Abstract: A few of features of long-term precipitation changes have been reported for mainland China for the last decades. The understanding of causes for the observed precipitation trends, however, is lacking. This paper comprehensively analyzes the long-term changes of multi-indicators of precipitation and atmospheric moisture over mainland China, the paleo-precipitation variations over representative areas, and the previous studies related to observed changes and possible causes of precipitation. The following conclusions are drawn: ① There is an obvious regional difference of recent precipitation trends in the country, but no significant long-term change is detectable over the past century or decades for mainland China on a whole. Frequency and amount of intense precipitation or rainstorms appear to increase over the last decades, and frequency of light rain events especially the trace rain events experiences a highly significant decrease over the same time period. ② Reanalysis data (NCEP/NCAR and ERA-Interim) shows a general increase in atmospheric moisture net budget over the last 3 decades, and sounding data and surface observations show significant upward trends of atmospheric perceptible water or specific humidity over the last decades. Tree-ring data and historical documental records indicate that the recent changes of precipitation are well within the ranges of historical natural variability, except for northeastern part of the Qinghai-Tibetan Plateau where the annual precipitation of the last century reconstructed based on tree-ring data seems to surpass the averages of any single century over the last ten centuries. ③ Instrumental observations of the last century show a distinct characteristic of multi-scale quasi-periodicals for annual total precipitation in the North China Plain, with each of them corresponding to the recognized variations of external forcings or internal modes of climate system, indicating the possible influence of natural forcings and variability on precipitation. The influence of increased atmospheric greenhouse gas concentration on precipitation in mainland China on a whole or in the eastern monsoon region of the country can hardly be detected, though the precipitation changes of Northwest China based on proxy data, instrumental data and modeling data are generally consistent with the theory expectation. ④ Weakening of regional surface wind speed is causing a systematic bias in observations of precipitation, and this is very likely to have led to, at least partially, a false upward trend of northern winter snowfall and annual intense precipitation frequency through increasing the catch-rate of rain gauges. The rising level of aerosols concentration in atmosphere is likely to be another major reason for the upward trend of intense precipitation frequency, and it is very likely to be one of the most important causes for the wide-spread decline of light and trace rain events in the monsoon region. ⑤ The data biases of the current observational data related to urbanization effects very likely account for an additionally substantial part of the reported increase in short-duration intense precipitation frequency and amount, and also for a large part of the observed decline of light and trace rain frequency in eastern monsoon region of the country.
Abstract: The Variable Infiltration Capacity (VIC) model and the Mann-Kendall with LOWESS test are employed to evaluate the influence of East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM) on runoff in the monsoon region of East China. The spatial variation of runoff coefficients in the region is also examined. The results indicate that the EASM-influenced area is much larger than the SASM-influenced area. EASM shows positive relationships with runoff in most area between Yangtze River and Songhua River, while negative EASM-runoff relationships are found in partial area of the South China. SASM shows positive and negative relationships with runoff in South China and partial areas of the upper Yangtze River basin, respectively. Moreover, the results indicate remarkable spatial disparities in runoff coefficients: it is a larger value for the Southeast Coast and the Yangtze River basin, and lower for the Yellow River and Haihe River basins. Understanding the relationships between EASM/SASM and the runoff has important implications in predicting the hydrologic change and water resources management in East China.
Abstract: The Precipitable Water Vapor (PWV) derived from Global Navigation Satellite System (GNSS) can be used for the study of precipitation forecasting, but it needs the support of ground measured meteorological data. In order to solve this problem, a method of precipitation forecasting without using the ground measured meteorological data is proposed and realized in this paper based on the characteristics of Zenith Tropospheric Delay (ZTD) affected by atmosphere. It is validated using the data from Continuously Operating Reference Station (CORS) of Zhejiang province and hourly precipitation during the period from May to June, 2015. The he results show that the proposed method is capable of forecasting 80% of rainfalls, which is equal to the results obtained based on PWV with meteorological data. This indicates that the short-term forecasting method based on the ZTD without considering the measured meteorological data is effective and feasible, which shows significant research and application value for short-term precipitation forecasting.
Abstract: Ascertaining water supply and drainage routes and water resource conditions can provide technical support in the comprehensive treatment of coal mining subsidence areas. The subsidence conditions in the Huainan Panxie coal mining area in 2010 and the meteorological data from 2001 to 2010 were used to simulate the local water cycle in mining subsidence areas in recent years by the distributed "river-subsidence depression-groundwater" coupling model, and the model has been verified. The results show that river confluence, precipitation, groundwater, and runoff formed 84.6%, 8.8%, 3.6%, and 3.0%, respectively, of the water supply. River discharge, evaporation, seepage, and water diversion constituted 80.6%, 8.2%, 1.3%, and 9.9%, respectively, of the water drainage. River confluence is the primary factor influencing the water cycle, followed by precipitation and evaporation, with groundwater exerting a negligible influence.
Abstract: To enable a detailed investigation of the runoff recharge sources in the Chishui forest region and the contribution of fog drip in Chishui forest region during the dry season, water samples (including fog drip water, spring water and stream water) were collected in December 2014 from three major streams. A comparison of D and 18O isotopic water sample results with isotopic data for precipitation in Zunyi, showed that fog drip is distinctly more enriched in heavy isotopes than precipitation. The isotopic composition of spring and stream water was plotted, together with that of November/December precipitation, with results showing that stream water has similar isotopic composition to spring water, distributed along the local meteoric water line(LMWL). Isotopic data indicate that runoff is mainly recharged by groundwater, which is a mixture of early intermittent precipitation and continuous fog drip. Fog drip is an important surface runoff source in the Chishui forest region during the dry season, but it does not recharge surface runoff directly. The average contribution of fog drip reached 24.1% in the Sidonggou, Shizhangdong, and Yanziyan sampling areas (when calculated by δD, when calculating results by δ18O, the corresponding proportion was 20.0%).
Abstract: In order to investigate the impacts of the Three Gorges Projects (TGP) operation on the recent channel adjustment in the Jingjiang Reach, bankfull channel dimensions at both section- and reach-scale were calculated annually from 2002 to 2013, with empirical relationships being proposed between these dimensions and the previous 5-year average fluvial erosion intensity during flood seasons at the Yichang hydrometric station. Hydrological data at this station were then estimated under the scenario without the TGP, and used to evaluate the corresponding bankfull dimensions. Differences were analyzed between the variations in bankfull dimensions under these two scenarios. The results indicate: ① after the TGP operation, the bankfull widths and depths at four typical sections increased gradually, with a remarkable increase in the width; ② the longitudinal channel slopes tended to flatten in the Jingjiang Reach, with an appreciable increase in the reach-scale bankfull depth and a slight change in the reach-scale bankfull width, which caused the geomorphic coefficient decreasing by 6.7%—10.3%; ③ Changes in bankfull channel geometry were slighter under the scenario without the TGP, with the increase ranges in the reach-scale depth and area accounting respectively for 16% and 18% of those under the scenario with the TGP. Thus, the TGP operation didn't alter the trend of the recent adjustment in bankfull channel geometry of the Jingjiang Reach, which tended to have a narrower and deeper channel geometry, but accelerated the adjustment process.
Abstract: Change of channel storage is a direct quantitative indication of river bed evolution. Boundary conditions and sediment transport are the major factors to change the channel volume. Topographic data of the North Branch of Yangtze River Estuary from 1986 to 2013 is collected for digital underwater elevation model during different periods by GIS technology. With the models channel storage variation and river bed evolution are analyzed in the paper. The results show that the channel volume under elevation 0 meter decreases 711 million cubic meters in the North Branch of Yangtze River Estuary since 1986. Among those, 400 million cubic meters, accounted for 56.3 per cent is caused by enclosure of side foreland and the rest 311 million cubic meters, accounted for 43.7 per cent is the result of sediment deposition. Specifically, in the upper reach, sediment deposition is the main factors for channel storage reduction and comprehensive development and utilization of the waterway ought to be in accord with characteristics of sediment transport. In the middle of the branch, reclamation on marginal bank and growth of sandbar towards bank are the main causes of channel storage reduction. With the boundary condition adjustment, it is strengthened of constraint of river flow and erosion in riverbed, and the bathymetry is advantageous to develop and utilize of the waterway after river cross-section adjustment. In the lower reach, both sediment deposition and reclamation on marginal bank are the major reasons for river storage shrinks, while the effect of the former is slightly larger than that of the latter. Because the groove under elevation -5 meters stable exists, river regime has basic conditions for development and utilization of the waterway in the lower reach. And there is margin for reclamation in the future on the south bank.
Abstract: In this paper, a hydrodynamic numerical model including bottom friction is developed to calculate the instabilities of longshore currents on two barred beaches with respective slopes of 1:40 and 1:100. This model enables to estimate wavelength, propagation velocity, growth rate and perturbation velocity field of the instabilities. Here, the effects of the bottom friction on the instabilities are analysed according to the beach slope. The results show that the propagation velocity of the instabilities ranges between 0.71—0.79. Furthermore, the instabilities develop faster on the 1:40 slope beach than on the 1:100 slope beach. It is also shown that the bottom friction has a great effect on the inhibition of the instabilities and that backshear is a key parameter in the instabilities development. Therefore sand bars can often be observed in this zone. Finally, the strongest energy of the instabilities generally occurs at the crest of bar and the milder the slope, the longer the wave length of the instabilities.
Abstract: The relationship of sheet-flow erosion and hydraulic factors on tapered engineering spoil bank slopes was investigated by laboratory simulation of scattered, tapered spoil banks in the red soil region of northern Jiangxi Province, China. An artificial rainfall experiment was conducted using a complete combinatorial design of four rainfall intensities (1.0—2.5 mm/min) and three gravel contents (10%—30%). Gray relational analysis was performed to assess the correlation between hydraulic parameters and soil detachment rate on the spoil bank slopes. The results showed that: ① Under the experimental conditions, there was a power function relationship between stream power and soil detachment rate; ② With a fixed gravel content of spoil bank, the analysis with rainfall intensity as a variable could reflect the correlation between hydraulic parameters and soil detachment rate on the spoil bank slopes; ③ Under a fixed rainfall intensity of greater than 1.5 mm/min, it was unsuitable to use the gravel content of spoil bank as a variable of gray relational analysis. In conclusion, stream power is the optimal hydraulic parameter to describe the erosion process of tapered engineering spoil banks, and it can be used to construct physical models of spoil bank erosion in the red soil region of northern Jiangxi.
Abstract: The hyporheic layer is an important part of riparian zones. To reveal the distribution of temperature and flow field of hyporheic layers in riparian zones under the influence of low temperature water, a real-time monitoring test of temperature and water level was used to study the thermal structure of a hyporheic layer in different seasons and spatial locations, which could be used to calculate the groundwater velocity. Our results show that the temperature field of the hyporheic layer is characterized by seasonal reversal of thermal stratification: surface-warm and deep-cold during the summer and surface-cold and deep-warm during the winter. Among the four methods of calculation of the groundwater flow using temperature tracer, the Hatch phase method yielded the highest accuracy. The flow velocities ranged from 1.03×10-4 to 7.96×10-4m/s during the period of Dec. 15—31, 2014, which decreased with the increasing depth in section and the groundwater flow velocity curves were close to parallel.
Abstract: To understand the time-averaged transient motion characteristics of Q-events for open-channel uniform flow (first-quadrant (Q1), second-quadrant(Q2), third-quadrant(Q3), fourth-quadrant(Q4)), a high-frequency particle image velocimetry system was used to measure three two-dimensional instantaneous velocity vector fields of turbulent open-channel flows. The Reynolds stress, occurrence frequency, and measured area of Q-events in fluctuating velocity fields in open-channel flow and the relationship between Q-events and vortex motions were statistically analyzed. The results indicated that the time-averaged characteristics of Q1 and Q3 were similar, with low occurrence frequency, small area, and negative instantaneous fluctuating momentum flux. The time-averaged characteristics of Q2 and Q4 were opposite to those of Q1 and Q3. In addition, the occurrence frequency of Q4 increased with water depth to reach a maximum at about 0.8H, whereas the occurrence frequency of Q2 reached a maximum near the walls and decreased with water depth. The transient motion characteristics of the open channel were evident mainly in the downstream movement of Q4 resulting from the water surface area and in the extrusion, uplift, and climbing behavior of the Q2 structure in the bed region accompanying the transient development process of its deformation.
Abstract: Our field experiment made a thorough investigation of the influences of dam operations on the characteristics of the river water eco-environment, and studied the spatial variation of water quality at different control modes (0 m3/s, 20 m3/s, 40 m3/s and 60 m3/s). We also monitored ecological indicators to allow us to analyze the long-and short-term effects of the dam on the river water eco-environment. The results showed that a flow of 60 m3/s benefitted oxidation and decomposition of water pollutants downstream of the dam, and improved river water self-purification. An increase in disturbance of water flow promoted pollutant transfer from the sediment into the water so that a sudden pollution accident resulting from sediment disturbance downstream of the dam could easily take place. Frequent operations occurring in a relatively short period of time significantly affected the density distribution of plankton. What's more, the long-term effects of dam operations led to the development of a very simple biological community and structure, the water eco-environment deteriorated markedly, and the negative effects on the river upstream of the dam were more serious than downstream. The results of this study are useful in providing reliable information for ecological river restoration and sustainable river basin management.
Abstract: Aiming at the characteristics of complexity, dynamism and uncertainty among water transfer, water diversion and water supply in joint regulation of large-scale inter-basin water supply reservoir group, on the basis of bi-level programming model, applying game theory, tri-level programming model of inter-basin reservoir group water supply operation rules is built up and inter-basin reservoir group optimization operation rules after combining water transfer, water diversion and water supply is carried out, revealing the independence and interconnection of principal and subordinate hierarchy among inter-basin reservoir group in deep level; and applying particle swarm optimization based on immune evolutionary to have hierarchical optimization solution for model. Taking the lower reaches of the Luanhe River inter-basin reservoir group as research object, the calculation results show: ① reduce water loss and increase the utilization ratio of water resource; ② increase the guaranteed rate of water supply in Tangshan and Tianjin as well as lower lack of water damage depth.
Abstract: In order to improve the water diversion effectiveness of intake reservoir in inter-basin water diversion project, the intake reservoir operation model coupling long-term runoff forecast is studied. First, the information of runoff forecast in flood season is employed, and the prior probability is corrected by runoff forecast probability to describe the runoff uncertainty. The stochastic dynamic programming model (BSDP-LTF) is established. Then the model is compared with stochastic dynamic programming model considering inflow correlation only (SDP-I) and stochastic dynamic programming model considering long-term forecast only (SDP-LTF) in Biliuhe reservoir. Comparative results show that the water diversion is reduced by 8.2% and 4.1% for the BSDP-LTF model when compared with SDP-I and SDP-LTF in condition of basically the same water supply reliability and not increasing operation risk. The results indicate that the BSDP-LTF model improves the runoff description effectively, and increases the effectiveness of the inter-basin water diversion.
Abstract: Overland flow is that part of rainfall which exceeds the infiltration capacity of the soil surface and any depression storage, which usually is assumed to flow downslope as a uniform thin sheet of water. In reality however, overland flow takes place along gullies and rivulets as non-steady non-uniform flow. It is one of the basic processes in the catchment hydrological cycle that has significant roles in processes such as soil erosion, sediment and pollutant transport. In this paper, different approaches of modeling and simulating overland flow including their pros and cons, assumptions and limitations are summarized and analyzed. From the literature survey, it can be concluded that the distributed conceptual approach based on the time-area relationship and linear reservoir has further development potential. In this study, a new approach based on the watershed variable isochrone method that uses the DEM and has the potential to represent the non-linear effects of the runoff generating mechanism is proposed. To implement this approach it is necessary to monitor runoff resulting from urban low impact developments (LID).
Abstract: Aimed to get scientific "water stage-duration-frequency" (S, D, F) thresholds for wetland formation, the theory and method to determine wetland (S, D, F) thresholds were analyzed based on the related principles of pedology, plant ecology, system theory, geographic system theory, and inversion theory, etc. The result suggested that: ① Under normal circumstances, the S threshold for hydric soil formation and hydrophyte development should be determined in terms of the thickness of capillary fringe and the depth of the major portion of hydrophyte root zone in upper wetland boundary respectively; in lower wetland boundary, the S threshold should be determined at the maximum depth to which submerged plants normally grow; in a given year, the D threshold could only be inverted in stage hydrograph in terms of the altitude of wetland soil boundary or vegetation boundary; for stable wetland soil boundary or stable wetland vegetation boundary, the D threshold should only take the average value of the years, but for fluctuant wetland vegetation boundary, its D threshold is a constant. ② Under abnormal circumstances, the (S, D, F) thresholds of wetlands should refer to the (S, D, F) thresholds of wetlands "under normal circumstances" which belong to the same HGM regional subclass. ③ To test whether (S, D, F) thresholds is scientific, wetland hydrological boundary determined by the (S, D, F) thresholds must be coupled with wetland soil boundary or wetland vegetation boundary. The construction of the theory and method makes it possible for wetland scientists to study (S, D, F) thresholds of different wetland types in different regions.