Basin-scale Hydrological Model Research Articles

Understanding and modelling the effects of wetland on the hydrology and water resources of large African river basins

Wetlands are important components of many large river systems. Some basin scale hydrological models do include explicit sub-models to deal with wetland impacts, but one of the key challenges is to estimate appropriate parameter values to represent the channel-wetland exchange processes. A combined modelling approach is applied in this study and involves the use of the detailed, daily time-step, LISFLOOD-FP hydraulic model to improve the understanding of channel-wetland exchange dynamics and to quantify the wetland parameters of a basin scale hydrological model. While there remain, many uncertainties associated with a lack of sufficient validation data, the LISFLOOD-FP results largely reflect the physical characteristics of the two floodplains (the Luangwa and Barotse in the Zambezi River basin). The LISFLOOD-FP results were also used to estimate the wetland parameters of the basin scale hydrological model with greater confidence and improved the downstream simulations results (albeit marginally). The results suggest that the influence of the floodplain on the monthly Luangwa flow regime is minimal, whereas the Barotse floodplain significantly attenuates the high flows and regulates the low flows of the Upper Zambezi River. The approach implemented in this study presents an important step towards the improvements of water resource assessments modelling for research and practical purposes in data-scarce river basins, however, further work is required to refine the model setup using additional field information related to exchange dynamics as well as high quality remote sensing data.

Integrated flood risk assessment of the Arial Khan River under changing climate using IPCC AR5 risk framework

Abstract Bangladesh is situated at the confluence of GBM basins, with 90% of the basin area locating outside the country. Future climate change will lead to intense, prolonged, and frequent floods in Bangladesh. An integrated flood risk assessment that transforms flood risks from transboundary river basins to the local administrative level is necessary. A 1D/2D hydrodynamic model is developed for flood vulnerable Arial Khan River feed by basin-scale hydrologic model for low (RCP2.6) and high (RCP8.5) climate scenarios. An increasing trend in flood depth, duration, and area is observed from the early (2020s) to the end (2080s) of the century for both scenarios. The difference between both RCPs is minimal from the 2020s to 2050s but becomes very pronounced in the 2080s. The depth-duration-area with equal weightage provides better hazard results for the area. Flood risk is assessed using the IPCC AR5 framework incorporating vulnerability and exposure. Some medium-hazard zones fall into high-risk zones due to high exposure and vulnerability to flooding. The areas along the left reach are found more hazard-prone, while the areas on the right side are more risk-prone in the 2080s of RCP8.5. The hazard/risk maps will help policymakers identify priority areas for planning a sustainable flood management strategy.

TOPMELT 1.0: a topography-based distribution function approach to snowmelt simulation for hydrological modelling at basin scale

Abstract. Enhanced temperature-index distributed models for snowpack simulation, incorporating air temperature and a term for clear sky potential solar radiation, are increasingly used to simulate the spatial variability of the snow water equivalent. This paper presents a new snowpack model (termed TOPMELT) which integrates an enhanced temperature-index model into the ICHYMOD semi-distributed basin-scale hydrological model by exploiting a statistical representation of the distribution of clear sky potential solar radiation. This is obtained by discretizing the full spatial distribution of clear sky potential solar radiation into a number of radiation classes. The computation required to generate a spatially distributed water equivalent reduces to a single calculation for each radiation class. This turns into a potentially significant advantage when parameter sensitivity and uncertainty estimation procedures are carried out. The radiation index may be also averaged in time over given time periods. Thus, the model resembles a classical temperature-index model when only one radiation class for each elevation band and a temporal aggregation of 1 year is used, whereas it approximates a fully distributed model by increasing the number of the radiation classes and decreasing the temporal aggregation. TOPMELT is integrated within the semi-distributed ICHYMOD model and is applied at an hourly time step over the Aurino Basin (also known as the Ahr River) at San Giorgio (San Giorgio Aurino), a 614 km2 catchment in the Upper Adige River basin (eastern Alps, Italy) to examine the sensitivity of the snowpack and runoff model results to the spatial and temporal aggregation of the radiation fluxes. It is shown that the spatial simulation of the snow water equivalent is strongly affected by the aggregation scales. However, limited degradation of the snow simulations is achieved when using 10 radiation classes and 4 weeks as spatial and temporal aggregation scales respectively. Results highlight that the effects of space–time aggregation of the solar radiation patterns on the runoff response are scale dependent. They are minimal at the scale of the whole Aurino Basin, while considerable impact is seen at a basin scale of 5 km2.

The Long-term Projection of Surface Runoff in the Regions above Danjiangkou in Hanjiang River Basin based on Water-energy Balance

The projection of surface runoff in the context of climate change is important to the rational utilization and distribution of water resources. This study did a case study in regions above Danjiangkou in Hanjiang River Basin. A basin scale hydrological model was built based on macroscale processes of surface runoff and water-energy balance. This model can describe the quantity relationship among climatic factors, underlying surface and surface runoff. Driven by hypothetical climatic scenarios and climate change dataset coming from CMIP5, the climate change impacts on surface runoff in the regions above Danjiangkou in Hanjiang River Basin can be addressed. The results showed that: (1) Compared with other distributed hydrological models, the hydrological model in this study has fewer parameters and simpler calculation methods. The model was good at simulating annual surface runoff. (2) The surface runoff was less sensitivity to climate change in the regions above Danjiangkou in Hanjiang River Basin. A 1°C increase in temperature might results in a surface runoff decrease of 2~5% and a 10% precipitation increase might result in a streamflow increase of 14~17%. (3) The temperature across the Fu River Basin were projected to increase by 1.4~2.3°C in 1961 to 1990 compared with that in 1961 to 1990. But the uncertainty existed among the projection results of precipitation. The surface runoff was excepted to decrease by 1.3~23.9% without considering the climate change projected by NorESM1-M and MIROC-ESM-CHEM, which was much different from other GCMs.

SWAT Check: A Screening Tool to Assist Users in the Identification of Potential Model Application Problems.

The Soil and Water Assessment Tool (SWAT) is a basin-scale hydrologic model developed by the United States Department of Agriculture Agricultural Research Service. SWAT's broad applicability, user-friendly model interfaces, and automatic calibration software have led to a rapid increase in the number of new users. These advancements also allow less experienced users to conduct SWAT modeling applications. In particular, the use of automated calibration software may produce simulated values that appear appropriate because they adequately mimic measured data used in calibration and validation. Autocalibrated model applications (and often those of unexperienced modelers) may contain input data errors and inappropriate parameter adjustments not readily identified by users or the autocalibration software. The objective of this research was to develop a program to assist users in the identification of potential model application problems. The resulting "SWAT Check" is a stand-alone Microsoft Windows program that (i) reads selected SWAT output and alerts users of values outside the typical range; (ii) creates process-based figures for visualization of the appropriateness of output values, including important outputs that are commonly ignored; and (iii) detects and alerts users of common model application errors. By alerting users to potential model application problems, this software should assist the SWAT community in developing more reliable modeling applications.

WATERSHED RUNOFFAND RIVER FLOOD MODELING IN LAND USE PLANNING

In land use planning along river paths it may be useful to consider the statistics of the flooding process of the river. The set of rules regulating land use planning in Italy results in the return period required being very long and, as a result, there are very high river discharge peaks which are taken into consideration and not much possibility of making experimental observations. Correct planning of land use should include some description of river flooding in these critical conditions. To do this a basin scale hydrological model and a robust numerical scheme of the 2D complete SWE have to be integrated. Knowing that experimental validation is very difficult we showed the reliability of the numerical schemes used to get consistent solutions. A watershed runoff forecast model was used to obtain the river hydrograph to apply as a boundary condition in the study of river flood inundation on the flat plain near the Olbia airport (Sardinia, Italy). A threshold of 1 cm was used as a condition to consider whether or not to include the cell in the computational field in the description of the wetting-drying process. And this seems to fit well in the model. The numerical model is conservative, ensuring preservation of water volumes with a precision of 10-4. The great surface water gradient in some sections is evident proof of the importance of the SWE inertial terms in wave front propagation. The flow peak loss during the alluvial plane flooding resulted in a reduction of about 10% of the discharge peak at the river mouth. This numerical method, which has been validated in previous similar applications, describes sufficiently well flooding in a complex area with river morphology limited by airport and road infrastructures.

A GIS-BASED REGIONAL PLANNING TOOL FOR IRRIGATION DEMAND ASSESSMENT AND SAVINGS USING SWAT

Regional planning for irrigated agriculture requires a thorough understanding of the hydrological processes andspatial and temporal variations associated with hydrological factors such as rainfall, soils, and crops grown in different unitsof the region. The objective of this study was to improve the capabilities of a basin-scale hydrologic simulation model forregional planning of irrigated agriculture. In this study, a Geographical Information System (GIS) based hydrological model,Soil and Water Assessment Tool (SWAT), was configured as a regional planning tool with a canal irrigation capability forestimating irrigation demand. The tool was capable of simulating hydrological processes associated with soil-plant-waterinteractions and capable of capturing the spatial and temporal variability of the major factors, which are important inregional planning. The tool was applied to the irrigation districts in the Lower Rio Grande Valley in Texas. It was validatedfor crop evapotranspiration and canal conveyance efficiency and applied to analyzing the demand and potential watersavings of alternative water conservation measures. Estimated potential water savings were 234.2, 65.9, and 194.0 Mm3 forconservation measures related to on-farm management improvements, replacing sugarcane with corn, and improving canalconveyance efficiency, respectively. Results indicated that on-farm management measures might be as beneficial asimproving canal conveyance systems. The planning tool (with hydrological modeling and GIS capabilities) and estimationsmade would be useful for regional planners and irrigation district managers. The tool could be used for other irrigationsystems as well.

Topographic Influence on the Seasonal and Interannual Variation of Water and Energy Balance of Basins in North America

A large area basin-scale (LABs) hydrologic model is developed for regional, continental, and global hydrologic studies. The heterogeneity in the soil-moisture distribution within a basin is parameterized through the statistical moments of the probability distribution function of the topographic (wetness) index. The statistical moments are derived using GTOPO30 (30 arc sec; 1-km resolution) digital elevation model data for North America. River basins and drainage network extracted using this dataset are overlaid on computed topographic indices for the continent and statistics are extracted for each basin. A total of 5020 basins with an average size of 3255 square kilometers, obtained from the United States Geological Survey HYDRO1K data, is used over the continent. The model predicts runoff generation due to both saturation and infiltration excess mechanisms along with the baseflow and snowmelt. Simulation studies are performed for 1987 and 1988 using the International Satellite Land Surface Climatology Project data. Improvement in the terrestrial water balance and streamflow is observed due to improvements in the surface runoff and baseflow components achieved by incorporating the topographic influences. It is found that subsurface redistribution of soil moisture, and anisotropy in hydraulic conductivities in the vertical and horizontal directions play an important role in determining the streamflow and its seasonal variability. These enhancements also impact the surface energy balance. It is shown that the dynamics of several hydrologic parameters such as basin mean water table depth and saturated fraction play an important role in determining the total streamflow response and show realistic seasonal and interannual variations. Observed streamflow of the Mississippi River and its subbasins (Ohio, Arkansas, Missouri, and Upper Mississippi) are used for validation. It is observed that model baseflow has a significant contribution to the streamflow and is important in realistically capturing the seasonal and annual cycles.

Retrospective simulation of a storm event: A first step in coupled climate/hydrologic modeling

Global and regional climate models are valuable tools for assessing the effects of natural and anthropogenic perturbations to climate and hydrology. Results of a coupled regional climate and hydrologic model system, designed for the integrated assessment of climate‐hydrologic impacts at regional scales demonstrate that (a) simulated precipitation in a storm event is sensitive to the spatial resolution of the regional climate model and (b) spatial variability of precipitation and hydraulic variables must be accounted for in order to realistically capture the basin‐scale hydrologic response to a storm event. The regional climate model (with a spatial resolution of 4 to 36 km) can be driven either by global climate model output (with resolutions at the order of 100 km) or by observed climate data. The meteorological fields simulated over the mid‐Atlantic region of the USA were disaggregated to drive the basin‐scale hydrologic model (with a resolution of 1 km). With the improved treatment of spatial variability, the simulated streamflow at the basin outlet compares well with observations. These results from coupled climate‐hydrologic models at regional scales suggest that climate‐hydrology modeling studies that do not allow for spatial variability may be misleading.

Using a basin-scale hydrological model to estimate crop transpiration and soil evaporation

Increasing populations and expectations, declining crop yields and the resulting increased competition for water necesitate improvements in irrigation management and productivity. A key factor in defining agricultural productivity is to be able to simulate soil evaporation and crop transpiration. In agribusiness terms, crop transpiration is a useful process while soil and open-water evaporations are wasteful processes. In this study a distributed hydrological model was used to compute daily evaporation and transpiration for a variety of crops and other land covers within the 17,200 km 2 Gediz Basin in western Turkey. The model, SLURP, describes the complete hydrological cycle for each land cover within a series of sub-basins including all dams, reservoirs, regulators and irrigation schemes in the basin. The sub-basins and land covers are defined by analysing a digital elevation model and NOAA AVHRR satellite data. In this study, the model uses the FAO implementation of the Penman–Monteith equation to simulate soil evaporation and crop transpiration. The results of the model runs provide time series of data on streamflow at many points along the river system, abstractions and return flows from crops within the irrigation schemes and areally distributed soil evaporation and crop transpiration across the entire basin on each day of an 11 year period. The results show that evaporation and transpiration vary widely across the basin on any one day and over the irrigation season and can be used to evaluate the effectiveness of the various irrigation strategies used in the basin. The advantages of using such a model as compared to deriving evapotranspiration from satellite data are that the model obtains results for each day of an indefinitely long period, as opposed to occasional snapshots, and can also be used to simulate alternate scenarios.

Low‐flow frequency exacerbation by irrigation withdrawals in the agricultural midwest under various climate change scenarios

As a possible outcome of global climate change, reductions in precipitation, while directly decreasing surface water streamflows and reserves, can also initiate or exacerbate the surface water demand by regional agriculture. Driven by the desire to maintain consistent yields and hedge the risk of drought, farmers may implement or increase supplemental irrigation applications, obtaining water from either surface sources or aquifers. This paper presents results of an investigation of the impact of these effects on streamflows in the midwestern United States. The investigation examines the direct effect of precipitation reduction and the indirect effects of riparian and nonriparian irrigation. The crop‐growth and farm‐scale hydrologie model erosion‐productivity impact calculator is used in conjunction with the routing features of the basin‐scale hydrologic model soil water analysis tool to simulate direct and indirect effects of global change on streamflows. The analysis shows that the coupled effects of decreases in runoff and increases in irrigation may be devastating to the streams of Illinois and other midwestern states. For the example basin a 25% decrease in mean precipitation under optimal irrigation practices by both riparian and nonriparian farmers yields an increase in the annual (mean) occurrence of the historical 7Q10 from 3 days/year to 13 days/year, despite the streamflow accretion from groundwater‐supplied irrigators.

Automated calibration applied to watershed-scale flow simulations

Complexity in simulating the hydrological response in large watersheds over long times has prompted a significant need for procedures for automatic calibration. Such a procedure is implemented in the basin-scale hydrological model (BSHM), a physically based distributed parameter watershed model. BSHM simulates the most important basin-scale hydrological processes, such as overland flow, groundwater flow and stream–aquifer interaction in watersheds. Here, the emphasis is on estimating the groundwater parameters with water levels in wells and groundwater baseflows selected as the calibration targets. The best set of parameters is selected from within plausible ranges of parameters by adjusting the values of hydraulic conductivity, storativity, groundwater recharge and stream bed permeability. The baseflow is determined from stream flow hydrographs by using an empirical scheme validated using a chemical approach to hydrograph separation. Field studies determined that the specific conductance for components of the composite hydrograph were sufficiently unique to make the chemical approach feasible. The method was applied to the Big Darby Creek Watershed, Ohio. The parameter set selected for the groundwater system provides a good fit with the estimated baseflow and observed water well data. Copyright © 1999 John Wiley & Sons, Ltd.

Automated calibration applied to watershed‐scale flow simulations

Complexity in simulating the hydrological response in large watersheds over long times has prompted a significant need for procedures for automatic calibration. Such a procedure is implemented in the basin-scale hydrological model (BSHM), a physically based distributed parameter watershed model. BSHM simulates the most important basin-scale hydrological processes, such as overland flow, groundwater flow and stream–aquifer interaction in watersheds. Here, the emphasis is on estimating the groundwater parameters with water levels in wells and groundwater baseflows selected as the calibration targets. The best set of parameters is selected from within plausible ranges of parameters by adjusting the values of hydraulic conductivity, storativity, groundwater recharge and stream bed permeability. The baseflow is determined from stream flow hydrographs by using an empirical scheme validated using a chemical approach to hydrograph separation. Field studies determined that the specific conductance for components of the composite hydrograph were sufficiently unique to make the chemical approach feasible. The method was applied to the Big Darby Creek Watershed, Ohio. The parameter set selected for the groundwater system provides a good fit with the estimated baseflow and observed water well data. Copyright © 1999 John Wiley & Sons, Ltd.

Water resources of the Texas Gulf Basin

A geographic information system (GIS) has been integrated with a distributed parameter, continuous time, nonpoint source pollution model SWAT (Soil and Water Assessment Tool) for the management of water resources. This integration has proven to be effective and efficient for data collection and to visualize and analyze the input and output of simulation models. The SWAT-GIS system is being used to model the hydrology of eighteen major river systems in the United States (HUMUS). This paper focuses on the integration of SWAT (basin scale hydrologic model) with the Geographical Resources Analysis Support System (GRASS-GIS) and a relational database management system. The system is then applied to the Texas Gulf River basin. Input data layers (soils, land use, and elevation) were collected at a scale of 1:250,000 from various sources. Average monthly simulated and observed stream flow records from 1970-1979 are presented for the hydrologic cataloging units (HCU) defined by the United States Geological Survey (USGS) in the Texas Gulf basin. Average annual sediment yields computed from sediment rating curves are compared against simulated sediment yields from seven river basins within the Texas Gulf showing reasonable agreement.

Water resources of the Texas Gulf basin

A geographic information system (GIS) has been integrated with a distributed parameter, continuous time, nonpoint source pollution model SWAT (Soil and Water Assessment Tool) for the management of water resources. This integration has proven to be effective and efficient for data collection and to visualize and analyze the input and output of simulation models. The SWAT-GIS system is being used to model the hydrology of eighteen major river systems in the United States (HUMUS). This paper focuses on the integration of SWAT (basin scale hydrologic model) with the Geographical Resources Analysis Support System (GRASS-GIS) and a relational database management system. The system is then applied to the Texas Gulf River basin. Input data layers (soils, land use, and elevation) were collected at a scale of 1:250,000 from various sources. Average monthly simulated and observed stream flow records from 1970–1979 are presented for the hydrologic cataloging units (HCU) defined by the United States Geological Survey (USGS) in the Texas Gulf basin. Average annual sediment yields computed from sediment rating curves are compared against simulated sediment yields from seven river basins within the Texas Gulf showing reasonable agreement.

APPLICATION OF AN INTEGRATED BASIN‐SCALE HYDROLOGIC MODEL TO SIMULATE SURFACE‐WATER AND GROUND‐WATER INTERACTIONS1

ABSTRACT: Hydrologic models have become an indispensable tool for studying processes and water management in watersheds. A physically‐based, distributed‐parameter model, Basin‐Scale Hydro‐logic Model (BSIIM), has been developed to simulate the hydrologic response of large drainage basins. The model formulation is based on equations describing water movement both on the surface and in the subsurface. The model incorporates detailed information on climate, digital elevation, and soil moisture budget, as well as surface‐water and ground‐water systems. This model has been applied to the Big Darby Creek Watershed, Ohio in a 28‐year simulation of rainfall‐runoff processes. Unknown coefficients for controlling runoff, storativity, hydraulic conductivity, and streambed permeability are determined by a trial‐and‐error calibration. The performance of model calibration and predictive capability of the model was evaluated based on the correlation between simulated and observed daily stream discharges. Discrepancies between observed and simulated results exist because of limited precipitation data and simplifying assumptions related to soil, land use, and geology.

LARGE AREA HYDROLOGIC MODELING AND ASSESSMENT PART II: MODEL APPLICATION1

ABSTRACT: This paper describes the application of a river basin scale hydrologic model (described in Part I) to Richland and Chambers Creeks watershed (RC watershed) in upper Trinity River basin in Texas. The inputs to the model were accumulated from hydro‐graphic and geographic databases and maps using a raster‐based GIS. Available weather data from 12 weather stations in and around the watershed and stream flow data from two USGS stream gauge station for the period 1965 to 1984 were used in the flow calibration and validation. Sediment calibration was carried out for the period 1988 through 1994 using the 1994 sediment survey data from the Richland‐Chambers lake. Sediment validation was conducted on a subwatershed (Mill Creek watershed) situated on Chambers Creek of the RC watershed. The model was evaluated by well established statistical and visual methods and was found to explain at least 84 percent and 65 percent of the variability in the observed stream flow data for the calibration and validation periods, respectively. In addition, the model predicted the accumulated sediment load within 2 percent and 9 percent from the observed data for the RC watershed and Mill Creek watershed, respectively.

Testing a GCM land surface scheme against catchment-scale runoff data

A GCM land surface scheme was used, in off-line mode, to simulate the runoff, latent and sensible heat fluxes for two distinct Australian catchments using observed atmospheric forcing. The tropical Jardine River catchment is 2500 km2 and has an annual rainfall of 1700 mm y–1 while the Canning River catchment is 540 km2, has a Mediterranean climate (annual rainfall of 800 mm y–1) and is ephemeral for half the year. It was found that the standard version of a land surface scheme developed for a GCM, and initialised as for incorporation into a GCM, simulated similar latent and sensible heat fluxes compared to a basin-scale hydrological model (MODHYDROLOG) which was calibrated for each catchment. However, the standard version of the land surface scheme grossly overestimated the observed peak runoff in the wet Jardine River catchment at the expense of runoff later in the season. Increasing the soil water storage permitted the land surface scheme to simulate observed runoff quite well, but led to a different simulation of latent and sensible heat compared to MODHYDROLOG. It is concluded that this 2-layer land surface scheme was unable to simulate both catchments realistically. The land surface scheme was then extended to a three-layer model. In terms of runoff, the resulting control simulations with soil depths chosen as for the GCM were better than the best simulations obtained with the two-layer model. The three-layer model simulated similar latent and sensible heat for both catchments compared to MODHYDROLOG. Unfortunately, for the ephemeral Canning River catchment, the land surface scheme was unable to time the observed runoff peak correctly. A tentative conclusion would be that this GCM land surface scheme may be able to simulate the present day state of some larger and wetter catchments but not catchments with peaky hydrographs and zero flows for part of the year. This conclusion requires examination with a range of GCM land surface schemes against a range of catchments.