Rainfall-Runoff Modeling and Hydrological Responses to the Projected Climate Change for Upper Baro Basin, Ethiopia

This paper presents the results of Rainfall-Runoff modeling and simulation of hydrological responses under changing climate using HEC-HMS model. The basin spatial data was processed by HEC-GeoHMS and imported to HEC-HMS. The calibration and validation of the HEC-HMS model was done using the observed hydrometeorological data (1989-2018) and HEC-GeoHMS output data. The goodness-of-fit of the model was measured using three performance indices: Nash and Sutcliffe coefficient (NSE) = 0.8, Coefficient of Determination (R2) = 0.8, and Percent Difference (D) = 0.03, with values showing very good performance of the model. Finally, the optimized HEC-HMS model has been applied to simulate the hydrological responses of Upper Baro Basin to the projected climate change for mid-term (2040s) and long-term (2090s) A1B emission scenarios. The simulation results have shown a mean annual percent decrease of 3.6 and an increase of 8.1 for Baro River flow in the 2040s and 2090s scenarios, respectively, compared to the baseline period (2000s). A pronounced flow variation is rather observed on a seasonal basis, reaching a reduction of 50% in spring and an increase of 50% in autumn for both mid-term and long-term scenarios with respect to the base period. Generally, the rainfall-runoff model is developed to solve, in a complementary way, the two main problems in water resources management: the lack of gauged sites and future hydrological response to climate change data of the basin and the region in general. The study results imply that seasonal and time variation in the hydrologic cycle would most likely cause hydrologic extremes. And hence, the developed model and output data are of paramount importance for adaptive strategies and sustainable water resources development in the basin.

Effects of land-use pattern change on rainfall-runoff and runoff-sediment relations:a case study in Zichang watershed of the Loess Plateau of China

The purpose of this article is to identify the effect of land use pattern on rainfall runoff and runoff sediment relations in Zichang Watershed of the Loess Plateau. From 1986 to 1997, many farmlands changed into grassland or woodland, especially the farmland in steep slope positions or far away from the river. The change of land use pattern altered the rainfall runoff and runoff sediment relationships, and led to higher slope of trend curves(STCs) of annual rainfall runoff mass curve and runoff sediment mass curve in 1990s than that in 1980s. It is implied that more soil and water loss yielded in 1990s. In order to reduce soil loss, more attentions should be paid to land use pattern and some grass or other herbaceous filter strips should be built along rivers.

Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.

Phosphorus transport with runoff of simulated rainfall from purple-soil cropland of different surface conditions

We investigated the patterns of phosphorus transport from purple-soil cropland of 5° and 10° slopes with bare and vegetated surfaces,respectively.Each type of land was tested under a simulated moderate rainfall of 0.33 mm/min,a downfall of 0.90 mm/min,and a rainstorm of 1.86 mm/min.Runoff dynamics and changes in the export amount of phosphorus are influenced by the rainfall intensity,the slope and surface conditions of cropland.The vegetation diverts rain water from the surface into soil and helps the formation of a subsurface runoff,but has little influence on runoff process at the same sloping degree.Vegetated soil has a smaller phosphorous loss,particularly much less in the particulate form.A heavier rainfall flushes away more phosphorous.Rainwater percolating soil carries more dissolved phosphorous than particulate phosphorous.Understanding the patterns of phosphorous transport under various conditions from purple soil in the middle of Sichuan basin is helpful for developing countermeasures against non-point-source pollution resulting in the eutrophication of water bodies in this region that could,if not controlled properly,deteriorate the water quality of the Three Gorges Reservoir.

Rainfall-runoff simulation and flood forecasting for Huaihe Basin

The main purpose of this study was to forecast the inflow to Hongze Lake using the Xin＇anjiang rainfall-runoff model. The upper area of Hongze Lake in the Huaihe Basin was divided into 23 sub-basins, including the surface of Hongze Lake. The influence of reservoirs and gates on flood forecasting was considered in a practical and simple way. With a one-day time step, the linear and non-linear Muskingum method was used for channel flood routing, and the least-square regression model was used for real-time correction in flood forecasting. Representative historical data were collected for the model calibration. The hydrological model parameters for each sub-basin were calibrated individually, so the parameters of the Xin＇anjiang model were different for different sub-basins. This flood forecasting system was used in the real-time simulation of the large flood in 2005 and the results are satisfactory when compared with measured data from the flood.

Hydrological daily rainfall-runoff simulation with BTOPMC model and comparison with Xin'anjiang model

A grid-based distributed hydrological model, the Block-wise use of TOPMODEL （BTOPMC）, which was developed from the original TOPMODEL, was used for hydrological daily rainfall-runoff simulation. In the BTOPMC model, the runoff is explicitly calculated on a cell-by-cell basis, and the Muskingum-Cunge flow concentration method is used. In order to test the model＇s applicability, the BTOPMC model and the Xin＇anjiang model were applied to the simulation of a humid watershed and a semi-humid to semi-arid watershed in China. The model parameters were optimized with the Shuffle Complex Evolution （SCE-UA） method. Results show that both models can effectively simulate the daily hydrograph in humid watersheds, but that the BTOPMC model performs poorly in semi-humid to semi-arid watersheds. The excess-infiltration mechanism should be incorporated into the BTOPMC model to broaden the model＇s applicability.

Experimental research on the influence of two cultivation practices on rainfall runoff-and (sandy and muddy) sediment-generating processes in purple soil environment

Rainfall simulations have been conducted to study the soil erosion process of purple soil in two cultiva-tion practices—contour cultivation and downslope cultivation. Results showed that under the two cultivation prac-tices,the surface runoff can be described by the logarithmic function formula. In the initial period of rainfall,the amount of runoff increased with the rainfall duration and 20 minutes later it became relatively constant. The chang-ing process of soil erosion rate may be described by the logarithmic function formula. The erosion rate increased with the rainfall duration and 20 minutes later it also became constant. Under downslope cultivation condition,the soil erosion rate increased more significantly than that under contour cultivation condition in the case of gentle rain-fall intensity,and there is no obvious difference in erosion rate for downslope cultivation and contour cultivation practices. However,with increasing rainfall intensity the soil erosion rate under the downslope cultivation condition could be more than 30 times that under the contour cultivation condition. But this kind of difference would be re-duced to some extent in the case of heavy rain.

Surface Treatments Effect on Rainfall Canopy Interception and Runoff-Rainfall Ratio for in-Field Rainwater Harvesting

The purpose of this study was to ascertain the effectiveness of surface treatments to quantify the partitioning of rainwater falling on the runoff strips and basins as well as to determine the fraction of rainwater available to intercept by maize canopy and infiltrate into the root zone. The rainfall canopy interception （RCI） was estimated as a function of basin leaf area ratio per rain event. The runoffrainfall （RR） ratio was determined for both a single rainfall event and the whole growing season. Infiltration ratio of basin to runoff area was analysed for every unit millimeter of water that infiltrate in the runoff section, some additional of water will infiltrate in the basin area. The plateau value of RCI-rainfall relationships rendered about double in the wider （1.0-1.1 mm） compared to the narrow runoff strips （0.5-0.6 mm）. Statistically, the combined surface treatments （RSL x ML） affected the RR ratio with higher efficiency in bare 1 m runoff （27%） and the lower efficiency group （〈 10%） is associated with the widest runoff length covered with mulch. Variations in fractions of rainwater that can infiltrate into basins and runoffareas can lead one to select alternative strategies for water harvesting techniques.

Effects of urban grass coverage on rainfall-induced runoff in Xi'an loess region in China

In this study, laboratory rainfall simulation experiments were conducted to investigate the regulatory effects of grass coverage on rainfallrunoff processes. A total of 80 grass blocks planted with well-grown manilagrass, together with their root systems, were sampled from an eastern suburban area of Xi'an City in the northwest arid area of China and sent to a laboratory for rainfall simulation experiments. The runoff and infiltration processes of a slope with different grass coverage ratios and vegetation patterns were analyzed. The results show that the runoff coefficient decreases with the increase of the grass coverage ratio, and the influence of grass coverage on the reduction of runoff shows a high degree of spatial variation. At a constant grass coverage ratio, as the area of grass coverage moves downward, the runoff coefficient, total runoff,and flood peak discharge gradually decrease, and the flood peak occurs later. With the increase of the grass coverage ratio, the flood peak discharge gradually decreases, and the flood peak occurs later as well. In conclusion, a high grass coverage ratio with the area of grass coverage located at the lower part of the slope will lead to satisfactory regulatory effects on rainfall-induced runoff.

Rainfall-runoff modeling for storm events in a coastal forest catchmen t using neural networks

The process of transformation of rainfall into runoff over a catchment is very complex and highly nonlinear and exhibits both tempor al and spatial variabilities. In this article, a rainfall-runoff model using th e artificial neural networks (ANN) is proposed for simula ting the runoff in storm events. The study uses the data from a coa stal forest catchment located in Seto Inland Sea, Japan. This article studies the accuracy of the short-term rainfall forecast obta ined by ANN time-series analysis techniques and using antecedent rainfa ll depths and stream flow as the input information. The verification results from the proposed model indicate that the approach of ANN rai nfall-runoff model presented in this paper shows a reasonable agreement in rainfall-runoff modeling with high accuracy.

Particle Swarm Optimization for Identifying Rainfall-Runoff Relationships

Rainfall-runoff processes can be considered a single input-output system where the observed rainfall and runoff are inputs and outputs, respectively. Conventional models of these processes cannot simultaneously identify unknown structures of the system and estimate unknown parameters. This study applied a combinational optimization and Particle Swarm Optimization (PSO) for simultaneous identification of system structure and parameters of the rainfall-runoff relationship. Subsystems in proposed model are modeled using combinations of classic models. Classic models are used to transform the system structure identification problem into a combinational optimization and can be selected from those typically used in the hydrological field. A PSO is then applied to select the optimized subsystem model with the best data fit. The parameters are estimated simultaneously. The proposed model is tested in a case study of daily rainfall-runoff for the upstream Kee-Lung River. Comparison of the proposed method with simple linear model (SLM) shows that, in both calibration and validation, the PSO simulates the time of peak arrival more accurately compared to the SLM. Analytical results also confirm that the PSO accurately identifies the system structure and parameters of the rainfall-runoff relationship, which are a useful reference for water resource planning and application.

Artificial Neural Networks for Event Based Rainfall-Runoff Modeling

The Artificial Neural Network (ANN) approach has been successfully used in many hydrological studies especially the rainfall-runoff modeling using continuous data. The present study examines its applicability to model the event-based rainfall-runoff process. A case study has been done for Ajay river basin to develop event-based rainfall-runoff model for the basin to simulate the hourly runoff at Sarath gauging site. The results demonstrate that ANN models are able to provide a good representation of an event-based rainfall-runoff process. The two important parameters, when predicting a flood hydrograph, are the magnitude of the peak discharge and the time to peak discharge. The developed ANN models have been able to predict this information with great accuracy. This shows that ANNs can be very efficient in modeling an event-based rainfall-runoff process for determining the peak discharge and time to the peak discharge very accurately. This is important in water resources design and management applications, where peak discharge and time to peak discharge are important input

Evaluating the Performance of HEC-HMS and SWAT Hydrological Models in Simulating the Rainfall-Runoff Process for Data Scarce Region of Ethiopian Rift Valley Lake Basin

A number of physically-based and distributed watershed models have been developed to model the hydrology of the watershed. For a specific watershed, selecting the most suitable hydrological model is necessary to obtain good simulated results. In this study, two hydrologic models, Soil and Water Assessment Tool (SWAT) and Hydrological Engineering Centre-The Hydrologic Modeling System (HEC-HMS), were applied to predict streamflow in Katar River basin, Ethiopia. The performances of these two models were compared in order to select the right model for the study basin. Both models were calibrated and validated with stream flow data of 11 years (1990-2000) and 7 years (2001-2007) respectively. Nash-Sutcliffe Error (NSE) and Coefficient of Determination (R2) were used to evaluate efficiency of the models. The results of calibration and validation indicated that, for river basin Katar, both models could simulate fairly well the streamflow. SWAT gave the model performance with the R2 > 0.78 and NSE > 0.67;and the HEC-HMS model provided the model performance with the R2 > 0.87 and NSE > 0.73. Hence, the simulated streamflow given by the HEC-HMS model is more satisfactory than that provided by the SWAT model.

Using SWAT Model and Field Data to Determine Potential of NASA-POWER Data for Modelling Rainfall-Runoff in Incalaue River Basin

Incalaue is a tributary of Lugenda River in NSR (Niassa Special Reserve) in North-Eastern Mozambique. NSR is a data-poor remote area and there is a need for rainfall-runoff data to inform decisions on water resources management, and scientific methods are needed for this wide expanse of land. This study assessed the potential of a combination of NASA-POWER (National Aeronautics and Space Administration and Prediction of Worldwide Energy Resources) remotely sensed rainfall data and FAO (Food and Agriculture Organization of the United Nations) soil and land use/cover data for modelling rainfall-runoff in Incalaue river basin. DEM (Digital Elevation Model) of 1:250,000 scale and a grid resolution of 30 m × 30 m downloaded from USGS (the United States Geological Survey) website;clipped river basin FAO digital soil and land use/cover maps;and field-collected data were used. SWAT (Soil and Water Assessment Tool) model was used to assess rainfall -runoff data generated using the NASA-POWER dataset and gauged rainfall and river flow data collected during fieldwork. FAO soil and land use/cover datasets which are globally available and widely used in the region were used for comparison with soil data collected during fieldwork. Field collected data showed that soil in the area is predominantly sandy loam and only sand content and bulk density were uniformly distributed across the soil samples. SWAT model showed a good rainfall-runoff relationship using NASA-POWER data for the area (R2 = 0.7749) for the studied period (2019-2021). There was an equally strong rainfall-runoff relationship for gauged data (R2 = 0.8131). There were uniform trends for the rainfall, temperature, and relative humidity in NASA-POWER meteorological data. Timing of peaks and lows in rainfall and river flow observed in the field and modelled were confirmed by residents as the trend in the area. This approach was used because there was no historical rainfall and river flow data since the river basin is ungauged for hydrologic data. The study showed that NASA-POWER data has the potential for use for modelling the rainfall-runoff in the basin. The difference in rainfall-runoff relationship with field-collected data could be because of landscape characteristics or topsoil layer not catered for in the FAO soil data.

基于物联网和GCNN-LSTM的河流水文预测方法

针对河流水文存在预测精度不高的问题,利用物联网技术设计了分布式的降雨和水文信息自动采集系统,并提出了一种基于图卷积神经网络和长短期记忆网络模型对河流水位和径流量进行预测的方法;首先通过分析确定了影响河流水文的主要因素,将流域范围内的降雨量信息组成网格化的二维图形矩阵;然后提出了GCNN-LSTM预测模型,将含有降雨信息的二维图形矩阵作为网络模型的输入,获取该流域内降雨与水文变化的时空分布特征;最后采用所提出的GCNN-LSTM预测模型对河南省周口市段颍河的历史水文数据进行训练,再利用训练后的网络对测试集数据进行预测,得到了较高精度的径流量和水位结果,径流量预测结果的RMSE、MAPE和MAE分别仅为17.09 m^(3)/s、1.68%和8.57 m^(3)/s,水位预测结果的RMSE、MAPE和MAE分别仅为0.32 m、0.65%和0.29 m,与其他几种预测方法相比表现出了优越性,对科学合理利用水资源和防洪减灾具有重要意义。

Impacts of water quality variation and rainfall runoff on Jinpen Reservoir,in Northwest China

The seasonal variation characteristics of the water quality of the Jinpen Reservoir and the impacts of rainfall runoff on the reservoir were investigated. Water quality monitoring results indicated that, during the stable stratification period, the maximum concentrations of total ni- trogen, total phosphorus, ammonia nitrogen, total organic carbon, iron ion, and manganese ion in the water at the reservoir bottom on September 6 reached 2.5 mg/L, 0.12 mg/L, 0.58 mg/L, 3.2 mg/L, 0.97 mg/L, and 0.32 rag/L, respectively. Only heavy storm runoff can affect the main reservoir and cause the water quality to seriously deteriorate. During heavy storms, the stratification of the reservoir was destroyed, and the reservoir water quality consequently deteriorated due to the high-turbidity particulate phosphorus and organic matter in runoff. The turbidity and concentrations of total phosphorus and total organic carbon in the main reservoir increased to 265 NTU, 0.224 mg/L, and 3.9 mg/L, respectively. Potential methods of dealing with the water problems in the Jinpen Reservoir are proposed. Both in stratification and in storm periods, the use of measures such as adjusting intake height, storing clean water, and releasing turbid flow can be helpful to safeguarding the quality of water supplied to the water treatment plants.

Effects of freeze-thaw on soil erosion processes and sediment selectivity under simulated rainfall

The freeze-thaw （FT） processes affect an area of 46.3% in China. It is essential for soil and water conservation and ecological construction to elucidate the mechanisms of the FF processes and its associated soil erosion processes. In this research, we designed the control simulation experiments to promote the understanding of FT-water combined erosion processes. The results showed that the runoff of freeze-thaw slope （FTS） decreased by 8% compared to the control slope （CS）, and the total sediment yield of the FTS was 1.10 times that of the CS. The sediment yield rate from the FTS was significantly greater than that from the CS after 9 min of runoff （P〈0.01）. Both in FTS and CS treatments, the relationships between cumulative runoff and sediment yield can be fitted well with power functions （R2〉0.98, P〈0.01）. Significant differences in the mean weight diameter （MWD） values of particles were between the CS and the FTS treatments in the erosion were smaller than those under FTS for both washed and observed for washed particles and splashed particles process （P〈0.05）. The mean MWD values under CS splashed particles. The ratio of the absolute value of a regression coefficient between the CS and the FTS was 1.15, being roughly correspondent with the ratio of K between the two treatments. Therefore, the parameter a of the power function between cumulative runoff and sediment yield could be an acceptable indicator for expressing the soil erodibility. In conclusion, the FTS exhibited an increase in soil erosion compared to the CS.

Soil detachment and transport under the combined action of rainfall and runoff energy on shallow overland flow

Rainfall and runoff energy results in soil erosion. This paper presents new the concepts of rainfall and runoff energy and analyzes the relationship of rainfall energy and runoff energy with sediment transport based on the conversion theory of kinetic and potential energy using artificial rainfall and mechanical calculation. The results show that the ratio of sediment detachment in sloping fallow overland flow increases with the slope gradient,rainfall energy and runoff energy, while the sediment detachment ratio under raindrop impact are significantly higher than those under no raindrop impact. The sediment concentration increases with the slope gradient and rainfall energy; when the slope gradient and rainfall energy are constant, the sediment concentration decreases as the runoff energy increases. Rainfall disturbance coefficients have a logarithmic correlation with the rate of rainfall energy and runoff energy. On the same slope gradient,when the rainfall energy is constant, the disturbance coefficient decreases as the runoff energy increases,while when the runoff energy is constant, the disturbance coefficient increases as the rainfall energyincreases. Rainfall energy results in sediment detachment, and runoff energy is the transportation for erosion sediment. This showed that rainfall energy and runoff energy are important in the sediment detachment and transportation of shallow overland flow.

Grey Relational Analysis on the Effects of Rainfall Factors on Runoff and Sediment in the Sloping Farmland with Different Plants in the Central South of Shandong Province

[Objective] The aim was to study the main rainfall factors influencing runoff and sediment in the sloping farmland with different plants in the central south of Shandong Province.[Method] Through grey relational analysis,the effects of different rainfall factors on runoff and sediment with different plants in the central south of Shandong were studied.[Result] In the sloping farmland with different plants,the effects of rainfall factors on runoff and sediment weren’t consistent.Rainfall was the dominant influencing factor of runoff,but PI30 had the greatest influence on runoff in natural grassland.Meanwhile,rainfall intensity was the main influencing factor of sediment,but PI had the greatest influence on sediment in Astragalus adsurgens Pall.plot.The compound factor had the minimal influence on runoff and sediment in Arachis hypogaea plot and natural grassland.In A.adsurgens Pall.plot,rainfall intensity had the minimal impact on runoff,but the compound factor had the least effect on sediment.[Conclusion] The study could provide theoretical references for the comprehensive control of slope soil erosion,the optimum utilization and sustainable development of land.

Sediment Load in Runoff Under Laboratory and Field Simulated Rainfall

Soil erosion is one of the most important problems in the Loess Plateau of China affectingsustainable agriculture. Near Luoyang (Henan Province, China), field plots were constructed tomeasure soil erosion rates under conventional tillage practices using field-simulated rainfall.Field rainfall experiments were carried out to compare previous results from laboratoryrainfall simulations on the same soil for interrill conditions. Although in the laboratoryexperiments, a strong correlation was found between the stream power of the runoff water andthe unit sediment load, this sediment transport equation overestimated the field rainfallsimulation results. Another sediment transport equation derived by Nearing et al. for rillerosion was in better agreement with the results of the field experiments, although it alsooverestimated these values. The measured sediment load values during the field rainfallsimulations were also lower than those found during field experiments on the same soil but witha loosened surface layer. This difference indicates the importance of soil physical conditionof surfce like soil structure and aggregate size, which may contribute to the discrepancybetween the field and laboratory experiment results.