Simple Rainfall-runoff Model Research Articles

Investigating the performance of SWAT and IHACRES in simulation streamflow under different climatic regions in Iran

It is often reported that simpler models, due to their low parameter requirements, perform better than more complex models. To test this, the current study compared a simple rainfall-runoff model (IHACRES) with a complex watershed model (SWAT). Based on these two approaches, six models were developed for three climatically distinct (arid, semi-arid and semi-humid) watersheds in Iran. The coefficient of determination (R 2 ) and the Nash-Sutcliffe model efficiency coefficient (NS) were calculated in each case. In arid, semi-arid, and semi-humid watersheds the SWAT model (R 2 = 0.52, 0.68, 0.66; NS = 0.54, 0.63, 0.64, respectively) outperformed the IHACRES model (R 2 = 0.37, 0.70, 0.57; NS = 0.22, 0.57, 0.56, respectively) for the same respective climate zones. Overall, SWAT performed better than IHACRES, although both models had acceptable performances in the semi-arid and semi-humid watersheds. In the arid watershed, the IHACRES model performed poorly compared to SWAT.

RAINWATER HARVESTING FOR FLOOD PEAK REDUCTION IN WAY AWI CATCHMENT, INDONESIA

This study is motivated by floodings which occur frequently in Jagabaya village, Way Awi catchment, Bandar Lampung city, Indonesia. In addition to the intensity of rainfall, this area is considered as an urban area with intense housing and insufficient drainage capacity during heavy rain. This study aims to analyze flood peak reduction by simulating the application of rain barrels for each house. The volume of rain barrels used in the simulation is 0.5 to 5 m3. An Intensity-Duration-Frequency (IDF) curve is generated using short-duration rainfall data (i.e. 5, 10, 15, 30, 60, 120, 180, 360 and 720 minutes) recorded from Panjang Meteorological Bureau, Lampung. The rational method, a simple rainfall-runoff model, is used to calculate runoff generated both from catchment and rooftop. The result shows that the application of rain barrels may reduce flood peak up to 28% for 2 year return period of flood, while for 100 year return period of flood, the reduction may reach 13.64%. From this study, it can be concluded that rainwater harvesting utilizing rain barrel is significant in reducing flood peak. Furthermore, this result can be used to persuade both the society as well as the local government to do such flood mitigation in this densely populated urban area

A systematic comparison of statistical and hydrological methods for design flood estimation

Abstract We compare statistical and hydrological methods to estimate design floods by proposing a framework that is based on assuming a synthetic scenario considered as ‘truth’ and use it as a benchmark for analysing results. To illustrate the framework, we used probability model selection and model averaging as statistical methods, while continuous simulations made with a simple and relatively complex rainfall–runoff model are used as hydrological methods. The results of our numerical exercise show that design floods estimated by using a simple rainfall–runoff model have small parameter uncertainty and limited errors, even for high return periods. Statistical methods perform better than the linear reservoir model in terms of median errors for high return periods, but their uncertainty (i.e., variance of the error) is larger. Moreover, selecting the best fitting probability distribution is associated with numerous outliers. On the contrary, using multiple probability distributions, regardless of their capability in fitting the data, leads to significantly fewer outliers, while keeping a similar accuracy. Thus, we find that, among the statistical methods, model averaging is a better option than model selection. Our results also show the relevance of the precautionary principle in design flood estimation, and thus help develop general recommendations for practitioners and experts involved in flood risk reduction.

Matlab/R workflows to assess critical choices in Global Sensitivity Analysis using the SAFE toolbox

Global Sensitivity Analysis (GSA) is a set of statistical techniques to investigate the effects of the uncertainty in the input factors of a mathematical model on the model’s outputs. The value of GSA for the construction, evaluation, and improvement of earth system models is reviewed in a companion paper by Wagener and Pianosi (2019). The present paper focuses on the implementation of GSA and provides a set of workflow scripts to assess the critical choices that GSA users need to make before and while executing GSA. The workflows proposed here can be adopted by GSA users and easily adjusted to a range of GSA methods. We demonstrate how to interpret the outcomes resulting from these different choices and how to revise the choices to improve GSA quality, using a simple rainfall-runoff model as an example. We implement the workflows in the SAFE toolbox, a widely used open source software for GSA available in MATLAB and R.•The workflows aim to contribute to the dissemination of good practice in GSA applications.•The workflows are well-documented and reusable, as a way to ensure robust and reproducible computational science.

Uncertainties of flood frequency estimation approaches based on continuous simulation using data resampling

Flood frequency analyses (FFAs) are needed for flood risk management. Many methods exist ranging from classical purely statistical approaches to more complex approaches based on process simulation. The results of these methods are associated with uncertainties that are sometimes difficult to estimate due to the complexity of the approaches or the number of parameters, especially for process simulation. This is the case of the simulation-based FFA approach called SHYREG presented in this paper, in which a rainfall generator is coupled with a simple rainfall-runoff model in an attempt to estimate the uncertainties due to the estimation of the seven parameters needed to estimate flood frequencies. The six parameters of the rainfall generator are mean values, so their theoretical distribution is known and can be used to estimate the generator uncertainties. In contrast, the theoretical distribution of the single hydrological model parameter is unknown; consequently, a bootstrap method is applied to estimate the calibration uncertainties. The propagation of uncertainty from the rainfall generator to the hydrological model is also taken into account. This method is applied to 1112 basins throughout France. Uncertainties coming from the SHYREG method and from purely statistical approaches are compared, and the results are discussed according to the length of the recorded observations, basin size and basin location. Uncertainties of the SHYREG method decrease as the basin size increases or as the length of the recorded flow increases. Moreover, the results show that the confidence intervals of the SHYREG method are relatively small despite the complexity of the method and the number of parameters (seven). This is due to the stability of the parameters and takes into account the dependence of uncertainties due to the rainfall model and the hydrological calibration. Indeed, the uncertainties on the flow quantiles are on the same order of magnitude as those associated with the use of a statistical law with two parameters (here generalised extreme value Type I distribution) and clearly lower than those associated with the use of a three-parameter law (here generalised extreme value Type II distribution). For extreme flood quantiles, the uncertainties are mostly due to the rainfall generator because of the progressive saturation of the hydrological model.

Scenario-based decision support for an integrated management of water resources

ABSTRACTIn this study, analyses of future scenarios of water demand and supply as well as an assessment of trade-offs for water allocation across the different water use sectors in the upper Blue Nile basin are made. Different periods of regulation of Lake Tana (Ethiopia) and subsequent impacts on the lake level hydrological regime are investigated. A decision support system is developed and available water supply for normal- and low-flow hydrological conditions are determined based on recorded flow data and a simple rainfall-runoff model. Different scenarios have been triggered and simulations are conducted to understand the implications of planned water resource developments in the area. We found that the annual inflows to Lake Tana under an average hydrological condition are about 5.7 × 109 m3 and are estimated to reduce by about 27% when all planned water resources development projects are implemented in the catchment. These projects aim at the generation of 460 MW hydroelectric power and about a billion m3 per annum supply of water to the large-scale irrigation schemes. During low-flow conditions, supply will run short of demands and the lake water level can drop by 0.3 m from the natural outlet level (1785 m a.s.l). Lake water levels and long-term lake level fluctuations have been affected significantly due to regulation with subsequent impacts on the lake ecology. An upstream–downstream cooperation, transparency and participation in the decision making and establishment of an adequate data acquisition system are critically important elements in the management of water resources in the basin.

Spatio-temporal runoff estimation using TRMM satellite data and NRSC-CN method of a watershed of Upper Subarnarekha River basin, India

Geographical Information System (GIS) and Remote Sensing (RS) have acquired great significance in the recent years for estimation of runoff from watersheds and agricultural fields. This study has made use of the well-established tool, Natural Resources Conservation Service Curve Number (NRCS-CN) method to observe runoff over the study area in conjunction with GIS and RS. Pixel-wise runoff depth of the catchment was estimated by incorporating Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) data, Tropical Rainfall Measuring Mission (TRMM) multi-satellite precipitation analysis data for the years 2001–2011, and Landsat Enhanced Thematic Mapper (ETM)+ Land Use/Land Cover (LULC) information within the simple rainfall-runoff model. NRSC-CN was modified for Indian condition and the Hydrologic Engineering Center’s Geospatial Hydrologic Modeling System (HEC-Geo-HMS) extension was utilized for evaluating the Curve Number (CN). Rainfall-Runoff model was executed to compute pixel-wise runoff, utilizing the model builder interface of ARC GIS 10. It was observed that there had been an increase in the average runoff depth ranging from 2.25 to 2.48 mm in different micro-watersheds of the study area. There was also an increase in total runoff depth from 61.24 to 68.47 m following an increase in mean CN value from 55 in the year 2001 to 57 in the year 2011. This indicated a lesser increase in lower runoff level range and a greater increase in higher runoff level range. In terms of runoff within the watershed, a higher percentage of its micro-watersheds showed lower runoff range compared to the micro-watersheds with higher runoff range. A direct correlation was observed between reduction in agriculture with increased runoff, increase in open land, and decrease in vegetation.

A new French flash flood warning service

The French State services in charge of flood forecasting supervise about 22,000 km among the 120,000 km of the French rivers within a warning procedure called Vigilance Crues (http://www.vigicrues.gouv.fr ). Some recent dramatic flood events on small watershed not covered by Vigilance Crues highlight the need for a new warning procedure to anticipate violent flash floods that regularly affect rapid river-basins. Thus the concept emerged of an automatic warning service specifically dedicated to local crisis managers. This service will be less elaborated than Vigilance Crues, probably with false alarms and missed events sometimes, but it will deliver a first information. The generation of the warning is based on a simple rainfall-runoff hydrological model developed by Irstea on all French rivers, fed with radar-gauge rainfall grids provided by Meteo-France. Every fifteen minutes, the hydrological model estimates the discharges on the rivers eligible to the service and determine if certain thresholds corresponding to a high or very high flood are likely to be exceeded. The last step of the real-time system is to determine which municipalities are concerned with flood risk and send them an automatic warning by voice call, optionally by sms or email. A specific web interface is available for users to monitor the evolution of the flood risk on maps that are updated every 15 minutes. This new flash flood warning service will be operational early 2017 as a free service for about 8,000 French municipalities.

Relevance of an at-site flood frequency analysis method for extreme events based on stochastic simulation of hourly rainfall

Extreme events are rarely observed, so their analysis is generally based on observations of more frequent values. The relevance of the flood frequency analysis (FFA) method depends on its capability to estimate the frequency of extreme values with reasonable accuracy using extrapolation. An FFA method based on stochastic simulation of flood event is assessed based on its reliability and stability. For such an assessment, different training/testing decompositions are performed for a set of data from more than 1000 gauging stations. We showed that the method enables relevant ‘predictive’ estimates, e.g. by assigning correct return periods to the record values that are systematically absent in calibration datasets. The model is also highly stable vis-a-vis the sampling. This characteristic is linked to the use of regional statistical rainfall data and a simple rainfall–runoff model that requires the calibration of only one parameter.Editor D. Koutsoyiannis Associate editor Q. Zhang

The River Systems in Small Catchments in the Context of the Horton’s and Schumm’s Laws – Implication for Hydrological Modelling. The Case Study of the Polish Carpathians

Abstract In ungauged catchments, flood hydrographs are usually simulated/reconstructed by simple rainfall-runoff and routing models. Horton’s and Schumm’s ratios serve as the input data for many of these models. In this paper, more than 800 Carpathian catchments (up to 35.2 km2 in area) were investigated in context of the “Horton’s and Schumm’s laws”. Results reveal that the “law of stream number” and “law of stream areas” are fulfilled in almost all catchments. The mean that values of the bifurcation ratio (RB) and the area ratio (RA) reach 3.8 and 4.8, respectively, and are thus comparable to values reported in other regions of the world. However, the “law of stream lengths” is not fulfilled in more than half of the catchments, which is not consistent with many theoretical studies reported in the literature. Only 383 (48%) catchments fulfill the “law of stream length”, with the mean value of the length ratio (RL)=2.3. There was no relationship found between the geological/geomorphological settings that influence river system development and the spatial distribution of catchments where the “law of stream length” was or was not was fulfilled. A similar conclusion was reached for the spatial distribution of the RB, RL, and RA ratios. These results confirmed that the use of Horton’s and Schumm’s ratios for the evaluation of the influence of geological/geomorphological settings on the river system development is limited. Among the lumped hydrological models, those requiring the RB, RL, and RA ratios have been extensively studied over last decades. This study suggests that the application of these models may be limited in small catchment areas; therefore, more attention should be placed on the development of hydrological models where the RB, RL, and RA ratios are not necessary.

Water balance of a lake with floodplain buffering: Lake Tana, Blue Nile Basin, Ethiopia

Summary Lakes are very important components of the earth’s hydrological cycle, providing a variety of services for humans and ecosystem functioning. For a sustainable use of lakes, a substantial body of knowledge on their water balance is vital. We present here a detailed daily water balance analysis for Lake Tana, the largest lake in Ethiopia and the source of the Blue Nile. Rainfall on the lake is determined by Thiessen polygon procedure, open water evaporation is estimated by the Penman-combination equation and observed inflows for the gauged catchments as well as outflow data at the two lake outlets are directly used. Runoff from ungauged catchments is estimated using a simple rainfall–runoff model and runoff coefficients. Hillslope catchments and floodplains are treated separately, which makes this study unique compared to previous water balance studies. Impact of the floodplain on the lake water balance is analyzed by conducting scenario-based studies. We found an average yearly abstraction of 420 × 106 m3 or 6% of river inflows to the lake by the floodplain in 2012 and 2013. Nearly 60% of the inflow to the lake is from the Gilgel Abay River. Simulated lake levels compare well with the observed lake levels (R2 = 0.95) and the water balance can be closed with a closure error of 82 mm/year (3.5% of the total lake inflow). This study demonstrates the importance of floodplains and their influence on the water balance of the lake and the need of incorporating the effects of floodplains and water abstraction for irrigation to improve predictions.

Modeling Watershed Response in Semiarid Regions With High-Resolution Synthetic Aperture Radars

In this paper, we propose a methodology devoted to exploit the outstanding characteristics of COSMO-SkyMed for monitoring water bodies in semiarid countries at a scale never experienced before. The proposed approach, based on appropriate registration, calibration, and processing of synthetic aperture radar (SAR) data, allows outperforming the previously available methods for monitoring small reservoirs, mainly carried out with optical data, and severely limited by the presence of cloud coverage, which is a frequent condition in wet season. A tool has been developed for computing the water volumes retained in small reservoirs based on SAR-derived digital elevation model. These data have been used to derive a relationship between storage volumes and surface areas that can be used when bathymetric information is unavailable. Due to the lack of direct measures of river's discharge, the time evolution of water volumes retained at reservoirs has been used to validate a simple rainfall-runoff hydrological model that can provide useful recommendation for the management of small reservoirs. Operational scenarios concerning the improvement in the efficiency of reservoirs management and the estimation of their impact on downstream area point out the applicative outcomes of the proposed method.

Bayesian scrutiny of simple rainfall–runoff models used in forest water management

Summary Simple rainfall–runoff models used in the assessment of land-use change and to support forest water management are subjected to a selection process which scrutinises their veracity and integrity. Veracity, the ability of a model to provide meaningful information is assessed using performance criteria, incorporating: a popular mean square error (MSE) approach; empirical distribution functions and information criteria. Integrity, a model’s plausibility reflected in its ability to extract information from data, is assessed using a Bayesian approach. A delayed rejection, adaptive Metropolis algorithm is used with a generalised likelihood to calibrate the models. Predictive uncertainty is assessed using a split sample procedure which uses high runoff data for calibration and drier data for validation. A simple multiplicative latent variable is used to accommodate input uncertainty in rainfall data, enabling a distinction to be made between uncertainty associated with data, parameters and the models themselves. The study demonstrates: the focus provided by setting model evaluation in a philosophical context; the benefits of using a more meaningful range of performance criteria than MSE-based approaches and the insights into integrity provided by Bayesian analyses. A hyperbolic tangent model is selected as the best of five candidates for its superior veracity and integrity under Australian conditions. Models with extensive application in South Africa, Australia and USA are rejected. Challenges to applying this approach in water management are identified in the pragmatic nature of the sector, its capacity constraints and a tendency of researchers to place confidence in accepted methods at the expense of rigour.

An operational flood warning system for poorly gauged basins: demonstration in the Guadalhorce basin (Spain)

This paper deals with the presentation of a flood warning system (GFWS) developed for the specific characteristics of the Guadalhorce basin (3,200 km2, SE of Spain), which is poorly gauged and often affected by flash and plain floods. Its complementarity with the European flood alert system (EFAS) has also been studied. At a lower resolution, EFAS is able to provide a flood forecast several days in advance. The GFWS is adapted to the use of distributed rainfall maps (such as radar rainfall estimates), and discharge forecasts are computed using a distributed rainfall–runoff model. Due to the lack of flow measurements, the model parameters calibrated on a small watershed have been transferred in most of the basin area. The system is oriented to provide distributed warnings and fulfills the requirements of ungauged basins. This work reports on the performance of the system on two recent rainfall events that caused several inundations. These results show how the GFWS performed well and was able to forecast the location and timing of flooding. It demonstrates that despite its limitations, a simple rainfall–runoff model and a relatively simple calibration could be useful for event risk management. Moreover, with low resolution and long anticipation, EFAS appears as a good complement tool to improve flood forecasting and compensate for the short lead times of the GFWS.

Quantifying effects of catchments storage thresholds on step changes in the flood frequency curve

[1] Previous work has shown that non linear catchment response related to a storage threshold may translate into a step change in the flood frequency curve. The aim of this paper is to understand the controls of this step change for catchments where runoff is generated by the saturation excess mechanism and a clear separation between a permanently saturated region and a variably saturated region with spatially uniform storage deficits exists. The magnitude of the step change is quantified by the maximum of the second derivative (curvature) of the flood peaks with respect to their return period. Sensitivity analyses with a stochastic rainfall model and a simple rainfall runoff model show that the magnitude of the step change decreases with increasing temporal variability of antecedent soil storage, and increases with increasing area of the variably saturated region. The return period where the step change occurs is very similar to the return period of the rainfall volume that is needed to exceed the storage threshold. Diagrams are presented that show the joint effects of spatial and temporal storage variability on the magnitude and return period of the step change. The diagrams are useful for assessing whether step changes in the flood frequency curve are likely to occur in catchments where the runoff generation characteristics are as examined here and the flood records are too short to indicate a step change.

Evaluating the performance of reservoirs in semi-arid catchments of Tigray: Tradeoff between water harvesting and soil and water conservation

Micro dams play a vital role towards boosting crop production in Northern Ethiopia as they can be built by pooling local resources, are simple to design and can be constructed quite quickly. However, the reservoirs do not always fulfill their intended purpose, and hence less land is irrigated than initially foreseen. Here, we evaluated the performance of twomicro dams in Tigray by analyzing rainfall characteristics, surface water inflows and combined evaporation and seepage losses. Given the scarcity of reliable meteorological stations, transfer of rainfall data from nearby stations to the dam sites was necessary. The rainfallmagnitude and its annual distribution were considered for the transfer of the rainfall data. The latterwas estimated based on a precipitation concentration index (PCI). Simple rainfall-runoff models, such as the curve number method proposed by the US Department of Agriculture Soil Conservation Service, or the rational method were used to predict the inflow to the reservoirs. Both methods slightly overestimated the monthly inflow for the catchment without soil and water conservation measures (rational method: bias of 24% and curve number method: bias of 9%). In the catchment where soil and water conservation measures were implemented, the inflow was overestimated by a factor three. The high losses of water through seepage and evaporation substantially decreased the irrigation capacity by up to 33%. This case study illustrates that an integrated assessment of the hydrological response in the catchment is necessary for an adequate design of water harvesting systems.

Characterizing streamflow response of a mountaintop-mined watershed to changing land use

Mountaintop removal mining is a dominant driver of land use/land cover changes in the Appalachian Region of the eastern United States and is expected to increase in scale in the coming decades. While several studies quantify land use/land cover changes attributed to traditional surface mining and at regional scales, no studies we are aware of focus specifically on mountaintop removal/valley fill mining practices at the watershed scale. Further, despite its scale and extent, its impact on runoff, particularly at larger spatial scales (103 km2), is poorly understood due to the complex relationships between climate, land use, and hydrology. To explore the impacts of this practice at broader scales, we estimated land use/land cover changes using Landsat 5 TM imagery over five periods between 1994 and 2010; used a simple rainfall–runoff model to estimate hydrologic response time; and conducted non-parametric trend analyses on annual hydrologic metrics (streamflow, Q/P, response time) for the Big Coal River watershed located in the southern West Virginia coalfields. No statistically significant trends were detected in any of the timeseries. The lack of detectable trends and correlations between land use changes and hydrology at the basin scale are not entirely unexpected due to the history and mosaic of land cover changes that span timescales larger than our study period. Further interannual variation likely overwhelms our ability to detect potential changes using monotonic trend analysis at the annual time scale, particularly in light of strong streamflow seasonality. Future studies therefore should include different methods of change detection applied to different timescales to more appropriately account seasonal and interannual variations. Until the significance of this practice on water resources (quality and quality) are understood, efforts to reduce the environmental problems associated with mountaintop mining will be difficult to achieve.

Parameter calibration and uncertainty estimation of a simple rainfall-runoff model in two case studies

The simple rainfall-runoff conceptual KIDS (Kielstau Discharge Simulation) model using PCRaster is applied to simulate continuously daily discharge of the Kielstau and XitaoXi basins. This work focuses on parameter calibration procedure and, in particular, assessment of model prediction uncertainty. We employ a simplistic analysis routine SUFI-2, coupled with the implementation of a Monte Carlo based sampling strategy for the joint investigation of parameter calibration and uncertainty estimation. The scatter plots of model performance and parameter exhibit high equifinality of parameter sets in fitting observations, while their histogram distribution patterns imply that most parameters can be well defined. This study investigates parameter sensitivities and finds interesting local results: soil and groundwater parameters are more sensitive in Kielstau models than in XitaoXi models, and only the soil parameters ‘Sfk’ and ‘Kc’ are found strongly correlated. Finally, the uncertainty bounds are always thin and the global shape of the hydrograph is well approximated for both basins. As the validated uncertainty bounds also represent the desired coverage (P factor >50%) of the observations, and the calculated R factor values are in the targeted range (R factor < 1), it demonstrates the efficiency and suitability of this revised SUFI method for the two case studies.

Estimating the impacts and uncertainty of changing spatial input data resolutions on streamflow simulations in two basins

The impact of different grid resolutions of spatial input data on modelled river runoff are investigated using the simple rainfall-runoff model KIDS (Kielstau Discharge Simulations) in PCRaster modelling language for two watersheds – Kielstau and XitaoXi. In this study, the grid-based spatial data are aggregated to coarser resolutions to support the multi-resolution, multi-calibration and multi-site analysis for grid-scale investigations. Daily streamflow is simulated and model parameters are calibrated at each spatial resolution. The study suggests that re-calibration is critically needed when the grid resolution is changed. Altering grid sizes has an apparent impact on the parameter distribution patterns. Resolution uncertainty bands obtained by the overlapping hydrographs generated with different resolutions of input data are reported with a sufficient coverage of the observations for both basins. The analysis of model efficiency in terms of IC-ratio (a ratio between the input grid area and the catchment area) indicates that coarser resolutions with an IC-ratio of <0.001 may be used as an effective alternative for conducting preliminary analyses in streamflow simulation for the Kielstau basin. The modelling outputs are more sensitive to the spatial distribution of input data at the XitaoXi watershed, showing that accurate input data are required to achieve optimum modelling performance.

Application of ArcGIS in the Calculation of Basins Rainfall-Runoff

Abstract It is key issue to predict the rainfall-runoff process on the Kuronagi River before the joint sediment flushing and sluicing of Dashidaira and Unazuki dams at the downstream of the Kurobe River. In this paper, the ArcGIS system is used to produce the digital basin of the Kuronagi River, the distributed Kinematic Wave hydrological model is used to calculate the rainfall-runoff process on the Kuronagi River, and the results are in good agreement with the observations. The results show that with the progress of rainfall observation techniques and computational methods, the development of digital land information and the effective application of GIS technology, a relatively simple rainfall-runoff model can get higher precision results.