查看更多>>摘要：Water transfers have been implemented globally as important and effective ecological restoration tools over the last several decades. However, the periodic impacts of large-scale ecological water transport projects (EWTP) on ecohydrological systems have been neglected. In this study, wavelet analysis was used to evaluate the effect of flow regimes of EWTPs on the dynamics of ecohydrological systems through real data from a megaproject in the Tarim River basin, China. The results reveal that comparing with natural stream, the restoration flow exhibits seasonal periodicities in the winter instead of flood season, and exhibits unstable yearly period-icities. These characteristics created a distinct groundwater dynamics, which are not coincident with the growth rhythm of riparian vegetation. To optimize the EWTP, two designed flow schemes based on the time lags between flow and vegetation growth which was estimated using the wavelet analysis at seasonal and annual scales were proposed to improve the ecosystem restoration efficiency. The NARX network was used to predict the ecological restoration result. The predicting results show an up to 40% increase comparing to original restoration flow with the same total water volume. These results provide a new insight on ecohydrological system dynamics under EWTP from the periodic perspective, and also quantitatively prove that the designed flows based on wavelet analysis can improve ecosystem restoration efficiency in EWTPs. The methodologies used in this research are mathematical rigorous and can be widely applied to other EWTPs.
查看更多>>摘要：Scale-dependent and -independent error and performance measures are used to evaluate hydrologic forecasting and simulation models. However, these single-valued measures may not always provide a comprehensive assessment of model performance developed for a specific hydrologic process and application. A new frequency-based performance measure (FBPM) that can incorporate application-specific information for model evaluation is proposed to address the limitations of existing measures. FBPM is derived using a data classification scheme to partition the observed data into several classes and evaluate frequencies of each class's chronologically paired observed and forecasted values. A variant of FBPM, composite performance measure (CPM), is also developed to include additional indices that evaluate error, variance, and other statistical characteristics of the observed and forecasted series. Several univariate and multivariate data classification schemes are initially evaluated, and the best one is selected for use in the measures. FBPM and CPM are used to assess the performance of daily streamflow forecasting models developed for the Tapi River, India, using a data-driven model tree (MT) approach. The measures are also evaluated using two synthetic datasets representing different model forecast scenarios. A comprehensive evaluation of streamflow forecasts using FBPM and CPM with the best data classification scheme (i.e., geometric interval scheme in this work) indicates a better and more robust assessment of the forecasting model performance than that from existing error and performance measures. The traditional measures such as coefficient of determination, index of agreement, Nash Sutcliffe, and Kling Gupta efficiency have overestimated model performances compared to FBPM and CPM on an average by at least 100%. The traditional measures have also failed to identify inferior models mainly due to their inflated numerical values compared to those from FBPM and CPM. The measures developed in this study allow the user-specific definition of classes and assignment of weights to these classes based on the intended purpose of the hydrologic modeling effort. The FBPM and CPM are scale-independent, informative, interpretable, and outlier-resistant. These measures can be used for visual and/or statistical evaluation of the performance of single or multiple hydrologic simulation models.
Cheng, YifanNijssen, BartHoltgrieve, Gordon W.Olden, Julian D....
11页
查看更多>>摘要：Capturing the ecological effects of climate-induced shifts in hydrologic and thermal regimes in regulated river systems remains a challenge in regional-scale studies. In this study, we used a well-established species distribution model to analyze the results of a process-based hydrologic modeling approach that accounts explicitly for regulation impacts on river flow and temperatures. We also accounted for the stream network fragmentation resulting from dam blockage. This combined model framework can be used to predict historical environmental suitability of river reaches for specific fish species and estimate changes in suitability in response to changes in climate and reservoir operations. As a case study in the highly regulated and fragmented Tennessee River system, we examined the environmental suitability for nonnative rainbow trout (Oncorhynchus mykiss), a species of high recreational value, and native blackfin darter (Etheostoma nigripinne), an endemic species of unique ecological importance. To quantify the impacts of reservoir regulation, we examined the historical environmental suitability, climate change signals, and the environmental drivers of change between the regulated and unregulated model setups. By the end of the 21st century (2080s), historically suitable streams for rainbow trout will disappear due to higher river temperatures. Only 8% of historically suitable streams for blackfin darter will remain but over half of them will be unreachable by current populations due to dam blockage. For river reaches influenced by reservoir regulations, the regulated model projects decreasing environmental suitability for blackfin darter while the unregulated model projects the opposite because of higher river temperatures. The contradictory climate signals between regulated and unregulated models highlight the necessity of considering reservoir regulation.
Du, JianwenShi, XiaoqingMo, ShaoxingKang, Xueyuan...
12页
查看更多>>摘要：The optimization for surfactant-enhanced aquifer remediation (SEAR) of dense non-aqueous phase liquid (DNAPL)-contaminated aquifers is usually accompanied by uncertainties, which may arise from the characterization of complex aquifer heterogeneity and DNAPL source zone architecture (SZA) due to measurement sparsity. Optimization under uncertainty is computationally expensive as it involves an enormous number of model runs. The huge computational burden can be alleviated by utilizing a surrogate model for repeated model evaluations. However, most of the developed surrogates are often limited to low-dimensional optimization problems that only consider simplified aquifer heterogeneity. In this study, we developed a multi-objective simulation-optimization framework to optimize the SEAR schemes considering the characterization uncertainties from both highly heterogeneous aquifer permeability and complex SZA. A fast-to-run convolutional neural network (CNN)-based surrogate model was developed to approximate the high-dimensional and highly complex input-output mapping of the DNAPL multiphase flow simulation model. We first used the rejection sampling strategy to generate random realizations of permeability and SZA conditioning on their limited measurements and then formulated a multi-objective optimization under uncertainty problem based on these realizations. The developed 3-D CNN was trained and used as the surrogate for repeated model runs in optimization to identify the optimal SEAR schemes under uncertainty. A 3-D numerical experiment was used to test the performance of the CNN-based simulation-optimization framework. Comprehensive analysis on the obtained Pareto fronts demonstrates that the proposed framework can efficiently identify reliable Pareto-optimal solutions with a 99.8% speedup compared to the traditional optimization coupled with the forward model. Moreover, the optimization considering multiple realizations enables us to perform the risk assessment to locate the risk zone where the NAPL phase possibly exists after remediation, which provides useful information for decision-making.
查看更多>>摘要：River networks of deltas are complex systems, responsible for the transport of water, sediment and nutrients between land and sea. Topological complexity, dynamic complexity and flux vulnerability are three characteristics to describe the material transport within a deltaic river network, and they reflect the channel number and connectivity, flux distribution, and sensitivity of flux to external disturbances, respectively. Here, graph theory was applied to estimate the three characteristics of the Pearl River Delta (PRD) in 1977 and 2008, when the human-induced uneven riverbed downcutting occurred on a large scale. By identifying the channels through which water flows from the apex to each outlet, the eight subnetworks corresponding to the eight outlets were distinguished. Although the topological complexity changes little during this period, the dynamic complexity and vulnerability have great adjustments. The dynamic complexity greatly decreases in the subnetworks that have larger riverbed downcutting comparing to their adjacent subnetworks. We further reveal the positive relation between the decrease in dynamic complexity and human-induced riverbed downcutting under the same topological complexity. Moreover, the local vulnerabilities of channels with relatively high riverbed downcutting increase, leading to the emergence of "high vulnerability channels ". These findings suggest that the human induced uneven riverbed downcutting is the main reason for the adjustments of dynamic complexity and vulnerability. The results obtained from this study may provide scientific guidance for the further development and utilization in the PRD and other deltaic river systems worldwide subject to intensive human intervention.
Marques, Amanda CarneiroVeras, Carlos EduardoRodriguez, Daniel Andres
13页
查看更多>>摘要：Economic development alongside unsustained population growth are among the leading factors of hydrological depletion. Facing climate change impacts, long-term policy planning via scenario analysis is an essential tool to ensure water security. This investigation utilized an approach based on numerical model experiments and sustainability indexes to assess the impact of public policies for water resources management over a long-term horizon. Streamflow projections (2011-2099) from the hydrological model MHD-INPE (Distributed Hydrological Model - National Institute for Space Research) were evaluated as means to investigate water supply scenarios. Monthly flows were accounted into 30-year moving average intervals. Sustainability Indexes were then calculated to evaluate the performance of a water system as IPCC's Specific Warming Levels were reached. In this study, the contribution of public policies for water resources sustainability under climate change scenarios in the Paraiba do Sul river basin, which supports the water supply of the two major Brazilian metropolitan areas, were analyzed. Results indicated that the system will operate with more stress facing climate change impacts. Finally, the assessment of water availability scenarios is concluded to benefit decision-makers in incorporating adaptation measures, identifying uncertainties, and foreseeing potential effects of climate change.
查看更多>>摘要：Instream plants, which act as biological processors, have emerged as potentially advantageous eco-morphologic tools to be used in river management and restoration. Most of the study on the geomorphic role of vegetation as it interacts with flow and sediment has focused on local patch-scale dynamics. In this study, we present flume experiments aimed at improving our understanding of how vegetation patches link together to impact reach scale hydraulics and suspended sediment transport and disposition. On the hydraulics side, we investigate a) the relationship between the imposed instream vegetation configuration and water surface slopes, b) the secondary flow patterns which arise because of the imposed vegetative obstructions, and c) the role of vegetative resistance on residence time within reach. We also examine how different vegetation arrangements determine the patterns, quantity, and caliber of suspended sediment deposited in the flume. A key result of vegetation within the channel is the overall non-uniformity in flow conditions it imposes upstream, within, and downstream of the vegetated reach. At steady-state, vegetated patches locally increase the resistance, leading to a backwater condition upstream of the patch and high water-surface slopes within the patch. In general, this leads to enhanced deposition of suspended sediment upstream of the patch and reduced deposition within the patch relative to a case with no vegetation at all.
Alonso-Gonzalez, EstebanRevuelto, JesusFassnacht, Steven R.Lopez-Moreno, Juan Ignacio...
9页
查看更多>>摘要：The duration of the seasonal snowpack determines numerous aspects of the water cycle, ecology and the economy in cold and mountainous regions, and is a balance between the magnitude of accumulated snow and the rate of melt. The contribution of each component has not been well quantified under contrasting topography and climatological conditions although this may provide useful insights into how snow cover duration could respond to climate change. Here, we examined the contribution of the annual peak snow water equivalent (SWE) and the seasonal melt rate to define the duration of the snowpack over temperate mountains, using snow data for mountain areas with different climatological characteristics across the Iberian Peninsula. We used a daily snowpack database for the period 1980-2014 over Iberia to derive the seasonal peak SWE, melt rate and season snow cover duration. The influence of peak SWE and melt rates on seasonal snow cover duration was estimated using a stepwise linear model approach.The stepwise linear models showed high R-adjusted values (average R-adjusted = 0.7), without any clear dependence on the elevation or geographical location. In general, the peak SWE influenced the snow cover duration over all of the mountain areas analysed to a greater extent than the melt rates (89.1%, 89.2%, 81.6% 93.2% and 95.5% in the areas for the Cantabrian, Central, Iberian, Pyrenees and Sierra Nevada mountain ranges, respectively). At these colder sites, the melt season occurs mostly in the spring and tends to occur very fast. In contrast, the areas where the melt rates dominated snow cover duration were located systematically at lower elevations, due to the high interannual variability in the occurrence of annual peak SWE (in winter or early spring), yielding highly variable melt rates. However, in colder sites the melt season occurs mostly in spring and it is very fast in most of the years. The results highlight the control that the seasonal precipitation patterns, in combination with temperature, exert on the seasonal snow cover duration by influencing the peak SWE and suggest a future increased importance of melt rates as temperatures increase. Despite the high climatological variability of the Iberian mountain ranges, the results showed a consistent behaviour along the different mountain ranges, indicating that the methods and results may be transferrable to other temperate mountain areas of the world.
查看更多>>摘要：The water resources in the upper Awash basin in central Ethiopia are intensively utilized by the densely populated urban centers and extensive agricultural activities in the wide rift plains surrounding the major cities. The green, blue, grey and total water footprints of major crops dominantly cultivated in the sub-basin (teff, maize, sorghum and sugar cane) are characterized. The water footprints were analyzed for the period 2000 to 2010 using climatic as well as soil and crop yield data from the Debrezeit, Wonji, Melkassa and Metehara stations. The temporal and spatial variations of total water footprints (TWFs) in the basin were analyzed and mapped. The temporal trends of the Water Footprints (WFs) are interpreted using Mann-Kendall and Sen's slope tests. The crop production in the sub-basin mainly depends on green water consumption. Teff and sorghum crops in the climatically similar Debrezeit and Melkassa areas had relatively higher TWFs (4205 m(3)/ton and 2539 m(3)/ ton, respectively) compared to maize. Blue water requirement to supplement rainfed agriculture decreases from Metehara, Melkassa, Wonji to Debrezeit in that order. The TWF of irrigated sugarcane (117-212 m(3)/ton) is less than those of rainfed crops such as maize which has a minimum TWF of 1752 m(3)/ton. The spatial and temporal variations in WFs in the sub-basin are determined by both climatic (effective rainfall, evapotranspiration, length of wet spell and length of growing period) and non-climatic parameters (such as fertilizer consumption, soil types, crop yields and agricultural management practices). Our results suggest cultivating less water-intensive, high-yield crops can significantly decrease the TWFs in the sub-basin. The results could be used to develop well-informed regional and national freshwater resource management policies. More broadly, our novel approach of characterizing WFs at the sub-basin scale using limited amount of locally measured data sets could be a useful tool in other parts of the world where locally measured data sets are scarce.
查看更多>>摘要：The northeastern Tibetan Plateau (NETP), bordering the endorheic lake basins and the Upper Yellow River region, has been disturbed by increasing human activities in recent years. The NETP water storage changes could be a combined effect of climate variability/change and human activities (e.g., reservoir operation). However, whether the human activities have evidently altered hydrological processes and become key drivers of total terrestrial water storage (TWS) changes in the NETP remains unclear. To explore the roles of human interventions in changing surface water storage (SWS) and thus influencing regional TWS changes in the NETP, in comparison with natural drivers, this study quantitatively disaggregated and compared the contributions of TWS changes from climate-dominated natural lakes and man-regulated reservoirs at different timescales. Time series of Gravity Recovery and Climate Experiment (GRACE) TWS anomalies (TWSA) exhibited an overall upward trend (0.78 +/- 0.06 Gt/yr, p < 0.01) with evident periodic fluctuations from April 2002 to August 2020. Although the GRACE TWSA was more substantially influenced by changes in natural lake water storage (0.96 +/- 0.02 Gt/ yr) rather than reservoirs (0.54 +/- 0.04 Gt/yr) in the long-term trend, the man-regulated reservoir water storage changes can significantly dominate the GRACE TWSA on interannual and intra-annual timescales, especially in the second sub-period (2013.01-2017.06; GRACE TWSA change rate:-1.82 +/- 0.29 Gt/yr, p < 0.01, in comparison with the change rate of reservoir water storage of-1.28 +/- 0.17 Gt/yr, and the natural lakes of 0.72 +/- 0.07 Gt/yr). In some abnormal years, the reservoir storage changes were even close to the overall signal of region-wide GRACE TWSA. In addition, the increase in soil moisture storage (long-term linear trend: 0.65 +/- 0.06 Gt/yr, p < 0.01) was also a key factor that cannot be neglected. Our results suggest that human activities are becoming one of the key factors influencing TWS changes in the NETP.
NSTL
Elsevier