Effects Of Antecedent Soil Moisture Research Articles

Surface‐to‐tile drain connectivity and phosphorus transport: Effect of antecedent soil moisture

AbstractMacropores connecting surface soils to tile drains can alter water and nutrient transport through the subsurface. In this study, laboratory rainfall simulations with artificial macropores combined with edge‐of‐field monitoring were used to evaluate surface‐to‐tile drain connectivity and phosphorus (P) transport as a function of antecedent moisture conditions. Laboratory rainfall simulations using repacked soil boxes with different macropore layouts (i.e., no macropore, surface‐connected macropores, and disconnected macropores) were used to examine changes in water sources and flow pathways to tile drains with varying degrees of connectivity and antecedent wetness. Water, tracer, and P fluxes from a tile‐drained field were also monitored to quantify linkages among water flow pathways, antecedent wetness, and P delivery to tile drains. Both laboratory and field results showed that surface‐to‐tile drain connectivity was important for water transport through the subsurface under both dry and wet antecedent conditions. When soil conditions were dry, discharge was minimal and primarily comprised of event water that bypassed the soil matrix. Increasing wetness resulted in similar event water transport, but greater mobilization of stored pre‐event water and greater discharge; thus, the dominant source of tile water and the magnitude of tile discharge were substantially altered with changing antecedent moisture. Field data revealed that changes in drainage water source and discharge with increasing wetness impacted dissolved P transport. Dissolved P concentration decreased and loading increased with increasing wetness. Findings indicate that greater mobilization of pre‐event water under wet antecedent conditions acted as both a hydrologic and chemical buffer for subsurface dissolved P transport. Comparison of study results to water quality data from a larger edge‐of‐field network suggest that relationships between antecedent moisture conditions, water flow pathways, and P transport from the current study are broadly applicable across tile‐drained fields. Understanding processes controlling P delivery to tile drains has direct applicability for conservation practice implementation and improving process representation in models.

Evaluation of cloud seeding on the securement of additional water resources in the Boryeong Dam Basin, Korea

This study evaluates the effect of cloud seeding on the increase of runoff or securing of additional water resources. Unlike previous studies, this study concentrates more on the change of various components of the hydrologic processes. Both the event-based analysis and the annual analysis are conducted to evaluate the change of these components. The Boryeong Dam Basin in Korea is considered as a study basin. The WRF (Weather Research and Forecasting) model is used in the cloud seeding simulation, while the PRMS (Precipitation Runoff Modeling System) model is used in the rainfall–runoff analysis. The target years of this study are 2018 and 2019. As results, the event-based analysis shows that the infiltration, effective rainfall, interflow, and direct runoff are increased relatively more among the eight rainfall-runoff components considered in this study. In particular, the increase of interflow is noticeable. More than 60 % of the increased rainfall is found to contribute to the runoff increase. In the annual analysis, this ratio is found to become even higher. The ratio is estimated to be more than 90 %, which is mostly due to the contribution of baseflow. As important factors controlling the effectiveness of cloud seeding, the effects of antecedent soil moisture and threshold daily rainfall depth on the increase of total runoff are also evaluated. The results show that wet soil condition is more favorable to the successful cloud seeding experiment to secure additional water resources. Also, it is confirmed that the cloud seeding experiment can be more effective when the daily rainfall is more than 20 mm. Finally, the results of this study imply the efficiency of cloud seeding and its economic values are potentially high.

Effects of antecedent soil moisture on rill erodibility and critical shear stress

Antecedent soil moisture is known to exert a complex, perhaps controversial, effect on rill erodibility and critical shear stress. To understand their dynamic nature as a function of antecedent soil moisture, the rill erodibility and critical shear stress for sandy loam and silty loam soil, representing coarse-grained and fine-grained soil, respectively, were measured using a hydraulic flume under six antecedent soil moisture contents, i.e., 3, 6, 9, 12, 15, and 18%. The results show that antecedent soil moisture had a different effect on critical shear stress and rill erodibility for the two different soil textures. As antecedent soil moisture increased, rill erodibility for the fine-grained soil first increased and then decreased, whereas for coarse-grained soil, rill erodibility exhibited a decreasing pattern. Conversely, as the antecedent soil moisture increased, the critical shear stress decreased first and then increased for the fine-grained soil, but for coarse-grained soil, the critical shear stress decreased after a slight increase. These different patterns can be interpreted by aggregate slaking, capillary force, soil cementation, and water separation. However, when the patterns of critical shear stress and rill erodibility were neglected, the differences in critical shear stress and rill erodibility between the coarse- and fine-grained soils were not statistically significant (P < 0.05). Therefore, indiscriminate treatments of critical shear stress and rill erodibility for different textural soils under changing antecedent soil moisture regimes may cause errors in soil erosion modeling. The relationship between rill erodibility and critical shear stress for coarse- and fine-grained soils could be fitted by a power and a polynomial function, with R2 value of 0.94 and 0.78, respectively. Future work should include additional soil textures to study the influence of soil physical characteristics in combination with antecedent soil moisture on soil erosion.

Restoring open canopy pine barrens from the ground up: Repeated burns correspond with increased soil hydraulic conductivity

Prescribed fire is widely used for ecosystem restoration, yet the mechanisms that determine its effectiveness remain poorly characterized. Because soil hydrology influences ecosystem processes like erosion, runoff, and plant competition, it is important to understand how fire affects soil hydrology. A systematic approach to understanding relationships among vegetation, topography, and fire is needed to advance knowledge of how fire influences soil properties that in turn affect restoration success. Our objective was to characterize relationships among burn severity, vegetation, and soil hydrology in a heterogenous landscape under restoration management. Our study took place in a barrens-forest mosaic with recent prescribed fire history ranging from 0 to 10 burns since 1960, and additional variation in fuel loading, burn severity, vegetation cover, topography, and soils. We measured soil hydraulic conductivity (SHC) during two consecutive years, which represented control, prefire, postfire, and 1-year postfire conditions. Regression tree analysis identified an important threshold effect of antecedent soil moisture on SHC; soils with initial moisture < 13% had lower SHC than soils with initial moisture > 13%. Furthermore, above this threshold, sites with intermediate to high recent burn frequency (4–10 burns) had significantly greater SHC than unburned control sites. High fuel loads associated with brush cutting and piling increased SHC at barrens sites but not brush or pine sites, suggesting an interaction between vegetation cover and fire effects on SHC. At the local hillslope scale, toe-slopes had greater SHC than summits. Our results suggest that repeated prescribed fires of moderate to high frequency may enhance SHC, thereby reducing soil water retention and potentially restoring functional pine barren processes that limit woody plant growth. Prescribed fire may therefore be an important management tool for reversing mesophication and restoring a global array of open canopy ecosystems.

Investigating the role of antecedent SMAP satellite soil moisture, radar rainfall and MODIS vegetation on runoff production in an agricultural region

Following results by Crow et al. (2017) [Geophys. Res. Lett. 44, 5495–5503] on the impact of antecedent soil moisture on runoff production, we investigate total runoff production during individual rainfall-runoff events in agricultural landscapes as a function of antecedent soil moisture, total rainfall, and vegetation cover for catchments with drainage areas ranging from 80 to 1000 km2 in the state of Iowa, USA. For our study, we use Enhanced SMAP soil moisture estimates, the MODIS enhanced vegetation index (EVI), gauge-corrected Stage IV radar rainfall, and USGS streamflow data. We analyze the event runoff ratio as a function of event-scale rainfall, antecedent SMAP soil moisture and soil-moisture-deficit-normalized rainfall for the events in a period from March 31, 2015 to October 31, 2018. Our goal is to confirm the relationships identified by Crow et al. (2017) in heavily managed agricultural landscapes and to refine some of their methodological steps to quantify the role of additional variables controlling runoff production. To this end, we define three different strategies to identify rainfall-runoff events and add a baseflow separation step to better insulate event scale stormflow runoff. We test the effects of antecedent soil moisture, rainfall, and vegetation on the event-scale runoff ratio. The antecedent SMAP soil moisture and event-scale rainfall are found to have significant predictive power in estimating event runoff ratio. Soil moisture deficit-normalized rainfall, introduced as the ratio of event-scale rainfall to available space in top soil before initiation of the event, exhibited a more distinct relationship with runoff ratio. The long-term analysis of runoff ratio, rainfall, and MODIS EVI indicated that, in an agricultural region, vegetation plays a significant role in determining event-scale runoff ratios. The methodology and outcome of our study have direct implications on real-time flood forecasting and long-term hydrologic assessments.

Combined effect of rain temperature and antecedent soil moisture on runoff and erosion on Loess

The effect of antecedent soil moisture content on runoff and soil erosion was investigated in many previous studies. These studies revealed contradictory findings. The present study investigated the combined effect of raindrop temperatures and antecedent soil moisture on interrill flow generation and erosion of a loamy soil (Loess), using a rotating disk rain simulator. The experiments were applied to soil with two pre-prepared moisture conditions: hygroscopic and field capacity. For each condition, three rainfall temperatures were applied: 2 (cold), 20 (mid-temperature), and 35°C (hot).The effect of antecedent soil moisture on soil erosion found to be depended on rainfall temperature. For the cold rainfall, the sediment yield of the dry soil was 5.2 times greater than that of the pre-wetted soil, whereas for the mid-temperature and for the hot rainfall it was 1.5 and 1.2, respectively. For the pre-wetted soil, the sediment yield in the mid-temperature rainfall was 3 times greater than in the cold one. In the light of the predicted changes in global climate characteristics, an increase in rainfall temperature might lead to enhanced soil loss in Loess.

Urbanisation impacts on storm runoff along a rural-urban gradient

Urbanisation alters the hydrological response of catchments to storm events and spatial measures of urban extent and imperviousness are routinely used in hydrological modelling and attribution of runoff response to land use changes. This study evaluates whether a measure of catchment urban extent can account for differences in runoff generation from storm events along an rural-urban gradient. We employed a high-resolution monitoring network across 8 catchments in the south of the UK - ranging from predominantly rural to heavily urbanised - over a four year period, and from this selected 336 storm events. Hydrological response was compared using volume- and scaled time-based hydrograph metrics within a statistical framework that considered the effect of antecedent soil moisture. Clear differences were found between rural and urban catchments, however above a certain threshold of urban extent runoff volume was relatively unaffected by changes and runoff response times were highly variable between catchments due to additional hydraulic controls. Results indicate a spatial measure of urbanisation can generally explain differences in the hydrological response between rural and urban catchments but is insufficient to explain differences between urban catchments along an urban gradient. Antecedent soil moisture alters the volume and timing of runoff generated in catchments with large rural areas, but was not found to affect the runoff response where developed areas are much greater. The results of this study suggest some generalised relationships between urbanisation and storm runoff are not represented in observed storm events and point to limitations in using a simplified representations of the urban environment for attribution of storm runoff in small urban catchments. The study points to the need for enhanced hydrologically relevant catchment descriptors specific to small urban catchments and more focused research on the role of urban soils and soil moisture in storm runoff generation in mixed land-use catchments.

Effect of dry spells and soil cracking on runoff generation in a semiarid micro watershed under land use change

Soil and water resources effective management and planning in a river basin rely on understanding of runoff generation processes, yield, and their relations to rainfall. This study analyzes the effects of antecedent soil moisture in an expansive soil and the influence of dry spells on soil cracking, runoff generation and yield in a semiarid tropical region in Brazil subject to land use change. Data were collected from 2009 to 2013 in a 2.8ha watershed, totaling 179 natural rainfall events. In the first year of study (2009), the watershed maintained a typical dry tropical forest cover (arboreal-shrub Caatinga cover). Before the beginning of the second year of study, gamba grass (Andropogon gayanus Kunth) was cultivated after slash and burn of native vegetation. Gamba grass land use was maintained for the rest of the monitoring period. The occurrence of dry spells and the formation of cracks in the Vertisol soil were the most important factors controlling flow generation. Dry spells promoted crack formation in the expansive soil, which acted as preferential flow paths leading to high initial abstractions: average conditions for runoff to be generated included soil moisture content above 20%, rainfall above 70mm, I30max above 60mmh−1 and five continuous dry days at the most. The change of vegetation cover in the second year of study did not alter significantly the overall conditions for runoff initiation, showing similar cumulative flow vs. rainfall response, implying that soil conditions, such as humidity and cracks, best explain the flow generation process on the semiarid micro-scale watershed with Vertisol soil.

Rainfall timing and runoff: The influence of the criterion for rain event separation

Abstract Rain is not uniform in time and space in semiarid areas and its distribution is very important for the runoff process. Hydrological studies usually divide rainfall into events. However, defining rain events is complicated, and rain characteristics vary depending on how the events are delimited. Choosing a minimum inter-event time (MIT) is a commonly used criterion. Our hypothesis is that there will be an optimal MIT that explains the maximum part of the variance of the runoff, with time to runoff used as a surrogate. The objective is to establish a procedure in order to decide upon this optimal MIT. We developed regressions between time to runoff (T0) and three descriptive variables of rain. Our results show that the optimum MIT is 1 hour, which seems to be the minimum period of time required for water in larger macropores to drain and sufficiently modify the effect of antecedent soil moisture on the runoff generation process. Rain events are classified into three significantly different groups: (1) large and intense rains, (2) light rains on wet soil, and (3) light rains on dry soil. Intense rains produce most of the runoff, but there were significant differences between small events in the runoff generated. Of rain events, 63.75% are single-tip events, and many could be dew.

Interpreting Dye Test Results for Improved Drip Irrigation Management for the Mulched Vegetable-Production Systems in South Florida

On-farm dye tests provide simple, low-cost methods to understand how water and dissolved nutrients (e.g., nitrogen) will move within beds at a given farm. If it is not feasible for the grower to conduct an on-farm dye test, results from a dye test with similar site characteristics—including region, soil type, bed geometry, and drip tape—can be used. The intent of this publication is to explain procedures of a dye test and describe the movement pattern for Immokalee fine sand, a typical soil found in central and south Florida. We also show the effect of antecedent soil moisture on water movement in the bed. This 6-page fact sheet was written by Sanjay Shukla, Nathan Holt, and Gregory Hendricks, and published by the UF Department of Agricultural and Biological Engineering, July 2014.

A Protocol for Conducting Rainfall Simulation to Study Soil Runoff

Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hr after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been prewetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.

A protocol for conducting rainfall simulation to study soil runoff.

Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hr after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been prewetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.

Evaluation of rapid approaches for determining the soil water retention function and saturated hydraulic conductivity in a hydrologically complex soil

Knowledge of the soil water characteristic (SWC) and saturated hydraulic conductivity (Ksat) are required for simulation of soil water movement in most Richards’ equation based soil-water models. This study compared van Genuchten (VG) parameter values and Ksat determined by desorption with two rapid approaches, evaporative flux from intact cores, and inverse solution of tension infiltration data. Estimated and measured Ksat varied up to four orders of magnitude depending on parameterisation approach and antecedent soil moisture content. The SWC differed markedly between the laboratory drying and in situ wetting approaches due to the effects of hysteresis, air entrapment, clay swelling and water repellence. The evaporative flux approach was subjected to errors associated with prior saturation of the soil core, lack of K(ψ) data near saturation, and extrapolation of values beyond the measurement range of the upper tensiometer. Inverse solution of cumulative infiltration data from tension infiltrometers was able to discern the effects of antecedent soil moisture on soil structure and water repellence, however the approach had difficulty in obtaining unique local minima when the residual soil water content (θr) was included in the objective function. Both the evaporative flux and inverse solution of tension infiltration data approaches were improved by independent determination of the θr. Researchers should be aware that initial moisture content and methodology may influence VG parameter values, and that laboratory analysis of intact cores may result in Ksat and VG values which do not represent the hydraulic behaviour of field soils.

Modulation of soil moisture–precipitation interactions over France by large scale circulation

How soil moisture affects precipitation is an important question—with far reaching consequences, from weather prediction to centennial climate change—, albeit a poorly understood one. In this paper, an analysis of soil moisture–precipitation interactions over France based on observations is presented. A first objective of this paper is to investigate how large scale circulation modulates soil moisture–precipitation interactions, thanks to a weather regime approach. A second objective is to study the influence of soil moisture not only on precipitation but also on the difference between precipitation and evapotranspiration. Indeed, to have a total positive soil moisture–precipitation feedback, the potential decrease in precipitation associated with drier soils should be larger than the decrease in evapotranspiration that drier soils may also cause. A potential limited impact of soil moisture on precipitation is found for some weather regimes, but its sign depends on large scale circulation. Indeed, antecedent dry soil conditions tend to lead to smaller precipitation for the negative phase of the North Atlantic Oscillation (NAO) regime but to larger precipitation for the Atlantic Low regime. This differential response of precipitation to soil moisture anomalies depending on large scale circulation is traced back to different responses of atmospheric stability. For all circulation regimes, dry soils tend to increase the lifted condensation level, which is unfavorable to precipitation. But for the negative phase of the NAO, low soil moisture tends to lead to an increase of atmospheric stability while it tends to lead to a decrease of stability for Atlantic Low. Even if the impact of soil moisture anomalies varies depending on large scale circulation (it is larger for Atlantic low and the positive phase of the NAO), dry soils always lead to a decrease in evapotranspiration. As the absolute effect of antecedent soil moisture on evapotranspiration is always much larger than its effects on precipitation, for all circulation regimes dry soil anomalies subsequently lead to positive precipitation minus evapotranspiration anomalies i.e. the total soil moisture feedback is found to be negative. This negative feedback is stronger for the Atlantic Low and the positive phase of the NAO regimes.

Effects of antecedent soil moisture on losses of rare earth elements and phosphorus in runoff

The effects of antecedent soil moisture on losses of rare earth elements (REEs) and phosphorus (P) in runoff were evaluated through a simulated rainfall experiment at the rate of 83 mm h−1. The results revealed that antecedent moisture was a significant factor affecting the amounts of REE and P losses. It was observed that most REEs and P transported with sediments in the runoff. There was a significant correlation between the total amounts of REE losses and those of P losses in the runoff. The optimal antecedent moisture for minimization of losses for REEs ranged from 10.19 to 11.17% and it was 10.91% for P.

Effects of antecedent soil moisture on runoff modeling in small semiarid watersheds of southeastern Arizona

Abstract. This study presents unique data on the effects of antecedent soil moisture on runoff generation in a semi-arid environment, with implications for process-based modeling of runoff. The data were collected from four small watersheds measured continuously from 2002 through 2010 in an environment where evapo-transpiration approaches 100% of the infiltrated water on the hillslopes. Storm events were generally intense and of short duration, and antecedent volumetric moisture conditions were dry, with an average in the upper 5 cm soil layer over the nine year period of 8% and a standard deviation of 3%. Sensitivity analysis of the model showed an average of 0.05 mm change in runoff for each 1% change in soil moisture, indicating an approximate 0.15 mm average variation in runoff accounted for by the 3% standard deviation of measured antecedent soil moisture. This compared to a standard deviation of 4.7 mm in the runoff depths for the measured events. Thus the low variability of soil moisture in this environment accounts for a relative lack of importance of storm antecedent soil moisture for modeling the runoff. Runoff characteristics simulated with a nine year average of antecedent soil moisture were statistically identical to those simulated with measured antecedent soil moisture, indicating that long term average antecedent soil moisture could be used as a substitute for measured antecedent soil moisture for runoff modeling of these watersheds. We also found no significant correlations between measured runoff ratio and antecedent soil moisture in any of the four watersheds.

Effect of antecedent soil moisture on preferential flow in a texture-contrast soil

The effect of soil moisture status on preferential flow in a texture-contrast soil was investigated by applying 25 mm Brilliant Blue dye tracer to soil profiles at high and low antecedent soil moisture. Differences in soil morphology and chemistry between soil profiles had little effect on the depth of dye infiltration and dye distribution down the profile. Antecedent soil moisture strongly influenced the type, depth and rate of dye tracer movement. In the wet treatment, the dye tracer infiltrated to depths between 0.24 and 0.40 m, at an average rate of 120 mm h−1. Whilst in the dry treatment, the same volume of dye tracer infiltrated to between 0.85 and 1.19 m depth at an average rate of 1160 mm h−1. In dry antecedent conditions, finger flow developed in the A1 horizon as a result of water repellency. In the wet treatment, the wetting front developed permutations but did not break into fingers. Despite similar particle size distributions, flow in the A2e was slower than the A1 horizon, due to the absence of macropores. In the dry treatment, the dye tracer ponded on the upper surface of the B21 horizon, which then spilled down the sides of the large clay columns as rivulets, at rates of between 2000 and 3000 mm h−1. The dye tracer accumulated at the base of the columns resulting in backfilling of the inter column shrinkage cracks, at an estimated rate of 750 mm h−1. In the subsoil, water movement occurred via shrinkage cracks which resulted in flow by-passing 99% of the soil matrix in the B21 horizon and 94% of the soil matrix in the B22 horizon. Evidence of rapid and deep infiltration in ‘dry’ texture-contrast soils has implications for water and solute management. This knowledge could be used to: (i) improve irrigation and fertilizer efficiency (ii) explain variations in crop yield (iii) reduce salinity through improved leaching practices, (iv) reduce the risk of agrochemicals contaminating shallow groundwater.

Reply to comment by Jack Lewis et al. on “Forests and floods: A new paradigm sheds light on age‐old controversies”

Reply to comment by Jack Lewis et al. on “Forests and floods: A new paradigm sheds light on age‐old controversies”

Effects of antecedent soil moisture on runoff and soil erosion in alley cropping systems

Alley cropping systems may prevent soil and water erosion. The objective of this paper was to assess the effects of antecedent soil moisture on runoff and soil loss in alley cropping systems. Five land use treatments with three replications were included in this study. The treatments were mono peanut cropping (P), younger trees (T 1), older trees (T 2), peanut ( Arachis hypogaea) intercropped with younger trees (T 1P), and peanut intercropped with older trees (T 2P). The trees used were deciduous Choerospondias axillaris. Runoff and soil loss from the experimental plots were monitored and related to rainfall and antecedent soil water potential. Results showed that T 1 and T 2 produced the highest runoff and lowest soil loss while P produced the greatest soil loss. Soil loss was 25.3% less in T 1P and 32.0% in T 2P than in P. Runoff was 62.6% less in T 1P than in T 1 and 56.1% less in T 2P than in T 2. Regardless of land use, soil loss was more closely correlated to runoff than to rainfall ( R > 0.95 versus R < 0.40). Runoff and soil loss varied with season and antecedent soil moisture. The largest amounts of runoff and soil loss were recorded in the soil water surplus phase (rainy season). In spite of less rainfall in the soil water deficit phase, soil loss was greater than that in the soil water recovery phase. The runoff coefficient was exponentially correlated to the inverse of antecedent soil water potential in the rainy season, while the runoff coefficient was negatively and linearly correlated to antecedent soil water potential in the dry season. These results suggest that saturation excess runoff may be dominant in the rainy season and infiltration excess runoff may become dominant in the dry season.

Hydrological and erosion response of a badlands system in semiarid SE Spain

A long term monitoring program is being conducted to study runoff and erosion processes in a semiarid badlands environment (Tabernas Desert, SE Spain). The first six years of data from an instrumented experimental area with nested microcatchments are presented. The overall area is composed of a complex mosaic of soil surfaces with contrast hydrological and erosion behaviour. At microcatchment scale, runoff and erosion are controlled by the types of soil surfaces: small bare microcatchments had the highest runoff coefficients and the highest erosion rates, while those completely covered by vegetation had the lowest. Rainfall intensity significantly affected water and sediment budgets. The effect of antecedent soil moisture could only be observed when soil was near saturation and a few millimetres of additional rainfall were sufficient to produce Horton-type runoff, but it was very difficult to separate this from the effect of surface crusts formed in the first minutes of rainfall. Most of the rainfall events were below the threshold for producing runoff although they were important for sediment preparation through weathering. Small magnitude, low-intensity rainfall events along with protective plant cover over half of the total surface, are the main factors explaining low overall erosion rates at microcatchment scale.