Semi-distributed Model Research Articles

A System Dynamics Model to Evaluate Temporary Water Transfers in the Mexican Conchos Basin

The flows of the Rio Conchos are of vital economic importance not only to the agricultural sector in the Mexican side of the Rio Grande basin but also for meeting Mexico’s obligation to deliver water to the United States. During the previous decade, a severe drought dramatically decreased the basin’s runoff, generating serious economic, social, and political problems in both countries. A System Dynamics (SD) model designed to serve as a decision-support system (DSS) for water managers has been created. This DSS is a lumped semi-distributed model operating on a monthly basis. This DSS incorporates the most important elements of the Conchos basin’s water resources system: main rivers, irrigation distribution canals, reservoirs, aquifer, and the three Irrigation Districts. The DSS simulates different short and long term scenarios combining inside and outside Irrigation Districts (IDs). Also, different short scenarios are implemented to investigate the benefits of water transfer from Mexico to the United States. This study has prompted awareness with regards to the degree of complexity and uncertainty of the water right allocation process to different economic variables such as crop yield, production costs, crop prices, subsidies, and water distribution efficiencies.

Water demand and flows in the São Francisco River Basin (Brazil) with increased irrigation

Most activities that support economic growth in the São Francisco River Basin (Brazil) need water. Allocation of the water resources to each competing use needs quantification in order to develop an integrated water management plan. Irrigation agriculture is the largest water consuming activity in the basin. It has produced large economic and social advancements in the region and has potential for further development. The local development agency in the São Francisco River has projected an increase of more than 500,000 ha in irrigation developments distributed within the basin. Water requirements of the projected irrigation expansions and their effects on river flow were quantified. A semi-distributed model was constructed to simulate the water balance in 16 watersheds within the basin. The watersheds were hydrologically characterized by the average precipitation, atmospheric demand and runoff as well as their variability. Water requirements for increased irrigated agriculture were calculated using an agronomic mass balance. A Monte Carlo procedure generated the variability of irrigation requirements and resulting decreased river flows from the multidimensional probability distribution of the hydrologic variables of each watershed. Irrigation requirements were found to be more variable during the wet season because of weather variability. In contrast to what might be expected, in drier years, irrigation requirements were often larger during the wet season than in the dry season because the cropped area is largest in the wet months and variability of precipitation is greater. Increased irrigation shifted downward the distribution of river flows but not enough to affect other strategic water uses such as hydropower. Further irrigation expansion may be limited by wet season flows.

From lumped to distributed via semi-distributed: Calibration strategies for semi-distributed hydrologic models

Summary Modeling the effect of spatial variability of precipitation and basin characteristics on streamflow requires the use of distributed or semi-distributed hydrologic models. This paper addresses a DMIP 2 study that focuses on the advantages of using a semi-distributed modeling structure. We first present a revised semi-distributed structure of the NWS SACramento Soil Moisture Accounting (SAC-SMA) model that separates the routing of fast and slow response runoff components, and thus explicitly accounts for the differences between the two components. We then test four different calibration strategies that take advantage of the strengths of existing optimization algorithms (SCE-UA) and schemes (MACS). These strategies include: (1) lumped parameters and basin averaged precipitation, (2) semi-lumped parameters and distributed precipitation forcing, (3) semi-distributed parameters and distributed precipitation forcing and (4) lumped parameters and basin averaged precipitation, modified using a priori parameters of the SAC-SMA model. Finally, we explore the value of using discharge observations at interior points in model calibration by assessing gains/losses in hydrograph simulations at the basin outlet. Our investigation focuses on two key DMIP 2 science questions. Specifically, we investigate (a) the ability of the semi-distributed model structure to improve stream flow simulations at the basin outlet and (b) to provide reasonably good simulations at interior points. The semi-distributed model is calibrated for the Illinois River Basin at Siloam Springs, Arkansas using streamflow observations at the basin outlet only. The results indicate that lumped to distributed calibration strategies (1 and 4) both improve simulation at the outlet and provide meaningful streamflow predictions at interior points. In addition, the results of the complementary study, which uses interior points during the model calibration, suggest that model performance at the outlet can be further improved by using a semi-distributed structure calibrated at both interior points and the outlet, even when only a few years of historical record are available.

Application of TOPMODEL in Buliu River catchment, Pearl River basin and comparison with Xin'anjiang model

TOPMODEL是一种以地形为基础的半分布式流域水文模型.对珠江流域布柳河流域的DEM信息进行处理,提取流域的水系、子流域边界、地形指数及水流路径距离的分布,将TOPMODEL应用于该流域中.另外将新安江模型也应用于该流域进行比较.此外,分析了两种模型结构差异所带来的模拟功能差异.两种模型模拟结果精度差异不大,而TOPMODEL实现了空间产流面积分布的可视化.;TOPMODEL is a semi-distributed model in which the predominant factors determining the formation of runoff are represented by the topography of the basin. In this paper we dealed with DEM information of Buliu river basin, extracting drainage network, sub-basin area, topographic index and distribution of runoff distance, and applied TOPMODEL in the basin. For the sake of comparison, the Xin'anjiang model was also applied in the basin. Here we analyzed the difference of simulation function due to the frameworks of the two models. The simulation results of the two models have little difference; moreover TOPMODEL realized the visualization of spatial source area distribution

Hydrological system analysis and groundwater recharge estimation using semi-distributed models and river discharge in the Meki River Basin

Hydrological system analysis and groundwater recharge estimation using semi-distributed models and river discharge in the Meki River Basin

General calibration methodology for a combined Horton-SCS infiltration scheme in flash flood modeling

Abstract. Flood forecasting undergoes a constant evolution, becoming more and more demanding about the models used for hydrologic simulations. The advantages of developing distributed or semi-distributed models have currently been made clear. Now the importance of using continuous distributed modeling emerges. A proper schematization of the infiltration process is vital to these types of models. Many popular infiltration schemes, reliable and easy to implement, are too simplistic for the development of continuous hydrologic models. On the other hand, the unavailability of detailed and descriptive information on soil properties often limits the implementation of complete infiltration schemes. In this work, a combination between the Soil Conservation Service Curve Number method (SCS-CN) and a method derived from Horton equation is proposed in order to overcome the inherent limits of the two schemes. The SCS-CN method is easily applicable on large areas, but has structural limitations. The Horton-like methods present parameters that, though measurable to a point, are difficult to achieve a reliable estimate at catchment scale. The objective of this work is to overcome these limits by proposing a calibration procedure which maintains the large applicability of the SCS-CN method as well as the continuous description of the infiltration process given by the Horton's equation suitably modified. The estimation of the parameters of the modified Horton method is carried out using a formal analogy with the SCS-CN method under specific conditions. Some applications, at catchment scale within a distributed model, are presented.

Nonlinear and fully distributed field effect transistor modelling procedure using time-domain method

An accurate and efficient modelling approach for field effect transistors (FET) as nonlinear active transmission lines is presented. The nonlinear active multiconductor transmission line (NAMTL) equations are obtained by considering the transistor as three active coupled lines operating in a nonlinear regime. This modelling procedure accurately spots the effect of wave propagation along the device electrodes. This modelling approach is applied to an FET by solving the NAMTL equations using a finite-difference time-domain technique. The results of this model are compared with the semi-distributed (slice) model. This method produces more accurate results than the slice model, especially at high frequencies.

A Decision Support System to Improve Water Resources Management in the Conchos Basin

The Conchos basin is the largest tributary to the lower part of the Rio Grande/Rio Bravo basin. During recent years a severe drought has affected Mexico’s ability to deliver water from the Conchos basin as required by the 1944 Treaty. In addition, it has generated not only economic problems in the USA and Mexico but also political frictions between these two countries. The Mexican Conchos river has historically contributed with the highest amount of water to USA as established on the water treaty. A Decision Support System (DSS) was developed for the Conchos basin in order to gain a better understanding of the water resources management process in the basin, and to identify the alternatives to improve the cited process. The DSS is a semi-distributed model, based on System Dynamics, and developed using Powersim software. The DSS has been used to evaluate 25 long and short tem water resources allocation alternatives for the two main basin’s users: Irrigation Districts and Water Treaty. Some of the most important factors being tested on the 25 water management alternatives include National Commission of Water’s yearly water allocation policy, reservoir operation rules, improvement on water distribution efficiencies, etc. The DSS model shows that the historic water resources allocation implemented by the Federal government produces adequate results as compared with the other tested water management alternatives. However, for short term drought scenarios, it is showed that there could be other management alternatives that could perform better than the current water management allocation. In general, the DSS shows what we already expect of dynamic models of systems to provide that understanding the effects of multiple interacting variables in necessary to develop good natural resource management policies.

A stochastic approach for the description of the water balance dynamics in a river basin

Abstract. The present paper introduces an analytical approach for the description of the soil water balance dynamics over a schematic river basin. The model is based on a stochastic differential equation where the rainfall forcing is interpreted as an additive noise in the soil water balance. This equation can be solved assuming known the spatial distribution of the soil moisture over the basin transforming the two-dimensional problem in space in a one dimensional one. This assumption is particularly true in the case of humid and semihumid environments, where spatial redistribution becomes dominant producing a well defined soil moisture pattern. The model allowed to derive the probability density function of the saturated portion of a basin and of its relative saturation. This theory is based on the assumption that the soil water storage capacity varies across the basin following a parabolic distribution and the basin has homogeneous soil texture and vegetation cover. The methodology outlined the role played by the soil water storage capacity distribution of the basin on soil water balance. In particular, the resulting probability density functions of the relative basin saturation were found to be strongly controlled by the maximum water storage capacity of the basin, while the probability density functions of the relative saturated portion of the basin are strongly influenced by the spatial heterogeneity of the soil water storage capacity. Moreover, the saturated areas reach their maximum variability when the mean rainfall rate is almost equal to the soil water loss coefficient given by the sum of the maximum rate of evapotranspiration and leakage loss in the soil water balance. The model was tested using the results of a continuous numerical simulation performed with a semi-distributed model in order to validate the proposed theoretical distributions.

Sensitivity of a lumped and semi-distributed hydrological model to several methods of rainfall interpolation on a large basin in West Africa

Summary This paper examines the sensitivity of a hydrological model to several methods of spatial interpolation of rainfall data. The question is investigated in a context of scarcity of data over a large West African catchment (100,000 km2) subject to a drastic trend of rain deficit since the 1970s. Thirteen widely scattered rainfall stations and their daily time series were used to interpolate gridded rainfall surfaces over the 1950–1992 period via various methods: Thiessen polygons, inverse distance weighted (IDW) method, thin smooth plate splines (spline), and ordinary kriging. The accuracy of these interpolated datasets was evaluated using two complementary approaches. First, a point-by-point assessment was conducted, involving comparison of the interpolated values by reference to observed point data. Second, a conceptual rainfall–runoff model (Hydrostrahler) was used in order to assess whether and to what extent the alternative sets of interpolated rainfall impacted on the hydrological simulations. A lumped modelling exercise over a long period (1952–1992) and a semi-distributed exercise over a short period (1971–1976) were performed, using calibrations aimed at optimizing a Nash–Sutcliffe criterion. The results were evaluated for each interpolated forcing dataset using statistical analysis and visual inspection of the simulated and observed hydrographs and the parameters obtained from calibration. Assessment of the interpolation methods by reference to point data indicates that interpolations using the IDW and kriging methods are more efficient than the simple Thiessen technique, and, to a lesser extent, than spline. The use of these data in a daily lumped modelling application shows a different ranking of the various interpolation methods with regard to various hydrological assessments. The model is particularly sensitive to the differences in the rainfall input volume produced by each interpolation method: the IDW dataset yields the highest hydrological efficiency while the spline dataset gets the poorest results. Although the calibration procedure makes it possible to partly compensate for the differences (or errors) between rain input datasets, the semi-distributed hydrological model remains sensitive to volumetric and spatial differences. Then, assessment of these combined differences through the sensitivity of the semi-distributed model provides us with more complete discrimination between the interpolated data inputs. The output results at the basin outlet do not decrease between the lumped and semi-distributed modelling exercises with the IDW and kriging datasets, in contrast to the Thiessen and spline datasets, which tends to indicate the superiority of the former two interpolated inputs. In this hydrological application, the IDW dataset is still shown to provide the most realistic results. Moreover, despite the scarcity of rainfall data, coherent semi-distributed values of the model parameters are obtained by calibration over a large gradient of climate conditions. Finally, it is observed that although the model reproduced the rainfall–runoff relationship before 1970 very well, regardless of which interpolated datasets were used, it was not able to satisfactorily simulate the basin behaviour after the change in rainfall regime. This inability needs further investigation and is the subject of ongoing research.

Effect of watershed subdivision on water-phase phosphorus modelling: An artificial neural network modelling application

This study is an effort to incorporate low-cost time-variant remote sensing (RS) information in watershed-scale total phosphorus (TP) modelling. Four watershed subdivisions were delineated to assess the impact of watershed subdivision on the prediction accuracy of TP concentration in stream water. Four TP artificial neural network (ANN) models were designed to incorporate RS data into a semi-distributed approach. The remotely derived enhanced vegetation index and the normalized difference water index were successful in representing vegetation dynamics in the devised models. The models were applied to a 15.6 km2 watershed in the Canadian Boreal Plain. Eight measures of goodness-of-fit statistics were used for model evaluation. Although statistical model evaluation did favour the finest resolution in this case study, the differences in performance indicators among the four models were insignificant for any practical application. The encouraging results from this exercise demonstrate the applicability of the ANN semi-distributed modelling approach and the usefulness of RS data in simulating TP dynamics. Such models can potentially serve as valuable tools for watershed-scale forest management.

Impacts of logging residue and stump removal on nitrogen export to a stream: A modelling approach

The use of forest chips for energy can decrease net carbon emissions to the atmosphere, but harvesting logging residues and stumps may have adverse effects on the environment, including changes in nutrient export to water-bodies. The aim of this study was, with the aid of a computer model, to simulate the effects of logging residue and stump removal on nitrogen (N) export from a clear-cut area to a stream. A spatially semi-distributed FEMMA ecosystem model (tool for Forestry Environmental Management) was used to simulate N export from a catchment subject to clear-cutting and four different scenarios of logging residue and stump removal. These scenarios were compared with a conventional clear-cutting scenario, where the logging residues were left on site. Simulations suggested that the logging residue recovery does not decrease N export to the stream. In the model this was explained by a decrease in microbial immobilization, which in the case of conventional clear-cutting reduces net release of N in decomposition and mitigates the export of N. The decrease in immobilization is directly related to the removal of the woody debris from the site. Simulations suggested that harvesting of logging residues in low atmospheric N-deposition areas is not an effective strategy for reducing N loads in water-bodies.

Modelling the non‐linear hydrological behaviour of a small Mediterranean forested catchment

AbstractA progressive perceptual understanding approach was used to identify a model structure able to represent the non‐linear behaviour of the hydrological cycle in a small intermittent Mediterranean stream. The initial lumped model structure consisting of a series of four connected water tanks (LU3) progressed to a model with five tanks (LU4), and finally to a semidistributed model structure (SD4) in which spatial variability of the evapotranspiration according to the vegetation cover and to the local aspect was considered. In the final model structure, which gave the best fit (Nash–Sutcliffe efficiency index = 0·78), an additional tank representing the riparian zone was included (SD4‐R). Results showed that the abrupt changes of the riparian water table during summer and the formation of a perched water table during the transition from dry to wet conditions were the main mechanisms leading to the non‐linear hydrological behaviour. The transpiration process from the saturated zone and the spatial variability of evapotranspiration resulted in key factors successfully representing the annual water balance. The spatial and temporal validations carried out for each of the four model structures considered in this study supported the hypothesis adopted during the calibration process. Copyright © 2008 John Wiley & Sons, Ltd.

Comparison of conceptual model performance using different representations of spatial variability

The objective in this study is to explore a solution to the question whether model input data having higher spatial resolution and higher model resolution, as most people assume, lead to better model performance within a given modelling objective. An attempt was made to modify the conceptual rainfall-runoff model HBV to incorporate a spatially distributed structure. Additionally, three more model structures based on the HBV model concept were designed: lumped, semi-lumped and semi-distributed. An automatic calibration procedure based on simulated annealing optimization algorithm was followed for maximizing an objective function composed of Nash-Sutcliffe coefficients of several temporal aggregation steps. The predictive performance from each model was then assessed and compared with other model structures with respect to stream flow prediction at the catchment outlet. The spatial variation of the meteorological input was produced using external drift kriging method from available limited point measurements. The models were applied to a mesoscale catchment located in central Europe. The simulated hydrographs obtained using different model structures were analyzed through comparison of their Nash-Sutcliffe coefficients and other goodness-of-fit indices. For the present study, semi-distributed and semi-lumped model structures outperformed the distributed and fully-lumped model structures. A possible explanation why the distributed model did not perform better than the simpler model structures is the use of limited available spatial information. The models use interpolated precipitation and temperature as input, which probably cannot reflect the true spatial variability. Another possible explanation is that only discharge at the catchment outlet was predicted; which is the purpose for which lumped and semi-distributed models were actually designed.

Simulation of runoff in West Africa: Is there a single data-model combination that produces the best simulation results?

Summary Is there a single combination of hydrologic model and data that yields the best simulations of runoff from a set of catchments in West Africa in the coming decades? To answer this question, a semi-distributed modelling platform was developed. It comprises two models (GR2M and Water Balance Model) and various datasets as inputs to these models (three potential evapotranspiration [PET] grids and four soil water holding capacity [WHC] grids). The platform makes it possible to regionalise runoff flows, which are discretised in grids of mesh size 0.5° × 0.5°. On the basis of these datasets and models, we compare the performance of the various possible data-model combinations. The study area contains 49 catchments located in Cote d’Ivoire, Guinea, Mali, Burkina Faso and Niger. The analysis shows that the selected models are hardly sensitive at all to the different PET grids but more sensitive to the soil grids. The GR2M model clearly gives the best results for the set of catchments, but does not perform well over the entire study area, whatever the grid dataset used: • It is thus seen to be difficult to define a single data-model combination that is optimal for simulating runoff in West Africa. • As to the existence of a “general” model that could be used anywhere, we find that, for the selected study area, neither of the two models selected fully meets the objective.

Lumped Approach to a Multi-Period–Multi-Reservoir Cyclic Storage System Optimization

Cyclic storage system (CSS) refers to the joint development and operation of surface impoundment and subsurface subsystems with natural and physical interaction and a prespecified operating rule which manages the inter-relation between different components of the system. This paper presents a lumped modeling approach to a generalized large scale cyclic storage system. The model is capable to optimally design and operate a cyclic system in an irrigable area. The excitation units with pronounced impact and a complexity of the semi-distributed model are replaced with approximated lumped functions, while maintaining a desirable level of accuracy in the system’s performance in a long-term planning horizon. The proposed model has a MINLP structure, which is solved using powerful well-known LINGO solver. Design capacities of different components of the system and the associated operating rules parameters are considered as decision variables that minimize total cost of operating costs over the planning horizon. Extensive simulation runs show that the derived operating rules perform quite satisfactory with non-significant deficits over the entire horizon.

Water protection and buffer zones: How much does it cost to reduce nitrogen load in a forest cutting?

Uncut buffer zones between clear-cuttings and water bodies can reduce export of nutrients to surface waters, but decrease in harvested stock volume result in losses of income for the landowner. Thinning in the buffer zones increases the income, but the effect of thinning on nutrient export is not well known. The FEMMA ecosystem model was applied to simulate nitrogen (N) export from a catchment with clear-cuttings and buffer zones. FEMMA is a spatially semi-distributed model calculating water and nitrogen fluxes in a scale of head-water catchments. The calibrated FEMMA model was applied to produce scenarios with different thinning intensities in buffer zones of varying dimensions. Reductions in N export achieved with buffer zones were computed for a 5-year period following the cutting. The economic current value of the stand left in the buffer zone represented an opportunity cost of the buffer zone. The unit cost of N reduction (€kg−1 N reduced) calculated from these simulations ranged from €219 to €1578 kg−1 N. A similar reduction in N export could be achieved with different combinations of buffer zone dimension and thinning intensity, but the unit costs of N reduction differed remarkably. The results indicate that cost-effective water protection can be achieved when the dimension of buffer zone and the intensity of thinning are optimized. Experimental research is warranted to verify these simulation results.

충주댐 상류유역의 유사 발생에 대한 시공간적인 특성

A physically based semi-distributed model, SWAT was applied to the Chungju Dam upstream watershed in order to investigate the spatial and temporal characteristics of watershed sediment yields. For this, general features of the SWAT and sediment simulation algorithm within the model were described briefly, and watershed sediment modeling system was constructed after calibration and validation of parameters related to the runoff and sediment. With this modeling system, temporal and spatial variation of soil loss and sediment yields according to watershed scales, land uses, and reaches was analyzed. Sediment yield rates with drainage areas resulted in excluding some upstream sub-watersheds and showed around 0.51 ton/ha/yr above the areas of . Annual average soil loss according to land use represented the higher values in upland areas, but relatively lower in paddy and forest areas which were similar to the previous results from other researchers. Among the upstream reaches, Pyeongchanggang and Jucheongang showed higher sediment yields which was thought to be caused by larger area and higher fraction of upland than other upstream sub-areas. Monthly sediment yields at the main outlet showed same trend with seasonal rainfall distribution, that is, approximately 62% of annual yield was generated during July to August and the amount was about 208 ton/yr. From the results, we could obtain the uniform value of sediment yield rate and could roughly evaluate the effect of soil loss with land uses, and also could analyze the temporal and spatial characteristics of sediment yields from each reach and monthly variation for the Chungju Dam upstream watershed.

Assimilation of meteorological and remote sensing data for snowmelt runoff forecasting

A versatile data assimilation scheme for remote sensing snow cover products and meteorological data was developed, aimed at operational use for short-term runoff forecasting. Spatial and temporal homogenisation of the various input data sets is carried out, including meteorological point measurements from stations, numerical weather predictions, and snow maps from satellites. The meteorological data are downscaled to match the scale of the snow products, derived from optical satellite images of MODIS and from radar images of Envisat ASAR. Snow maps from SAR and optical imagery reveal systematic differences which need to be compensated for use in snowmelt models. We applied a semi-distributed model to demonstrate the use of satellite snow cover data for short-term runoff forecasting. During the snowmelt periods 2005 and 2006 daily runoff forecasts were made for the drainage basin Ötztal (Austrian Alps) for time lags up to 6 days. Because satellite images were obtained intermittently, prognostic equations were applied to predict the daily snow cover extent for model update. Runoff forecasting uncertainty is estimated by using not only deterministic meteorological predictions as input, but also 51 ensemble predictions of the EPS system of the European Centre for Medium Range Weather Forecast. This is particularly important for water management tasks, because meteorological forecasts are the main error source for runoff prediction, as confirmed by simulation studies with modified input data from the various sources. Evaluation of the runoff forecasts reveals good agreement with the measurements, confirming the usefulness of the selected data processing and assimilation scheme for operational use.

Predicting Groundwater Rebound in the South Yorkshire Coalfield, UK

The semi-distributed model GRAM (groundwater rebound in abandoned mineworkings) has been applied to part of the South Yorkshire Coalfield, UK, to predict the pattern of groundwater rebound, in particular the timing and rates of changes in mine water flows between abandoned collieries. The model is based upon the mining hydrogeologist's concept of ‘ponds’ (discrete volumes of interconnected workings) and calculates water balances over time for all ponds in a multi-pond mined system. GRAM was successfully calibrated against observed groundwater levels over a 5 year period from 2001 to 2005 before being used to predict future rates of groundwater rebound, in accordance with different scenarios, including average, low, and high rainfall scenarios. The results reveal that it could take up to 22 years before an inflow of water occurs into the last remaining colliery in the area at Maltby, with the first surface discharge expected in approximately 15 years time from an old mine shaft. If Maltby is closed and pumping ceases across the area, then it could be 100 years before groundwater rebound is complete.