Antecedent Soil Moisture Content Research Articles

The Contradictory Issue of the Impact of Antecedent Soil Moisture to Interrill Erosion in Clay Soil: A Two-Year Field Study

The impact of antecedent soil moisture content on soil erosion has been a contradictory issue in erosion research, as well as process-based soil loss estimation models. The objective of this study was to investigate the impact of antecedent soil moisture content on the loss of clay soil through two-year runoff plot experiments under natural rainfall. Volumetric soil moisture sensors were used to monitor soil moisture changes, and readings were used along with rainfall records to quantify the antecedent soil moisture conditions. The results of this study show that the impact of antecedent soil moisture on interrill erosion is conditional, and the impact only exists in erosion events with a low Rainfall–Runoff Erosivity Index. The coefficient of determination between antecedent soil moisture content and soil loss per the Rainfall–Runoff Erosivity Index (Soil Loss/EI30) varies from 0.222 to 0.758, depending on the rainfall duration and Rainfall–Runoff Erosivity. The results of this study also suggest that accumulative rainfall within 48 h (Pp48) prior to an effective erosion event is strongly correlated with Soil Loss/EI30, particularly when the duration of an effective erosion event is either 3~7 h or 10~30 h. Hence, Pp48 can be considered as a replacement for antecedent soil moisture in process-based soil loss simulation models.

Infiltration-Based Variability of Soil Erodibility Parameters Evaluated with the Jet Erosion Test

Soil erosion by water on agricultural hillslopes leads to numerous environmental problems including reservoir sedimentation, loss of agricultural land, declines in drinking water quality, and requires deep understanding of underlying physical processes for better mitigation. It is imperative to accurately predict soil erosion caused by overland flow processes so that soil conservation efforts can be undertaken proactively before large-scale sedimentation problems arise. Soil detachment is often described by the excess shear stress equation that contains two physical soil erodibility parameters, erodibility coefficient, and critical shear stress. These parameters are normally assumed to be constant but can change across varying soil texture classes as well as during surface runoff events due to changes in soil cohesion and potential dependency on soil moisture content. These changes may significantly affect soil erosion rates at the field and watershed scale. In this study, the erodibility parameters of three soil types (sandy loam, clay loam, and silty clay loam) were analyzed using a laboratory mini-Jet Erosion Test (JET) to determine the effect of soil sample infiltration and moisture condition. Results from the experiments depicted a dynamic relationship between the soil erodibility parameters and amount of infiltrated mass of water. Data analysis displayed that for soils of different texture critical shear stress exhibited local minimum with higher values for very dry and saturated soils, while erodibility coefficient tended to increase with the increase of mass of soil water. Utilizing these dynamic soil erodibility parameters did not result in a significant difference in soil erosion rates when compared to using the averaged soil erodibility parameters taken from the experiment but the range of potential erosion rates increases with the increase of applied sheer stress to soil surface. The erosion rates with the experiment-based coefficients were found to be higher than with the baseline WEPP-based coefficients. These results highlight the importance of evaluating the effect of intrastorm dependent factors during surface runoff events, such as antecedent soil moisture content, time to peak from the start of runoff, soil cohesion, etc., on soil erodibility parameters to accurately calculate erosion rates, especially for initially dry soils or during earlier stages of surface runoff when critical shear stresses were highly affected. Further assessment of such factors with JET or other laboratory and field tests is recommended.

Influence of antecedent soil moisture content and land use on the surface runoff response to heavy rainfall simulation experiments investigated in Alpine catchments

In small Alpine catchments, floods are mostly triggered by surface runoff generation during convective heavy precipitation events. Their magnitude also depends on the antecedent soil moisture content, which was shown in several previous studies. This study aims at understanding (a) which sites change their surface runoff response to rainfall events with high precipitation intensity under very moist pre-conditions to what extent and (b) on which site characteristics this depends on. Therefore, we conducted repeated rainfall simulation experiments (40–80 m2, 1 h, 100 mm h−1) at 20 sites in five Eastern Alpine areas and analyzed their results on the basis of soil-physical parameters derived from collected soil samples.The hay meadow sites reacted with a strong increase in surface runoff to reduced saturation deficits, the pasture sites showed a smaller but visible response. The forest sites had the highest water retention capacities. The change in the surface runoff response is a function of the saturation deficit at the beginning of the initial experiment (r = −0.58). The soil physical parameters, especially the fine pore fraction (r = 0.56), correlate with the difference of the total surface runoff coefficient between the initial and the repeated experiment. The fine pore fraction also shows a high correlation (r = −0.78) with the saturation deficit at the beginning of the initial experiment, although pores of this fraction were saturated during all experiments. (Non-quantifiable) Land use effects, which in turn influence the soil physical parameters, play an important role in explaining how the surface runoff response in the repeated rainfall simulation experiment differs from the initial experiment. The information on land use and soil characteristics allowed the sites to be categorized into four types in terms of surface runoff disposition and the increase in total surface runoff coefficient in the second rainfall simulation experiment.

The contribution of several sub-watersheds within the Garang watershed in supplying the floods on 6 and 24 February 2021

The flood incident of Garang watershed on 6 and 24 February 2021 inundated some of Semarang City. Total area of inundated area is about 47% of Semarang City or 176 km2. A research was conducted to estimate the contribution of sub-watersheds in flood peak and flood volume, and to analyze the causes of the flooding and its solutions. The flood peak discharge was estimated using Rational method and flood volume using Curve Number (CN) method. Geographic Information Syatem (GIS) is used for calculating Runoff coefficient and Curve Number. Overlay of landcover map, slope map, and soil map produce runoff coefficient map while the CN value was obtained from over lapping land cover maps, soil hydrology group, application of soil and water conservation techniques, hydrological conditions, and antecedent soil moisture content in each sub watershed. Garang watershed consists of 4 sub watersheds namely Garang upland, Kreyo, Kripik, and Garang lowland with area of 85.33; 65.36; 38.83; and 23.20 km2. The results showed that specific flood peak on 6 February 2021 were 3.9; 3.2; 3.6; and 3.4 m3/second/km2 for the Garang upland, Kreyo, Kripik, and Garang low land subwatershed. Specific flood volume on Feb 6, 2021 were 91,471; 91,396; 96,605; and 99,058 m3/km2. Garang up land sub watershed has highest specific peak flow and Lower Garang sub watershed has highest specific flood volume. The cause of flooding in the Garang watershed was caused by high rainfall intensity and watershed degradation. Flood peak and flood volume can be reduced by applying some water conservation techniques and increasing vegetation cover.

Peak flood volume and its suspended sediment at various rainfall in Kedungbulus catchment in Gombong, Central Java, Indonesia

Flood is a natural disaster that frequently happens and causes many material and immaterial losses. During flooding, the suspended sediment is carried along by the streamflow. The amount of sediment transported varies and depends on natural and anthropogenic factors. Limited studies have been conducted regarding the relationship between peak flood volume and its sediment content. Therefore, a study with the purpose to understand the relationship of rainfall characteristics, peak flood volume, and suspended sediment was undertaken in Kedungbulus Catchment in Gombong, Central Java, Indonesia. The size of Kedungbulus catchment is 37.8 km2. To collect the required data, an automatic stream water level recorder was installed in the outlet of the catchment. In addition, an automatic and two conventional rain gauges were set up inside the catchment. Hydrograph and statistical analysis were conducted on 2016-2017 data. The results showed that during the study period, the highest peak flood volume occurred on October 8, 2016. The flood duration was 490 minutes, with the time to peak was 135 minutes. At the highest peak flood volume, the stream water was 5,091,221 m3, and the suspended sediment was around 2,394 tons. Rainfall depth significantly affects the peak flood volume and its suspended sediment. The rainfall intensity and Antecedent Soil Moisture Content (ASMC) weakly correlate with peak flood volume and its suspended sediment content.

Urban flood event and associated damage in the Benue valley, Nigeria

Flooding events in the Lower Benue valley of Nigeria are often associated with huge damage to properties and loss of life in the adjoining communities. Specific objectives of this study were to (i) examine the characteristics of rainfall and discharge at the major river in the study area—Benue trough of Nigeria; (ii) assess the occurrence of extreme rainfall conditions and other flood-triggering/exacerbating factors; and (iii) determine flood damage extent and available warning system in the area. Specific reference was made to the 2017 flood event in the area. Method used was an integrated environmental approach that combines analysis of rainfall and discharge data with social surveys, remote sensing and geographical information system. Standardized Precipitation Index (SPI), Precipitation Concentration Index (PCI) as well as flood damage curves were analysed with land use/cover change and soil data to establish the nature of the flood and its impacts. Result showed that rainfall has increased in the study area in October–December and February (b ≤ 0.13) but has decreased in the other months, albeit insignificantly (R2 < 0.5). Rainfall–runoff relationship at the gauge station was weak (b = 16.67, R2 = 0.21), and indicates the influence of antecedent soil moisture content at the gauge station, while the well-drained nature of the soil, its sedimentary geology and land use/cover analysis would indicate the dominance of infiltration-excess flow. The results of the SPI and PCI, which categorized the study area as largely wet during the study period (13.5% of the years classified as extremely wet and 54.1% wet), as well as high record of consecutive rain days revealed the vulnerability of the area to flood hazards in the wet months. Eighty-five per cent of the vulnerable residents are considerably poor, earning an equivalent of US $4.3 daily, and live in non-reinforced concrete masonry (64%) and wooden buildings (24%). The study recommends extensive flood control policy for the area and similar flood-prone communities.

Direct and indirect effects of rainfall and vegetation coverage on runoff, soil loss, and nutrient loss in a semi‐humid climate

AbstractSoil and nutrient loss play a vital role in eutrophication of water bodies. Several simulated rainfall experiments have been conducted to investigate the effects of a single controlling factor on soil and nutrient loss. However, the role of precipitation and vegetation coverage in quantifying soil and nutrient loss is still unclear. We monitored runoff, soil loss, and soil nutrient loss under natural rainfall conditions from 2004 to 2015 for 50–100 m2 runoff plots around Beijing. Results showed that soil erosion was significantly reduced when vegetation coverage reached 20% and 60%. At levels below 30%, nutrient loss did not differ among different vegetation cover levels. Minimum soil N and P losses were observed at cover levels above 60%. Irrespective of the management measure, soil nutrient losses were higher at high‐intensity rainfall (Imax30&gt;15 mm/h) events compared to low‐intensity events (p &lt; 0.05). We applied structural equation modelling (SEM) to systematically analyze the relative effects of rainfall characteristics and environmental factors on runoff, soil loss, and soil nutrient loss. At high‐intensity rainfall events, neither vegetation cover nor antecedent soil moisture content (ASMC) affected runoff and soil loss. After log‐transformation, soil nutrient loss was significantly linearly correlated with runoff and soil loss (p &lt; 0.01). In addition, we identified the direct and indirect relationships among the influencing factors of soil nutrient loss on runoff plots and constructed a structural diagram of these relationships. The factors positively impacting soil nutrient loss were runoff (44%–48%), maximum rainfall intensity over a 30‐min period (18%–29%), rainfall depth (20%–27%), and soil loss (10%–14%). Studying the effects of rainfall and vegetation coverage factors on runoff, soil loss, and nutrient loss can improve our understanding of the underlying mechanism of slope non‐point source pollution.

Runoff response to rainfall events considering initial soil moisture – Analysis of 9-year records in a small Alpine catchment (Brixenbach valley, Tyrol, Austria)

Study regionBrixenbach catchment (10 km²), Kitzbuehel Alps, Tyrol, Austria. Study focusThis study presents the data of one of the rare soil moisture networks in the Alps, a 9-year soil moisture time series recorded at 8 sites with in-situ measurements (six pasture and two forest sites). We aim at understanding the soil moisture behaviour in general, its reaction to rainfall considering the site characteristics and the runoff reaction depending on the antecedent soil moisture content. We analysed soil moisture, rainfall and discharge data with a temporal resolution of one hour (summer months) and two hours (autumn to spring) respectively and interpreted the results in terms of land use and topographical features. New hydrological insights for the regionThe medians of the soil moisture positively correlate with the sites’ altitude. Comparing spatial standard deviation of soil moisture versus spatial mean shows a high scatter of the standard deviations, contrary to previous studies, which use considerably shorter time series. The spatial variability increases with spatial mean, thus the highest spatial variability is recorded at wet conditions. The catchment shows clear threshold behaviour: Runoff coefficients above 0.23 only occurred when the soil moisture spatial mean of the eight sites overrun 43.5 vol% which can be translated into a saturation deficit of 0.28.

On the shape of forward transit time distributions in low-order catchments

Abstract. Transit time distributions (TTDs) integrate information on timing, amount, storage, mixing and flow paths of water and thus characterize hydrologic and hydrochemical catchment response unlike any other descriptor. Here, we simulate the shape of TTDs in an idealized low-order catchment and investigate whether it changes systematically with certain catchment and climate properties. To this end, we used a physically based, spatially explicit 3-D model, injected tracer with a precipitation event and recorded the resulting forward TTDs at the outlet of a small (∼6000 m2) catchment for different scenarios. We found that the TTDs can be subdivided into four parts: (1) early part – controlled by soil hydraulic conductivity and antecedent soil moisture content, (2) middle part – a transition zone with no clear pattern or control, (3) later part – influenced by soil hydraulic conductivity and subsequent precipitation amount, and (4) very late tail of the breakthrough curve – governed by bedrock hydraulic conductivity. The modeled TTD shapes can be predicted using a dimensionless number: higher initial peaks are observed if the inflow of water to a catchment is not equal to its capacity to discharge water via subsurface flow paths, and lower initial peaks are connected to increasing available storage. In most cases the modeled TTDs were humped with nonzero initial values and varying weights of the tails. Therefore, none of the best-fit theoretical probability functions could describe the entire TTD shape exactly. Still, we found that generally gamma and log-normal distributions work better for scenarios of low and high soil hydraulic conductivity, respectively.

Forecasting of Landslides Using Rainfall Severity and Soil Wetness: A Probabilistic Approach for Darjeeling Himalayas

Rainfall induced landslides are creating havoc in hilly areas and have become an important concern for the stakeholders and public. Many approaches have been proposed to derive rainfall thresholds to identify the critical conditions that can initiate landslides. Most of the empirical methods are defined in such a way that it does not depend upon any of the in situ conditions. Soil moisture plays a key role in the initiation of landslides as the pore pressure increase and loss in shear strength of soil result in sliding of soil mass, which in turn are termed as landslides. Hence this study focuses on a Bayesian analysis, to calculate the probability of occurrence of landslides, based on different combinations of severity of rainfall and antecedent soil moisture content. A hydrological model, called Système Hydrologique Européen Transport (SHETRAN) is used for the simulation of soil moisture during the study period and event rainfall-duration (ED) thresholds of various exceedance probabilities were used to characterize the severity of a rainfall event. The approach was used to define two-dimensional Bayesian probabilities for occurrence of landslides in Kalimpong (India), which is a highly landslide susceptible zone in the Darjeeling Himalayas. The study proves the applicability of SHETRAN model for simulating moisture conditions for the study area and delivers an effective approach to enhance the prediction capability of empirical thresholds defined for the region.

Do wildfire and slope aspect affect soil water repellency in eucalypt plantations? – A two-year high resolution temporal dataset

Wildfire can induce, enhance, or destroy natural soil water repellency (SWR) depending mostly on soil burnt severity, soil and vegetation types, soil organic matter (SOM) content and type, soil texture, peak soil temperature and remaining time and, antecedent soil moisture content (SMC). In Portugal, SWR in eucalypt stands has been shown to increase surface runoff under dry antecedent SMCs in both burnt and unburnt sites, thereby enhancing soil erosion. Despite the many hydrological implications of SWR, intensive field monitoring under a wide range of SMCs is still limited. This study aimed to improve our understanding of the role of slope aspect and wildfire on the temporal evolution of SWR in Mediterranean environments, which will be helpful for hydrological modelling and post-fire soil erosion risk assessment. In this sense, two burnt eucalypt plantations (wildfire of July 2010) were selected along a neighbouring, long-unburnt eucalypt stand, in north-central Portugal, in order to assess SWR and SMC’s in a high temporal resolution. During the first two post-fire years, at 1–2 week intervals, surface (2.5 cm depth) SWR and SMC were monitored using the “molarity of an ethanol droplet” (MED) test and a soil probe, respectively. The results showed that the observed annual SWR was very high to extreme (80% of measurements ≥ 6 ethanol class) for all three sites. Wildfire reduced the annual median SWR by one class (extreme to very high) for both post-fire years. During prolonged dry periods the unburnt site was significantly more repellent (P < 0.01) and less spatially variable (P < 0.01) than the recently burnt site, while in the wet periods there was no significant difference. After burning, slope aspect did not have a strong impact on the annual median SWR class. However, the north-west aspect site recorded significantly (p < 0.01) greater annual frequencies of extreme repellency than the south-east aspect site (70–73% vs. 51–55%).

Salmonella Survival in Soil and Transfer Onto Produce via Splash Events

Nearly one-half of foodborne illnesses in the United States can be attributed to fresh produce consumption. The preharvest stage of production presents a critical opportunity to prevent produce contamination in the field from contaminating postharvest operations and exposing consumers to foodborne pathogens. One produce-contamination route that is not often explored is the transfer of pathogens in the soil to edible portions of crops via splash water. We report here on the results from multiple field and microcosm experiments examining the potential for Salmonella contamination of produce crops via splash water, and the effect of soil moisture content on Salmonella survival in soil and concentration in splash water. In field and microcosm experiments, we detected Salmonella for up to 8 to 10 days after inoculation in soil and on produce. Salmonella and suspended solids were detected in splash water at heights of up to 80 cm from the soil surface. Soil-moisture conditions before the splash event influenced the detection of Salmonella on crops after the splash events-Salmonella concentrations on produce after rainfall were significantly higher in wet plots than in dry plots (geometric mean difference = 0.43 CFU/g; P = 0.03). Similarly, concentrations of Salmonella in splash water in wet plots trended higher than concentrations from dry plots (geometric mean difference = 0.67 CFU/100 mL; P = 0.04). These results indicate that splash transfer of Salmonella from soil onto crops can occur and that antecedent soil-moisture content may mediate the efficiency of microbial transfer. Splash transfer of Salmonella may, therefore, pose a hazard to produce safety. The potential for the risk of splash should be further explored in agricultural regions in which Salmonella and other pathogens are present in soil. These results will help inform the assessment of produce safety risk and the development of management practices for the mitigation of produce contamination.

Using an inverse modelling approach with equifinality control to investigate the dominant controls on snowmelt nutrient export

AbstractThere is great interest in modelling the export of nitrogen (N) and phosphorus (P) from agricultural fields because of ongoing challenges of eutrophication. However, the use of existing hydrochemistry models can be problematic in cold regions because models frequently employ incomplete or conceptually incorrect representations of the dominant cold regions hydrological processes and are overparameterized, often with insufficient data for validation. Here, a process‐based N model, WINTRA, which is coupled to a physically based cold regions hydrological model, was expanded to simulate P and account for overwinter soil nutrient biochemical cycling. An inverse modelling approach, using this model with consideration of parameter equifinality, was applied to an intensively monitored agricultural basin in Manitoba, Canada, to help identify the main climate, soil, and anthropogenic controls on nutrient export. Consistent with observations, the model results suggest that snow water equivalent, melt rate, snow cover depletion rate, and contributing area for run‐off generation determine the opportunity time and surface area for run‐off–soil interaction. These physical controls have not been addressed in existing models. Results also show that the time lag between the start of snowmelt and the arrival of peak nutrient concentration in run‐off increased with decreasing antecedent soil moisture content, highlighting potential implications of frozen soils on run‐off processes and hydrochemistry. The simulations showed TDP concentration peaks generally arriving earlier than NO3 but also decreasing faster afterwards, which suggests a significant contribution of plant residue Total dissolved Phosphorus (TDP) to early snowmelt run‐off. Antecedent fall tillage and fertilizer application increased TDP concentrations in spring snowmelt run‐off but did not consistently affect NO3 run‐off. In this case, the antecedent soil moisture content seemed to have had a dominant effect on overwinter soil N biogeochemical processes such as mineralization, which are often ignored in models. This work demonstrates both the need for better representation of cold regions processes in hydrochemical models and the model improvements that are possible if these are included.

Variations in near-saturated hydraulic conductivity of arable mineral topsoils in south-western and central-eastern Finland

Soil hydraulic properties play an important role in determining the level of crop productivity and the extent of environmental loading. Consequently, measurement of near-saturated soil hydraulic conductivity (K(h)) by tension infiltrometer (TI) is an interesting technique. To provide reference values for near-saturated K(h) in arable mineral topsoils of Finland and to investigate variability in these values caused by tillage, antecedent soil moisture content and earthworm burrows, field measurements were conducted in south-western and central-eastern Finland using the TI technique, at supply pressure head –6, –3, and –1 cm. The range of near-saturated K(h) values obtained was 0.02–12.6 mm h-1 at –6 cm, 0.30–85.9 mm h-1 at –3 cm, and 2.55–250 mm h-1 at –1 cm. At –6 cm pressure head, clay soils tended to show lower values than coarser-structured soils, but the order was reversed at –1 cm. The spatial variation in near-saturated K(h) was moderate and was exceeded by the temporal variation.

中梁山岩溶槽谷区不同土地利用方式坡地产流规律

PDF HTML阅读 XML下载 导出引用 引用提醒 中梁山岩溶槽谷区不同土地利用方式坡地产流规律 DOI: 10.5846/stxb201812132723 作者: 作者单位: 西南大学地理科学学院,西南大学,中国地质科学院岩溶研究所,西南大学地理科学学院,西南大学,西南大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2016YFC0502306）；国家自然科学基金项目（41472239）；西南大学基本科研业务费专项基金项目（XDJK2015C071） Characteristics of different land-use types of slope runoff in a karst trough valley located in Zhongliang Mountain, Chongqing Author: Affiliation: Southwest University,Southwest University,,,, Fund Project: The national key research and developmental program of China (2016YFC0502306);The National Natural Science Foundation of China (41472239);The special fund project of basic scientific research operating expenses of southwest university (XDJK2015C071) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:坡地产流是造成岩溶区水土流失的主要驱动力，研究典型岩溶槽谷区坡地产流规律，对岩溶区防治水土流失、合理利用地下水资源具有重要理论意义。在重庆市中梁山龙凤和龙车槽谷选取不同土地利用方式的4个标准径流小区，对降水、地表径流、壤中流、裂隙流和土壤含水率进行了同步监测，探讨了坡地产流特征。结果表明：（1）4个不同土地利用方式的径流小区，坡地总产流量从大到小依次为：耕地（3696.9L）> 果园地（3657.2L）> 竹林地（2922.9L）> 林地（2211.1L），总径流系数（3.1%-5.2%）远低于非岩溶区（约20%）；（2）4个径流小区的产流形式主要为地表径流，壤中流和裂隙流产生滞后于地表径流；（3）降水因子、前期土壤含水率共同影响地表径流，但降水因子对地表径流的影响远大于前期土壤含水率。降水因子中，15min最大雨强是影响耕地、果园地的地表径流的主要因素，降水量是影响林地、竹林地的地表径流的主要因素；前期土壤含水率对耕地、林地、果园地地表径流影响较大，对竹林地地表径流影响较小。 Abstract:Slope runoff is the most important soil erosion force in karst areas, the properties of which in a typical karst trough valley are of great significance for soil erosion prevention and for groundwater resources management. In this study, four standard runoff plots with different land-use patterns were set in a typical karst trough valley located in the Zhongliang Mountain, Chongqing. Land-uses in the trough valley, were farmland, orchard, bamboo land and forest. Hydrological characteristics, including precipitation, surface runoff, soil-layer flow, fissure flow and soil moisture content, were monitored simultaneously, and then slope runoff properties in the typical karst trough valley were determined by slope runoff plots. The results were:(1) In the four runoff plots, the total runoff coefficient (3.1%-5.2%) was significantly lower than that of non-karst areas (approximately 20%), and the total slope runoff of the four kinds of land-use decreased in an orderly way, with farmland being observed to have the greatest amount (3696.9L), followed by orchards (3657.2L), then bamboo land (2922.9L), and finally forest (2211.1L). (2) Surface runoff was the dominant runoff form in the four runoff plots, and this was followed by soil-layer flow and fissure flow. (3) Precipitation factors and antecedent soil moisture content together affected surface runoff discharge; however, precipitation factors were the predominant factor. Four precipitation factors were involved in the surface runoff formation analysis, in which the maximum intensity of continuous rainfall in 15 minutes was the predominant factor in farmland and orchards, and precipitation was the predominant factor in forests and bamboo land. Meanwhile, the antecedent soil moisture content had relatively greater impact on farmland, followed by forest land and then orchards, than bamboo land. 参考文献 相似文献 引证文献

From structure to function: Understanding shrub encroachment in drylands using hydrological and sediment connectivity

Hydrological and sediment connectivity can help us to understand better how physical and process-based linkages govern ecogeomorphic feedbacks and identify locations where degradation is likely to be pronounced. In this study we investigate how hydrological and sediment connectivity affect ecogeomorphic feedbacks in transitional landscapes. We propose a novel approach, the Relative Connectivity Index (RCI), to quantify landscape connectivity which explicitly integrates structural measures of landscape connectivity (SC) with functional measures of hydrological and sediment connectivity (FC) that are derived from runoff and sediment-transport modelling. We use the RCI calculated for runoff (RCIH) and sediment (RCIS) to identify locations and times when functional connectivity exceeds structural connectivity thresholds – where land degradation is likely to be pronounced – and explore how these thresholds are affected by rainfall-event size and antecedent soil-moisture content. We find that there are non-linear increases in RCIH values with an increase in shrub cover, which suggest that ecogeomorphic feedbacks become more important in modifying system structure and function during late stages of shrub encroachment. Thresholds of sediment connectivity appear to be directly related to thresholds of hydrological connectivity, although rainsplash appears to be an important mechanism in creating connected sediment transport where there is no connected runoff. High RCIH values are most widely distributed for the largest (45 mm) rainfall event, whilst high RCIS values are observed to some extent across all stages of the grass to shrub transition for rainfall events as small as 10 mm. Whilst particularly large events have a low return period, they appear to be particularly instrumental in shaping ecogeomorphic feedbacks that are likely to drive catastrophic shifts in ecosystem state. The strength of the indicator approach used here is that it enables identification of regions with pronounced ecogeomorphic feedbacks, which act as potential trigger points for catastrophic shifts in ecosystem state, and thus, we demonstrate how the static limitations of existing approaches to developing connectivity indices may be overcome. The dynamic RCI allows the evaluation of the vulnerability or resilience of a particular system to variable driving mechanisms. The RCI can therefore be used to guide management interventions aimed at reducing or mitigating undesirable ecosystem state change, by focussing on specific locations/regions with high RCI values, to prevent further chances in system structure and function and to maximise the provision of ecosystem services.

Incorporating Antecedent Moisture Conditions and Intraevent Variability of Rainfall on Flood Frequency Analysis in Poorly Gauged Basins

AbstractRainfall‐runoff models are frequently used for the prediction of flood discharges from extreme rainfall data in poorly gauged basins. However, the conventional methods used to estimate the frequency of flood discharges from precipitation data do not incorporate a realistic representation of the spatial and temporal structure of rainfall at the study site nor of the antecedent soil moisture content. Temporally and spatially idealized rainfall patterns that do not represent properly the intraevent variability of rainfall are in general assumed. In this paper, we propose a methodology for flood frequency analysis based on the hydrological simulation of potentially hazardous real storm events. The aim of the proposed method is to incorporate the impact of the spatial and temporal intraevent variability of rainfall on flood discharge estimates without making strong assumptions about the spatial and temporal patterns of storms. It also includes a calibrated relation between the antecedent rainfall depth and the soil infiltration capacity, in order to consider the combined effect of antecedent soil moisture content and rainfall intensity. The flood frequency estimates obtained with the proposed methodology are compared to those estimated with a conventional method based on the definition of synthetic design hyetographs from local intensity‐duration‐frequency curves. The analysis is presented in two watersheds of 84 and 353 km2 located in the NW of Spain. Results highlight the role of the antecedent soil moisture in flood frequency analysis and show that the conventional methodology tends to overestimate the flood discharges when compared to the proposed approach.

Effects of subsequent rainfall events with different intensities on runoff and erosion in a coarse soil

A deeper understanding of the hydrological response to subsequent rains would be useful in the prediction of runoff production for planning vegetation restoration and assessing flood risks. We used subsequent rains to study the role of rain intensity and antecedent soil moisture content (ASMC) on runoff and erosion for coarse soil of the semiarid Loess Plateau in China. The study used a rain simulator in a field planted with alfalfa (Medicago sativa), which is widely grown for animal feed to develop livestock operations, reduce soil erosion, and improve soil fertility/quality. A slope of 18% was selected because most of the land with slopes <18% in the region is used for cropland. We tested three rain intensities (20, 40, and 60 mm h−1, corresponding to low, moderate, and high intensities, respectively) with five successive rains (an initial and four subsequent rains) in triplicate. We quantified the changes of runoff depth (RD), sediment yield (SY), and sediment concentration (SC) over time and then analyzed the relationships between ASMC and runoff in 0–50 cm soil layers for all 45 simulated rains. Runoff commencement time (RCT) was shorter, the runoff coefficient (RC) was larger, and runoff was higher for the moderate and high intensities than the low intensity. Intermittency and the characteristics of the sequential rains also influenced these processes. A general linear model identified significant effects of rain sequence and intensity on RCT, RD, RC, SY, and SC (P < 0.01), but their interaction did not have a significant effect on RCT and SY. An exponential fit between ASMC and RC was best for the 0–10 cm and 10–20 cm layer (R2 = 0.38, P < 0.000), and R2 decreased from the 0–20 cm to the 30–40 cm layers. Soil moisture content (SMC) was an important factor controlling runoff, and the sequential rains led to high runoff and sediment transport, because runoff from storms on highly permeable soils is controlled by the saturation of the topsoil horizon and is more dependent on initial conditions.

The research status of flash flood warning in China

The article discusses from the disaster mechanism of flash flood to the current situation of early warning system. The formation of flash flood is closely related to rainfall intensity, underlying surface conditions and antecedent soil moisture content, and analysis of the physical process of flash flood disasters is crucial for the study of flash flood warning. Flash flood disaster warning indexes are mainly divided into two types: rainfall warning index and water level warning index. Data-driven statistical induction method and hydro-hydraulic methods based on physical mechanisms are used to determine rainfall warning index; The water level warning index can be directly determined by the upstream and downstream corresponding water level method or by the disaster water level. And summed up the current situation and development trend of China's flash flood warning research.

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.