Water Erosion Prediction Project Research Articles

New approach to estimate the shear stress and the force of raindrops and their effect on erodibility of agricultural soils

The objective of this work was to the study the erosive force of raindrops and the shear stress on the soil erodibility of disturbed and saturated agricultural soil. A mathematical development was used to determine a new approach to the shear stress. The soil erodibility is calculated using the WEPP (water erosion prediction project) model. To realize this work, an experimental study was led in a laboratory using the rainfall simulator. The soil tray used in this study has a length of 2 m, width of 50 cm and a depth of 15 cm and the slope was adjusted with a system. The soils used were sandy and silty agricultural soils. The results show that the relationship between the erosive force of raindrops and the shear stress on the soil erodibility increased respectively as a power and linear function with an important coeffiient of determination. As regards the relationships between soil erodibility and the mean raindrop diameter, the evolution is represented by a power function with high coeffiient of determination.

Effects of forest litter cover on hydrological response of hillslopes in the Loess Plateau of China

Forest litter layer plays an important role in controlling water and soil loss; however, few studies have examined how litter cover affects hydrological processes. In this research, the effects of forest litter cover on interception, runoff, infiltration and soil erosion were investigated using rainfall simulation on a loess hillslope in China. Field experimental plots (10 m × 1.5 m, 5°) with two litter species (needle-leaf species and broad-leaf species) and three litter masses (300, 500 and 800 g m−2) were exposed to two rainfall intensities (30 and 60 mm h−1) for 40 min. A modified Merriam interception model as well as a WEPP (Water Erosion Prediction Project) Hillslope model were subsequently employed to analyze the experimental data of litter interception as well as runoff generation and soil erosion, respectively. Results showed that litter interception storage capacity ranged from 0.55 to 2.10 mm; thus, 1.8–9.2% of total rainfall was intercepted by the litter layer. Interception storage increased with increasing litter mass and rainfall intensity, and broad-leaf litter could intercept more rainwater than needle-leaf litter. Litter cover reduced runoff rates from plots covered with needle-leaf and broad-leaf litter by 18.6% and 25.9%, respectively, compared to the bare plot. Although runoff rates were slightly lower in litter-covered plots than in the bare plot, soil loss was effectively controlled when litter mass levels reached a threshold value of 500 g m−2. Compared to that from the bare plot, the mean soil loss rate for litter-covered plots was lowered by 58.5%, 74.5% and 78.3% for litter masses of 300, 500 and 800 g m−2, respectively. These results indicate that the litter layer was more conducive to controlling soil loss than runoff generation. Furthermore, the determination coefficient and Nash-Sutcliffe efficiency coefficient of the modified Merriam model ranged between 0.838–0.998 and 0.912–0.998, respectively, indicating that this model could successfully simulate the litter interception process. The WEPP model predictions also agreed well with the measured runoff and soil loss rates, but may have under-estimated the measured data in low rainfall intensity events and over-estimated the measured data in high rainfall intensity events. The performance of the WEPP model could be obviously improved by reducing the effective hydraulic conductivity and soil erodibility. Overall, this study will enable the development of more accurate modeling approaches and lead to a better understanding of hydrological processes under litter cover conditions.

Geospatial-Interface Water Erosion Prediction Project (GeoWEPP) application for the planning of Bompon Watershed conservation-prioritized area, Magelang, Central Java, Indonesia

Bompon watershed is located in the Quaternary Volcano (Mt. Sumbing) and tertiary (Mt. Menoreh) transition zones. The implication is that the soil material is well developed with super thick characteristic and is sensitive to erosion. The existence of land processing interventions by the locals supports the increasingly high rate of erosion. The use of the GeoWEPP model facilitates the rapid calculation of erosion rates and evaluation of conservation applications. The aim of the study was to calculate the erosion rate and determine the priority areas with the GeoWEPP erosion model. The GeoWEPP application was chosen because of its ability to show the spatial distribution of erosion and sedimentation. Evaluation of prioritized areas is carried out with the erosion rate criteria of the model and the important value of the land. The results of the Bompon watershed erosion model show variations in erosion and sedimentation. High erosion is in hilly morphology (slope of > 25%) with agricultural land annual crops (moor) and mixed gardens. High sedimentation is on the colluvial plains with moorland and rice fields land use. The existence of agricultural areas with cassava, corn and rice commodities has important value for villagers. Agriculture is the main livelihood of the community so that it has priority in handling conservation to maintain the productivity of the agricultural land. The assessment criteria for rate erosion and important value of the land produce priority sub-watershed that location covering 2 locations with an erosion rate of 441 tons/ha and 438.2 tons/ha.

Impacts of sediment load and size on rill detachment under low flow discharges

Rigorous validation of the first-order detachment-transport coupling concept using different sediment sizes is nonexistent in the literature. We hypothesized that particle sizes in a sediment-laden flow can affect soil detachment. The objectives of this study were to investigate the relationship between detachment rates by rill flows and hydraulic parameters under low flow discharges, and to quantify the responses of soil detachment rates to sediment loads and median sizes. A concentrated flow flume test was conducted under three low flow discharges (0.00033, 0.00067 and 0.00100 m2·s−1) and three sediment concentrations (50, 100 and 200 kg·m−3) with five median sizes (0.233, 0.204, 0.169, 0.115 and 0.078 mm). The results showed that the relationship between soil detachment capacity and shear stress fits the Water Erosion Prediction Project (WEPP) model well (R2 = 0.89). Stream power, compared with shear stress, is a better hydraulic parameter in simulating soil detachment rates under different sediment concentrations. The soil detachment rates by sediment-laden rill flows were negatively related to both sediment loads and sediment median sizes, validating the first-order sediment feedback relationships used in the WEPP model. The overall responses of soil detachment rates to sediment loads and sediment median sizes followed multivariate linear relationships, further demonstrating the negative feedbacks of sediment load and size on soil detachment by rill flow.

Updated climate database and impacts on WEPP model predictions

CLImate GENerator (CLIGEN) (v5.3), a stochastic weather generator, is widely used in conjunction with the Water Erosion Prediction Project (WEPP) model for runoff and soil loss predictions. CLIGEN generates daily estimates of weather based on long-term observed weather station data statistics. For the United States, the original CLIGEN database released with WEPP in 1995 was derived using inconsistent periods of climate records through 1992 that could lead to significant variations in runoff and soil loss predictions on spatial and temporal scales. To achieve more reliable estimates of runoff and soil loss, an updated climate database was derived from a consistent 40 years of recent climate records of 1974 to 2013 in the United States. The objectives of this study were to (1) examine the spatial patterns in trends of differences in precipitation and maximum and minimum temperatures between the two databases, and (2) evaluate the impacts on WEPP-predicted mean annual runoff and soil loss, from the original to the updated databases. For runoff and soil loss estimates, WEPP simulations were conducted under a tilled fallow condition for 1,600 CLIGEN locations in the contiguous United States for a slope profile of 22.1 m length, 9% slope gradient, and silt loam soil. Comparison of precipitation and maximum and minimum temperatures between the original and updated databases showed variations in spatial patterns both annually and seasonally. Annual precipitation and minimum temperature generally increased across most of the country while maximum temperature increased in the western half of the United States and parts of the Northeast. Seasonally, increases in precipitation are evident in the Midwest in spring, fall, and winter, the Northwest in spring, and the Southeast in fall. Maximum daily temperature has increased in the western half of United States and parts of the Northeast in the winter, fall, and spring, whereas minimum daily temperature has increased in all seasons across the United States. Changes in WEPP-simulated mean annual runoff and soil loss from the use of the original to the updated CLIGEN database showed increases in runoff and soil loss in most of the United States. However, some stations showed either increases or decreases in runoff and/or soil loss with the updated database primarily because of differences in monthly precipitation and intensity values in the two databases. Understanding the impacts of the use of the updated database on runoff and soil loss from this study will help in making informed decisions for conservation planning and management when utilizing the WEPP erosion model.

The effectiveness of forestry best management practices at skidder stream crossings in Virginia

Sediment is the most common nonpoint source pollutant associated with timber harvesting in the southeastern United States. Sediment is of particular concern at operational stream crossings because sediment delivery potential is increased by stream proximity and any compromised streamside management zone buffers. This study quantifies the effectiveness of water quality best management practices (BMPs) implemented at operational skidder stream crossings in three physiographic regions of Virginia. We located 79 operational skid trail crossings and assessed implementation of state BMP manual recommendations, percentage positive response to a Virginia Department of Forestry BMP audit questionnaire, and potential soil erosion as predicted by the Universal Soil Loss Equation (USLE)-Forest methodology and Water Erosion Prediction Project: Road interface. Estimated erosion rates decreased with increasing BMP scores for skid trails (p

Testing a new rill flow resistance approach using the Water Erosion Prediction Project experimental database

AbstractIn this paper, a recently theoretically deduced rill flow resistance equation, based on a power‐velocity profile, was tested using the Water Erosion Prediction Project database. This database includes measurements of flow velocity, water depth, cross section area, wetted perimeter, and bed slope that were made in rills shaped on experimental sites distributed across the continental United States. In particular, three different experimental conditions (only rainfall, only flow, and rain with flow) were examined, and for each condition, the theoretically based relationship for estimating the Γ function of the power velocity profile was calibrated. The results established that (a) the Darcy‐Weisbach friction factor can be accurately estimated using the proposed theoretical approach, and (b) the flow resistance increases with the effect of rainfall impact.

Кількісна оцінка ерозійної небезпеки сільськогосподарських угідь

The largest and practically non-renewable losses of erosion in all sectors of the economy undergoes agrarian sphere. The area of land damaged by water erosion in Ukraine reaches 33.3% or 13.3 million hectares, of which 4.5 million hectares are medium and strongly ground, of which 68 thousand hectares completely lost the humus horizon. The reasons for the acceleration of erosion processes in Ukraine are the mass ignoring of the simplest agrotechnical anti-erosion measures, the imperfection of the land management organization of the territory to provide elementary anti-erosion protection, underestimation of the role of wild forest belts, ineffective use of funds aimed at preventing erosion, resulting in degradation processes lately unprecedented. High degree of cultivation of agricultural land and excessive saturation of crop rotation with crop rotation against the background of non-compliance with the basic provisions of a set of measures to increase and maintain soil fertility is a direct way to the destruction of soil cover as a basis for the existence of life on our planet. The quantitative estimation of water erosion involves two systems of evaluation criteria: the actual soil erosion and the potential danger of erosion at a certain level of probability of the effects of erosion factors (the world experience in the organization of anti-erosion protection indicates that it is sufficient to calculate 10% security). To update the outdated data on soil erosion in Ukraine, it is necessary to conduct a repeated continuous survey of soil cover on a modern methodological basis, which requires significant financial costs. However, it is possible to assess the erosion hazard using mathematical models of erosion, in particular the Water Erosion Prediction Project (WEPP) model, which provides information on the intensity and tension of erosion processes and the determination of the magnitude of possible erosion losses in the soil. WEPP is a physically grounded model that allows the modeling of erosion processes of agricultural lands located on small water catchments (up to 250 hectares). The model is based on mathematical equations describing physical processes of soil erosion and hydrology of erosion runoff. In this case, the catchment area, according to its relief, is divided into elementary units - slopes and watercourses. The model allows you to trace the routes of drainage and flushing along the elements of the relief up to the exit of the catchment. Simulation can be carried out in two modes: in the mode of long-term modeling and in mode of modeling of a single shower. The input data for the model are data on the terrain, the characteristics of the catchment soil, types of cultivating soil and agricultural vegetation on its fields, parameters characterizing the climatic conditions of the terrain. Two series of forecast calculations were conducted: the first one was for the conditions of the existing land placement, the second one for the case of implementation of the project of soil protection of the territory. For this purpose, in both cases, the preferred lines of the drain lines were determined, for each runoff line, soil erosion loss calculation using the WEPP model was performed, after which regularization and interpolation of the obtained data were performed and erosion hazard maps for each case were constructed. Quantitative estimation of two series of forecast calculations for the conditions of existing land placement and in the case of implementation of the project of soil protection of the territory using WEPP erosion model and specialized software showed that in the event of a 10% rainstorming of equipment, the territory of forest bands and drainage facilities significantly reduces erosion danger, even in the black pair.

Climate impacts on soil erosion and muddy flooding at 1.5 versus 2°C warming

AbstractFollowing the 2015 ‘Paris Agreement’ that seeks to contain global mean temperature increase (GMTI) to well below 2°C and more ambitiously within 1.5°C, recent studies have begun assessing the response of various sectors to these levels of warming. Most studies have so far concentrated on temperature‐sensitive sectors. Given the links between a warmer atmosphere and rainfall intensity, there is also a need to examine impact sectors driven primarily by changing rainfall characteristics. One example is soil erosion and muddy flooding from agricultural land, which damages the natural and built environment. Using a case‐study hillslope in eastern Belgium—an area particularly impacted by muddy floods—this study examines (a) whether soil erosion and muddy flooding will increase in the future; and (b) whether containing GMTI to 1.5°C would help limit the problem versus 2°C. The Water Erosion Prediction Project model was used to simulate muddy flooding for the present‐day and under a range of future scenarios derived from climate models that correspond to 1.5 and 2°C GMTI. The main findings reveal no statistically significant differences between muddy flooding at 1.5 and 2°C GMTI. Limiting GMTI to 1.5°C therefore does not appear to make much difference to soil erosion and muddy flooding, because the timing of changing rainfall intensity does not always follow clear patterns with increased warming. Regardless of the magnitude of future warming, an earlier and longer muddy flooding season is projected—highlighting that mitigation measures should be continually adapted to remain resilient to climate change.

Predicting soil loss and sediment characteristics at the plot and field scales: Model description and first verifications

Soil loss models are useful tools for making land management decisions to prevent soil and water quality problems. Several soil loss models have been developed, including the process-based Water Erosion Prediction Project (WEPP) model and the empirical Revised Universal Soil Loss Equation (RUSLE). Although process-based models provide accurate soil loss estimates, they are infrequently used for conservation planning because of their complexity and data need. On the other hand, models such as RUSLE cannot predict the soil loss nor the sediment composition associated with individual events, both of which are critical for designing accurate soil and water conservation practices. Therefore, the objective of this study was to develop a model for estimating sediment delivery on an event scale while predicting its clay, silt and sand fractions. For this purpose, the WEPP model was implemented using measured soil and climate data from Central Chile to generate a soil loss database for many hillslope configurations and management practices. More than 200,000 erosion events were generated using data from 83 sites. Using multiple regression analysis, the main variables controlling soil loss were identified, which included rainfall erosivity, soil erodibility, hillslope geometry, antecedent soil moisture and total precipitation. These variables were incorporated into a soil loss model, which was calibrated using data from 32 sites (R2 = 0.81–0.83) and validated for the remaining 51 sites (R2 = 0.66–0.89). The model provided accurate estimates for the clay and silt fractions (R2 = 0.86 and 0.78, respectively) but showed difficulties for predicting the sand fraction (R2 = 0.31). Contour plowing and vegetative filter strip routines were also incorporated into the soil loss model, providing reliable soil loss (R2 = 0.51–0.78), clay (R2 = 0.54–0.75), and silt (R2 = 0.57–0.68) estimates. The developed model is remarkably easy to use and, due to its simplicity, allows incorporating other soil conservation routines, providing a flexible tool for soil conservation planning. This study provides a detailed description and methodology for building such a model and discusses its advantages and limitations.

Integrated impact assessment of soil and water conservation structures on runoff and sediment yield through measurements and modeling in the Northern Ethiopian highlands

Developing countries with an increasing population like Ethiopia experience degradation of land and water resources. To tackle this problem soil and water conservation (SWC) has been practiced and recently promoted by the Ethiopian government. However, the effectiveness of SWC practices on runoff and soil erosion have not been studied in detail for their long- and short-term effects. An integrated measurement and modeling study was conducted from 2012 to 2014 in the Gumara-Maksegnit sub watershed to assess the impacts of SWC structures on runoff and sediment yield using the Geospatial Interface for the Water Erosion Prediction Project (GeoWEPP) model. The study was conducted in two adjacent, smaller watersheds where SWC structures were constructed in one of the watersheds (treated sub watershed), while the other one was a control watershed without SWC structures (untreated sub watershed). The treated sub watershed has an area of 27.1 ha and the untreated sub watershed has an area of 31.7 ha. Runoff and sediment yield were compared based on the observations and GeoWEPP model simulations. The GeoWEPP model simulation results predicted the daily runoff satisfactorily for both sub watersheds (R2 = 0.68 and NSE = 0.43 for untreated and R2 = 0.61 and NSE = 0.84 for treated sub watershed). Similarly, the model prediction showed satisfactory results in sediment yield (R2 = 0.61 and NSE = 0.59 for untreated and R2 = 0.57 and NSE = 0.81 for treated sub watershed). SWC structures reduced slope gradient and changed flow accumulation. The observation and simulation study concluded that the treated sub watershed surface runoff was reduced by about 19% as compared to the untreated sub watershed. Similarly, the model estimated that SWC structures constructed in the treated sub watershed reduced the total area that generates soil loss above the set target limit of 10 t ha−1 y−1 from 49% to 38% of the watershed area. SWC has led to a significant reduction in sediment yield by 28 to 38% in these highland watersheds of Ethiopia. The results confirmed that SWC structures have a significant impact to prevent land degradation in the Ethiopian highlands.

Impacts of Climate Change on Soil Erosion in the Great Lakes Region

Quantifying changes in potential soil erosion under projections of changing climate is important for the sustainable management of land resources, as soil loss estimates will be helpful in identifying areas susceptible to erosion, targeting future erosion control efforts, and/or conservation funding. Therefore, the macro-scale Variable Infiltration Capacity—Water Erosion Prediction Project (VIC-WEPP) soil erosion model was utilized to quantify soil losses under three climate change scenarios (A2, A1B, B1) using projections from three general circulation models (GFDL, PCM, HadCM3) for the Great Lakes region from 2000 to 2100. Soil loss was predicted to decrease throughout three future periods (2030s, 2060s, and 2090s) by 0.4–0.7 ton ha−1 year−1 (4.99–23.2%) relative to the historical period (2000s) with predicted air temperature increases of 0.68–4.34 °C and precipitation increases of 1.74–63.7 mm year−1 (0.23–8.6%). In the forested northern study domain erosion kept increasing by 0.01–0.18 ton ha−1 year−1 over three future periods due to increased precipitation of 9.7–68.3 mm year−1. The southern study domain covered by cropland and grassland had predicted soil loss decreases of 0.01–1.43 ton ha−1 year−1 due to air temperature increases of 1.75–4.79 °C and reduced precipitation in the summer. Fall and winter had greater risks of increased soil loss based on predictions for these two seasons under the A2 scenario, with the greatest cropland soil loss increase due to increased fall precipitation, and combined effects of increases in both precipitation and air temperature in the winter. Fall was identified with higher risks under the A1B scenario, while spring and summer were identified with the greatest risk of increased soil losses under the B1 scenario due to the increases in both precipitation and air temperature.

Interrill erodibility in relation to aggregate size class in a semi-arid soil under simulated rainfalls

Interrill erodibility can be affected by soil aggregates, especially by those aggregate size classes that are dominant in the soil. In the Water erosion Prediction Project (WEPP) model, interrill soil erodibility (Ki) is estimated using very fine sand content. Despite that some studies have indicated an effect of aggregate stability on the Ki, information on the relationship between the aggregate size class and Ki and factors controlling it, particularly in semi-arid region is limited. This study was conducted to determine the variation of Ki for different aggregate size classes under various rainfall intensities and evaluation of the WEPP model in estimating the Ki for different aggregate fractions. Five aggregate size classes (0.25–2, 2–4.75, 4.75–5.6, 5.6–9.75 mm, and 9.75–12.7 mm) were separated from a sandy clay loam soil sampled in an agricultural land and put in laboratory flumes of 100 cm × 50 cm. The flumes were placed on a 9% slope and exposed to ten sequential rainfall simulations varying from 10 to 60 mm h−1 for 30 min. The Ki of each aggregate size classes was determined using the interrill sediment delivery rate and compared this with the values estimated using WEPP. All physicochemical properties were also determined in the aggregate size classes. Organic matter content in the aggregate size classes was very low (0.65–0.73%) and didn't show strong relationships with the aggregate stability and hydraulic conductivity, whereas clay was major factor controlling determining these properties for the different aggregate fractions. Significant differences were found among the aggregate size classes in clay content (P < 0.05), aggregate stability measured using both wet-sieving method (P < 0.05) and water drop test method P < 0.05, saturated hydraulic conductivity (Ks), and measured Ki (P < 0.05). The measured Ki was about 34 and 90 times bigger than the estimated Ki for the fine aggregates and coarse aggregates, respectively. The fine aggregates showed higher susceptibility to interrill detachment with increasing rainfall intensity as compared with the coarse aggregates. Significant decrease was observed in the measured Ki with increasing the aggregate size which was associated with increases in clay content, aggregate stability and Ks. The stability of aggregates against raindrop impact (CND) was an important indicator describing the effect of aggregate size on the interrill erodibility in semi-arid soils. Therefore, this indicator can be taken into account as a soil structure measure to develop a proper equation for estimating interrill erodibility (Ki) for agricultural lands. The minimum use of tillage practices is essential to prevent aggregate breakdown and control interrill erosion in semi-arid regions.

Modeling biophysical and anthropogenic effects on soil erosion over the last 2,000 years in central Mexico

AbstractErosion prediction models recreate past scenarios, assess future ones, and determine the best explanatory variables of the soil erosion process. They are widely used and contribute valuable data for landscape management. This paper presents an estimation of soil erosion in the Teotihuacan Valley Basin in central Mexico, assessing its response to biophysical and anthropogenic components during 4 periods within the past 2,000 years. The valley has undergone past and recent anthropogenic erosion and, during the past 2 millennia, has experienced a marked variation in precipitation, variations in land use, soil management, and to a lesser extent, variations in soil type. With the use of the Water Erosion Prediction Project model, we estimated how the above‐mentioned parameters affect soil losses under 4 scenarios: (a) humid conditions (900 mm yr−1) during the Teotihuacan Period (1–650 CE), (b) dry conditions (370 mm yr−1) during the Aztec Period (1325–1521 CE), (c) humid conditions (900 mm yr−1) during the Aztec Period, and (d) present conditions (after 1970 CE; 560 mm yr−1). Comparison of scenarios and a principal component analysis of soil loss according biophysical components showed topography to be the most closely related parameter to soil erosion. Land use and soil type also showed a relationship with soil erosion, particularly during the Aztec Period; climate change did not appear to be the most significant factor in soil loss. Estimation of soil erosion by means of models is an inexpensive way to find answers to future challenges concerning soil erosion in a changing environment.

Predicting plot soil loss by empirical and process-oriented approaches. A review

Soil erosion directly affects the quality of the soil, its agricultural productivity and its biological diversity. Many mathematical models have been developed to estimate plot soil erosion at different temporal scales. At present, empirical soil loss equations and process-oriented models are considered as constituting a complementary suite of models to be chosen to meet the specific user need. In this paper, the Universal Soil Loss Equation and its revised versions are first reviewed. Selected methodologies developed to estimate the factors of the model with the aim to improve the soil loss estimate are described. Then the Water Erosion Prediction Project which represents a process-oriented technology for soil erosion prediction at different spatial scales, is presented. The available criteria to discriminate between acceptable and unacceptable soil loss estimates are subsequently introduced. Finally, some research needs, concerning tests of both empirical and process-oriented models, estimates of the soil loss of given return periods, reliability of soil loss measurements, measurements of rill and gully erosion, and physical models are delineated.

Impact of Landuse Changes on Soil Erosion and Sedimentation in the Tono Reservoir Watershed Using GeoWEPP Model

Sediment delivery from the Tono Reservoir watershed in the Upper East Region of Ghana is of major concern, necessitating the need to estimate the rate of siltation of the reservoir. This study determined the current volume of silt in the reservoir, mapped landcover changes using Landsat images and employed Water Erosion Prediction Project (WEPP) model, to simulate hydrology and sediment dynamics for three landuse/landcover scenarios. The Geo-spatial interface for WEPP (GeoWEPP) was used to characterize upland overland flow elements based on their landuse/landcover, soil, and slope profiles. Using characteristics obtained from GeoWEPP as inputs for the WEPP model runoff fluxes, soil loss rates, and sediment delivery ratio (SDR) for three environmental scenarios: landuse/landcover with agricultural lands under fallow tilled management (Scenario 1), landuse/landcover with agricultural lands under corn, soybean no till management (Scenario 2), landuse/landcover with non-agricultural lands under shrub-perennial (Scenario 3) were estimated. Over the simulated 29-year period; runoff depth, soil loss rate and SDR were estimated to be 118.4 mm, 22.8 t/ha, and 0.68 for Scenario 1; 94.6 mm, 2.8 t/ha, and 0.31 for Scenario 2; and 57.7 mm, 0.6 t/ha, and 0.92 for Scenario 3. Shrubland had decreased by 8 %, bareland area had increased by 9.1 %, and the reservoir area had also decreased by 3.7 %. The study indicates landuse/landcover change impacts significantly on land degradation and hydrology of the Tono reservoir and subsequently accounts for the reduction in reservoir capacity by about 1.74 % on annual basis observed through the bathymetric survey.

MODELING OF PHOSPHORUS LOSSES BY WATER EROSION

ABSTRACT Phosphorus losses in runoff water and eroded sediment may increase the risk of eutrophication. Erosion prediction models can be used to assess and quantify nutrient losses and transport in different soil management scenarios. This study aimed to assess the performance of models to estimate the losses of available phosphorus in eroded sediments and assess their spatial variability pattern. The experiment was installed on a eutrophic Red Ultisol located in Tabapua, northwestern Sao Paulo State, Sao Domingos Stream Watershed. Aiming at estimating and validating the models, measurements were made from 2007 to 2015 at 17 observation points (slopes), determining soil phosphorus content (Psoil), eroded sediments (Psed), and enrichment rate (ERsed). The models applied to estimate the enrichment rates of phosphorus in the eroded sediment and runoff are efficient when in use with the predictions of the model Water Erosion Prediction Project (WEPP). The enrichment rates obtained presented a Nash-Sutcliffe (NS) coefficient close to 1. Losses of soluble phosphorus in runoff above 0.02 mg L−1, a critical value for eutrophication, can be obtained in 81% of the watershed area with a probability higher than 75%.

The Daily Erosion Project – daily estimates of water runoff, soil detachment, and erosion

AbstractWater runoff and sediment transport from agricultural uplands are substantial threats to water quality and sustained crop production. To improve soil and water resources, farmers, conservationists, and policy‐makers must understand how landforms, soil types, farming practices, and rainfall interact with water runoff and soil erosion processes. To that end, the Iowa Daily Erosion Project (IDEP) was designed and implemented in 2003 to inventory these factors across Iowa in the United States. IDEP utilized the Water Erosion Prediction Project (WEPP) soil erosion model along with radar‐derived precipitation data and government‐provided slope, soil, and management information to produce daily estimates of soil erosion and runoff at the township scale (93 km2 [36 mi2]). Improved national databases and evolving remote sensing technology now permit the derivation of slope, soil, and field‐level management inputs for WEPP. These remotely sensed parameters, along with more detailed meteorological data, now drive daily WEPP hillslope soil erosion and water runoff estimates at the small watershed scale, approximately 90 km2 (35 mi2), across sections of multiple Midwest states. The revisions constitute a substantial improvement as more realistic field conditions are reflected, more detailed weather data are utilized, hill slope sampling density is an order of magnitude greater, and results are aggregated based on surface hydrology enabling further watershed research and analysis. Considering these improvements and the expansion of the project beyond Iowa it was renamed the Daily Erosion Project (DEP). Statistical and comparative evaluations of soil erosion simulations indicate that the sampling density is adequate and the results are defendable. The modeling framework developed is readily adaptable to other regions given suitable inputs. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.

Adjustment of a weather generator to represent actual rain erosivity in the northern Black Forest – Germany

To estimate the impact of highly erosive precipitation on existing and planned forest infrastructure we deem the Forest Service WEPP Interfaces, based on the Water Erosion Prediction Project (WEPP), feasible.As a first step towards testing WEPP and especially the implemented weather generator CLIGEN for conditions in Germany we evaluated the application of CLIGEN to calculate rain erosivities from generated time series. CLIGEN parameters were taken from time series of up to 17years with 10-minute resolution from three sites in the Northern Black Forest, southwestern Germany. We assessed a rain kinetic energy function for this region from field measurements with a laser disdrometer to compare CLIGEN performance using the local function to using common kinetic energy functions.We showed that running CLIGEN with unaltered input parameters is not suitable to model climatic conditions and erosivity indices in the Northern Black Forest. R-factors from unaltered model runs deviated extremely from observed R-factors, resulting in just one third of observed values. Model performance and parameter uncertainties do not benefit much from the use of a site specific kinetic energy function. Differences in model errors and sensitivities compared to a well-established kinetic energy function remain negligible. However, model output was improved by empirical calibration of input data. Virtual best parameter sets for best model results could be identified.To reproduce observed rain erosivities the input parameters of CLIGEN have to be manipulated to model a precipitation regime where daily precipitation amounts and maximum precipitation intensities are higher at a lower number of rainy days.We also identified the input parameters to which the model is most sensitive to when manipulated, i.e. precipitation amount and frequency, and maximum peak precipitation. These parameters are especially important when implementing future climate change scenarios.

Land use and climate change impacts on runoff and soil erosion at the hillslope scale in the Brazilian Cerrado

Land use and climate change can influence runoff and soil erosion, threatening soil and water conservation in the Cerrado biome in Brazil. The adoption of a process-based model was necessary due to the lack of long-term observed data. Our goals were to calibrate the WEPP (Water Erosion Prediction Project) model for different land uses under subtropical conditions in the Cerrado biome; predict runoff and soil erosion for these different land uses; and simulate runoff and soil erosion considering climate change. We performed the model calibration using a 5-year dataset (2012–2016) of observed runoff and soil loss in four different land uses (wooded Cerrado, tilled fallow without plant cover, pasture, and sugarcane) in experimental plots. Selected soil and management parameters were optimized for each land use during the WEPP model calibration with the existing field data. The simulations were conducted using the calibrated WEPP model components with a 100-year climate dataset created with CLIGEN (weather generator) based on regional climate statistics. We obtained downscaled General Circulation Model (GCM) projections, and runoff and soil loss were predicted with WEPP using future climate scenarios for 2030, 2060, and 2090 considering different Representative Concentration Pathways (RCPs). The WEPP model had an acceptable performance for the subtropical conditions. Land use can influence runoff and soil loss rates in a significant way. Potential climate changes, which indicate the increase of rainfall intensities and depths, may increase the variability and rates of runoff and soil erosion. However, projected climate changes did not significantly affect the runoff and soil erosion for the four analyzed land uses at our location. Finally, the runoff behavior was distinct for each land use, but for soil loss we found similarities between pasture and wooded Cerrado, suggesting that the soil may attain a sustainable level when the land management follows conservation principles.