Abstract: The digital twin watershed is an important part of the digital twin earth. Clarifying the theoretical definition and connotation of the digital twin watershed is the premise and foundation for the research and construction of the digital twin watershed, and it is of great significance for the intelligent management of the watershed. Based on the digital twin theory and technology, the following research has been carried out in this paper. ① The definition of a digital twin watershed is given, and it is considered that a digital twin watershed is a new infrastructure and new paradigm serving the entire life-cycle management of the watershed, which is the interactive mapping, co-intelligence evolution, and virtual reality integration between physical and virtual watersheds driven by the full amount of data and domain knowledge, and the differences between a digital twin watershed and traditional modeling and simulation are analyzed. ② The connotation of a digital twin watershed is to realize the full life-cycle control of physical watershed objects by loading the physical watershed into the virtual watershed, mapping the physical watershed with the virtual watershed, and then managing and controlling the physical watershed using the virtual watershed. Its characteristics include high fidelity, evolution autonomy, real-time synchronization, closed-loop interaction, and symbiotic evolution. ③ The basic model of a digital twin watershed is composed of a physical watershed, a virtual watershed, the real-time connection and interaction, the digital enabling service, the twin watershed data, and the twin watershed knowledge. Its core capabilities include physical watershed perception and control, digital expression of all of the water-related elements, visual dynamic presentation of real scene, watershed data fusion supply, watershed knowledge fusion supply, watershed simulation and deduction, and self-learning and optimization of digital twin watershed. ④ This paper puts forward the key scientific problems and key technical systems to be solved in the digital twin watershed, and looks forward to the development direction of the digital twin watershed from the perspective of a perception network, data network, knowledge network, model network, and service network, and expounds the enabling field of the digital twin watershed. This paper aims to provide theoretical guidance for the application of digital twin watershed technology through the new research paradigm of digital twin watershed theory and to provide useful inspiration and reference for future smart watershed research and the application of digital technology in watershed governance and management.
Abstract: To avoid external shocks and challenges and to maintain regional peace and stable development, the research on the resilience of the water resources- water environment- social economy complex system is one of the important ways. Based on the ideas of projection pursuit and differential equation, this study constructs a new resilience evaluation model to evaluate the resilience of the water resources-water environment-social economy complex system in the Yangtze River Economic Belt from 1999 to 2018. Taking the level of resilience of Yangtze River Economic Belt in 2011 as turning point, the results confirmed that the level of resilience maintain stable before 2011 and steady improve after 2011. The findings also revealed that the factor affecting the level of resilience in Jiangxi and Yunnan was natural resource endowment conditions, the factors affecting the level of resilience in Shanghai were technological development and government macroeconomic policy, While the level of resilience in other provinces were undergo a transition between the above factors. The order of optimal control factors was ranked as adaptability > restoration > resistance, and the optimal control factors gradually shifted from resistance to adaptability.
Abstract: As the link between energy balance and water cycle, changes in evaporation are of critical importance for regional hydrological cycle and water resources management of the Yangtze River basin (YZRB). In this study, the spatio-temporal characteristics and driving mechanisms of the long-term changes in pan evaporation (Epan) of the YZRB from 1960 to 2019 were investigated using the PenPan model, and changes in actual evapotranspiration (Ea) were further evaluated using the latest generalized complementary relationship of evaporation. Results show that: ① Both Epan and Ea of the whole YZRB decreased and then increased before and after 1990. The decreases of wind speed and net radiation were the main drivers for decreasing trend of Epan before 1990, but the rise of temperature and decrease of relative humidity were the main drivers for increasing trend of Epan after 1990. ② Trends of pan evaporation in both major climatic regions of YZRB (i.e., plateau climatic region and subtropical climatic region) were reversed before and after 1990 and were driven by different mechanisms. During 1960—1989, Epan decrease in the plateau climatic region was driven by changes in temperature and radiation, while Epan decrease in subtropical climatic region was driven by changes in wind speed and radiation. ③ During 1990—2019, Epan increase in the plateau climatic region was mainly driven by the rising temperature, increased wind speed and decreased relative humidity, while Epan increase in the subtropical climatic region was largely driven by the rising temperature and decreased relative humidity. This study can provide as a reference for the water cycle change detection and water resources allocation in the YZRB.
Abstract: This research aimed to determine the evolution and non-stationarity characteristics of summer precipitation structure over the Yangtze River Delta (YRD) in a changing environment. Based on the daily precipitation data from 72 rain gauges over the YRD during 1960—2016, the methods of Pettit and Mann-Kendall were applied to investigate the spatio-temporal variation rules of summer precipitation, considering the variables of precipitation amount, days, intensity and the incidence rates of light rain, moderate rain, heavy rain, and rainstorms, and analyze their causes. The results showed that the incidence rate of light rain decreased through time at most gauges, but the other six indices increased at most gauges. Among these, the non-stationarity in the incidence rate of light rain decreased monotonically, while the non-stationarity characteristics of precipitation amount, intensity, and incidence rates of heavy rain and rainstorms increased monotonically. These gauges were mainly scattered in the Tai Lake Basin, suggesting that this region is likely to face even greater risks from flooding. For most gauges, the intensity of the East Asian summer monsoon was positively associated with the incidence rate of light rain, but it was negatively associated with the other six indices. Take the Tai Lake basin as an example, urbanization increased the precipitation amount, intensity and incidence rates of heavy rain and rainstorms, with contribution rates of 25.4%, 27.9%, 54.6%, and 25.5%, respectively. However, urbanization decreased the precipitation days and the incidence rates of light rain and moderate rain, with contribution rates of -37.3%, -33.2%, and -100%, respectively.
Abstract: Rapid urbanization processes alter the regional underlying surface, leading to changes in the hydrological cycle. Such changes have made it difficult to explain the traditional water yielding and runoff routing mechanism, which necessitates our new exploration. In this paper, taking the Yangtze River Delta region as an example, we have conducted the experimental observations in basins with the different urbanization levels and different space scales. Via the collected first-hand hydrologic data, namely, rainfall, soil moisture, and streamflow with high resolutions (5 min time intervals), we adopted data-driven flood feature analysis to reveal the responses of the flood characteristics, such as flood lag time and peak discharge. Then, we discussed the response mechanism of rainstorm and flood in rapid urbanization areas. The main conclusions are as follows: ① Compared with other land use/cover types, the response of soil moisture for urban land are more intense under different rainstorm events (usually increasing more than 4% for the surface layer). The change of underlying surface in urbanized area affects the processes of surface runoff by influencing the dynamics of soil moisture. The soil moisture content of urban land and wasteland with low vegetation coverage showed steep rise and fall with the beginning and end of rainfall, while that of land use with higher coverage showed slow rise and decline trends. ② Flood peak lag time and peak discharge are mainly controlled by watershed scale. There have power law relationships between flood lag time and peak flow with watershed scale, and factors such as impervious surface and topography also have some influences on flood characteristics. ③ Rainstorm is a direct driving factor of flood in the Yangtze River Delta region. Rainfall characteristics are strongly correlated with the peak discharge, peak discharge per unit area, and runoff depth, with correlation coefficients above 0.49, 0.41 and 0.78, respectively. In general, the natural geographical characteristics and rainfall are the main factors affecting the flood characteristics, but the impact of the urban underlying surface on the flood characteristics cannot be ignored. The processes of rainstorm floods have been directed affected by the modification of soil moisture dynamics due to urbanization. Under the dual role of urbanization and climate change, the regional flood risk would be intensified in the future.
Abstract: Sediment transport in tidal estuaries is complex and changeable. How to scientifically classify the forms of sediment transport and evaluate its impact on channel sedimentation is the key to clarify the source of sediments deposited in the channel and formulate channel siltation reduction measures. In this paper, a new method identifying three forms of sediment transport, that is the bed load (BL), the suspended load (SL) and the bed-suspended conversion load (BSCL), was proposed based on analyzing the grain size of surficial bed sediment (SBS) and near bottom suspended sediment (NBSS). The sediment samples were collected along the Deepwater Navigational Channel (DNC) in the Yangtze Estuary (YE) during the flood and dry seasons of 2015 and 2018, and the contributions of three forms of sediment transport to the channel sedimentation was quantified. The results show that the upper turning point of grain size cumulative frequency curve is able to well represent the sediment transport form transition from BL to SL. There exists a significant sediment exchange between SBS and NBSS at the South Channel (SC) as well as the North Passage (NP) of YE. The sediment transport in DNC are not only in forms of BL and SL, but also in BSCL, which accounts for the proportion of 50% to 60% of the channel sedimentation. The contribution of BL to the channel deposition at SC segment of DNC in flood and dry season are 36% and 26% respectively, which is higher than that of SL occupying 6% and 13%. In contrast, the contribution of SL to the channel deposition at NP segment of DNC ranges from 44% to 48%, which is much higher than that of BL only accounting for 3% to 6%. The proposed method based on the grain size analysis provides a new sight on understanding the characteristics of sediment movement in tidal estuary and identifying the source of sediments deposited in the channel.
Abstract: To enhance the resilience of riparian countries associated with the Lancang-Mekong River (LMR) to drought under a changing environment, there is a pressing need to project future droughts across this river basin. Bias corrected projections from five CMIP6-GCMs under three Shared Socioeconomic Pathways (SSPs) were used as forcing data of a distributed hydrologic model (CREST-Snow) to project future streamflow of the LMR, and to examine meteorological and hydrological droughts across the LMR basin during 2020—2050. The regulation effect of cascade reservoirs on the mainstem of the Lancang River on downstream streamflow in the future was also quantified. Results show that although the entire basin will likely experience an overall wetting trend, the frequency of extreme dry and wet events across the LMR basin is likely to increase during 2020—2050. Droughts will more frequently occur during 2020—2029, as opposed to wet events that will be mainly concentrated during 2030—2050. From a spatial perspective, Laos and Thailand are likely to experience more frequent and severe droughts than other riparian countries. Cascade reservoirs on the Lancang River in China can effectively increase dry-season streamflow in downstream areas (decreasing from 99% in the upper stream to 68% in the downstream), playing a positive and important role in mitigating water shortage during dry seasons or droughts. We advocate for enhancing the cooperation through improving regulation of reservoirs across the entire basin, which should benefit water security and mitigation of droughts for all riparian countries of the LMR.
Abstract: Multi-source precipitation merging is a crucial way to estimate the spatiotemporal distribution of precipitation accurately. The commonly used merging methods mainly focus on bias correction of the total precipitation amount or precipitation intensity but often neglect to identify short-duration precipitation. In this study, we proposed a merging framework of multi-source precipitation by identifying rain and no rain and constructed a precipitation merging method considering both rain area identification and rainfall estimation by coupling the geographical weighted logistic regression (GWLR) and geographically weighted regression models (GWR). Then, the merging experiments of the Multi-Source Weighted-Ensemble Precipitation Version 2.1 (MSWEP V2.1) and the daily precipitation observed by the ground gauges network over the Han River basin were implemented. The results show that the proposed method successfully reproduces the spatial pattern of rain and no rain and catches the precipitation center. It overall strengthens the performance of MSWEP V2.1 to estimate ground precipitation, reduces the false alarm rate (RFA) and false precipitation (PF) by more than 60%, and improves the critical success index (ICS) and Kling-Gupta efficiency coefficient (EKG) by more than 40%. Moreover, the gains of correcting PF and improving EKG are higher than 10% against the spatially interpolated precipitation. Meanwhile, compared with reference data, precipitation fusion enhances the classification accuracy of heavy precipitation events (intensity ≥ 50 mm/d) by not less than 60%. The innovative method effectively improves the performance of precipitation estimation and provides a new idea for multi-source precipitation merging.
Abstract: To investigate a more accurate method for potential evapotranspiration estimation under climate change, three sets of experiments were conducted using small lysimeters at Wudaogou experimental station on the Huaibei Plain (China), and a new model of potential evapotranspiration was proposed by integrating the advection dynamics term and introducing a correction parameter for surface net radiation fluxes on the basis of the energy balance principle. The results revealed the following: ① The correlation between evapotranspiration of the grass cover group (E14 and E25) with different measurement methods was better (R=0.95) among the three sets of experiments. ② The Nash-Sutcliffe efficiency coefficient (0.85) and root mean square error (0.83) of the proposed potential evapotranspiration model were better than those of existing empirical methods such as the Penman equation in the two experiments covered with gras. ③ The model demonstrated capability for estimation of evapotranspiration under grass cover and marked advantages in its application to the Huaibei Plain area. The proposed model can improve the accuracy of regional potential evapotranspiration simulation, and provide scientific reference for water cycle process simulation and water resources utilization.
Abstract: This study aimed to characterize the temporal and spatial variation in isotopes of different water sources of the Pingshuo mining area to identify the significance of coal mining activities to the regional water cycle. Surface water, groundwater, and mine water samples were collected in August and December, 2020. The hydrogen and oxygen stable isotopes of the samples were measured and analyzed. The contributions to mine water from different water sources were calculated using the MixSIAR Bayesian mixed model. The results indicate that the summer δD and δ18O isotopes of surface water and mine water exceeded those in winter. There was no obvious seasonal difference in groundwater δD and δ18O. Hydrogen and oxygen isotopes of surface water increase along the flow path, but were partially depleted in mine water. The hydrogen and oxygen isotopes of groundwater gradually increased along the direction of runoff. Hydrogen and oxygen isotopes of water in the coal mining area exceeded those in the non-mining area. Seasonal effects resulted in the area of high shallow groundwater hydrogen and oxygen isotopes in August significantly exceeding those in December. Plotting of δD and δ18O showed that surface water was affected by evaporative fractionation after being recharged by atmospheric precipitation. Sources of recharge of shallow groundwater were more complex. Deep groundwater was recharged by shallow groundwater and surface water through infiltration of the fracture zone formed by coal mining. Mine water was recharged by surface water, shallow groundwater, and deep groundwater. Deep groundwater was the main source of mine water recharge, accounting for 61.60% to 67.20% of total mine water recharge, with its contribution higher in winter than in summer. Recharge of mine water by shallow groundwater demonstrated significant seasonal differences.
Abstract: For the composite riverbank, the continuous erosion of the lower non-cohesive layer results in the failure of upper cohesive layer. The cohesive soil block deposits at bank toe, which can alter the flow structure and the following erosion process in the bend. To reveal the effect of failed soil block, a three-dimensional numerical model was developed to simulate the flow structure and wall shear stress pattern in the Shishou bend with different failed block. The results indicate that soil block deposit at bank toe shifts the dynamic axis of flow away from the outer bank, decreases the intensity of the secondary flow, and changes the direction of the secondary flow. The effect of failed block on the wall shear stress changes greatly with space. For the riverbed and inner bank, the average wall shear stress tends to increase, while decreases in the head and upstream area of the failed block for the outer bank. The larger the failed block is, the greater the variation of wall shear stress will be. In comparison, The variation of wall shear stress is about 2%—10% of the variation of cross-sectional area of the failed block. The results are expected to provide a basic theoretical and technical support for river regulation and riverbank planning.
Abstract: A rock landslide in channel reservoirs typically undergoes a disintegration process during the rundown on an inclined plane, that is, disintegrating into numerous blocks of different shapes and sizes. In previous studies on landslide-generated waves, landslides were mainly represented by a rigid body or a granular cluster of uniform granulates. However, the effect of landslide disintegration on landslide generated waves has not yet received significant attention. In this study, the effect of the disintegration process of a landslide during rundown on free-surface characteristics of landslide generated waves in a wave basin was preliminarily investigated. The results showed that the maximum wave amplitude and maximum wave height decreased with increasing disintegration index parameter. The leading wave amplitude and wave height attenuation in the landslide axis during wave propagation could be satisfactorily described based on the solitary wave theory. Moreover, the leading wave amplitude and wave height decay behaviours were mainly dependent on the maximum wave amplitude and the maximum wave height, respectively. It was also found that the wave attenuation was higher in a wave basin than in a wave channel.
Abstract: The river hyporheic zone is the main area of surface-subsurface connection and exchange. Surface-subsurface water exchange promotes the transport and transformation of biogenic substances and can conserve water resources, stabilize regional ecological environment, which provide a great habitat for aquatic life. Therefore, understanding the relationship between the activities of aquatic animals and surface-subsurface water exchange is the key to deep cognition and scientific protection of aquatic ecosystems. This paper reviews previous studies on the feedback of aquatic activities to the surface-subsurface water exchange process, for example, the biofilm formed by benthic microorganisms can absorb or retain biogenic substances, prolonging and changing the migration time and path of substances; the activities of aquatic animals can affect the physical characteristics of riverbed, such as permeability and porosity of streambed, which in turn affect the hyporheic exchange flux and substances transformation efficiency; the block and disturbance of water flow by aquatic plants can also affect the surface-subsurface water exchange process. According to the current researches in this field, three important research directions of the relationship between river hyporheic exchange and aquatic organisms are proposed in this study: the theory of mutual feeding between hyporheic exchange and aquatic organisms; relationship between surface-subsurface water exchange and aquatic ecological function; biogeochemical coupling processes in hyporheic zone.
Abstract: Multi-pond systems are common small-scale water conservancy projects in agricultural watersheds. The spatially interlaced structure of pond-ditches leads to complex and variable processes of hydrological connectivity, which is of great importance to source reduction and pollution control for watershed nutrients. To better understand the impact of hydrological connectivity on phosphorus transport in multi-pond systems, we summarize assessment methods of hydrological connectivity index in multi-pond systems based on the definition and connotation of multi-pond systems and hydrological connectivity. Landscape patterns, hydrological processes, and biogeochemical processes play an important role in regulating phosphorus transport in multi-pond systems. The impacts of hydrological connectivity on phosphorus transport environment through driving drying-wetting cycles and on phosphorus transport flux by changing water residence time are illustrated. We point out that the driving mechanism of hydrological connectivity changes, scale extension of nutrient retention efficiency, quantitative simulation, and optimal regulation are important directions for future research on the environmental effects of multi-pond systems. This review will provide a theoretical basis for ensuring the water quality improvement function of multi-pond systems.