Evaluation of Using Remote Sensing Evapotranspiration Data in SWAT

This study applied a time series evapotranspiration (ET) data derived from the remote sensing to evaluate Soil and Water Assessment Tool (SWAT) model calibration, which is a unique method. The SWAT hydrologic model utilized monthly stream flow data from two US Geological Survey (USGS) stations within the Big Sunflower River Watershed (BSRW) in Northwestern, Mississippi. Surface energy balance algorithm for land (SEBAL), which utilized MODerate Resolution Imaging Spectro-radiometer (MODIS) to generate monthly ET time series data images were evaluated with the SWAT model. The SWAT hydrological model was calibrated and validated using monthly stream flow data with the default, flow only, ET only, and flow-ET modeling scenarios. The flow only and ET only modeling scenarios showed equally good model performances with the coefficient of determination (R²) and Nash Sutcliffe Efficiency (NSE) from 0.71 to 0.86 followed by flow-ET only scenario with the R² and NSE from 0.66 to 0.83, and default scenario with R² and NSE from 0.39 to 0.78 during model calibration and validation at Merigold and Sunflower gage stations within the watershed. The SWAT model over-predicted ET when compared with the Modis-based ET. The ET-based ET had the closest ET prediction (~8% over-prediction) as followed by flow-ET-based ET (~16%), default-based ET (~27%) and flow-based ET (~47%). The ET-based modeling scenario demonstrated consistently good model performance on streamflow and ET simulation in this study. The results of this study demonstrated use of Modis-based remote sensing data to evaluate the SWAT model streamflow and ET calibration and validation, which can be applied in watersheds with the lack of meteorological data.     

Simulating streamflow and water table depth with a coupled hydrological model

A coupled model integrating MODFLOW and TOPNET with the models interacting through the exchange of recharge and baseflow and river-aquifer interactions was developed and applied to the Big Darby Watershed in Ohio,USA.Calibration and validation results show that there is generally good agreement between measured streamflow and simulated results from the coupled model.At two gauging stations,average goodness of fit(R2),percent bias(PB),and Nash Sutcliffe efficiency(ENS)values of 0.83,11.15%,and 0.83,respectively,were obtained for simulation of streamflow during calibration,and values of 0.84,8.75%,and 0.85,respectively,were obtained for validation.The simulated water table depths yielded average R2 values of 0.77and 0.76 for calibration and validation,respectively.The good match between measured and simulated streamflows and water table depths demonstrates that the model is capable of adequately simulating streamflows and water table depths in the watershed and also capturing the influence of spatial and temporal variation in recharge.     

Separation of the Impact of Landuse/Landcover Change and Climate Change on Runoff in the Upstream Area of the Yangtze River,China

Landuse/landcover change (LULCC) and climate change (CC) impacts on streamflow in high elevated catchments are very important for sustainable management of water resources and ecological developments. In this research, a statistical technique was used in combination with the Soil and Water Assessment Tool (SWAT) to the Upstream Area of the Yangtze River (UAYR). Different performance criteria (e.g., R², NSE, and PBIAS) were used to evaluate the acceptability of the model simulation results. The model provided satisfactory results for monthly simulations in the calibration (R²; 0.80, NSE; 0.78 and PBIAS; 22.3%) and the validation period (R²; 0.89, NSE; 0.75 and PBIAS; 19.1%). Major landuse/landcover transformations from 1990 to 2005 have occurred from low grassland to medium grassland (2%) and wetlands (0.9%), bare land to medium grassland (0.2%), glaciers to wetland (16.8%), and high grassland to medium grassland (5.8%). The results show that there is an increase in average annual runoff at the Zhimenda station in UAYR by 15 mm of, which approximately 98% is caused by climate change and only 2% by landuse/landcover change. The changes evapotranspiration are larger due to climate change as compared to landuse/landcover change, particularly from August to October. Precipitation and temperature have increased during these months. On the contrary, there has been a decrease in evapotranspiration and runoff from October to March which depicts the intra-annual variations in the vegetation in the study area.

     

Effects of Land-Use and Climate Change on Hydrological Processes in the Upstream of Huai River, China

Land use/land cover and climate change can significantly alter water cycle at local and regional scales. Xixian Watershed, an important agricultural area in the upper reach of the Huaihe River, has undergone a dramatic change of cultivation style, and consequently substantial land use change, during the past three decades. A marked increase in temperature was also observed. A significant monotonic increasing trend of annual temperature was observed, while annual rainfall did not change significantly. To better support decision making and policy analysis relevant to land management under climate change, it is important to separate and quantify the effect of each factor on water availability. We used the Soil and Water Assessment Tool (SWAT), a physically based distributed hydrologic model, to assess the impact of Land use and climate changes separately. The SWAT model was calibrated and validated for monthly streamflow. Nash-Sutcliff efficiency (NSE), percentage bias (PBIAS), and coefficient of determination (R ²) were 0.90, 6.3 %, and 0.91 for calibration period and 0.91, 6.9 %, and 0.911 for validation period, respectively. To assess the separate effect of land use and climate change, we simulated streamflow under four scenarios with different combinations of two-period climate data and land use maps. The joint effect of land use and climate change increased surface flow, evapotranspiration, and streamflow. Climate variability increased the surface water and stream-flow and decreased actual evapotranspiration; and land use change played a counteractive role. Climate variability played a dominant role in this watershed. The differentiated impacts of land-use/climate variabilities on hydrological processes revealed that the unapparent change in stream-flow is implicitly because the effects of climate variability on hydrological processes were offset by the effects of land use change.     

Establishing a Multi-scale Stream Gaging Network in the Whitewater River Basin,Kansas, USA

Investigating the routing of streamflow through a large drainage basin requires the determination of discharge at numerous locations in the channel network. Establishing a dense network of stream gages using conventional methods is both cost-prohibitive and functionally impractical for many research projects. We employ herein a previously tested, fluid-mechanically based model for generating rating curves to establish a stream gaging network in the Whitewater River basin in south-central Kansas. The model was developed for the type of channels typically found in this watershed, meaning that it is designed to handle deep, narrow geomorphically stable channels with irregular planforms, and can model overbank flow over a vegetated floodplain. We applied the model to ten previously ungaged stream reaches in the basin, ranging from third- to sixth-order channels. At each site, detailed field measurements of the channel and floodplain morphology, bed and bank roughness, and vegetation characteristics were used to quantify the roughness for a range of flow stages, from low flow to overbank flooding. Rating curves that relate stage to discharge were developed for all ten sites. Both fieldwork and modeling were completed in less than 2 years during an anomalously dry period in the region, which underscores an advantage of using theoretically based (as opposed to empirically based) discharge estimation techniques.     

目标函数对滦河流域SWAT模型径流模拟不确定性的影响

针对水文模型参数和径流模拟结果不确定性问题,选取2Nash-Sutcliffe效率系数(NSE)、改进的决定系数(R_m²)、相对误差(PBIAS)、Kling-Gupta效率系数(KGE)4种目标函数,对构建的滦河流域潘家口水库上游SWAT模型进行参数率定及验证,分析了不同目标函数下模型参数的敏感性差异及径流模拟的不确定性。结果表明：参数敏感性会随迭代次数增加和抽样范围变化发生改变,不同目标函数下率定的参数范围和最优值显著不同;NSE和KGE作为目标函数在各站点径流模拟中更稳健,分别表现出较高的模拟精度和较低的模拟不确定性。     

Assessing the Hydrological Response of Ayamama Watershed from Urbanization Predicted under Various Landuse Policy Scenarios

This study investigated the effects of urbanization predicted using the SLEUTH urban growth model (an acronym taken from Slope, Landuse, Exclusion, Urban extent, Transportation and Hillshade) under four landuse policy scenarios on the hydrological response of Ayamama watershed using the Hydrologic Engineering Center Release 1 (HEC-1) hydrological model. The SLEUTH model was calibrated based on the Brute Force Monte Carlo iteration technique using the urban extents of Istanbul in 1987, 2000, 2009 and 2013 and was verified by considering Kappa coefficient as evaluation criteria. HEC-1 was calibrated and verified using observed rainfall-runoff event and based on the coefficient of determination (R²), Nash-Sutcliffe coefficient of efficiency (CE) and percentage of bias (PBIAS) as performance indicators. The urbanization prediction results showed that the urban extent of Ayamama watershed would reach 50.3 km², 44 km², 63 km² and 60 km² under Scenarios 1, 2, 3 and 4, respectively, in 2050. The hydrological simulation results under these urban extents showed that the urban extent of Ayamama watershed under Scenario-3, a scenario that allows unrestricted growth with the implementation of Project Canal Istanbul (PCI), resulted in the highest peak discharge and the shortest time to peak. Such an increase in the peak discharge and reduction in the time to peak will increase the risk of flooding and, therefore, extreme care needs to be taken before and during the implementation of PCI.     

Evaluating the SWAT Model for Hydrological Modeling in the Xixian Watershed and a Comparison with the XAJ Model

Already declining water availability in Huaihe River, the 6th largest river in China, is further stressed by climate change and intense human activities. There is a pressing need for a watershed model to better understand the interaction between land use activities and hydrologic processes and to support sustainable water use planning. In this study, we evaluated the performance of SWAT for hydrologic modeling in the Xixian River Basin, located at the headwaters of the Huaihe River, and compared its performance with the Xinanjiang (XAJ) model that has been widely used in China. Due to the lack of publicly available data, emphasis has been put on geospatial data collection and processing, especially on developing land use-land cover maps for the study area based on ground-truth information sampling. Ten-year daily runoff data (1987?C1996) from four stream stations were used to calibrate SWAT and XAJ. Daily runoff data from the same four stations were applied to validate model performance from 1997 to 2005. The results show that both SWAT and XAJ perform well in the Xixian River Basin, with percentage of bias (PBIAS) less than 15%, Nash-Sutcliffe efficiency (NSE) larger than 0.69 and coefficient of determination (R²) larger than 0.72 for both calibration and validation periods at the four stream stations. Both SWAT and XAJ can reasonably simulate surface runoff and baseflow contributions. Comparison between SWAT and XAJ shows that model performances are comparable for hydrologic modeling. For the purposes of flood forecasting and runoff simulation, XAJ requires minimum input data preparation and is preferred to SWAT. The complex, processes-based SWAT can simultaneously simulate water quantity and quality and evaluate the effects of land use change and human activities, which makes it preferable for sustainable water resource management in the Xixian watershed where agricultural activities are intensive.     

Development of a New Integrated Framework for Improved Rainfall-Runoff Modeling under Climate Variability and Human Activities

The relationship between rainfall and runoff is a complex phenomenon and understanding the physical processes, hydrological components and their impacts on response of watershed to precipitation is one of the challenging issues in watershed hydrology and planning. There is still a need to improve conceptual hydrological models in water scarce regions, such as Iran mainly because in many cases there is not enough data to fully describe this phenomenon. In this research, we aimed to present an improved and parsimonious framework that increases the performance of a conceptual model in water balance and discharge modeling for Delichay watershed located in Hablehroud basin, Iran as one of the main source of water supply for downstream fertile agricultural areas that produce a considerable amount of cereals and play a major role for food and water security of the region. In areas where data for water cycle components are not available or limited, it is recommended to use parsimonious approach in order to have an acceptable level of understanding of the system with minimum possible predictor variables. The Salas model used in current research to model water balance over the period 1983–2012 and evaluation of the results indicated an unsatisfactory performance when the entire period was modeled altogether (NSE?=?0.35, d?=?0.70, R²?=?0.63, RSR?=?0.80, PBIAS?=?4.96 and RMSE?=?41.87). A key reason is that this watershed is intensively impacted by human activities and homogeneity analysis confirmed a sudden shift in runoff data during 1998–1999. Such a sudden shift reveals the role of human activities impacts on the watershed with a total reduction of 58 mm of runoff per year while the climate variability has not occurred in the region. Thus, the entire period (i.e. 1983–2012) was divided into two homogenous sub-periods of before and after the change point (i.e., pre-change and post-change periods). The results indicated that modeling performance in the sub-periods improved (e.g. the NSE was 0.77 and 0.66 for pre-change and post-change, respectively, vs. 0.35 for entire period). Meanwhile, it is revealed that water balance affected by human activities over the time and application of historical data for water balance modeling cannot be reliable without considering the homogeneous data. Since, many watersheds in the world have been affected by human activities or climate variability, it is recommended to consider the homogeneity of observed data before any application.

     

Rainfall-runoff Modeling in a Watershed Scale Using an Object Oriented Approach Based on the Concepts of System Dynamics

Relying on a linear causal thinking, most of the hydrological models fail to incorporate socio-economic characteristics of a watershed with hydrological and environmental attributes. Based on a systems thinking philosophy, the paper aims to adopt an Object-Oriented (OO) approach based on the concepts of System Dynamics (SD) such as stocks and flows to analyze the dynamics in a hydrological system in a watershed scale. Object-Oriented modeling is a way to organize data into discrete, recognizable entities called objects. These objects could be concrete (such as a river reach) or conceptual (such as a policy decision). In the present paper, VENSIM PLE has been used for the modeling purpose. The application was illustrated in an Iranian watershed. The model was examined using validity and verifying tests. The results showed that the model is capable of generating the monthly runoff quite well. The values of R² are 0.69 and 0.61 for generated discharge values at Polchehr and Doab stations respectively. Also the values of NSE are 0.66 and 0.64 for estimated discharge values at the same stations. The capability of model was more clarified comparing R² and NSE coefficients obtained by a SWAT model with those obtained by Watershed Hydrological Model developed in this study.     

基于相似流域法的SWAT模型模拟黄河中游无资料地区径流

选用黄河中游两个小流域,基于相似流域法探求分布式水文模型SWAT在黄河中游小流域无资料地区径流模拟的适用性。通过距离、流域面积相近及属性相似的方法,用已知流域率定参数移植到无资料流域进行径流模拟。选取2009-2013年的日径流与月径流进行模型率定,以效率系数(NS)和决定系数(R2)为评价指标,率定出4个模型敏感系数,并用2014-2016年的日径流与月径流进行模型验证。结果显示:率定期月径流模拟的R2为0. 76,NS为0. 70;日径流模拟的R2为0. 70,NS为0. 64;验证期月径流模拟的R2为0. 82,NS为0. 74;日径流模拟的R2为0. 78,NS为0. 68。说明基于相似流域法的SWAT模型对于无资料的小流域月径流量模拟具有很好的适用性。     

基于最小二乘法的鄱阳湖水位流量关系研究

为了进一步揭示鄱阳湖与长江及其流域来水之间的"江河湖"关系,选取鄱阳湖湖口水文站作为研究对象,以三峡工程的蓄水时间(2003)为分界点,应用最小二乘法对其1978-2007年的水文数据序列(逐月平均水位与月平均流量)进行线性、多项式(三次曲线)拟合及其对数拟合,根据建立拟合曲线的判断系数R2大小选出最优的鄱阳湖水位流量关系拟合曲线,并对影响3种曲线拟合精度的影响因素进行探讨,最后对湖口水文站年均水位及年平均流量变化趋势进行分析。研究结果表明:2003年前后,鄱阳湖湖口水文站水位流量关系拟合曲线均以三次曲线拟合精度为最高,以对数拟合精度为最低;湖口水文站历年年均水位呈现下降趋势,而年平均流量则呈现上升趋势,年均水位和年平均流量最大值均出现在1998年,最小值则分别出现在2006和1979年。研究结果能够为鄱阳湖湖区水资源合理利用与水环境安全保护提供一定的参考依据。     

Hydrological Simulation in a Forest Dominated Watershed in Himalayan Region using SWAT Model

The present study is taken up to test the suitability of SWAT (Soil and Water Assessment Tool) model for estimation of runoff and to understand sensitiveness of model input parameters in a predominantly forested watershed in Kumaun region of Himalaya. The study area Dabka is a small watershed (69.41 km²) lies in North West of Nainital in Uttarakhand. The SWAT is calibrated at an upstream intermediate gauging site Bagjhala draining approximately an area of 65.78 km² on monthly basis due to non-availability of observed data at main outlet. A local sensitivity analysis is performed on 13 input variables in terms of model outputs such as water yield, surface runoff and baseflow to gain in depth understanding of the role of different model parameters for their proper selection. The study concluded that model performed well with Root Mean Square Error (RMSE) value 0.242 for calibration and 0.81 for validation. Nash Sutcliffe Efficiency (NSE) for calibration and validation period is obtained as 0.77 and 0.73 respectively whereas Coefficient of determination (R²) for calibration and validation period is 0.86 and 0.90 indicating good model performance. The most sensitive model parameters affecting water yield are CN2, GWQMN and SOL_Z. On the basis of sensitiveness of model parameters, the ranking of most sensitive parameters from highest sensitive to relatively lesser sensitiveness on stream flow are CN2, SOL_K and SOL_AWC whereas for base flow SOL_AWC, SOL_Z and GWQMN are found to be more sensitive followed by CN2, ESCO and SOL_K.     

Short-Term Predictions of Hydrological Events on an Urbanized Watershed Using Supervised Classification

Many tasks of operational watershed management at the local level require stream flow predictions delivered to decision makers in a timely manner. In highly urbanized watersheds with an impermeable surface, stormwater runoff can cause rapid increases in water levels in streams leading to flood and even flash flood events. Usually, such rapid increases in water flow characteristics are predicted by process-based models with high levels of uncertainty. In this study, the prediction of magnitudes of the stream hydrological characteristics is replaced by the forecasting of an event (i.e., flood or no-flood) using data collected by stream and rain gauges at the watershed. The proposed approach is based on a black box model developed as an ensemble of classifiers generated by independent inducers to predict the class of a future hydrological event in a small highly urbanized watershed. Eight inducers were investigated in the phase space reconstructed from observation data using time-delay embedding extended to multiple observation sites. Five inducers were selected for the ensemble, where the final decision is made by majority vote. The developed model generates 45-minute and hourly predictions of high-flow events with more than 80 % precision – a threshold used in operational flood management. Model site-specific parameterization is replaced by the training step using observation data on water levels and precipitation which are collected at 15-minute intervals and are readily available. The proposed approach to developing a prediction tool can be used by local authorities as one of the methods for flood management.     

Modeling and Simulation of Baseflow to Drainage Ditches During Low-flow Periods

Quantification of baseflow to drainage ditches is essential in understanding flow dynamics in a watershed. The mass balance estimation for a stream section may not give an accurate measure of the baseflow during low-flow periods due to the lack of accuracy in flow measurements in the flumes. Modeling may be useful for estimation of baseflow during low-flow periods. In this study, numerical and analytical solutions of the Boussinesq equation were used to simulate baseflow rates during low-flow periods in two watersheds, namely the Big Ditch watershed and the Upper Embarras River watershed in Illinois, USA. Additionally, MODFLOW was also used to simulate baseflow for these periods. At each site, a stream section of 200 m was selected for baseflow simulation and six observation wells were installed at one bank of each stream section for model calibration. A total of seven low-flow periods were considered for baseflow simulation. The mean baseflow rates simulated by the numerical model were higher than that simulated by the other two models. There is no significant difference between the mean baseflow rates simulated by the analytical model and MODFLOW. It was observed that proper estimation and/or measurement of model parameters were necessary for simulation of reliable baseflow rates. Since flow measurements during low-flow periods may include possible errors, the model results might also be acceptable for all practical purpose.     

Estimation of Design Flood Hydrograph for an Ungauged Watershed

Based on the physiographical features of the studied watershed of 102.5 km² in northern Ontario and the meteorological data of one nearby climatic station, through the combination of the regionalization of flood and the HEC-1 modeling, this article presents an approach that may be used to determine the desired peak flows for the ungauged watershed. The empirical equations used to determine the desired peak flows were developed by the Cumming Cockburn Ltd. (CCL) who has carried out the studies on flood regionalization by using flow data at 380 gauging stations in Ontario. CCL has proposed four methods to estimate peak flows, namely 1) regression method describing multiple linear relationships between flood flow and related parameters; 2) index flood frequency curve; 3) regional flood frequency curve and 4) isoline map for unit peak flow. The desired peak flows for studied watershed determined by CCL methods were used to calibrate the HEC-1 model for the rainfall-runoff simulation for this watershed which consists of 15 subwatersheds. Through slight adjustment in the CN number used in the HEC-1 model, the calibrated HEC-1 model could be used for rainfall-runoff simulation for this ungauged watershed. This approach could be recommended for hydrological design and watershed management for ungauged watersheds provided the analyses of flood regionalization could be conducted. In addition, comparing to the Bavaria forest region, Germany, some questions have been discussed in this article.     

基于信息熵对新安江水文模型参数及预报结果不确定性的量化分析

将GLUE方法与信息熵结合,分析新安江水文模型参数及预报结果的不确定性。首先用信息熵公式初步判断参数的敏感程度,根据GLUE方法求出90％置信度下流量的不确定范围;其次应用信息熵和U不确定公式共同量化分析模型预报结果的不确定性。以资水水系的新宁站集水区为研究区域,得出结论：①GLUE方法能够用来分析新安江水文模型参数的不确定性;②信息熵公式能够初步判断模型参数的敏感程度;③模型预报结果的不确定性随着实测资料的增加而降低。     

An automatic parameter calibration method for the SWAT model in runoff simulation

Runoff simulation is highly significant for hydrological monitoring, flood peak simulation, water resource management, and basin protection. Runoff simulation by distributed hydrological models, such as the soil and water assessment tool (SWAT) model which is the most widely used, is becoming a hotspot for hydrological forecasting research. However, parameter calibration is inefficient and inaccurate for the SWAT model. An automatic parameter calibration (APC) method of the SWAT model was developed by hybrid of the genetic algorithm (GA) and particle swarm optimization (PSO). Multi‐station and multi‐period runoff simulation and accuracy analysis were conducted in the basin of the Zhangjiang River on the basis of this hybrid algorithm. For example, in the Yaoxiaba Station, the calibration results produced an R² of 0.87 and Nash Sutcliffe efficiency (NSE) index of 0.85, while verification results revealed an R² of 0.83 and NSE of 0.83. Results of this study show that the proposed method can effectively improve the efficiency and simulation accuracy of the model parameters. It can be concluded that the feasibility and applicability of GA‐PSO as an APC method for the SWAT model were confirmed via case studies. The proposed method can provide theoretical guidance for many hydrological research fields, such as hydrological simulation, flood prevention, and forecasting.     

空间均化水文模型及其验证

本文基于空间均化方法构建了空间均化水文模型SAHM.该模型采用基于空间均化方法建立的宏观尺度水文控制方程描述了计算单元内入渗、壤中流和坡面汇流等基本水文过程,在方程中直接包含了土壤饱和导水率和微地形的空间非均匀性,使SAHM在保持传统"点"尺度方程机理性的同时从理论上避免了方程适用尺度和模型应用尺度的不匹配问题.模型在半干旱半湿润的沁河流域上游进行了验证,并对模型参数敏感性进行了分析,结果 表明,模型具有较高的计算精度和计算效率,可用于大中尺度流域水文模拟、水资源评价和洪水预报.     

珠江梧州水文站枯季月径流预报

梧州站流量作为珠江下游河口地区压咸控制流量,其上游来水的丰枯直接关系到珠江流域枯季水量统一调度的成功实施。基于梧州站枯季(10月-3月)月径流资料,采用逐步回归法提取径流序列的趋势项、周期项,自回归方法预测随机项的组合预测方法建立了梧州站枯季径流预报模型。结果表明:逐步回归与自回归组合的方法在径流预报中取得了较好的预报效果,1月径流预报精度达到甲等,10月、11月、12月、2月以及3月预报精度均达到乙等,可用于实际水文预报工作中。