Long Term Soil and Water Assessment Tool (SWAT) Calibration from an Ecohydrology Perspective

The performance on prediction by mathematical models which represent the conceived image of a system such as hydrology is oftentimes represented through calibration and verification processes. Oftentimes a best fit between observed and predicted flows is obtained through correlation coefficient (R2) and the Nash Sutcliffe model efficiency (NSE) by minimizing the average Root Mean Square Error (RMSE) of the observed versus simulated flows. However, these days, a new paradigm is emerging wherein accounting for the flow variability for the protection of freshwater biodiversity and maintenance of goods and services that rivers provide is paramount. Therefore, from an ecohydrology perspective, it is not clear if the existing method of model calibration meets the needs of the riverine ecosystem at its best. Thus, this study investigates and proposes a methodology using entropy theory to gage the calibration of Soil and Water Assessment Tool (SWAT) from an ecohydrology perspective characterized by the natural flow-regime paradigm: Indicators of Hydrologic Alteration.

Integrated Hydrological Modeling of the Godavari River Basin in Maharashtra Using the SWAT Model: Streamflow Simulation and Analysis

Hydrological modeling plays a crucial role in efficiently managing water resources and understanding the hydrologic behavior of watersheds. This study aims to simulate daily streamflow in the Godavari River Basin in Maharashtra using the Soil and Water Assessment Tool (SWAT). SWAT is a process-based hydrological model used to predict water balance components, sediment levels, and nutrient contamination. In this research, we used integrated remote sensing and GIS data, including Digital Elevation Models (DEM), land use and land cover (LULC) maps, soil maps, and observed precipitation and temperature data, as input for developing the SWAT model to assess surface runoff in this large river basin. The Godavari River Basin under study was divided into 25 sub-basins, comprising 151 hydrological response units categorized by unique land cover, soil, and slope characteristics using the SWAT model. The model was calibrated and validated against observed runoff data for two time periods: 2003-2006 and 2007-2010 respectively. Model performance was assessed using the Nash-Sutcliffe efficiency (NSE) and the coefficient of determination (R2). The results show the effectiveness of the SWAT2012 model, with R2 value of 0.84 during calibration and 0.86 during validation. NSE values also ranged from 0.84 during calibration to 0.85 during validation. These findings enhance our understanding of surface runoff dynamics in the Godavari River Basin under study and highlight the suit-ability of the SWAT model for this region.

Combining CLUE-S and SWAT Models to Forecast Land Use Change and Non-point Source Pollution Impact at a Watershed Scale in Liaoning Province, China

Non-point source(NPS) pollution has become a major source of water pollution. A combination of models would provide the necessary direction and approaches designed to control NPS pollution through land use planning. In this study, NPS pollution load was simulated in urban planning, historic trends and ecological protection land use scenarios based on the Conversion of Land Use and its Effect at Small regional extent(CLUE-S) and Soil and Water Assessment Tool(SWAT) models applied to Hunhe-Taizi River Watershed, Liaoning Province, China. Total nitrogen(TN) and total phosphorus(TP) were chosen as NPS pollution indices. The results of models validation showed that CLUE-S and SWAT models were suitable in the study area. NPS pollution mainly came from dry farmland, paddy, rural and urban areas. The spatial distribution of TN and TP exhibited the same trend in 57 sub-catchments. The TN and TP had the highest NPS pollution load in the western and central plains, which concentrated the urban area and farm land. The NPS pollution load would increase in the urban planning and historic trends scenarios, and would be even higher in the urban planning scenario. However, the NPS pollution load decreased in the ecological protection scenario. The differences observed in the three scenarios indicated that land use had a degree of impact on NPS pollution, which showed that scientific and ecologically sound construction could effectively reduce the NPS pollution load in a watershed. This study provides a scientific method for conducting NPS pollution research at the watershed scale, a scientific basis for non-point source pollution control, and a reference for related policy making.

Simulation of hydrological processes of mountainous watersheds in inland river basins: taking the Heihe Mainstream River as an example

The hydrological processes of mountainous watersheds in inland river basins are complicated.It is absolutely significant to quantify mountainous runoff for social,economic and ecological purposes.This paper takes the mountainous watershed of the Heihe Mainstream River as a study area to simulate the hydrological processes of mountainous watersheds in inland river basins by using the soil and water assessment tool(SWAT)model.SWAT simulation results show that both the Nash–Sutcliffe efficiency and the determination coefficient values of the calibration period(January 1995 to December 2002)and validation period(January 2002 to December 2009)are higher than 0.90,and the percent bias is controlled within±5%,indicating that the simulation results are satisfactory.According to the SWAT performance,we discussed the yearly and monthly variation trends of the mountainous runoff and the runoff components.The results show that from 1996 to 2009,an indistinctive rising trend was observed for the yearly mountainous runoff,which is mainly recharged by lateral flow,and followed by shallow groundwater runoff and surface runoff.The monthly variation demonstrates that the mountainous runoff decreases slightly from May to July,contrary to other months.The mountainous runoff is mainly recharged by shallow groundwater runoff in January,February,and from October to December,by surface runoff in March and April,and by lateral flow from May to September.

Defining Soil and Water Assessment Tool(SWAT)hydrologic responseunits(HRUs)by field boundaries

The Soil and Water Assessment Tool(SWAT)is widely used to relate farm management practices to their impacts on surface waters at the watershed scale,yet its smallest spatial unit is not generally defined by physically meaningful boundaries.The hydrologic response unit(HRU)is the smallest spatial unit of the model,and the standard HRU definition approach lumps all similar land uses,soils,and slopes within a subbasin based upon user-defined thresholds.This standard method provides an efficient way to discretize large watersheds where simulation at the field scale may not be computationally feasible.In relatively smaller watersheds,however,defining HRUs to specific spatial locations bounded by property lines or field borders would often be advantageous,yet this is not currently possible within the ArcSWAT interface.In this study,a simple approach is demonstrated that defines HRUs by field boundaries through addition of uniquely named soils to the SWAT user soil database and creation of a field boundary layer with majority land use and soil attributes.Predictions of nitrogen,phosphorus,and sediment losses were compared in a case study watershed where SWAT was set up using both the standard HRU definition and field boundary approach.Watershed-scale results were reasonable and similar for both methods,but aggregating fields by majority soil type masked extremely high soil erosion predicted for a few soils.Results from field-based HRU delineation may be quite different from the standard approach due to choosing a majority soil type in each farm field.This approach is flexible such that any land use and soil data prepared for SWAT can be used and any shapefile boundary can divide HRUs.

A Modified Groundwater Module in SWAT for Improved Streamflow Simulation in a Large, Arid Endorheic River Watershed in Northwest China

Interactions between surface water and groundwater are dynamic and complex in large endorheic river watersheds in Northwest China due to the influence of both irrigation practices and the local terrain. These interactions interchange numerous times throughout the middle reaches, making streamflow simulation a challenge in endorheic river watersheds. In this study, we modified the linear-reservoir groundwater module in SWAT(Soil and Water Assessment Tools, a widely used hydrological model) with a new nonlinear relationship to better represent groundwater processes; we then applied the original SWAT and modified SWAT to the Heihe River Watershed, the second largest endorheic river watershed in Northwest China, to simulate streamflow. After calibrating both the original SWAT model and the modified SWAT model, we analyzed model performance during two periods: an irrigation period and a non-irrigation period. Our results show that the modified SWAT model with the nonlinear groundwater module performed significantly better during both the irrigation and non-irrigation periods. Moreover, after comparing different runoff components simulated by the two models, the results show that, after the implementation of the new nonlinear groundwater module in SWAT, proportions of runoff components changed-and the groundwater flow had significantly increased, dominating the discharge season. Therefore, SWAT coupled with the non-linear groundwater module represents the complex hydrological process in the study area more realistically. Moreover, the results for various runoff components simulated by the modified SWAT models can be used to describe the hydrological characteristics of lowland areas. This indicates that the modified SWAT model is applicable to simulate complex hydrological process of arid endorheic rivers.

基于RBF-SWAT的气候变化下汉江上游流域径流预测及特征分析

为研究气候变化下汉江上游流域的径流响应,基于RBF神经网络降尺度模型,利用2020—2099年CanESM2模式下RCP8.5(高温室气体排放)和RCP2.6(低温室气体排放)两种气候情景,生成未来气温与降水数据;耦合SWAT水文模型,模拟分析流域2020—2099年径流变化对不同气候情景的响应特征。结果表明,汉江上游年径流量均呈不明显增加趋势,RCP8.5情景下的径流增加趋势比RCP2.6情景稍小,径流量年内分配与基准期大致相同,两种情景下汛期径流量稍有减小,可能是降尺度模型生成的降水量极大值偏小导致的。研究结果可为汉江流域水文气象综合管理提供一定的科学依据。

Application of SWAT99.2 to sensitivity analysis of water balance components in unique plots in a hilly region

Although many sensitivity analyses using the soil and water assessment tool(SWAT) in a complex watershed have been conducted, little attention has been paid to the application potential of the model in unique plots. In addition, sensitivity analysis of percolation and evapotranspiration with SWAT has seldom been undertaken. In this study, SWAT99.2 was calibrated to simulate water balance components for unique plots in Southern China from 2000 to 2001, which included surface runoff, percolation, and evapotranspiration. Twenty-one parameters classified into four categories, including meteorological conditions, topographical characteristics, soil properties, and vegetation attributes, were used for sensitivity analysis through one-at-a-time(OAT) sampling to identify the factor that contributed most to the variance in water balance components. The results were shown to be different for different plots, with parameter sensitivity indices and ranks varying for different water balance components. Water balance components in the broad-leaved forest and natural grass plots were most sensitive to meteorological conditions, less sensitive to vegetation attributes and soil properties, and least sensitive to topographical characteristics. Compared to those in the natural grass plot, water balance components in the broad-leaved forest plot demonstrated higher sensitivity to the maximum stomatal conductance(GSI) and maximum leaf area index(BLAI).

Use of SWAT to Model Impact of Climate Change on Sediment Yield and Agricultural Productivity in Western Oregon, USA

Climate change predictions for the Pacific Northwest region of the United States of America include increasing temperatures, intensification of winter precipitation, and a shift from mixed snow/rain to rain-dominant events, all of which may increase the risk of soil erosion and threaten agricultural and ecological productivity. Here we used the agricultural/environmental model SWAT with climate predictions from the Coupled Model Intercomparison Project 5 (CMIP5) “high CO2 emissions” scenario (RCP8.5) to study the impact of altered temperature and precipitation patterns on soil erosion and crop productivity in the Willamette River Basin of western Oregon. An ensemble of 10 climate models representing the full range in temperature and precipitation predictions of CIMP5 produced substantial increases in sediment yield, with differences between yearly averages for the final (2090-2099) and first (2010-2019) decades ranging from 3.9 to 15.2 MT·ha-1 among models. Sediment yield in the worst case model (CanESM2) corresponded to loss of 1.5 - 2.7 mm·soil·y-1, equivalent to potentially stripping productive topsoil from the landscape in under two centuries. Most climate models predicted only small increases in precipitation (an average of 5.8% by the end of the 21st century) combined with large increases in temperature (an average of 0.05°C·y-1). We found a strong correlation between predicted temperature increases and sediment yield, with a regression model combining both temperature and precipitation effects describing 79% of the total variation in annual sediment yield. A critical component of response to increased temperature was reduced snowfall during high precipitation events in the wintertime. SWAT characterized years with less than basin-wide averages of 20 mm of precipitation falling as snow as likely to experience severe sediment loss for multiple crops/land uses. Mid-elevation sub-basins that are projected to shift from rain-snow transition to rain-dominant appear particularly vulnerable to sediment loss. Analyses of predicted crop yields indicated declining productivity for many commonly grown grass seed and cereal crops, along with increasing productivity for certain other crops. Adaptation by agriculture and forestry to warmer, more erosive conditions may include changes in selection of crop kinds and in production management practices.

A Comparison of SWAT Model Calibration Techniques for Hydrological Modeling in the Ganga River Watershed

恒河是印度最长的河流,目前正遭受人类活动和气候变化的影响,其中瓦拉纳西区域所受的影响尤为严重。预计气候变化和不断扩张的人口会进一步影响水资源的有效利用。本研究利用水土评价工具(soil and water assessment tool,SWAT)模型进行水文模拟,研究区选择恒河流经的印度北方邦南部地区,覆盖面积达15 621.612 km^2。本研究主要目标如下:(1)检验SWAT模型在径流和产沙量预测方面的可行性和适用性,(2)对序贯不确定性分析(SUFI-2)、普适似然不确定性估计(GLUE)和并行求解(ParaSol)这3种常规校准算法进行对比分析,并确定出最佳校准算法。SWAT模型中输入数据的来源为航天飞机雷达地形测绘任务(SRTM)获取的数字高程模型(DEM)、Landsat-8卫星图像、土壤数据和逐日气象数据。首先,本研究将研究流域划分为46个子流域,使用土地利用/土地覆被(LULC)图和土壤图创建了水文响应单元(HRU)。然后,构建了基于SUFI-2、GLUE和ParaSol算法的模型,并基于5类标准对这些校准算法进行了比较,标准包括目标函数、使用概念、性能、P因子和R因子值。研究结果表明:(1) SUFI-2算法需要的运行时间较少,同时校准结果最好,ParaSol算法最差;(2)使用SUFI-2算法对模型进行校准后,获得对模拟结果影响最显著的5个敏感参数——主河道水力传导率(CH_K2)、USLE方程水土保持因子(USLE_P)、主河道曼宁系数值(CH_N2)、地表径流滞后时间(SURLAG)以及土壤有效含水量(SOL_AWC);(3) 40号子流域(SW#40)产生的径流量最大,土地利用类型为荒地的36号子流域(SW#36)的产沙量最大,达到50 t·a^(–1)。研究区的平均蒸散量为411.55 mm·a^(–1)。校准后的模型可以用于探究未来LULC的变化、气候变化和土壤侵蚀的影响。

Impacts of Land Cover Changes on Runoff and Sediment in the Cedar Creek Watershed,St.Joseph River,Indiana,United States

The relation between runoff and sediment and land cover is investigated in the Cedar Creek Watershed (CCW), located in Northeastern Indiana, United States. The major land cover types in this watershed are cultivated land, woodland and pasture /Conservation Reserve Program (CRP), which account for approximate 90 % of the total area in the region. Moreover, land use was changed tremendously from 2000 to 2004, even without regarding the effect of the crop rotation system (corn & soybean). At least 49 % of land cover types were changed into other types in this period. The land cover types, ranking by changing area from high to low series, are rye, soybean, corn, woodland and pasture/CRP. The CCW is divided into 21 sub- watersheds, and soil and water loss in each sub-watershed is computed by using Soil and Water Assessment Tool (SWAT). The results indicate that the variations in runoff and sediment have positive relation to the area of crops (especially corn and soybean); sediment is more sensitive to land cover changes than runoff; more heavy rainfall does not always mean more runoff because the combination of different land cover types always modify runoff coefficient; and rye, soybean and corn are the key land cover types, which affected the variation in runoff and sediment in the CCW.

SWAT模型融雪模块的改进

水土评价工具模型(SWAT)是一个具有物理基础的分布式水文模型,利用SCS径流曲线数方法计算地表径流,而采用相对简单的度日因子方法计算融雪径流。因此在湿润半湿润、雨量丰富的平原地区应用SWAT模型进行径流模拟时可以得到较好的模拟结果,但是在干旱半干旱、降水稀少,且春汛期间融雪径流是重要补给来源的高寒山区,模拟的融雪径流明显偏小,不能很好的反映这些地区的融雪过程,导致河道径流模拟精度偏低。FASST模型是具有物理机制的陆面过程模型,其采用能量平衡的方法计算融雪径流,能够较好的模拟复杂地形山区流域的融雪径流。以黑河山区流域为研究区,将FASST模型集成到SWAT模型,改善SWAT模型融雪径流的计算方法。通过对比SWAT模型集成前后莺落峡出山口的河道月径流、融雪径流和地表径流对河道的贡献等几个方面,表明了集成FASST融雪模块的SWAT模型能更好的反映黑河山区流域的融雪径流过程,从而提高河道径流的整体模拟精度。

SWAT模型在三峡库区流域非点源污染模拟的适用性研究

将SWAT（Soil and Water Assessment Tool）模型应用于库区大尺度流域的污染模拟研究,对其进行适用性评价及模拟应用分析。模型校验采用的是2002—2008年的水文月数据及水质水期数据,径流模拟效果最好,评价指标ENS（Nash-Suttclife Efficiency）均在0.9以上;泥沙模拟评价指标ENS在0.46~0.9;营养盐模拟评价指标ENS个别出现了〈0.36的情况,但总体模拟效果满足要求。应用SWAT模型对库区降水与地表产流、产沙、营养盐负荷进行了研究。结果表明：库区地表产流与降水的相关性趋势最好;地表产沙与产流、降水的总体趋势一致,但偶尔出现4、5月份地表产沙先于产流出现峰值的情况,这可能是由于春耕对地表扰动后又逢较强降水引起的水土流失;营养盐污染负荷尤其是TP的峰值趋势与地表产流相比,更接近地表产沙趋势。本文还对库区不同土地利用类型的污染负荷做了分析,得到各类土地利用类型的年均污染负荷总量排序及单位面积污染负荷,再次验证了SWAT模型在三峡库区流域的适用性。根据分析结果,库区耕地为非点源污染产出的主要源头,可将耕地耕种措施转变及土地利用类型转换作为库区非点源污染削减的重要手段。

SWAT模型在国内外非点源污染研究中的应用进展

模型模拟是定量估算非点源污染负荷的有效工具,也是对其进行规划、控制和管理的前提。近年来SWAT模型在国内外得到了快速的发展和应用,是目前全球评价大范围和环境变化条件下非点源污染问题的一个有效工具。简介SWAT模型的发展历程及原理,概述了SWAT模型目前在国内外的水文评价、污染物流失模拟、输入参数、土地利用及气候变化对水文响应的影响等方面的研究现状,并对SWAT模型的发展方向提出了建议,为模型的进一步完善与应用提供参考。结果显示,SWAT模型对水文评价(如径流量、泥沙量)可得到较好的模拟和预测结果,能够模拟污染物(如农药和化肥)在农田和河网中的迁移过程,模拟与分析土地利用/覆被变化及气候变化对水文过程的影响。模型参数的确定及其对地下水流与溶质运移的模拟是模型的主要问题,需要进一步研究与完善。

基于SWAT模型的汉江流域径流模拟

应用SWAT(Soil and Water Assessment Tool)分布式水文模型对汉江流域1971—2000年30年逐月径流进行了模拟。结果表明:模型模拟精度高于评价标准(模拟效率Ens>0.5,相关系数r2>0.6),SWAT模型适用于汉江流域的径流模拟;水量平衡各要素中,30年月、年平均蒸散发量、地表径流量、土壤对地下水补给量、土壤含水变化量、地下水侧流量分别占降水量的55.97%、25.88%、17.64%、0.26%、0.25%,蒸散发是该流域水量的主要输出项;各月30年平均降水量变化趋势与地表径流量变化趋势较一致,而与基流量变化趋势一致性较差;30年流域降水量年变化趋势与地表径流量、基流量的变化趋势较一致;30年月、年地表径流量对降水的响应程度高于基流。

SWAT模型辅助下的生态恢复水文响应--以陇西黄土高原华家岭南河流域为例

生态环境问题受到了日益广泛的关注,生态恢复也在各地蓬勃开展,但生态恢复工程的开展迫切需要相关理论研究的指导。采用假定生态恢复情景的方法,在遥感和地理信息系统的支持下,利用分布式水文模型SWAT(Soil and Water Assessment Tool)对陇西黄土高原的典型流域——华家岭南河流域进行了多种生态恢复情景模型的设计,并模拟了不同生态恢复情景下径流和蒸散发的响应情况。得出:在南河流域草地比森林植被涵养水源的作用更强,模拟年均径流深比林地低9.1%,而蒸散发却高2.2%,所以南河流域生态恢复过程中种草是十分必要的。结果同时表明,应用SWAT模型进行流域尺度的生态恢复水文响应研究是可行高效的。

新安江上游流域SWAT模型的构建及适用性评价

以新安江上游屯溪流域为研究区域,建立了SWAT模型的气象、土壤、土地利用和农作物管理等数据库,并利用2000-2010年逐月实测的径流、泥沙及非点源溶解态氮负荷数据进行了多参数、多站点的率定和验证,使用多目标(纳氏系数、线性相关系数和相对误差)对模型适用性进行了评价。结果表明:径流模拟效果非常好,泥沙和营养盐模拟结果令人满意,SWAT模型在屯溪流域适用性较好,可以模拟分析该地区的非点源污染问题,研究所构建的数据库和率定的参数可为进一步研究新安江流域的水环境管理提供科学依据和决策支持。