Abstract: Study on the evolution law of hydrological cycle and water resources driven by climate change is not only an important scientific issue,but also a global issue of concern to the international community. The Yarlung Zangbo River basin was selected as the study area. Linear trend estimation and multiple linear regression methods were applied to test the change characteristics of meteorological factors,and to reveal the evolution law of underlying surface. The elastic coefficient method based on Budyko framework was applied to analyze the runoff changes and make attribution analysis. Results showed that from 1961 to 2014,the temperature in the entire Yarlung Zangbo River basin showed an upward trend,and the precipitation showed an increasing trend,indicating that the Yarlung Zangbo River basin was experiencing climate warming and wetting. The vegetation showed a greening trend,while there was a certain degradation in the northwest and downstream. The annual runoff series showed the cyclic periods of 3-4 years,12 years,20 years and 32 years. The contribution of precipitation,potential evapotranspiration,underlying surface and glacier changes to the increase of runoff accounted on 39.62%,-2.74%,32.32% and 30.94%,respectively. The results have significant reference for understanding the runoff evolution law of the Yarlung Zangbo River basin under the condition of climate changing and underlying surface changing.
Abstract: To clarify the characteristics of substance transport and transformation in large reservoirs along the Lancang River,new equipment has been independently developed for automatic monitoring in the subsurface zone and intelligent sampling of water and sediment in a high and large reservoir. In-suit water samples with the maximum working water depth of 280 meters have been collected in 9 cascade reservoirs along the 1 290 km of Upper Langcang River in 2016,2017,and 2018. In addition,multi-index monitoring at the water-sediment interface in reservoir riparian has also been conducted. It is found that cascade dams promoted the increase of the proportion of bioavailable phosphorus and ammonia nitrogen in water and the release of bioavailable phosphorus in sediments;The distribution of methylmercury in sediments was related to sediment particle sedimentation,regulated by hydraulic retention time and reservoir age. The emission flux of greenhouse gases increased due to the dam construction,while it was far lower than the world average level. The increase in frequency and area of wetting drying alternation in the subsurface flow zone strengthened the effect of nitrogen removal and thus reduced greenhouse gas release in reservoir riparian. The bacterial community could not be isolated by the dams. Water temperature was the key factor affecting the bacterial community on both the river scale and reservoir scale.
Abstract: In order to clarify the interaction of thermokarst lake and permafrost,a water-ice-heat coupling model considering heat conduction and convection processes was established at a typical thermokarst lake area in the Beiluhe Basin. The degradation characteristics of permafrost and the water balance of thermokarst lake were simulated. Furthermore,the effects of the geological environment and climate warming on permafrost and water balance of thermokarst lake were analyzed. Results showed that the permafrost around the thermokarst lake degraded gradually,resulting in a melt-through zone,causing the groundwater circulation mode to change. The thickness of the active layer was 3.35 m under the effect of the ground-surface temperature. Thermokarst lake exhibited a negative balance during the entire simulation period and its discharge increased significantly during the 285-388 years. Additionally,the formation permeability determined the development directions of thermokarst lake and ecological environment;climate warming accelerated the conversion of permafrost into seasonal frozen soil. This study can provide references to understanding of eco-hydrological processes in cold and arid regions.
Abstract: Climate change and human development have significantly altered the processes of natural water cycling,aggravating the challenge of worldwide water governance. China has initiated a new paradigm of water governance. However,the gap between concept and reality widened due to a lack of appropriate data and methodology. Current water management focuses on limiting the water withdrawals and improving the water use efficiency,and is not yet able to ensure the implementation of the new water governance paradigm. After a thorough study of the advanced development and achievement of water governance policies both at home and abroad,the conclusion has been reached that the total water consumption should be introduced as an additional management indicator to implement a dual control of water withdrawal and consumption. The paper proposes to:① Establish water consumption monitoring infrastructure with evapotranspiration remote sensing monitoring as its core component. ② Implement the rigid water resources constraint by determining available water consumption targets of human activities in the basin,considering water requirements of environmental flow and ecosystem restoration,and establish a cascading system assigning targets to the sectors and/or stakeholders. ③ Implement the water consumption reduction schemes by limiting agricultural planting areas and optimizing ecosystem restoration with indigenous species. It is expected that the proposed approaches will effectively ensure the implementation of China's new water resources governance paradigm with innovative data,methods,and measures.
Abstract: Near-real-time satellite precipitation retrievals have the advantages of wide coverage,spatial continuity,short latency and open access,serving as an important precipitation data source that is globally available. For the 20 July 2021 extreme rainfall event in Henan Province,the performance of four GPM near-real-time satellite precipitation products-IMERG early,IMERG late,GSMaP NOW and GSMaP Gauge NOW-is comprehensively evaluated in this study. Based on the observations of 116 ground meteorological gauges and the interpolated rainfall fields,their skills to characterize heavy rainfall are compared.①The results show that the underestimation of accumulated rainfall by IMERG early and IMERG late is about 20%,while GSMaP NOW and GSMaP Gauge NOW overestimates it by about 35% and 70% respectively. However,the latter two are found to be easier to detect accumulated rainfall of above 500mm. ②In terms of rainfall process,the four GPM datasets are able to detect hourly precipitation events,but fail to capture major rainfall peaks. The estimation error of hourly rain rate is prominent,and it is negatively correlated with the ground observed rainfall magnitude. Specifically,the four products tend to overestimate hourly rainfall event that is less than 10 mm/h and underestimate rainfall event exceeding 30 mm/h. ③As for spatial pattern,the evaluation metrics of all the datasets show strong temporal fluctuations. The spatial correlation coefficient and volume critical success index of IMERG data are generally better than those of GSMaP data,but the latter is more sensitive to high-magnitude precipitation events. ④For IMERG products,it is found that the accuracy of IMERG late is greatly improved upon IMERG early;for GSMaP products,GSMaP Gauge NOW has a better detection skill of high-intensity rainfall compared against GSMaP NOW,but it also shows an increased estimation error of low-magnitude rainfall. This study has deepened the understanding of the performance of various GPM near-real-time satellite precipitation products,and provided critical feedbacks for improving the GPM-era satellite precipitation retrieval algorithms and enhancing their skills to monitor extreme precipitation.
Abstract: Study on water vapor transport is beneficial for better understanding the process of extreme precipitation. However,the precipitation system is complex and precipitation isotopes exhibit randomness,which makes it large uncertainty to use precipitation isotopes to trace water vapor transport. Information entropy has been employed to study the probability distribution characteristics of precipitation isotopic compositions in China,and it shows a strong linear relationship between hydrogen and oxygen precipitation isotopic information entropies,with a slope that is close to one. The spatial and temporal distributions of precipitation isotope information entropy were compared with the mean value of precipitation isotopes. Results showed that the spatial distribution of precipitation isotopic information entropy can suitably reveal the movement of water vapor from the ocean to continents,but this feature is not reflected by the spatial distribution of the mean value of precipitation isotopes. Precipitation isotope information entropy was applied to trace the three moisture corridors driven by monsoon system in China. Results showed that the spatial distribution of precipitation isotope information entropy can accurately reflect the vapor source and movement of the three moisture corridors and their seasonal changes.
Abstract: Using the traditional drought-flood abrupt alternation index (DFAI),it was difficult to classify abrupt alternations which leads to the misjudgment and omission for certain alternations. This study proposed an improved standardized drought-wetness abrupt alteration index (SDWAI),by clarifying the definition of drought-wetness abrupt alteration. Simulation and case study showed that the range of DFAI was large. The larger the weight parameter of DFAI was,the smaller the misjudgment rate of abrupt alternation event was but the larger the omission rate was,implying that misjudgment and omission of abrupt alternation events were unavoidable. The misjudgment generally occurred when a normal event turned into a severer flood or a severer flood turned into a normal for the adjacent flows. The omission normally occurred when adjacent drought and flood were light. Due to small differences between the ranges of SDWAI and drought-wetness index,the classified levels and their thresholds of drought-wetness abrupt alternations were consistent with those of drought-wetness assessment. The misjudgment of an abrupt event was avoided by recognizing in advance that the adjacent events were drought and wetness events,respectively. The omission of an abrupt event was avoided by the reconstructed weight parameter. In the Dongjiang River basin,which is the source of water supply to the Guangdong-Hong Kong-Macao Greater Bay Area,33.8% the abrupt alternations from drought to flood mainly occurred in April and May at the beginning of the former flood season,and 18.5% of that from flood to drought mainly occurred in October at the end of the latter flood season. In addition,there were twelve years for the coexistence of the abrupt alternations from drought to flood and from flood to drought.
Abstract: To increase the robustness of the estimation of Haihe River basin precipitation resources,we divided the basin into three regions:windward mountainside,leeward mountainside,and plains. Assistant by the artificial neural network machine learning and consistency correction principle,we constructed a comprehensive multisource fusion dataset of Haihe River basin precipitation from 2001 to 2019. The results showed that the original satellite precipitation products overestimated precipitation in the basin. The fusion dataset present that the average precipitation of the Haihe River basin from 2001 to 2019 was 515.2 mm,and the rainfall resources were 163.94 billion m3,respectively. The evaluation parameter of the fusion dataset represented a significant improvement in the accuracy of precipitation estimation. The fusion dataset also better explored the spatial distribution of precipitation in the basin and showed that more rainfall was collected in the northeastern,southeastern,southwestern,and west-central regions of the basin,whereas less was collected in the northwestern and east-central areas. Precipitation over the plains regions of the basin showed a distinct spatial pattern,and precipitation on both windward and leeward mountainsides was related to elevation.
Abstract: This study aims to maximize the water-saving potential of inland river basins in cold and arid areas and demonstrate the feasibility of replacing plains reservoirs with mountain reservoirs. The "Three Sources and One Mainstream" of the Tarim River basin (i.e.,Aksu River,Yarkand River,Hotan River,and the Tarim River mainstream) are employed as the research objects. According to the guidance of the"Water Saving Priority"water control strategy,the water demand of various industries,plains reservoirs,and mountain reservoirs are considered. Moreover,simulation and optimization models of cascade reservoir operation and allocation in current and future years are established and then solved. Results indicate that:① The key to saving water in cascade reservoir operation is to reduce ineffective loss through evaporation and leakage in river channels and plains reservoirs. ② Through the optimal operation and allocation of mountain reservoirs,the maximum water-saving potential will be 246 million m3 by 2035. ③ The plan for replacing plains reservoirs with mountain reservoirs is formulated,i.e.,the storage capacity of the six plains reservoirs of Jieranlike,Dazhai,Qiman,Paman,Kaerquga,and Tarim will be reduced by 17%,17%,17%,33%,100%,and 100%,respectively. This scheme can increase the water-saving potential of 21 million m3 while ensuring the water supply task of the mainstream of the Tarim River. These research findings provide theoretical and technical support for realizing the scientific regulation of water resources and ensuring regional water security and ecological security.
Abstract: In this study,observations from meteorological stations in and around the Hailar River basin from 1981 to 2020 were selected and combined with hydrological data to estimate regional evapotranspiration using the BTOP distributed hydrological model applicable to sparsely vegetated substrates,and then to analyze its influence characteristics on evapotranspiration under the influence of asymmetric warming phenomena. The results show that the asymmetric warming phenomenon in the basin from 1981 to 2020 is significant,mainly due to the diurnal asymmetric warming dominated by a larger increase in nighttime temperature and the asymmetric warming of ground air dominated by a larger increase in surface temperature. The main meteorological factors affecting evapotranspiration were relative humidity,wind speed,ground temperature difference and diurnal temperature difference,and relative humidity,diurnal temperature difference and ground temperature difference had the opposite trend of evapotranspiration,among which relative humidity and wind speed had a stable interannual variation,while temperature factor had an increasing intensity year by year. And the influence of asymmetric warming on basin evapotranspiration increases year by year,and the enhancement of surface warming rate is the main reason for the asymmetric warming of ground gas,under which the regional evapotranspiration shows a decreasing trend,so the temperature difference change cannot be ignored when exploring the reasons for the change of evapotranspiration.
Abstract: The main and branch channels are positioned vertically in irrigated areas,and damage occurs at the side wall structure near the bleeder,owing to scouring and deposition of sediment particles. The divergence and confluence angles of natural rivers typically acute. In this paper,the open channel at a 30° water separation angle was used as the research object. The three-dimensional instantaneous velocity was measured using an acoustic Doppler velocimeter,and the distribution of the average velocity,circulation intensity,turbulence intensity,turbulence kinetic energy and bed shear stress at typical cross-sections were analyzed. The experimental results showed that for the 30° water separation angle,the lateral velocity of the water flow at the water outlet varied significantly along the canal width,and easily formed circulations,causing local erosion and deposition. The turbulent intensity near the branch channel changed sharply and irregularly,and the maximum value was observed at the forefront section of the bleeder. The kinetic energy of the lower flow significantly exceeded that of the upper flow at the water outlet,and the higher value was mostly concentrated near the water inlet of the side channel. The bed shear stress at the end of the water diversion section of the main channel was high,eroding the side wall and reducing stability. Compared to the right bleeder,the 30° water separation angle adversely caused the sediment particles to enter the side channel and decreased the erosion rate of the water flow to the bottom and side walls of the channel. This study provides a reference for channel design and operation in irrigation areas.
Abstract: Rock weirs are commonly used eco-friendly river training structures. However,water flow over rock weirs can cause local scour,resulting in structural failure. To improve the prediction accuracy of scour dimensions at rock weirs,flume tests were conducted to study the clear-water scouring process at rock weirs. Additionally,the effects of flow intensity,submergence,and weir permeability on scour development were analyzed. The results reveal that for clear-water scour,the scour hole develops fast initially before progressively slowing down. At a specific time,the clear-water scour depth and length increase with increasing flow intensity and decrease with increasing flow submergence. The increase in weir permeability increases the scour length but decreases the scour depth. Moreover,as scour develops,the scour hole profile converges gradually,and its area is linearly and positively correlated with the product of the scour depth and length. Based on the experimental data and theoretical analyses,predictors for calculating the temporal clear-water scour depth,length,and volume at rock weirs are proposed for designing purposes.
Abstract: A dammed lake caused by a landslide is a common natural disaster in mountainous areas. The emergency response depends on scientific knowledge and a realistic evaluation of the failure risk and procedures. The mechanical behavior of landslide dams under external loads,the progressive failure mechanism of the dammed lake,and the prediction theory of outburst flood are critical scientific issues in the risk assessment of dammed lakes. This study investigates the failure risk and process after the formation of the dammed lake and analyses the hazard assessment methods for the dammed lake from qualitative and quantitative perspectives. The breach mechanism and process and influencing factors of the dammed lake are also described in terms of small-scale,large-scale,and supergravity field test technologies. In addition,the progress of empirical formula approaches and simple and thorough numerical simulation techniques in predicting dammed lake outburst floods is presented and evaluated from the viewpoint of mathematical methods. However,the research on risk assessment of landslide-induced dammed lakes is still in the initial stage worldwide. Future research directions will include integrated monitoring technologies of space-air-ground,uncertain problems in hazard evaluation of dammed lakes,erosion characteristics of landslide debris and breach mechanisms of landslide dams,and elaborate simulation of breach flood of dammed lakes. The review can be a valuable resource for disaster prevention and mitigation of dammed lakes and the risk management of water engineering facilities located within the related catchment.
Abstract: Sewage discharged through an underground spout into the ocean often contains a certain quantity of suspended solids,which exhibit complex diffusion and sedimentation characteristics near sewage outlet,and with representative transport processes of a sediment-laden jet. This paper therefore systematically reviews the research progress of sewage sediment-laden jet in still water,crossflow,wave and wavy-crossflow environment,and finds that there are significant differences in sediment deposition patterns for sediment-laden jets in different dynamic environments. Methods on how to accurately describe the multiple dynamic coupling processes of wave-current jet interaction and its influence on sediment transport and sedimentation processes have been a difficult task in the study of sewage discharged sediment-laden jets. Therefore,a recommendation for systematically studying the motion law of sediment-laden jet under the joint action of wave and current based on PIV/PLIF solid-phase separation physical experiment,particle tracking two-phase flow numerical model,and Lagrange integral model is proposed. It is intended to provide an important reference for the optimal design of ocean sewage disposal projects.