TOPMODEL for Streamflow Simulation of a Tropical Catchment Using Different Resolutions of ASTER DEM: Optimization Through Response Surface Methodology

The unavailability of proper hydrological data quality combined with the complexity of most physical based hydrologic models limits research on rainfall-runoff relationships, particularly in the tropics. In this paper, an attempt has been made to use different resolutions of DEM generated from freely available 30 m-based ASTER imagery as primary input to the topographically-based hydrological (TOPMODEL) model to simulate the runoff of a medium catchment located in the tropics. Response surface methodology (RSM) was applied to optimize the most sensitive parameters for streamflow simulation. DEM resolutions from 30 to 300 m have been used to assess their effects on the topographic index distribution (TI) and TOPMODEL simulation. It is found that changing DEM resolutions reduces the TOPMODEL simulation performance as the resolutions are varied from 30 to 300 m. The study concluded that the ASTER 30 m DEM can be used for reasonable streamflow simulation of a data scarce tropical catchment compared with the resampled DEMs.     

AGREE 算法在秦淮河流域河网水系提取中的应用

为解决在平原城市化流域通过数字高程模型（DEM）提取虚拟河网出现河道偏移,平行河网的问题,以典型的秦淮河流域作为研究对象,采用 AGREE 算法进行流域内河道信息校正,对比分析 SRTM DEM 和 ASTER GDEM 两种数据源的河网提取结果。经 AGREE 算法校正后,将 SRTM DEM 和 ASTER GDEM 两种数据源校正后的河网提取结果与2013 版《水利年鉴》 中该流域面积和河道位置、长度进行对比分析,平行河网和河道偏移问题得到解决,同时发现ASTER GDEM 在秦淮河流域提取的虚拟河网效果更优。     

Assessing Impact of Flood on River Dynamics and Susceptible Regions: Geomorphometric Analysis

Natural climatic hazards like flood, an important hydro-geomorphic process of earth’s surface, have different regional and local impacts with significant socio-economic consequences. Similar was the case in Gujarat State, India during last week of June 2005. This study is about assessing the impact of Gujarat flood on river dynamics. It deals with extraction of water bodies information using radiance image and standard water indices i.e., Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI) for pre- and post-flooding periods. Geomorphometric analysis along with drainage network extraction was done using two different Digital Elevation Models (DEMs) i.e., Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topographic Mission (SRTM) and compared. Finally, depressions mapping and comparative analysis of magnitude and directional change of drainage networks was carried out. Results confirmed better accuracy of MNDWI in separating water bodies. The water bodies area increased by 10.4 % in post-flood monsoon compared to pre-flood monsoon and by 3.8 % in post-flood dry season compared to pre-flood dry season. Geomorphometric analysis indicated that ASTER DEM gave more values of maximum slope, average slope, and standard deviation as compared to SRTM. Aspects distribution algorithm did not work well in low relief regions. The drainage network generated using SRTM DEM was more accurate. The depressions identified were more susceptible to flood events. Change analysis of drainage network (deviating 100–300 m) indicated that 5.22 % points deviated between October, 2004 and 2005 and 3.18 % between February, 2005 and 2006.     

Evaluating the Importance of Non-Unique Behavioural Parameter Sets on Surface Water Quality Variables under Climate Change Conditions in a Mesoscale Agricultural Watershed

The parameter uncertainty in the eco-hydrological model Soil and Water Assessment Tool (SWAT) was estimated using non-unique parameter sets for the Altmühl watershed (Bavaria, Germany). The Sequential Uncertainty Fitting Algorithm (SUFI-2) was used to calibrate SWAT. The non-unique parameter sets found were subsequently applied to SWAT concurrently with climate change simulations to determine the variables of streamflow, nitrate nitrogen (NO₃^?-N) and total phosphorus (TP). A suite of seven bias corrected climate change simulations provided reference (1970–2000) and future (2041–2070) climate data. The non-unique behavioural parameter sets that met an objective function of NSE >0.6 during calibration were applied to SWAT with the reference climate and with the future climate simulations. The best parameter set was also propagated through SWAT with each reference and future climate simulation in turn. Combining the non-unique behavioural parameter sets for estimating uncertainty bounds with an ensemble of climate change simulations led to a wider mean monthly spread (difference between maximum and minimum) of simulated NO₃^?-N and TP than using the best run with the future climate simulations. More monthly data was considered using the non-unique approach, resulting in statistical significances for more months of the year and overall lower interquartile ranges. The study quantifies the non-unique behavioural parameter set contributions to the modelling prediction, which assists in making more informed decisions based on available knowledge, with its limitations, of the future simulations. We outline a simple approach that can easily be replicated for similar hydrological modelling studies.     

基于水文应用的多源数字高程模型精度分析

天空地监测技术的迅速发展使得可免费获取的地形数据越来越多,而不同地形数据的精度和现势性制约着水文科学的创新和发展。收集目前可免费获取的数字高程模型,基于分辨率、现势性、覆盖范围等属性筛选出SRTM、ASTER2 GDEM和ALOS World 3D三类数据源为研究对象,针对不同地形地貌区,计算分析与水文密切相关的DEM衍生特征的精度,进而提出不同数字高程模型在水文应用中的适用范围。经分析:各DEM在地势起伏大的区域,地形宏观描述基本一致;地势起伏小的区域,Aster2 DEM与其他三种DEM存在差异;在中小河流洪水预报的经验模型中,根据资料情况利用任何一种数字高程模型提取流域参数均可,不作为影响模型精度的重要指标。在地势起伏大的地区,除SRTM外各DEM对水系形态的描述精度较高;地势起伏小的地区,除ALOS world 3D能准确描述河口区域水系结构关系外,其余DEM均不能准确描述河口区域水系形态;分布式水文模型的产汇流分析、水文通视性分析等建议使用ALOS world 3D。     

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.     

Arc Hydro模型提取流域水文信息及精度分析——以松花江流域为例

流域水文模型已成为流域水文信息提取的重要手段。运用Arc Hydro模型以松花江流域为研究对象,以分辨率为90 m的SRTM DEM为数据源,以松花江流域1∶25万水系矢量数据为参照,分别在400,500和600 km2三个不同集水面积阈值下进行河网提取。运用图像比对软件Alike Duplicate Image Finder对所提取河网进行精度分析。结果显示:集水面积阈值为500 km2下提取的河网最为精确。在500 km2集水面积阈值基础上,运用Arc Hydro模型将松花江流域划分为642个子流域。基于Arc Hydro模型提取的松花江流域河网与实际河网基本一致,说明利用该模型进行流域水文信息提取是合理可行的。     

基于LiDAR的青藏高原山坡小流域地形提取方法

数字高程模型(DEM)的精度和分辨率影响着地形分析的结果,这种影响在高原、高山地带尤为明显。以拉萨河夺底沟小流域一处山坡为研究对象,选取典型剖面对比3种DEM数据对实际地形的还原效果。分析表明:SRTM和ASTER GDEM地形数据在青藏高原高山区存在高估山谷谷底高程、漏失地形要素的现象,使用LiDAR技术获取的DEM则可以准确反映实际地形。针对8种分辨率(1,2,5,10,15,20,25,30 m)的LiDAR DEM,使用局部方差均值分析坡度、平面曲率、剖面曲率等地形属性,发现低分辨率DEM在高山地区会遗失大量地形信息,造成地形平坦化和山坡微地形改变。为避免高山地区地形特征失真,给出了坡度和曲率研究适用的最小分辨率阈值:在坡度研究中使用的DEM分辨率应<5 m,曲率研究的最优分辨率为1 m。研究表明在青藏高原高山区,使用LiDAR技术提取高分辨率DEM具有远大的应用前景。     

Impact of Climate Change on the Hydrology of Upper Tiber River Basin Using Bias Corrected Regional Climate Model

The use of regional climate model (RCM) outputs has been getting due attention in most European River basins because of the availability of large number of the models and modelling institutes in the continent; and the relative robustness the models to represent local climate. This paper presents the hydrological responses to climate change in the Upper Tiber River basin (Central Italy) using bias corrected daily regional climate model outputs. The hydrological analysis include both control (1961–1990) and future (2071–2100) climate scenarios. Three RCMs (RegCM, RCAO, and PROMES) that were forced by the same lateral boundary condition under A2 and B2 emission scenarios were used in this study. The projected climate variables from bias corrected models have shown that the precipitation and temperature tends to decrease and increase in summer season, respectively. The impact of climate change on the hydrology of the river basin was predicted using physically based Soil and Water Assessment Tool (SWAT). The SWAT model was first calibrated and validated using observed datasets at the sub-basin outlet. A total of six simulations were performed under each scenario and RCM combinations. The simulated result indicated that there is a significant annual and seasonal change in the hydrological water balance components. The annual water balance of the study area showed a decrease in surface runoff, aquifer recharge and total basin water yield under A2 scenario for RegCM and RCAO RCMs and an increase in PROMES RCM under B2 scenario. The overall hydrological behaviour of the basin indicated that there will be a reduction of water yield in the basin due to projected changes in temperature and precipitation. The changes in all other hydrological components are in agreement with the change in projected precipitation and temperature.     

水稻的干旱指标与干旱预报

从作物的干旱机理和水稻节水栽培模式变化的角度,提出并论证了以土壤墒情作为水稻干旱 指标的合理性和可行性,并建立了稻田的水分平衡方程与土壤水分消退模型,确定了研究区域以土壤 墒情作为水稻干旱指标的指标取值和对应的干旱等级划分;同时,提出了以断水天数为指标的水稻干 旱预报新方法。应用表明,该方法适合于安徽江淮丘陵区的自然环境条件和作物生长习性。     

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.     

Application of dynamic contributing area for modelling the hydrologic response of the Assiniboine River Basin to a changing climate

The Prairie landscape consists of numerous pothole depressions which produce complex fill-and-spill runoff generation processes that result in intermittent hydrologic connectivity and dynamic contributing areas (DCA). We investigated the effect of including DCA in the modified version of the Soil and Water Assessment Tool (SWAT) model and its implication on future streamflow projection for the pothole dominated Assiniboine River Basin (ARB). The fill-and-spill processes that lead to DCA were captured using a physically-based approach, with a volumetric threshold to reduce the computational demand. Despite the challenges in accurately simulating prairie pothole hydrology, both in terms of timing and volume of runoff, the modified approach improved streamflow modelling performance, and reduced model uncertainty. Further, we evaluated the effects of representing DCA on projecting future streamflow by using eight statistically downscaled CMIP5 GCMs, forced with the RCP4.5 and RCP8.5 scenarios. End of century projections indicate increases in annual precipitation and temperature across the ARB, with decreasing summer precipitation relative to the 1976–2005 baseline period. Compared to the standard SWAT setup that does not allow for DCA, the modified model was found to be more responsive to climatic change with relatively larger projected increases in seasonal and annual flows at the majority of evaluated stations. This advance in DCA modelling will facilitate longer-term large basin-scale simulations that are more representative for the Prairie region.     

Effect of Forest Thinning on Water Yield in a Sub-Humid Mediterranean Oak-Beech Mixed Forested Watershed

Forested watersheds provide fresh water with best quality and forestry practices play important role on the water production in the watersheds. Therefore, the objective of this study was to investigate the effect of 18 % thinning, which was under the 20 % threshold value reported in the literature on water yield in a forested watershed. Two experimental watersheds with similar ecological conditions in the Belgrad Forest of Istanbul were studied. Following a 6-year calibration period from December 2005 to October 2011, a simple linear regression equation was developed between the monthly streamflows of two watersheds with a significantly high correlation coefficient (r = 0.95). After 18 % of standing volume was removed from one watershed and the other was left untreated as a control, the streamflow was monitored for 2 years starting in January 2012 in both watersheds. The change in the monthly runoff was estimated as the difference between measured and values calculated with the linear regression equation. Average monthly streamflows were about 19, 15 and 10 mm in the control and 21, 20, and 11 mm in the treatment watersheds for calibration, first and second post-treatment periods, respectively. Paired watershed analysis showed that monthly streamflow did not significantly increase in either watershed for the first or the second year after the harvest. The results revealed that thinning intensity had to be greater to increase water yield significantly in this forest ecosystem and the threshold value for a streamflow increase was greater than 18 % for this region.     

Uncertainty Intercomparison of Different Hydrological Models in Simulating Extreme Flows

A growing number of investigations on uncertainty quantification for hydrological models have been widely reported in past years. However, limited studies are found on uncertainty assessment in simulating streamflow extremes so far. This article presents an intercomparison of uncertainty assessment of three different well-known hydrological models in simulating extreme streamflows using the approach of generalized likelihood uncertainty estimation (GLUE). Results indicate that: (1) The three modified hydrological models can reproduce daily streamflow series with acceptable accuracy. When the threshold value used to select behavioral parameter sets is 0.7, XAJ model generates the best GLUE estimates in simulating daily flows. However, the percentage of observations contained in the calculated 95 % confidence intervals (P-95CI) is low (<50 %) when simulating the high-flow index (Q10). (2) Decreasing average relative length (ARIL), P-95CI and increasing average asymmetry degree (AAD) are found, when the threshold value increases for both daily-flows and high-flows. However, there is a significant inconsistence between sensitivity of daily-flows and high-flows to various threshold values of the likelihood function. Uncertainty sources from parameter sets, model structure and inputs collectively accounts for above sensitivity. (3) The best hydrological model in simulating daily-flows is not identical under different threshold values. High P-95CIs of GLUE estimate for high-flows (Q10 and Q25) indicate that TOPMODEL generally performs best under different threshold values, while XAJ model produces the smallest ARIL under different threshold values. The results are expected to contribute toward knowledge improvement on uncertainty behaviors in simulating streamflow extremes by a variety of hydrological models.     

土地覆被和气候变化对拉萨河流域径流量的影响

以拉萨水文站上游流域为研究对象,利用分布式水文模型SWAT对拉萨河流域水文过程进行模拟,分别用1995～2000和2003～2006年两个时间段的实测数据对模型进行校准和验证。结果显示月径流模拟相关系数和模拟效率系数分别为0.88和0.84。在此基础上通过建立情景模拟,探讨拉萨河流域气候波动和土地覆被变化对径流产流量的影响。结果表明:气候变化对年径流量影响显著,在各种模拟假设情景中最多可以使径流量增加89%。土地覆被变化相对于气候变化对径流量的年际影响较弱,但对径流量的季节变化影响显著。     

Impact of Human Intervention and Climate Change on Natural Flow Regime

According to the ‘natural flow paradigm’, any departure from the natural flow condition will alter the river ecosystem. River flow regimes have been modified by anthropogenic interventions and climate change is further expected to affect the biotic interactions and the distribution of stream biota by altering streamflow. This study aims to evaluate the hydrologic alteration caused by dam construction and climatic changes in a mesoscale river basin, which is prone to both droughts and monsoonal floods. To analyse the natural flow regime, 15 years of observed streamflow (1950–1965) prior to dam construction is used. Future flow regime is simulated by a calibrated hydrological model Soil and Water Assessment Tool (SWAT), using ensemble of four high resolution (~25 km) Regional Climate Model (RCM) simulations for the near future (2021–2050) based on the SRES A1B scenario. Finally, to quantify the hydrological alterations of different flow characteristics, the Indicators of Hydrological Alteration (IHA) program based on the Range of Variability Approach (RVA) is used. This approach enables the assessment of ecologically sensitive streamflow parameters for the pre- and post-impact periods in the regions where availability of long-term ecological data is a limiting factor. Results indicate that flow variability has been significantly reduced due to dam construction with high flows being absorbed and pre-monsoon low flows being enhanced by the reservoir. Climate change alone may reduce high peak flows while a combination of dam and climate change may significantly reduce variability by affecting both high and low flows, thereby further disrupting the functioning of riverine ecosystems. We find that, in the Kangsabati River basin, influence of dam is greater than that of the climate change, thereby emphasizing the significance of direct human intervention.     

利用GIS和RS技术分析青藏高原风火山小流域地形地貌特征

以30×30m DEM为基础,在GIS技术辅助下,以青藏高原风火山小流域为例,设计了水文响应单元划分的实现方案和算法,并结合不规则网格的有限体积法,进行流域水文模拟方式的探讨。从DEM中提取子流域,利用遥感图像进行土壤覆被类型划分,使得生成的每个水文单元有单一的土壤覆被类型,并根据所得类型图,进行流域积水面积阈值的求取;结合有限体积法不规则网格技术,对流域网格划分进行讨论,确定用于微分方程求解的编码方式。结果表明:结合RS和GIS能较准确地划分流域土地利用类型,求取河网集水面积阈值,划分流域网格单元和存储结点数据,实现了分布式流域建模的空间离散化,用于冻土草地区模型数值模拟具有方便、可行性。     

Hydrological Assessment of the 1973 Treaty on the Transboundary Helmand River,Using the SWAT Model and a Global Climate Database

Exploitation of the water resources of the Helmand River has been challenging for Iran and Afghanistan. Debates on this issue finally led to a treaty in 1973 between the two countries, in which a total amount of 26 m³/s water from the Helmand River should be delivered to Iran in a normal (or an above normal) water year. The treaty also specifies that a “normal water year” means the year during which the total volume of water at the hydrometric station of Dehrawud (upstream of the Kajakai Dam) is 5661.7 million cubic meter (MCM). This paper aims to assess the long term hydrological conditions of the Upper Helmand River, to detect the occurrence of any non-stationary process in its streamflow time series and compare the possible changes with the content of the 1973 water treaty. Due to very date scarce situation of this region, the SWAT (Soil & Water Assessment Tool) model and CRU (Climatic Research Unit) global dataset were applied to create the long term time series. The results showed that there has been no significant change in annual mean flows in the Upper Helmand River basin. However, there is a consistent increase in monthly flows from November to February and a decrease of the flows in June and July. The monthly changes can be attributed to an increasing trend in temperature in the study area, earlier snowmelts during winter and less snow pack in summer. The applied methodology of this study is useful to cope with the region’s data scarcity and can be applied for similar studies requiring long term time series of hydrological variables.     

Cascade Dam-Induced Hydrological Disturbance and Environmental Impact in the Upper Stream of the Yellow River

The construction of a dam converts the natural streamflow to human control. It is necessary to learn the accumulated effect of cascade dams on hydrological characteristics, sediment and nutrient pollution discharge. The current research describes the analysis and simulation of streamflow, sand concentration and nutrient pollutant discharge alterations caused by the construction of a cascade of eight dams along the Longliu section of the upper stream of the Yellow River. The analysis shows that the maximum monthly streamflow difference between the inlet and outlet of the Longliu section decreased from 430 to 115 m³/s, after the appearance of the cascade dams between 1977 and 2006. In the same period, the correlation coefficient (R ²) of monthly streamflow between the inlet and outlet of Longliu dropped from 0.959 to 0.375. The peak of streamflow shifted from June to May and October. The difference in sand concentration between two sections decreased from 0.52 to 0.39 kg/m³, which was the direct consequence of the operation of the reservoirs. The R ² value of sand concentrations of the inlet and outlet were also reduced from 0.504 to 0.356. A t-test analysis indicates that the original hydrological nature was significantly disturbed by the cascade dams. The influence of the dams on nutrient pollutant transport was simulated by the SWAT model. This simulation suggests that the cascade dams decreased the discharge of total nitrogen and total phosphorus from 15.4 × 10³ t and 1,996 t to 0.4 × 10³ t and 328 t, respectively. In conclusion, the accumulated impact of cascade dams on streamflow, sand concentration and nutrient pollutant discharge were analyzed, which were helpful for understanding the environmental features of the entire watershed.     

基于DEM的乌梁素海东部流域河网信息提取

以乌梁素海东部流域为研究区,基于免费获取的3〃的Shuttle Radar Topography Mission(SRTM)数字高程模型(DEM),利用HEC-GeoHMS模块,确定流域不同汇流累积量阈值的河网密度,通过二者关系曲线,得出东部流域最适汇流累积量阈值为15 km2.实现流域水系提取和子流域划分,继而将其与...