Abstract: Using dynamic segmentation and the Thiessen polygon method, precipitation amounts can be estimated for different spatial and temporal resolutions over the period 1951-2006. The resulting monthly, seasonal, flooding season and annual time series for both regional and national average precipitation are then analyzed. The spatial distributions, regional characteristics, variabilities, trends, abrupt changes, oscillation periods of monthly, flooding season and annual precipitation are examined. The temporal analysis is done for the three periods 1961-2006, 1980-2006 and 1961-1979, which represents the precipitation variabilities in long term, recent years and earlier term (or baseline). Compared to the earlier term values, the result shows that a recent southward trend is detected in the 600 mm of annual precipitation isoline in Bohai Bay. The annual amount of precipitation is on the rise recently in the west area of 110° E. The mean annual precipitation is down 10% in the mid-western part of Inner Mongolia, the coastal areas of the Haihe River, the middle part of the Yellow River and the northern part of the Huaihe River. In contrast, the mean annual precipitation is up 10% in the middle part of the Nenjiang River, the lower reach region of the Yangtse River, the coastal areas of South Fujian, the mid-northern part of Tibet and the middle part of Xinjiang. In particular, the mean annual precipitation is up 30% in the area of the Talimu River and the upper reach region of the Yili River.
Abstract: A signal-based anomaly detection method with the Box-Cox transformation technique are adopted in an effort to effectively extract anomalous information from multiple data sources, and to improve the identification of water vapor transport anomalies of flood-causing storms (FCSs). The combined approach is applied to the Huaihe River Basin (HRB) to studying the anomalous characteristics of 850 hPa water vapor flux for the years of 2003, 2005 and 2007. The results show that during FCS periods, the 850 hPa meridional flux of water vapor between longitude 105° E and longitude 125° E is likely to form a dipole pattern with the HRB as its center and the positive anomaly on the south and the negative on the north. The importance of water vapor transport channels varies with FCSs as revealed by the 850 hPa zonal transport anomalies of water vapor at lower latitudes.
Abstract: The study of spatial-temporal pattern of drought hazards has attached great importance to government and academia in China under a changing climate. The spatial-temporal pattern of drought hazards in China for the period 1689-1991 is reconstructed using the data extracted from the drought hazard document archived in the Forbidden City during the Qing dynasty, and the geographic information system (GIS) technique. The result shows that ① the areal extent of drought fluctuated three times with time during the study period, and a total of 9 typical drought years were identifiable from the reconstructed data; ② spatially, three drought-prone regions were found. These regions were in northwest China covering the Gansu province and the Ningxia-Hui Autonomous Region, in north China including the provinces of Shandong, Hebei and Henan as well as Tianjin Municipality, and in the Jianghuai area of Anhui and Jiangsu provinces; ③ seasonally, summer droughts were dominant during the Qing dynasty. The reconstructed spatial-temporal pattern of drought hazards based-on Forbidden City archives is in line with the historical facts during the Qing dynasty.
Abstract: In order to apply the satellite and gauges rainfall datasets in hydrological simulation and forecasting, the TRMM PR 3B42 V6 product is evaluated by ground-based observation rainfall in alpine and gorge region of Jin-sha River Basin, which involves 3-hourly, daily and monthly temporal scales. Concretely, the linear regression analysis is used to analyze correlation of the two datasets. The empirical orthogonal function and singular value decomposition methods (EOF-SVD) are adapted to examining the spatial patterns of precipitation. The indices of relative deviation (Bias), false alarm ratio (RFA) and the probability of detection (PD) are applied to evaluating the accuracy of the satellite dataset. The results indicate that a significant linear correlation is derived between the two datasets at different spatiotemporal scales, but the correlation coefficient will be decreased with the reduction on temporal scales. Good consistency is achieved in the overall spatial patterns of precipitation, even though local discrepancies are found in high altitude and high- gradient areas. The TRMM 3B42 data are accurate about 36.08% within 10% of the station locations. The altitude shows certain influence on the indices of RFA and PD, which demonstrate increasing on RFA but decreasing on PD with elevation rising. Overall, the accuracy of TRMM 3B42 data declined with elevation rising; the periods rainfall error decreased with temporal scale increasing and the light rain have the greatest contribution to satellite deviation but the heavy rainfall is the second. These results suggest that merge and correction would be necessary when the satellite data are used for hydrological simulation and forecasting on finer temporal scales in similar investigation areas.
Abstract: Drought is considered one of the weather disasters that restrict the socioeconomic development in China. The Haihe River basin is a typical region suffering from droughts. Daily meteorological observations from 58 stations are selected for the current drought study. The data covers the period 1961-2010 and the stations are located in the basin and its surrounding areas. The accumulated relative moisture index and FSPAAM (Fuzzy and set pair analysis evaluation method) are used in the study, as they can take into account the accumulated effect of drought as well as the fuzziness boundary conditions and the distribution of objects being evaluated. The characteristics of spatial and temporal drought variations in the Haihe River basin are analyzed. Results show that ① the Haihe River basin is dominated by moderate drought and severe drought, respectively affecting 73 000 km and 77 800 km. The severe drought-affected area increases significantly over the past 50 years; ② during the period 1986-2010, there is a tendency for the expansion of severe drought-prone areas. The latter has gone up to 149 000 km2, which is 1.6 times higher than that of 1961-1985.
Abstract: In order to investigate the feasibility of using numerical simulation to assessing the effectiveness of vegetative filter strips (VFS), the vegetative filter strip hydrology and sediment transport model (VFSMOD) is applied to the Heihe River headwaters area. The effect of VFS' width and slop on the removal rate of sediments is estimated by VFSMOD, and the appropriate design is subsequently determined for a VFS system. The VFS effectiveness for the load reduction of nonpoint source pollution in a watershed is assessed with the linear relationship between the sum of total phosphorus (TP) and total nitrogen (TN), and sediments. The results show that a grass filter strip with width in the range of 3-5 m is advisable and the slop gradient should be less than 60. The reduction of sediments, TP and TN would be 21.7%, 12.4% and 14.3%, respectively, after the installation of VFSs on all sensitive riparian zones of the Heihe River headwaters area. The study demonstrates that VFS can play an important role in the water quality control for the Heihe River headwaters area.
Abstract: The objective of this study is to investigate the scale effect of net inflow water productivity and net irrigation water productivity in the winter wheat production in well-canal combined irrigation areas. To achieve this goal, the 2007-2009 growing season data of winter wheat from the Shijing Irrigation District are collected. The Hydrus-1D software package and the USGS MODFLOW model (Modular Three dimensional Finite-difference Ground-water Flow Model) are applied to calculate the water budgets across different spatial scales including the crop, the field, the sub-main canal, the main canal and the irrigation system. The results show that ① from the crop scale to the irrigation system scale, the net inflow water productivity and net irrigation water productivity will be reduced by 9.49% and 16.59% respectively due to the increase in water loss; ② the groundwater depth is so large that too little percolation could recharge the groundwater system for water reuse during the growing season of winter wheat. Thus, the net irrigation water productivity has a marginal advantage in water reusing over the traditional irrigation water productivity; ③ on a multi-year time scale, all the percolation could recharge the groundwater for water reuse, and the net inflow water productivity increases with spatial scales. Meanwhile, the net irrigation water productivities for different spatial scales could be improved between 37% and 65% on the basis of those at the winter wheat time scale.
Abstract: The renewability of groundwater has been a hot topic in the field of groundwater science and engineering in recent years. However, the definition of groundwater renewability has not been uniform, and the assessment indices are also relatively diverse, of which the groundwater renewal period, recharge rate, age and residence time are commonly used. The assessment results of groundwater renewability on the basis of those indices are usually inconsistence with each other. This is because different physical characteristics are considered in the establishment of those indices, though close relationships do exist between them. Based on a case study from Beijing, a comparison is done on the applicability of two closely related indices (renewal period and recharge rate) for assessing the groundwater renewability. The results show that: ① the different conclusions could be reached for the relative strength of groundwater renewability in Beijing's districts and counties depending on the assessment indices used; ② the conclusion with the groundwater recharge rate seems to be more stable compared to the other one; ③ the groundwater recharge rate has more important practical significance being an assessment index for groundwater renewability.
Abstract: The soil moisture dynamics in the root zone of plants is studied through model simulation and observations. The simulation is done with the stochastic model for soil moisture dynamics developed by Laio et al. (Laio model). The observation covers a range of elements including growing season soil moisture and daily precipitation in fixed dunes and sandy grasslands of Horqin Sand Land for the period 2006-2010. The relationship between the soil moisture dynamics and the precipitation pattern is also analyzed. The probabilistic density function (PDF, or p(s)) of soil moisture is estimated using the Laio model. A sensitivity analysis is performed for the 13 parameters of the model. Results show that: ① the seasonal distribution of precipitation appears to be very uneven in the study area. The precipitation amount between April and October can account for 93% of the annual total precipitation. Precipitation events of 5 mm or less contribute only 25% of the annual total precipitation, but can comprise 73% of the total events. 38% of dry periods (intervals between precipitation events) are 10 days or less, which can account for 87% of the total dry periods during a year; ② on fixed dunes and sandy grasslands, the root zone depth is between 0-10 cm and 0-70 cm, respectively. The value of root-zone soil moisture in sandy grasslands is significantly higher than that in fixed dunes. In both cases, the highest soil moisture occurs in July relative to other growing season months; ③ the values of root-zone soil moisture during growing seasons follow a normal distribution on both fixed dune and sandy grassland. The peak value, the position and the scope of p(s) obtained by the Laio model are in good agreement with observations, indicating the Laio model is able to estimate the p(s) of soil moisture in Horqin Sand Land; ④ the estimation of the peak value of p(s) is more sensitive to the 5 parameters of the Laio model, which are the arrival rate of rainfall events (λ), the mean rainfall depth (α), the average daily maximum evapotranspiration rate (Emax), the soil moisture level at which plants begin closing stomata (s*) and the permanent wilting point (sw).
Abstract: The issue of water shortage has become more evident in North China Plain. The groundwater is an important component of water resources in this area, so how to reasonably and accurately calculate groundwater recharge plays an important role in and protection of groundwater resources. In this paper, the bromide tracer method was used to study groundwater recharge in irrigation and non-irrigated areas which locate in Piedmont Aggraded Valley Plain and Median Plain of the North China Plain. The results showed that the average groundwater recharge is 126.10mm, and 0.1852 for average recharge coefficient. The recharge and recharge coefficient in irrigated areas are greater than non-irrigated areas. Meanwhile, the tracer migration depth, water content distribution, rainfall irrigation, groundwater level depth and other influencing factors were analyzed. Compared to the recharge coefficient adopted by other scholars who used the tracer to estimate groundwater recharge, the results of this study is reliable, and can provide reference and guidance to water resources analysis of the North China Plain.
Abstract: The flow and sediment regime downstream of the Three Gorges Reservoir has been changed dramatically after impoundment of the reservoir. The fluvial processes of downstream channel reaches can be affected as a result of the change. In order to simulate the morphological changes in a long river section, a 2-D and 3-D coupled model for turbulent flow and sediment transport as well as bank erosion is developed. A new coupler is proposed for coupling of the 2-D and 3-D models on the basis of mass conservation for flow and sediment transport. The coupled model is tested on a 60 km long section of the middle Yangtze River for the period from October 1996 to October 1998. The result shows that the coupled model simulates well the alluvial channel migration processes, which demonstrates that the coupled model is able to provide an effective method to investigating the morphological changes in response to the changes of flow and sediment regime in the Jingjiang segment of the middle Yangtze River.
Abstract: A tsunami can mobilize a substantial amount of coastal sediments and change the coastal morphology considerably. A comprehensive numerical model is developed with the capability of modeling tsunami waves, including the effect of sediment transport and morphological changes. The numerical model includes a set of fully nonlinear and weekly dispersive Boussinesq equations and the sediment transport and morphological evolution modules. The weighted essentially non-oscillatory scheme (WENO) is used for the spatial discretization of morphological bed level equations. The Lax-Wendroff scheme and forward time backward space (FTBS) scheme are compared with WENO. The numerical model is validated using the available laboratory experimental data such as Synolakis, Kobayashi and Young. The result shows that the numerical model is capable of resolving the solitary wave propagate, breaking, run-up, rundown and scouring processes on the beach. The numerical model could be useful for the study of sediment transport under tsunami waves.
Abstract: A novel scheme was proposed for identifying and extracting vortex structures from two-dimensional velocity fields. The new scheme involves no threshold values and requires a lower spatial resolution than velocity-gradient based methods. The scheme was used to analyze the characteristics of vortex structures based on two-dimensional velocity data measured with particle image velocimetry in a turbulent open channel flow. The educed parameters show that population density and vorticity of spanwise vortex decrease along the wall-normal direction while the radius tend to increase all the way. In addition, vortex strength represented by the circulation stabilizes after a quick increase in the inner region. Comparison demonstrates that population density of the prograde vortex is larger than that of the retrograde one and the prograde vortices exhibit stronger swirl motion. Conditionally averaged velocity fields of vortical structures statistically verify the existence of hairpin vortex packets and the spatial correlation of retrograde-prograde vortices in open channel turbulence.
Abstract: Unstructured grids are usually adopted in the solution of complex boundary flows. In this study, a depth-averaged two-dimensional (2-D) flow model is developed for mixed unstructured grids. The model uses both triangular cells and quadrilaterals, which ensures an accurate representation of irregular boundaries and at the same time, achieving a high computational efficiency. The unsteady term in the 2-D shallow water equations is treated implicitly. While the convection and diffusion terms are respectively approximated using the TVD (Total Variation Diminishing) algorithm and the auxiliary-point method. The depth-averaged standard k-ε model is used for turbulent closure. Two classical test cases are chosen for model verification. The first one is a 2-D diversion flow case, and the second is a 90 degree bend-flow case. Results show that the proposed model performs well in terms of accuracy and presents good convergence characteristics.
Abstract: Accurate determination of sand grain equivalent roughness is the key to calculate sand grain resistance. In this paper, fractal dimensions were used to describe self-similar complexity and irregularity of sand bed profile. The fractal expression of sand grain equivalent roughness was obtained based on a large number of sand grain resistance experiments, which include sediment-glued flat bed, initially flat stationary bed and armoring bed. The median size d50, fractal dimension D and Froude number Fr are introduced in the proposed expression along with corresponding validation, comparison and discussion of results. The results showed that the expression can comprehensively reflect how equivalent roughness of sand grain is influenced by external factors such as grain size, gradation composition, random arrangement and flow condition.
Abstract: As an important component of stream-subsurface exchange processes, lateral hyporheic exchange plays a crucial role in maintaining health of river and riparian ecosystems. In order to reveal the discipline of lateral hyporheic exchange induced by bank morphology, 10 runs of circulation flume experiments with idealized sinusoidal curved bank and 4 runs of comparison experiments with straight bank were conducted in varying flow conditions. The experimental results showed that the lateral hyporheic exchange also consisted of advection (pumping exchange), diffusion and micro-circulation, which was similar to the vertical hyporheic exchange. The increasing stream Reynolds Number Re intensified the effect of diffusion and micro-circulation. The presence of curved bank morphologies produced additional exchange under all flow conditions. With increasing bank amplitude and flow velocity, the pumping exchange (advective exchange) gradually became the main exchange pattern in the earth time of hyporheic exchange.
Abstract: An experimental study was conducted in an indoor soil tank, to examine low-temperature infiltration and movement through unsaturated soil in topsoil layer of riparian zone. Low-temperature water infiltration tests were carried out at three different heads in the filling fine sand. Infiltration process, moisture and temperature fields were continuously monitored and analyzed to study the impacts of the water head, the infiltration parameters, and moisture and temperature fields. Results showed that the higher the infiltration head, the greater is the vertical (horizontal) migration distance of the wetting front. The migration velocity of the vertical wetting front also gradually decreased with increasing infiltration time, and becoming more and more stability at the end. Infiltration rater had the larger fluctuations at the head of 5 cm and the settling time is greater than the head of 25 cm and 45 cm. The higher the infiltration head, the faster is the decreasing rate of average temperature before the temperature fields could go into a relatively steady status. At the head of 25 cm, infiltration of the low temperature water basically reached steady status after 420 min and the head of 45 cm is after 240 min.
Abstract: The research adopts phospholipid fatty acid analysis to quantify the microbial community structure of sediments from Yunliang River in different water types during different periods. The results show the following aspects: ① the microbial biomass is significantly different in different water-stage while the temperature is the dominant factor; ② in the same period, the nutritional content is positively correlated to the microbial biomass; ③ G+ indiated by 16:0 iso、17:0 anteiso、15:0 iso is the main microbial community that affects the sediments microbial community structure and water-stage fluctuation significantly influences the sediments microbial community structure; ④ Monounsaturated PLFAs/ branched PLFAs could reflect the nutrition status as microorganism would turn the monounsaturated PLFAs to cyclopropyl PLFAs and saturated PLFAs in order to suit the new conditions when C/N increased in sediment; ⑤ [c(i15:0)+c(i17:0)]/[c(a15:0)+c(a17:0)] can be used as the indicator of Carbon content in water environment.
Abstract: Secondary salinization and underground structures erosion usually occurs in reclaimed regions, especially in the climate conditions that annual evaporation is much larger than annual rainfall in north China. Based on a brief review of the status and trends of land reclamation, this paper summarized the evolution of groundwater system and soil environment, and analyzed the main reasons contributing to these problems. Comparison of the climate differences between humid areas and semiarid areas, it was pointed out that the key to soil salinity control in the semiarid region was to guide the law of nature by utilizing rainwater and flood resources to build a long-term leaching mechanism. Meanwhile, in order to rebuild and maintain a healthy and stable ecosystem in the reclaimed areas, it was critical to plan the structure of soil layers, enhance the salt leaching and plant the green vegetation according to the local conditions.
Abstract: Snowmelt erosion has occurred in our country and in many parts of the world. Its role in the destruction of topsoil is increasingly being recognized. On the basis of summarizing the research results, this paper analyzed the impacts of snow accumulation and snowmelt.The impacts include climate, elevation, topography, and land use and other factors. This paper pointed out that snowmelt runoff, surface soil thaw depth and weak soil erodibility in early spring are the special influence factors induced snowmelt erosion. Meanwhile, the article points out that snowmelt erosion research should be strengthened in three areas. First, freezing-thawing on soil moisture migration should be taken into account in snowmelt erosion prediction model. Second, not completely thawed layer on the surface soil moisture effects should have a deeper understanding. The third area, snowmelt process research on slope should be focused on solving the problem in the future snowmelt erosion study.