluated based on satellite information from the Moderate Resolution Imaging Spectroradiometer snow cover product, and the snow melting equivalent and its contribution to the total runoff and baseflow were estimated by using degree-day model. The results showed that the snow cover percentage and the tendency of snow cover variability increased with rising altitude. From 2000 to 2012, warmer and wetter climate change resulted in an increase of the snow cover area. Since the 1960s, the start time for snow melt has become earlier by 0.9-3days/10a and the end time of snow melt has become later by 0.6-2.3days/10a. Under the control of snow cover and snow melting time, the equivalent of snow melting runoff in the Tuotuo River basin has been fluctuating. The average contributions of snowmelt to baseflow and total runoff were 19.6% and 6.8%, respectively. Findings from this study will serve as a reference for future research in areas where observational data are deficient and for planning of future water management strategies for the source region of the Yangtze River. © 2015 John Wiley & Sons, Ltd.

Description: This paper is focused on the lag time of flow confluence. Lag is described empirically by the precipitation factor in hydrological modelling, but the traditional way to establish the relationship between lag and intensity is not very satisfactory in arid and semi-arid regions. A total 215 rainfall-runoff experiments were conducted to reveal the effects of net rain duration on lag and intensity. The results show that a correlation between lag and rain intensity exists under certain conditions. There is a critical value in net rain intensity (0-8-1 mm min-1) in the correlation curve of lag and net rain intensity in the given experimental watershed in the laboratory. Similarly, a critical value of net rain duration also exists. This value is the total confluence time. The features of lag time change significantly if intensity or duration is less or greater than the critical value. The study also explores the joint effects of net rain intensity and duration on lag. The formula established among lag, intensity and duration resulted in a better fit. Therefore, the two-parameter (intensity and duration) empirical formula for lag is better than the traditional single-parameter (intensity) method. This two-parameter correlation formula can also be applied to a temporally and spatially uneven runoff processes. A typical field watershed is selected to test the results of the experiments. Copyright © 2006 John Wiley & Sons, Ltd.

Description: CryoSat-2 altimetry has become a valuable tool for monitoring the water level of lakes. In this study, a concentrated probability density function (PDF) method was proposed for preprocessing CryoSat-2 Geophysical Data Record (GDR) data. CryoSat-2 altimetry water levels were preprocessed and evaluated by in situ gauge data from 12 lakes in China. Results showed that the accuracy of the raw GDR data was limited due to outliers in most of the along-track segments. The outliers were generally significantly lower than the in situ values by several meters, and some by more than 30 m. Outlier detection, therefore, improves upon the accuracy of CryoSat-2 measurements. The concentrated PDF method was able to greatly improve the accuracy of CryoSat-2 measurements. The preprocessed CryoSat-2 measurements were able to observe lake levels with a high accuracy at nine of the twelve lakes, with an absolute mean difference of 0.09 m, an absolute standard deviation difference of 0.04 m, a mean root mean square error of 0.27 m, and a mean correlation coefficient of 0.84. Overall, the accuracy of CryoSat-2-derived lake levels was validated in China. In addition, the accuracy of Database for Hydrological Time Series of Inland Waters (DAHITI) and HYDROWEB water level products was also validated by in situ gauge data.

Description: Changes in climate and the resulting hydrologic variability are of great concern in international river basins. Based on observed station data, climate change and its impact on water availability in large international rivers across mainland Southeast Asia (MSA) were investigated by a combined method of trend detection and hydrologic budget balance analysis. This method can be applied easily to other studies to evaluate impacts of climate change on run-off and water resources at the basin scale. Precipitation showed a decreasing trend in the MSA during 1960–2016, especially in the dry season. Decreasing precipitation and increasing evapotranspiration were the main reasons for severe droughts during recent years. Climate change was the main reason for run-off changes over the MSA. The presence of dams in the upstream region was not enough to change the annual variability of natural run-off in the Mekong River. Run-off and precipitation changes showed significant variances in different basins and regions, and in different periods. The overall trend of precipitation and run-off showed a periodicity of about 35 years. Nonprecipitation effects were also significant in some regions, including increasing irrigation water demand in the Red River and increasing glacial melt in the Brahmaputra River basin. Melt increased at least 75.2 × 108 m3/10a during 1960–2003, representing 1.2% of mean annual run-off in the Brahmaputra River. The positive effect of glacial meltwater was almost equal to the negative effect of evapotranspiration on run-off change in the Lancang River. Increasing evapotranspiration played a dominant effect on run-off changes in the Yarlung Zangbo River basin during 1960–2010. © 2018 John Wiley & Sons, Ltd.

Description: Glaciers are significant freshwater storage systems in western China and contribute substantially to the summertime run-off of many large rivers in the Tibetan Plateau. Under the scenario of climate change, discussions of glacier variability and melting contributions in alpine basins are important for understanding the run-off composition and ensuring that water resources are adequately managed and protected in the downstream areas. Based on the multisource spatial data and long-term ground observation of climatic and hydrologic data, using the remote sensing interpretation, degree-day model, and ice volume method, we presented a comprehensive study of the glacier changes in number, area, and termini and their impacts on summertime run-off and water resource in the Tuotuo River basin, located in the source region of the Yangtze River. The results indicated that climate change, especially rising temperature, accelerated the glacier melting and consequently led to hydrological change. From 1969 to 2009, the glacier retreat showed an absolutely dominant tendency with 13 reduced glaciers and lost glacier area of 45.05 km2, accompanied by limited growing glaciers in the study area. Meanwhile, it indicated that annual glacial run-off was averagely 0.38 × 108 m3, accounting for 4.96% of the total summertime run-off, followed by the supply from precipitation and snowmelt. The reliability of this magnitude was assessed by the classic volume method, which also showed that the water resources from glacier melting in the Tuotuo River basin increased by approximate 17.11 × 108 m3, accounting for about 3.77% of the total run-off over the whole period of 1969–2009. Findings from this study will serve as a reference for future research about glacier hydrology in regions where observational data are deficient. Also, it can help the planning of future water management strategies in the source region of the Yangtze River. Copyright © 2017 John Wiley & Sons, Ltd.