查看更多>>摘要：This paper analyses a fractional kinematic wave equation (fKWE) for overland flow and evaluates its solutions for applications using data from overland flow flumes with simulated rainfall in the laboratory. Solutions of fKWE presented have been derived for large time or when the Laplace transform variable s -> 0, which is one of the most important situations for overland flow. The solutions include expressions for the depth, velocity, and unit discharge, of overland flow. Fitting the approximate solution for the depth of overland flow to the data yields the values of the order of space-fractional derivatives, rho, which is around rho = 1.5. It is found that rho increases with the slope gradient and the rainfall intensity. The approximate order of rho = 1.5, which is about the average of order 1 for the advection equation and 2 for the diffusion equation, implies that diffusive mechanisms manifest in the overland flow. The findings mean that either an fKWE is used or a diffusion term is needed to account for dynamic forces in overland flow as the fKWE captures more physical mechanisms.
查看更多>>摘要：Karst plant habitats are generally harsh and vulnerable to climate and human interferences. Restoration of karst vegetation and its effect on water resources are affected not only by climate and anthropological interferences but also by different bedrock lithologies. In this study, changes to climatic factors, vegetation indices of the normalized difference vegetation index (NDVI), the leaf area index (LAI) and runoff during 1982-2015 were statistically identified over the Yangchang river basin (YRB) with two contrasting bedrock lithologies (carbonate rock and detrital rock) in southwest China. The Budyko equation and the hydrological model in LPJ (the LundPotsdam-Jena Dynamic Global Vegetation Model) were calibrated and improved to separate runoff change that could be attributed to climate and vegetation changes during 1982 - 2015. LPJ was used to predict the potential vegetation for natural recovery without human interference and its effect on the hydrological budget in YRB. Results reveal that the execution of the major ecological restoration project (the Grain for Green Project) in YRB since the early 2000 s has significantly increased NDVI and LAI even in the drier period of 2004 - 2015. However, the human effort of vegetation restoration only reaches about 25% of the potential capacity in the whole study area. The reforestation in YRB could decrease runoff by about 7.0 to 7.6% in the period from 2004 to 2015, and 11.2% in the future when vegetation shifts from artificial to natural vegetation recovery. Meanwhile, thick soil in the non-carbonate area can store more water to support a large proportion of forest, and raise drought resistance. However, the limited water holding capacity of weathered bedrock in the carbonate area restricts large tree growth, and thus reduces drought resistance. These results point a need for consideration of how bedrock geology influences available water limitations when designing suitable reforestation strategies in southwest China.
查看更多>>摘要：Transpiration, a key component of the hydrological cycle, contributes greatly to the climate system by transferring large amount of water from soils to the atmosphere. Its correct representation within Land Surface Schemes in climate models is crucial to provide accurate and reliable climate projections. In this study, transpiration simulated by the Canadian Land Surface Scheme (CLASS) was compared to long-term observations of sap flow measurements in two boreal forest sites of eastern Canada dominated by balsam fir and black spruce. In general, CLASS adequately models daily transpiration during the growing season for most of the years at both sites. During the tree rehydration period (preceding the growing season), modeled transpiration was greatly underestimated because of overestimating the duration of the snowpack, the latter restricting transpiration. Moreover, CLASS did not capture the impact of extreme events on tree physiology and maintained high transpiration rates during a heat stress and a drought. During both observed and simulated drought events, transpiration modeled using CLASS was overestimated, due to insensitivity to substantial decreases in soil water content; modeled transpiration being strictly controlled by atmospheric variables (vapour pressure deficit and radiations). Thus, we also proposed and implemented a new equation that was able to increase the sensitivity of CLASS to decreasing soil water content. However, this equation needs to be further tested on different sites and tree species.
查看更多>>摘要：Due to the increased frequency and magnitude of urban flooding events, there is a pressing need to improve the accuracy of numerical tools to better assess the hydraulic performance of new drainage systems. Nowadays, such models are inherently challenging to verify due to the difficulty of acquiring reliable data during the flood event, meaning that most models are calibrated using only an estimated measure of the extent of flooding. To address this gap, this study investigated flooding scenarios using an experimental scale facility of an urban street and manhole network, delivering a novel data-set in terms of the scale of the facility used. Several hydraulic conditions are investigated within a variety of street configurations incorporating parking slots, cars on the road and various locations of the manhole within the street. This enabled the quantification of flow exchange during hypothetical flood events for multiple cases, as well as the characterisation of energy losses, a crucial parameter that is often a source of uncertainty within numerical modelling tools. Furthermore, the experimental system was equipped with an injection system to replicate the transport of pollutants during flooding events, and this enabled the estimation of the exchange of soluble pollutants between the minor and major systems for each flooding scenario. Results obtained have confirmed the applicability of the orifice equation for the estimation of flow exchange between the two systems, showing that i) the discharge coefficients obtained (0.126-0.138) decrease as the width of the street/channel becomes narrower, ii) the surface energy loss coefficient was unaffected by all street configurations tested, iii) all tested geometries displayed significant pollutant exchange from the sewer to the street, in the range of 28-39%, demonstrating that situating the manhole closer to the edge of the street increased the mass of pollutants being exchanged to the surface and the presence of parking spaces alone did not appear to affect the mass of pollutant exchanged. These results have provided a novel series of datasets (including flowrates, flow exchange, energy losses and discharge coefficients) that could be used to calibrate and validate numerical models and be utilised as a benchmark.
Lu, YaoGao, YangDungait, Jennifer A. J.Jia, Junjie...
11页
查看更多>>摘要：On the Qinghai-Tibet Plateau (QTP), salinity, area, and altitude are the three main environmental gradients, and they are also likely to be the main influencing factors of lake water and carbon (C) sources. We collected water samples from lake and river systems on the QTP to determine their associative physical, chemical, biological, and isotopic indicators. Firstly, the ionic composition of individual lake systems on the QTP varied significantly, and evaporation was the main controlling factor respective to most of their chemical characteristics. Secondly, glacial meltwater (8%), rainwater (26%), soil water (28%), and the evaporation effect (38%) were the main controlling factors of lake water on the QTP. Atmospheric exchange (72%), soil organic matter (SOM) (1%), and rock weathering (19%) were the main dissolved inorganic carbon (DIC) sources of lake water on the QTP. Thirdly, salinity and altitude were the main influencing factors of lake water and C sources, especially salinity. Findings from this study are intended to supplement the knowledge base on C and water coupling effects in plateau lake systems while also improving our understanding on the response of inland lake systems to climate change globally.
查看更多>>摘要：The equilibrium of natural groundwater systems can be disrupted by excessive withdrawal. Accurate estimation of groundwater levels is needed to assess water-level fluctuations caused by groundwater withdrawal and seasonal distributions of precipitation. This study aims to estimate the next-month's groundwater levels using monthly real-world data that includes rainfall, electricity-estimated pumping volumes, and current groundwater levels invoking time-dependent spatial regression. The new approach involves state-estimation and changeestimation methods, which will be evaluated to determine the optimal model based on its root mean square error values. The response of estimated future (next-month's) groundwater levels within the alluvial fan in Changhua and Yunlin, Taiwan is based on monthly precipitation and pumping. This study yields a data-driven explanation of how water levels temporally and spatially respond to groundwater pumping and rainfall infiltration in different regions within the alluvial fan. Results indicate that the proximal fan yields the smallest response to decreased groundwater levels and subsequent increases in pumping. The effect of reducing groundwater levels is greater in the southern areas of the study site than in the northern areas. Water levels in the mid-fan and distal-fan in the southern area show a greater drawdown due to larger pumping volumes compared to the northern area.
查看更多>>摘要：Recession analysis of -dQ/dt similar to Q is popularly used for determining catchment storage-discharge relationship, estimating the aquifer hydraulic properties, and predicting low flow processes. However, there are uncertainties arising from the numerical approximation of -dQ/dt by the finite difference (Delta Q/Delta t) for individual recession and the fitting cloud-like data of -dQ/dt similar to Q for many recession events in a catchment. In this study, we proposed an improved variable time step increment method (IVTS) to minimize the effects of the noisy observations on estimating -dQ/dt, and a fitting method in terms of the binning-average of -dQ/dt similar to Q data points to determine the basin synthetic recession parameters. The proposed methods are validated by using numerical generation of recessions with different noises and recession behaviors and the observed hydrographs from twenty catchments in Huai River Basin in China. The results from our proposed method are compared with those from the other popularly used methods. The IVTS method is proven to be robust for approximation of -dQ/dt, which can significantly reduce errors of the estimated -dQ/dt and the recession slope (b). Combining with the IVTS method, the fitting method in terms of the binning average by splitting range of -dQ/dt, instead of Q, could overcome the shortage of traditional recession analysis methods that underestimate the recession slope. Our study indicates that the more accurate and reliable calculation of -dQ/dt similar to Q data and estimation of basin synthetic recession parameters could increase the objectivity in interpretation of recession behaviors and accuracy in perdition of low flow processes.
Reberski, Jasmina LukacTerzic, JosipMaurice, Louise D.Lapworth, Dan J....
15页
查看更多>>摘要：A quarter of the world's population uses groundwater from karst aquifers. A range of emerging organic contaminants (EOCs) are considered a potential threat to water resources and dependant ecosystems, and karst aquifers are the most vulnerable groundwater systems to anthropogenic pollution. This paper provides the first global compilation (based on 50 studies) of EOCs in karst aquifers and explores EOC occurrence and the use of EOCs to understand karst systems. Of the 144 compounds detected in the reviewed studies, the vast majority in karst groundwater are pharmaceuticals and pesticides. Maximum concentrations of compounds varied over five orders of magnitude, and nearly half of the detected compounds exceed 100 ng/L. Karst groundwater is shown to have lower frequency of detection and lower concentrations compared to surface waters and local shallow intergranular aquifers, but overall higher concentrations compared to other major aquifer types. A growing number of studies have demonstrated the utility of EOCs and some legacy compounds for groundwater quality assessment and as tracers for characterising karst systems. They can improve understanding of vulnerability, storage, attenuation mechanisms, and in some cases have been used to assist with catchment delineation. This is a growing research area for karst hydrogeology, and more research is needed to understand EOC contamination of karst aquifers, and to develop EOCs as tracers within karst to improve our understanding of this critical water resource.
查看更多>>摘要：The overwhelming increase and variations in the extreme rainfall events demand the use of a nonstationary Intensity-Duration-Frequency (IDF) curve for the design and management of water resource infrastructure. Generally, nonstationary IDF curves are developed by incorporating the trend in the distribution parameter using Generalized Extreme Value distribution (GEV) with time as a covariate. The physical processes influencing the variations in a hydrologic variable can be captured by utilizing relevant climatic variables (climate-informed) as covariates, since time alone cannot be the best covariate. Hence this study investigates the potential climateinformed covariates influencing the extreme rainfall and incorporates the best covariates to develop a realistic nonstationary IDF relationship. Unlike previous studies, a Time Sliding Window (TSW) approach is employed to detect the changing distribution parameters before performing Nonstationary Modeling (NSM). The proposed covariate based TSW-NSM is effectively used to construct IDF curves for seven major metropolitan cities of India. Several models are generated based on the detected changing parameters and combinations of covariates. Then, Bayesian Differential Evolutionary Monte Carlo (DE-MC) algorithm is employed to estimate the uncertainty bound of the nonstationary parameters, and the best model is chosen using the Deviance Information Criterion (DIC). The results reveal that the best covariate combinations for short duration events are dominated by local processes (i.e., Local temperature changes and diurnal temperature changes), whereas the same for longer duration events are dominated by the global processes (global warming, ENSO Modoki cycle, and IOD). However, the acceptable nonstationary models reveal that all the temperature-based covariates are capable of capturing the dynamic behavior. It is also observed that the local processes carry the signature of global processes. Finally, the return levels computed through the best nonstationary model show that the return periods are decreasing, and the short duration events have undergone drastic changes than the longer duration events. Thus, the results suggest that employing climate-informed covariates based nonstationary IDF curves is indispensable for devising long-term strategies to address the changing climate.
查看更多>>摘要：This study focuses upon development of a new filter, referred to as Gaussian-Han-Fan (GHF) filtering, and its application within a comprehensive procedure for estimating groundwater changes. The Canadian Prairies was the study area. Variations in groundwater were estimated by using 15 years of Gravity Recovery And Climate Experiment (GRACE) twin-satellite observations (April 2002 to June 2017). Surface water storage (sum of soil moisture, snow water equivalent, canopy water, and surface water bodies) was subtracted from reconstructed GRACE-based Terrestrial Water Storage (TWS) changes through GHF filtering. To estimate the required hydro-logical parameters, both the Global Land Data Assimilation System (GLDAS) and Water Global Hydrology Model (WGHM) were used and evaluated. Water level changes for major surface water bodies were estimated using satellite altimetry-based products. The monthly average of GWS variations over the Prairies ranged between-200 mm and +230 mm. A positive trend was found for both TWS and GWS variations, with the highest values in the region surrounding Hudson Bay, particularly in northern Manitoba (about 55 mm/year). Estimated GWS anomalies error was equivalent to about 10% of its absolute value, with a mean of 19 mm. GWS variations results were validated using 116 active in-situ groundwater level measurements in five different river basins (Peace-Athabasca, Churchill, North Saskatchewan, South Saskatchewan, Missouri), which were all located in Alberta (Canada). Good agreement was achieved in each river basin (correlation 55 mm). Regardless of hydrological system (GLDAS or WGHM), better statistical metrics were found when the average of the five basins was considered (r |0.90|, P < 10-4), with lowest errors (RMSE or UnRMSE < 30 mm).
NSTL
Elsevier