Erosion Response Research Articles

Spatiotemporal dynamics of soil erosion response to land use land cover dynamics and climate variability in Maybar watershed, Awash basin, Ethiopia

ABSTRACT Soil erosion is a global problem that threatens sustainability and food security by washing away fertile soil, nutrients, and organic matter. Land use changes, land degradation, and soil erosion are increasing, resulting in annual losses of fertile soil and declining crop yields. The objective of this study was to examine how changes in land use and land cover affected soil erosion dynamics and determine which areas should receive priority for soil and water conservation interventions. The study employs remote sensing and Geographic information system techniques to assess the impact of land use and land cover change on soil erosion between 2004 and 2020. The RUSLE model estimates soil erosion rates. Mean annual rainfall, soil data, 2 m DEM, and satellite images are used to input data into the model to determine soil erosion. The study identifies six land use and cover types and shows that significant changes have occurred in bare land and shrubland, decreasing by 25.48% and 6.17%, respectively, from 2004–2020. On the other hand, forest land increased by 20.19%, and cultivated land increased by 3.52%. Additionally, the study evaluated the response of soil erosion to land use and land cover changes, showed that bare land, cultivated land, and grazing land have the highest annual loss. In contrast, forest land, shrubland, and water bodies have the lowest. The analysis of soil erosion risk indicated a decline in the mean annual soil loss rate at the watershed scale, with rates decreasing from 12.8t ha−1 yr-1 in 2004 to 3.21t ha-1 yr-1 in 2020. The watershed is classified into five severity classes, and the study area was divided into five priority categories based on their average annual soil losses. The study emphasized that prioritizing interventions for watershed types with high erosion risks is crucial for reducing on-site soil loss and off-site effects together with conserving water resources. The findings support the importance of long-term watershed management in reducing soil erosion. To effectively reduce soil erosion and improve environmental quality, it is recommended to encourage afforestation and reforestation, develop sustainable land use policies, strengthen soil conservation measures, and improve monitoring and evaluation of land use changes.

How erosional efficiency modulates landscape response to drainage reorganization: New empirical evidence from the Andes

The fluvial network in active mountain ranges is considered to evolve from longitudinal to transverse-dominated drainage systems. This hypothesis links to the forelandward migration of the orogen, while crustal thickening modifies the range's flank slopes, enhancing erosional efficiency. We probe such a proposition with new empirical observations from the Colombian Andes by studying the recent capture of the longitudinal Suárez and Chicamocha Rivers by the transverse Sogamoso River. Firstly, by integrating published low-temperature thermochronology and quantitative topographic metrics like χ, we found that rejuvenated rock uplift in the Cocuy and Yariguies ranges delays the transition from longitudinal to transverse-dominated drainage systems by compensating the across-divide contrasts in erosion. To further constrain the spatiotemporal response of the Suárez and Chicamocha Rivers after the discrete capture, we computed sediment-gauge erosion rates in conjunction with rainfall-normalized channel steepness and Gilbert metrics. We observe stark contrasts in erosion rates between the Chicamocha (maximum of 148.22 ± 44.86 m/Myr) and Suárez Rivers (maximum of 71.9 ± 21.5 m/Myr). Higher erosion rates in the former are expressed with widely distributed slope-break knickpoints that migrated further upstream with catchment expansion at the expense of the less efficiently erosive Suárez River basin. We interpret these erosional differences as a lithological control on the pace of topographic response to an external perturbation (discrete capture), given low-lying sedimentary rocks delay the erosional response of the Suárez River basin. Our research therefore emphasizes the role that lithology poses in keeping the landscape in an unsteady topographic condition.

OBSERVATION AND NUMERICAL MODELING OF A DUNE OVERWASH AND BREACHING EVENT

Sea level rise will significantly increase the need for building and upgrading coastal protection such as artificial coastal dunes or berms (Wong et al., 2014). Human constructed dunes are frequently deployed to limit wave runup and overtopping and mitigate damage from flooding events (e.g., Gallien et al., 2015). Although dune erosion modeling and validation on storm surge dominated beaches is common in the literature, only limited work considers energetic long period swell conditions typical of coastal California. In this study three morphological models are used to simulate dune erosion response to long period swell and compared to high resolution in-situ hydromorphological field observations.

Tan DEM‐X Preserves the Relationship Between Hilltop Curvature and Erosion Rate in the Qilian Shan

AbstractHilltop curvature (CHT) can record erosional responses to tectonic forces and/or climate change. Although CHT has a linear relationship with the erosion rate, which is a significant advantage over traditional indicators, it is not widely used, mainly because it requires high‐resolution terrain data. Previous studies show that terrain steepness is strongly correlated with catchment‐wide erosion rates in the Qilian Shan. This relationship enables us to test the potential of CHT based on medium‐resolution terrain data (e.g., Tan DEM‐X with a resolution of ∼12 m) as an indicator of the erosion rate. We selected three typical sites in the Qilian Shan with evenly spaced ridge valleys and a continuous soil cover. At each site, we produced a high‐resolution digital surface model (DSM) using uncrewed aerial vehicles (UAVs), and then compared CHT from the UAV DSM with that from Tan DEM‐X, via LSDTopoTools. The results show that both Tan DEM‐X and the UAV DSM record similar spatial patterns of CHT, although the magnitudes vary between the three selected areas. We then examined the relationship between CHT based on Tan DEM‐X and the catchment‐wide erosion rate in the Qilian Shan. CHT has a linear relationship with the erosion rate in an area of clastic rocks, where the erosion rate is below 400 mm/Kyr. CHT extracted by Tan DEM‐X is superior to the mean basin slope in predicting the erosion rate in this clastic rock landscape. Overall, our results demonstrate the utility of Tan DEM‐X in calculating CHT to indicate the erosion rate.

Effects of prescribed fire on the post‐fire hydrological processes in agro‐forest ecosystems: A systematic review and a meta‐analysis

AbstractPrescribed fires are one of the most effective tools to reduce the risk of wildfires but this treatment may negatively affect the hydrological and erosive response of soil, with noticeable increases in surface runoff and soil erosion. Many studies have been published on this matter but there is no consensus in the literature on the magnitude and duration of these effects since the relevant hydrological conditions are site‐specific. Moreover, the relationship between post‐fire hydrology and its main environmental drivers has been little explored. This study has carried out a bibliographic review and a meta‐analysis of the changes resulting from prescribed fire applications (water infiltration, soil water repellency (SWR), surface runoff and soil erosion) using a database of 85 case studies from 41 academic papers that have been published over the last 23 years. The effects of annual precipitation, soil slope, burn severity, fire application season, post‐fire ground cover, and vegetation type on those changes have also been statistically explored. The bibliographic review has revealed that previous case studies have not been equally distributed across the globe but concentrated in only a few countries, mainly the United States and Spain. The meta‐analysis has revealed that (i) water infiltration generally decreases and SWR appears with noticeable increases in surface runoff and soil erosion immediately after the prescribed fire, while the pre‐fire values progressively recover over time; (ii) the window of disturbance in burned soils may last a few months (with some exceptions); (iii) annual precipitation and soil slope significantly influence water infiltration and surface runoff, but not soil erosion, in both the short‐term and medium‐term; (iv) moderate‐to‐high levels of soil burn severity severely enhance surface runoff and soil erosion, and noticeably reduce water infiltration in the short‐term; (v) the level of ground cover burning is important for reducing the runoff rates, but it plays a minor role in water infiltration and soil erosion rates;and (vi) the prescribed fire applied in spring results in lower increases in short‐term runoff and erosion, while fire applications in summer and in shrublands produce the highest increases in soil loss. The following practical recommendations arise from this study: (i) research should be better distributed across all environmental contexts on a global scale; (ii) post‐fire management actions should be immediately implemented after the prescribed fire application; (iii) prescribed fire should be carried out in spring and the soil burn severity should be kept low during burning; (iv) the monitoring studies should be prolonged at least for some years (more than two or three) after prescribed fire; (iv) the catchment‐scale investigations, although more difficult and expensive, should be encouraged (avoiding, however, areas to sparsely burnt in the context of the whole catchment); (v) the monitored variables should also include the most important physical, chemical and biological properties of soil, the cover and structure of regenerating vegetation, as well as the water quality parameters; (vi) the effects of repeated applications of prescribed fire should be experimentally assessed; and (vii) guidelines for standardized and appropriate measurements and analytical methods in experimental activities should be set up. These indications support the use of land managers in the monitoring of the hydrological impacts of the prescribed fire and in the choice of sites where post‐fire management actions must be implemented. The last recommendation of this study is the creation of an experimental database supporting the bibliographic review and the meta‐analysis, which is made available to other researchers and land managers, to create a public, easily‐accessible and comprehensive tool for future research needs and professional use.

Soil Erosion in a British Watershed under Climate Change as Predicted Using Convection-Permitting Regional Climate Projections

Climate change can lead to significant environmental and societal impacts; for example, through increases in the amount and intensity of rainfall with the associated possibility of flooding. Twenty-first-century climate change simulations for Great Britain reveal an increase in heavy precipitation that may lead to widespread soil loss by rising the likelihood of surface runoff. Here, hourly high-resolution rainfall projections from a 1.5 km (‘convection-permitting’) regional climate model are used to simulate the soil erosion response for two periods of the century (1996–2009 and a 13-year future period at ~2100) in the “Rother” catchment, West Sussex, England. Modeling soil erosion with EROSION 3D, we found a general increase in sediment production (off-site erosion) for the end of the century of about 43.2%, with a catchment-average increase from 0.176 to 0.252 t ha−1 y−1 and large differences between areas with diverse land use. These results highlight the effectiveness of using high-resolution rainfall projections to better account for spatial variability in the assessment of long-term soil erosion than other current methods.

Soil Erosion in Extensive versus Intensive Land Uses in Areas Sensitive to Desertification: A Case Study in Beira Baixa, Portugal

The occurrence of long periods of drought followed by extreme episodes of rainfall and ineffective soil conservation practices are the main causes of soil erosion in the Mediterranean region. The objective of this paper is to assess and compare the hydrological and erosional responses related to land use changes in agricultural landscapes that are sensitive to erosion and that are a result of the significant replacement of traditional land uses. Such changes are characterized by the replacement of extensive olive groves associated with pastureland by intensive almond production, where deep plowing and heavy machinery are required. In each sampling site, runoff initiation, runoff coefficient, and soil loss were evaluated under simulated rainfall (55 mm h−1), at plot scale (0.25 m2), at the end of the hot and dry summer period. Slope gradient, soil texture, bulk density, soil organic matter content, soil water content, and plant cover were also determined. The results showed the impact of recently planted intensive almond orchards (IAOs) on accelerating soil erosion risk compared with the extensive traditional olive groves (EOGs), although runoff initiation and discharge are very similar between the studied land uses. The mean values recorded for soil loss and sediment concentration were 118 g m−2 h−1 and 12 g m−2 h−1 and 3.1 g L−1 and 0.7 g L−1, respectively, for IAOs and EOGs. Our results also demonstrated that maintaining a vegetation cover is a determining factor for the prevention and control of soil erosion, especially in IAOs, where retaining high percentages of natural plant-residue mulch layers (>70%) reduced soil loss by about 70% in this study.

Parametric analysis of erosion wear of sponge iron slag-filled ramie–epoxy composites using Taguchi and preference selection index methods

The present work reports on the development of a novel set of ramie–epoxy composites filled with sponge iron (SI) slag (0–30 wt.%) and on their response to solid particle erosion wear under different test conditions. SI slag is a by-product generated during the processing of SI to steel in arc or induction furnace. While these composites are fabricated using the conventional hand layup technique, the erosion tests are carried out using an air jet erosion tester following ASTM G76 test standard as per Taguchi's L27 orthogonal array. Mechanical characterization of ramie–epoxy composites suggests that the incorporation of SI slag improves their tensile strength by about 52%, flexural strength by 10% and micro-hardness by about 30%. A parametric appraisal of the erosion response carried out using Taguchi method reveals that the filler content, impact velocity and impingement angle are the most significant control factors influencing the erosion rate of these composites. The individual effects of different factors in wider ranges (impact velocity 25–125 m/s, filler content 0–30 wt.% and impingement angle 30–90°) are ascertained by conducting steady-state erosion experiments in controlled conditions. Preference selection index method, which is an effective multi-criteria decision-making tool is used to select the best candidate among all composites based on different physical, mechanical and wear test results. It is found that the composite with 30 wt.% SI slag content displays the optimal combination of properties. The worn morphologies of the eroded surfaces of the composites are studied and analyzed using electron microscopy to identify possible mechanisms causing the wear loss.

Soil erosion and nutrient loss due to changes in rainfall intensity under different wind directions

AbstractIn nature, wind often occurs simultaneously with rainfall, causing nutrient loss in soil and water on slopes. However, the influence of different rainfall intensities combined with different wind directions on soil erosion and nutrient loss remains unclear. This study utilized wind‐driven rainfall laboratory flume experiments to analyse the influence of different wind directions (windward, leeward and crosswind) and rainfall intensities (30, 60 and 90 mm h−1) with constant wind speed (5 m s−1) on slope runoff, sediment yield and the associated losses of different forms of N ( , ) and P ( ‐P). The response of soil erosion, N and P loss to rainfall changes with different wind directions. When the rainfall intensity was constant, runoff, sediment yield and sediment‐associated total nitrogen (TN) and total phosphorus (TP) losses on slopes showed a trend of leeward > crosswind > windless > windward, whereas runoff‐associated TN and TP losses showed a trend of windward > crosswind > windless > leeward. Runoff, sediment yield and sediment‐associated TN and TP losses on leeward slopes were 1.09–1.17, 1.25–1.44, 1.33–1.62, and 1.40–1.66 times than windless slopes. Moreover, with constant wind direction, the runoff, sediment yield and associated N and P losses increased significantly with increasing rainfall intensity. When the rainfall intensity increased from 30 to 60 and 90 mm h−1, the runoff, sediment yield and associated TN and TP losses increased 2.02–2.28, 3.65–5.35, 3.96–34.39 and 4.28–8.45 times, respectively. The effects of rainfall on soil erosion and nutrient loss were significantly greater than those of wind. The loss of different forms of N and P associated with runoff and sediment was consistent with that of TN and TP losses. However, with an increase in rainfall intensity, the growth rates of runoff, sediment yield and associated N and P losses exhibited a gradually weakening trend for all wind directions. An increase in rainfall intensity enhanced the vertical vector force of wind‐driven rainfall, which increasingly decreased the angle between the rain incidence and the normal line of the horizon; therefore, the direction of the rain erosion force gradually approached that of windless conditions.

A comprehensive experimental study of enhanced solid particle erosive resistance on the inner/outer surface of graphene nanoplatelets modified basalt/epoxy composite pipe

AbstractBasalt fiber reinforced polymer (BFRP) composite pipe is an excellent alternative to glass and carbon fiber reinforced composite pipes in industry and promising in high recycling for polymer composite used in aerospace, marine, and automotive. To enhance the solid particle erosion (SPE) properties of filament‐wound BFRP composite pipe while preserving its mechanical properties, reinforced BFRP composite pipes were prepared to employ non‐functionalized graphene nanoplatelets (GnPs) at a reinforcement concentration of 0.25 wt.% and ultrasonication mixing technique. The SPE behavior of GnPs reinforced and non‐reinforced BFRP composite pipes were characterized by axial and radial positioning of the inner and outer surfaces of the pipes. In each case, the erosion rates of these composite pipes were evaluated at five impingement angles (30°, 45°, 60°, 75°, and 90°) and an impact velocity of 34 m/s. The erosion response of both BFRP composite pipes' outer surfaces showed a semi‐ductile in the axial positioning, with a maximum erosion rate at a 60° impingement angle. However, these composite pipes' inner surfaces in the same positioning presented a maximum erosion rate at a 45° impingement angle. Besides, it is explored that the GnPs contribute to an improvement of approximately 10%–55% in erosive wear resistance of the non‐reinforced BFRP composite pipes. The damage analysis of eroded surfaces was examined through scanning electron microscopy (SEM), and the GnPs effect upon composite pipes' erosion micromechanisms was presented and discussed in detail.Highlights GnPs increased the BFRP composite pipe's erosion resistance. Erosion rate on the inner surface increases due to particle accumulation. GnPs improved erosion behavior via solid lubrication and mechanical properties.

Confining stress effects on global and local responses of internal erosion in gap-graded cohesionless soils

Confining stress effects on global and local responses of internal erosion in gap-graded cohesionless soils

Soil erosion after fire in volcanic terrain: Assessment and implications for post-fire soil losses

Wildfires can dramatically modify the hydrologic and erosion response of ecosystems, increasing risks to population and assets downslope of fire affected hillslopes. This applies especially to volcanic areas in fire-prone regions which often exhibit steep terrain and high population densities. However, the effects of fire on key hydrologic and erosion parameters, which are critical for modelling runoff-erosion processes, predicting related post-fire risks and for selecting effective mitigation measures, have not been extensively assessed in this terrain type. Here we evaluate water erosion processes of two contrasting volcanic soils in recently burned forest areas of Tenerife (Canary Islands, Spain) at hillslope scale using erosion plots monitoring and rill erosion simulation experiments. The results show that both the lithology and the degree of weathering of the volcanic material govern the post-fire water erosion by concentrated flow (rill erosion experiments) and by the combination of interrill and rill erosion (erosion plots). Mature volcanic soils showed less susceptibility to erosion than weakly weathered volcanic soils and soils with non-volcanic lithologies. The results also show that the availability of easily detachable and transportable soil particles swiftly decreases after the fire, leading to the exhaustion of sediments and a decrease of the erosion rates with cumulative runoff events. These findings have direct implications for the modelling of runoff-erosion processes in volcanic terrain.

A coupled CFD-DEM investigation into hydro-mechanical behaviour of gap-graded soil experiencing seepage erosion considering cyclic hydraulic loading

The internal erosion of soils is a critical factor that can cause infiltration damage in slope and embankment works. Under conditions of heavy rainfall, storm surge, and waves, the soil is subjected to the cyclic changing hydraulic loads that are different from constant or monotonically changing hydraulic gradient loads, resulting in significant differences in the internal erosion response. The internal erosion response of gap-graded soil under cyclic hydraulic gradient is investigated in microscopic view based on the three-dimensional coupled computational fluid dynamics and discrete element (CFD-DEM) method. Three average hydraulic gradients (i.e., i¯= 7, 9, 11) and different cyclic hydraulic gradient amplitudes (i.e., Δi = 2 ∼ 10) are considered. It is found that the erosion mass me is significantly increased under cyclic hydraulic loading, as the amplitude of the cyclic hydraulic gradient increases, the erosion ratio gradually increases. The particle migration in the upstream layer is more susceptible to the influence of cyclic hydraulic gradients, and the distribution of fine particles is more uniform after erosion with the increase of Δi. The mechanism of the effect of cyclic hydraulic gradient is revealed from a micro perspective, including coordination number, connectivity distribution, particle force characteristics, local packing profile and the force chain evolution, it is found that the cyclic hydraulic loading affects the erosion process mainly by disturb or destroy the local clogging. The work provides insights into the effect of more complex hydraulic loading on internal erosion from a micromechanical perspective.

Coral reef island shoreline change and the dynamic response of the freshwater lens, Huvadhoo Atoll, Maldives

Low-lying coral reef islands have been projected to become uninhabitable by the end of the century due to sea level rise, but such projections of vulnerability assume that reef islands are static landforms that flood incrementally with sea level rise. In fact, GIS-based reef island shoreline analyses have demonstrated that reef islands are highly dynamic landforms that may adjust their shorelines in response to changing environmental conditions. However, the vast majority of reef island shoreline analyses have been undertaken in the Pacific Ocean, leaving our understanding of changes in the Indian Ocean more limited. Further, our knowledge of how island dynamics can impact groundwater resources is restricted due to the assumption that islands will exhibit purely erosional responses to sea level rise. Here, we analyse shoreline evolution on 49 reef islands over a 50-year timeframe in Huvadhoo Atoll, Maldives. Additionally, rates of shoreline change were used to undertake numerical modelling of shifts in freshwater lens volume in 2030, 2050 and 2100 in response to changes in recharge. Despite sea level rising at 4.24 mm/year (1969-2019), accretion was prevalent on 53% of islands, with the remaining islands eroding (25%) or remaining stable (22%). Average net shoreline movement was 4.13 m, ranging from -17.51 to 65.73 m; and the average rate of shoreline change (weighted linear regression) was 0.13 m/year, ranging from -0.07 to 2.65 m/year. The magnitudes and rates of reef island evolution were found to be highly site-specific, with island type found to be the only significant predictor of either net shoreline movement or weighted linear regression. Results suggest that freshwater lens volume was substantially impacted by shoreline change compared to changes in recharge whereby accretion and erosion led to large increases (up to 65.05%) decreases (up to -50.4%) in les volume, respectively. We suggest that the capacity of reef islands to both (1) adjust their shorelines, and even accrete, under conditions of sea level rise; and (2) increase their storage of groundwater over the coming decades represents highly valuable geomorphic ecosystem services.

Evaluating hydrological and soil erosion processes in different time scales and land uses in southern Brazilian paired watersheds

ABSTRACT Land use is a driver for hydrological and soil erosion responses at the watershed scale. This study aimed to assess the hydrological and soil erosion processes in small watersheds under three different land uses, at three time scales. We investigated four small watersheds in southern Brazil: Agricultural North watershed (ANW), Agricultural South watershed (ASW), Eucalyptus watershed (EW), and Grassland watershed (GW). The SWAT (Soil and Water Assessment Tool) model was used to simulate streamflow (SF) and sediment yield (SY) at monthly, daily and hourly time scales. EW had the lowest SF and SY, whereas ANW showed the highest SY with an increase of 90% and ASW had the highest SF with an increase of 70%. The SWAT model had a satisfactory performance in all time scales and watersheds for SF and SY (NSE and R2 ≥ 0.3 and Pbias ≤ ± 39%). Overall, land use has a major impact on hydrological and soil erosion responses, and the magnitude of these processes depends on the time scale.

Water and wind erosion response to ecological restoration measures in China's drylands

Soil erosion is the most severe form of land degradation threatening terrestrial ecosystems globally. Drylands with fragile ecosystems are particularly sensitive to soil erosion. China's drylands face the threat of soil erosion by wind and water. Currently, more studies need to be focused on wind and water erosion response to ecological restoration measures at monthly resolution in these areas. This is key to understanding ecological restoration measures' effectiveness under changing environments. Here, we assessed the monthly water and wind erosion in China's drylands from 2001 to 2020 using the G2 model and revised wind erosion equation (RWEQ). The Sequential linear regression slopes (SeRGS) explored water and wind erosion intensities. We also discuss the mitigation benefits of two ecological restoration measures, afforestation and grassland restoration. The results showed that water and wind erosion in China's drylands is mild (47.35%) and slight (58.76%). Water erosion increased between 2001 and 2020, while wind erosion decreased. At the monthly level, a higher water and wind erosion rate occurred from April to June and February to March, respectively. Water erosion dominated 50.64% of the China's drylands, while wind erosion was the most critical form of erosion in 47.88%. Nevertheless, the erosion pattern in China's drylands is changing. The average mitigation benefits of afforestation on water and wind erosion were −61.12% and −57.05%, respectively, and the average mitigation benefits of grassland restoration on water and wind erosion were −57.05% and 7.95%, respectively. This study can help managers identify the best ecological restoration strategies to mitigate land degradation in drylands.

High-Temperature Solid Particle Erosion of Environmental and Thermal Barrier Coatings

Solid particle erosion (SPE) is a common phenomenon observed in gas turbine engines. Particles entrained in the gas flow impact engine hardware, resulting in micro-scale damage that leads to deleterious effects such as material removal. For protective coatings, damage due to SPE is a key concern, since it can negatively affect the durability of the coating and subsequently the life of the underlying component. In this work, the high-temperature SPE behavior of two state-of-the-art environmental barrier coatings (EBCs) deposited via air plasma spray (APS) is investigated using alumina erodent to understand the effect of particle kinetic energy, impingement angle, and temperature. The SPE behavior of the EBCs is also compared to APS and electron beam–physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) to elucidate similarities and differences in the erosion response. The EBCs were more susceptible to SPE than the EB-PVD TBC but had greater SPE resistance compared to the APS TBC. Coating microstructure and porosity were shown to have a strong influence on the observed behavior.

Response of soil erosion to vegetation restoration and terracing on the Loess Plateau

Soil erosion exhibited significant decrease due to the implementation of considerable soil and water conservation practices on the Loess Plateau, and further induced less sediment discharged into the Yellow River. However, the influences of these practices on soil erosion have not been comprehensively investigated over large-scale regions. This study analyzed spatiotemporal variation of vegetation cover, and identified the distribution of terraces by using Google Earth remote sensing images in the whole Loess Plateau. The USLE model (Universal Soil Loss Equation) was applied to estimate responses of soil erosion to vegetation restoration and terraces. The annual regional-averaged NDVI increased from of 0.46 in 2000 to 0.63 in 2018, suggesting significant vegetation improvement due to afforestation. We detected 4.73 × 104 km2 of terraces by 2018, which covered approximately 1.5% of the whole Loess Plateau. The terraces were mainly distributed in the upstream of the Weihe River, Fenhe, Zuli, Jinghe, and Taohe River basins. The validated soil erosion model showed that vegetation changes caused a remarkable reduction of 51.2% soil erosion from 2000 to 2018 across the Loess Plateau. A scenario modelling with terraces reduced 19.4% of soil erosion, indicating their significant effects on soil erosion controlling. This study could give a useful reference to assess soil erosion changes response to vegetation restoration and terrace at a large scale. The results can be used to optimize the spatial layout of the measures for soil erosion control in the Loess Plateau in the future.

A call for strategic water-quality monitoring to advance assessment and prediction of wildfire impacts on water supplies

Wildfires pose a risk to water supplies in the western U.S. and many other parts of the world, due to the potential for degradation of water quality. However, a lack of adequate data hinders prediction and assessment of post-wildfire impacts and recovery. The dearth of such data is related to lack of funding for monitoring extreme events and the challenge of measuring the outsized hydrologic and erosive response after wildfire. Assessment and prediction of post-wildfire surface water quality would be strengthened by the strategic monitoring of key parameters, and the selection of sampling locations based on the following criteria: (1) streamgage with pre-wildfire data; (2) ability to install equipment that can measure water quality at high temporal resolution, with a focus on storm sampling; (3) minimum of 10% drainage area burned at moderate to high severity; (4) lack of major water management; (5) high-frequency precipitation; and (6) availability of pre-wildfire water-quality data and (or) water-quality data from a comparable unburned basin. Water-quality data focused on parameters that are critical to human and (or) ecosystem health, relevant to water-treatment processes and drinking-water quality, and (or) inform the role of precipitation and discharge on flow paths and water quality are most useful. We discuss strategic post-wildfire water-quality monitoring and identify opportunities for advancing assessment and prediction. Improved estimates of the magnitude, timing, and duration of post-wildfire effects on water quality would aid the water resources community prepare for and mitigate against impacts to water supplies.

Basal boundary conditions for granular surface flows over fragile and brittle erodible beds

Many granular surface flows occur as shear flows of finite thickness, over erodible beds composed of the same granular material. Such beds may be fragile, and offer no more resistance to erosion than to sustained shear. Or they may be brittle, and offer instead an excess resistance to erosion. To take this contrast into account, new basal boundary conditions are proposed. Their implications for parallel flows down infinite slopes are then examined for three different cases: stationary flows; starting; and stopping transients. For all three cases, flow behaviour is altered significantly when beds present an excess resistance to erosion. For stationary flows, non-unique velocity profiles are obtained, implying hysteresis or history-dependence. For starting transients, a power law growth of the flow thickness is predicted, instead of the jump to finite or infinite depth that would otherwise occur. For stopping transients, flows start to decelerate with a finite basal shear rate, even over erodible substrates. Analytical solutions to the corresponding free and moving boundary problems are obtained, and checked against numerical results. Model predictions are then compared with experimental measurements. Overall, good agreement is obtained. In particular, the model describes well the very different erosional responses observed for fragile and brittle beds.