Effect of time resolution of rainfall measurements on the erosivity factor in the USLE in China

Rainfall erosivity, one of the factors in the Universal Soil Loss Equation, quantifies the effect of rainfall and runoff on soil erosion. High-resolution data are required to compute rainfall erosivity, but are not widely available in many parts of the world. As the temporal resolution of rainfall measurement decreases, computed rainfall erosivity decreases. The objective of the paper is to derive a series of conversion factors as a function of the time interval to compute rainfall erosivity so that the R factor computed using data at different time intervals could be converted to that computed using 1-min data. Rainfall data at 1-min intervals from 62 stations over China were collected to first compute the ‘true’ R factor values. Underestimation of the R factor was systematically evaluated using data aggregated at 5, 6, 10, 15, 20, 30, and 60-min to develop conversion factors for the R factor and the 1-in-10-year storm EI₃₀ values. Compared with true values, the relative error in R factor using data at fixed intervals of ≤10min was <10% for at least 44 out of 62 stations. Errors increased rapidly when the time interval of the rainfall data exceeded 15 min. Relative errors were >10% using 15-min data for 66.1% of stations and >20% using 30-min data for 61.3% of stations. The conversion factors for the R factor, ranging from 1.051 to 1.871 for 5 to 60-min data, are higher than those for the 1-in-10-years storm EI₃₀, ranging from 1.034 to 1.489 for the 62 stations.     

基于IMERG反演降水数据估算广东省降雨侵蚀力

近年来遥感反演降水产品的时空分辨率不断提高，为估算区域尺度上具有空间连续性的降雨侵蚀力提供了新的可能。但以往研究在应用遥感降水产品估算降雨侵蚀力时多忽略了其与站点观测数据间的差异和对其纠偏的可能性。该研究以广东省86个气象站2001—2020年的逐时降水资料估算的降雨侵蚀力为观测值，评估两套IMERG（integrated multi-satellite retrievals for GPM）遥感降水产品-GPM_3IMERGHH（0.1°，逐30-min）和GPM_3IMERGDF（0.1°，逐日）对广东省降雨侵蚀力的估算精度并量化偏差，再结合拟合纠偏确定基于遥感反演降水数据估算广东省降雨侵蚀力的最优方法。结果表明：这两套产品均不适宜直接估算降雨侵蚀力指标，不同时间尺度、不同方法直接应用时精度均较低，克林-古普塔效率系数（Kling-Gupta efficiency, KGE）小于等于0.51。但多年平均和极端次事件降雨侵蚀力与对应观测值间具有强相关性（皮尔逊相关系数大于等于0.78），具备纠偏的潜力。因此，本研究发展线性模型对IMERG估算结果进行纠偏，交叉验证结果表明纠偏后GPM_3IMERGHH估算多年平均降雨侵蚀力（R因子）的KGE可达0.79，10年一遇EI₃₀的KGE可达0.64，优于采用站点日降水估算降雨侵蚀力并插值的精度（KGE分别为0.60和0.59），与采用站点小时降水估算降雨侵蚀力并插值的精度相近（KGE分别为0.77和0.66）。当前研究结果充分展示了遥感反演降水在土壤水蚀领域的应用潜力和前景。     

Development of an appropriate procedure for estimation of RUSLE EI30 index and preparation of erosivity maps for Pulau Penang in Peninsular Malaysia

Pluviographic data at 15 min interval from 6 stations in Pulau Penang of Peninsular Malaysia were used to compute rainfall erosivity factor (R) for the revised universal soil loss equation (RUSLE). Three different modelling procedures were applied for the estimation of monthly rainfall erosivity (EI₃₀) values. While storm rainfall (P) and duration (D) data were used in the first approach, the second approach used monthly rainfall for days with rainfall ≥ 10 mm (rain₁₀) and monthly number of days with rainfall ≥ 10 (days₁₀). The third approach however used the Fournier index as the independent variable. Based on the root mean squared error (RMSE) and the percentage error (PE) criteria, models developed using the Fournier index approach was adjudged the best with an average PE value of 0.92 and an average RMSE value of 164.6. Further, this approach was extended to the development of a regional model. Using data from additional sixteen stations and the Fournier index based regional model, EI₃₀ values were computed for each month. ArcView GIS was used to generate monthly maps of EI₃₀ values and also annual rainfall erosivity (R). The rainfall erosivity factor (R) in the region was estimated to vary from 9000 to 14,000 MJ mm ha^− 1 h^− 1 year^− 1.     

基于降雨量和降雨时间的月降雨侵蚀力简易算法——以陕北黄土丘陵沟壑区为例

 降雨侵蚀力简易算法是较大尺度应用USLE/RUSLE进行土壤侵蚀评价研究的必要内容。基于降雨量和降雨时间建立月降雨侵蚀力计算模型,并以陕北黄土丘陵沟壑区为例,进行模型的拟合。结果表明:随着自变量中降雨量和降雨时间表示方式的改变,模型的拟合优度表现出明显的差异;对于不同因变量而言,以ΣEI30(或lg(ΣEI30))和以ΣEI10(或lg(ΣEI10))为因变量的模型拟合优度在整体上比较接近甚至相同,而以ΣE60I10(或lg(ΣE60I10))为因变量的模型拟合优度在整体上略低;就尺度效应而言,在时间尺度上,整个汛期的模型拟合优度低于1个月份或多个月份模型的拟合优度,在空间尺度上,区域模型中的拟合优度低于至少1个流域的模型拟合优度;在实际应用中,可以选择以ΣEI30为因变量的月降雨侵蚀力公式对该区域进行土壤侵蚀评价。     

黔西高原地区降雨侵蚀力的简易算法

[目的]对黔西高原地区侵蚀性降雨特性进行分析并探索降雨侵蚀力的简易算法,为该区土壤侵蚀预报模型的建立提供理论依据。[方法]利用径流小区观测法,基于毕节小区2012—2014年53次降雨过程资料进行分析。[结果](1)降雨量(P)和最大60min降雨动能(E60)是影响坡面产流、产沙的两个主要因子。坡面产流、产沙与最大60min雨强(I_(60))显著相关;(2)坡面产流产沙与二元复合因子的相关系数显示,EI_(60),PI_(60)和I30I_(60)是影响坡面产流、产沙的3类主要降雨复合指标,EI30和EI_(60)与坡面产流产沙的相关系数间相差较小;(3)基于坡面产流、产沙与降雨单指标和降雨复合指标的相关关系,确定了简易算法的参数。[结论]基于可比性,以R=EI30作为参照值对3种简易算法的结果进行决定系数和偏差率比较后,得到研究区便捷、快速的降雨侵蚀力简易算法为:R=0.344(PI_(60))。     

Soil erosion on Alfisols in Western Nigeria: III. Effects of rainfall characteristics

The applicability of various erosivity indices was tested for runoff and soil loss from plowed bare-fallow field runoff plots of 25 × 4 m established on an Alfisol with natural slopes of 1, 5, 10 and 15%. The correlation coefficients of percent runoff from individual rainstorms with various indices such as kinetic energy (E), EI₃₀, KE > 1, rainfall amount (A), maximum intensity (I_m), and AI_m, were generally low. The correlation coefficients of all these indices with soil loss per storm were high and did not differ significantly from one another. The use of an empirical relation (kinetic energy = 916 + 331 log₁₀, I is in inches/h) may underestimate the kinetic energy of tropical rainstorms. The kinetic energy of tropical rainstorms may be significantly influenced by other factors such as wind velocity, drop size distribution and high rainfall intensity. The index AI_m has the advantage of simplicity of computation, and it incorporates one of the most important factors, peak intensity (I_m). Further improvements can be made in this index by incorporating a factor which accounts for the kinetic energy of a rainstorm. In the meantime, the index, AI_m, may be used to prepare an “iso-erodant” map, i.e. places with equal erosion potential. There also exists a linear correlation between rainfall amount per storm and AI_m. Such a relationship may be useful in estimating AI_m for regions where data from recording rain gauges are not available.     

Runoff and soil loss from bench terraces. 1. An event-based model of rainfall infiltration and surface runoff

Overland flow resulting from an excess of rain over infiltration is an essential component of many models of runoff and erosion from fields or catchments. The spatially variable infiltration (SVI) model and a set of associated equations relating depth of runoff and maximum rate of ‘effective’ runoff (as used in the GUEST erosion model) to storm depth, depth‐averaged intensity of rainfall, average maximum infiltration capacity and an additional amount of initial infiltration were validated and tested on back‐sloping bench terraces in volcanic upland West Java, Indonesia. Data used were runoff rate and depth from 31 small (1.0–8.2 m²) bounded plots representing sections of terrace beds or risers and from six larger (53–231 m²) terrace units with hydrologically defined boundaries. Modelled runoff rates using rainfall intensity data corresponded well with observed patterns and the storm‐based equations were used successfully to model runoff depths and maximum effective runoff rates for individual events. Resulting values for maximum average infiltration rate (I_m) varied between 18 and 443 mm hour^?1 and reflected effects of vegetation or mulch cover and soil compaction. We conclude that the SVI model and the derived equations provide a robust and accurate method for predicting runoff at the investigated scale.     

An improved rainfall erosivity index obtained from experimental interrill soil losses in soils with a Mediterranean climate

The most common index to predict rainfall erosivity is based on the kinetic energy (KE) and the maximum intensity in a 30-min period. However, rainfalls recorded in the Mediterranean climate are, in most cases, the short duration (<30 min) and the high intensity. The goal of this work was to improve rainfall erosivity indices for the Mediterranean conditions from experimental interrill soil losses measured in natural conditions in 1-m² plots. The plots were located in three vineyard fields, whose soils are classified as Typic Calcixerept, Typic Xerofluvent and Typic Xerorthent, and ploughed at the same time as the vineyards. Soil losses and runoff were collected after each rainfall event during 1 year and rainfall data were obtained from bucket gauges installed at the same places. Mean intensity of the storms was less than 10 mm h⁻¹, but maximum intensities in short periods were as high as 103 mm h⁻¹. Kinetic energy was calculated using different expressions proposed in the literature and improved with our data obtained with a disdrometer type Joss Waldvogel. Soil losses were related to kinetic energy and to different combinations of kinetic energy and maximum intensity for different time intervals. The best correlation was that obtained between soil losses and the product of kinetic energy by Sempere Torres and the maximum intensity in 5-min intervals (I₅), which explained more than 80% of the variability. When a surface crust was formed quickly there was no significant relation between soil loss and rainfall parameters.     

Evaluation of CLIGEN for storm generation on the semiarid Loess Plateau in China

The Stochastic generation of storm patterns is often necessary for driving process-based hydrological and ecological models. CLIGEN is the only weather generator being able to generate internal storm patterns. Its goodness needs to be evaluated for its proper application. This paper aims to find the advantages and limitations of CLIGEN on semiarid areas and provide references for custom-built weather generators for the Loess Plateau. The daily rainfall time series (1957–2002) and breakpoint rainfall data (more than 20 years) on six stations on the Loess Plateau were used to estimate input parameters for CLIGEN and to compare with CLIGEN-generated 50 years of storm data. Precipitation occurrence (wet day and dry day sequence) is well-simulated without significant difference across months and sites. Errors of monthly average number of wet days range from − 0.67 to 1.08 days, standard deviations range from − 1.19 to 0.76 days, and the distributions of continuous number of wet and dry days on the semiarid Loess Plateau are adequately simulated. Daily rainfall amount is not simulated as well as precipitation occurrence. The relative errors of average daily rainfall range from − 12.93% to 8.64% and those of standard deviations range from − 21.35% to 27.46%. During the rain seasons (May–September), among 30 month–location combinations, all the Mann–Whitney tests for the means passed, 47% for squared ranks tests rejected the null hypothesis of equality of standard deviations, and 73% for K–S test suggested that the generated and measured distributions of daily rainfall were different at 0.01 level of significance Three variables to describe internal storm patterns in CLIGEN are storm duration, relative peak intensity, and time to peak. Storm duration was not well-reproduced because none of squared ranks tests and K–S test passed at the significance level of 0.01. The frequency of short duration storms (< 300 min) was over-predicted while frequency of long duration storms (400–1200 min) was significantly under-predicted. The distribution of maximum 5 min rainfall intensity (ip₅) was well-simulated for four sites out of the six because all tests passed. However, generated maximum ip₅ for all six sites are around 190 mm/h, which are much larger than the measured (70 to 150 mm/h). Ip₃₀ is simulated better than ip₅, suggesting that CLIGEN can reliably generate rainfall erosivity. Time to peak was well-simulated because all the tests passed with P values significantly greater than the significance level of P = 0.01. Improvement for CLIGEN has to be made in terms of the daily rainfall simulation in rainfall-concentrated seasons and storm pattern generation in order to generate reliable rainfall time series on the Loess plateau.     

Effect of land management on runoff and soil losses from two small watersheds in St Lucia

The influence of land use on runoff and soil loss was assessed on two small watersheds in the Eastern Caribbean island of St Lucia, under contrasting land management regimes. The data generated from these watersheds revealed that the soil losses from an intensively cultivated agricultural watershed were 20‐times higher in magnitude than that of a forested watershed both for peak rainfall event and for total duration of analysis. This was due to higher surface runoff rates and exposure of soil to direct raindrop impact within cultivated areas. Whereas the forest canopy cover in combination with higher infiltration capacities of the forested land reduced the erosive runoff from the forest watershed and thus the soil loss. Moreover, the energy intensities of large storms in excess of 40 mm were estimated and found to range between 400 MJ mm ha⁻¹ h⁻¹ and 1834 MJ mm ha⁻¹ h⁻¹. 1

1 Megajoules‐millimeters per hectare‐hour.

Soil loss from the agricultural watershed was strongly correlated (R² = 0·85) to storm energy‐intensity (EI₃₀). However, the correlation of soil loss with the EI₃₀ (R² = 0·71) was poor for the forest watershed due to the effect of canopy vegetation, which significantly reduced the energy of raindrop impact. Over the study period, cumulative soil losses were 10·0 t ha⁻¹ for the agricultural site and 0·5 t ha⁻¹ for the forest site. 2

2 Metric tons per hectare.

The largest storm observed during the study period resulted in erosion losses of 3·78 t ha⁻¹ and 0·2 t ha⁻¹ from the agricultural and forest sites respectively. The regression models were developed using the measured data for prediction of runoff and soil loss over the watersheds of St Lucia under similar conditions. This study contributed towards efficient watershed management planning and implementation of suitable water conservation measures in St Lucia. Copyright © 2005 John Wiley & Sons, Ltd.     

Using rainfall simulation and site measurements to predict annual interrill erodibility and phosphorus generation rates from unsealed forest roads: Validation against in-situ erosion measurements

The measurement of soil erosion rates under natural rainfall conditions is costly and time consuming. Data provided by rainfall simulation and static site measurements can be used to predict erosion rates under natural conditions, however the accuracy of this method is largely untested. This is especially true for erosion rates from unsealed forest roads. In this study, the values for a range of erodibility indices calculated from rainfall simulation experiments are compared to observed erodibility index values from 1 year of detailed in-situ erosion monitoring of seven different forest road types. The prediction of phosphorus generation rates from rainfall simulation and/or soil sampling was also evaluated. The results showed that a series of commonly used erodibility indices such as sediment per unit rainfall, sediment per unit runoff, sediment per unit EI₃₀, and sediment per unit rainfall energy were poorly predicted from the rainfall simulation experiments. Five of the six indices tested substantially overpredicted the observed erodibility at one site, a gravel road subjected to minimal traffic. For the other six road sites predictions were poor and highly variable, the coefficient of efficiency ranging from − 13.32 to 0.17 for these erodibility indices. A modified index, the ratio of sediment per unit rainfall energy to the mean rate of rainfall energy input, was able to predict annual erosion rates from six different road surfaces using rainfall simulation data with a coefficient of efficiency of 0.9. The results indicate that existing erodibility indices are not suitable for predicting observed erosion rates on forest roads using rainfall simulation data as collected in this study. It is argued that the modified index is more suited to sites (such as compacted roads) where interrill processes dominate, and erosion rates are less sensitive to peak flows. With respect to nutrient generation rates, rainfall simulation was able to accurately predict the observed proportion by mass of total phosphorus (TP) in runoff with a coefficient of efficiency of 0.96. Direct soil sampling of the road surface could also be used to predict the proportion by mass of TP in runoff. Concentrations of total nitrogen in forest road materials were found to be at the lower detection limit of the laboratory instruments.     

红壤区裸露坡地不同类型次降雨的产流产沙规律

为探究红壤区裸露坡地在不同类型次降雨下的产流产沙规律,研究收集长汀县水土保持科教园红壤裸露坡地径流小区2013年1月至2020年12月共388场降雨—径流—土壤侵蚀观测资料,采用K-means将降雨划分为4类进行分析。结果表明:(1)主要降雨类型有A(短历时、大雨强、小雨量、低频次)、B(长历时、小雨强、大雨量、中频次)、C(中等历时、小雨强、小雨量、高频次)3类,B、C为研究区主要产流产沙来源,贡献85%以上的径流和土壤侵蚀量。(2)次降雨径流深及土壤侵蚀量与降雨量(P)、最大30 min雨强(I₃₀)和降雨动能(E)呈线性正相关,与降雨侵蚀力(EI₃₀)呈幂函数关系。但降雨特征对产流产沙的总解释度小于65%,且随着降雨历时的增加而减小。(3)降雨特征与产流产沙存在3种约束关系,其约束线表明降雨特征对次降雨潜在最大产流产沙的影响。其中,潜在最大径流深主要由P和E决定,潜在最大土壤侵蚀量的上限为800~900 t/hm²。从降雨特征单因子影响、综合影响和约束效应3个方面分析了红壤裸露坡地的产流产沙特征,为红壤区水土流失防治提供了数据基础。     

北京地区旱稻作物需水与降水的耦合分析

基于4a的田间试验资料，采用农田水分平衡法确定了旱稻出苗后各生育阶段的需水量；利用1971年-2000年北京地区逐日降水资料，计算了旱稻各生育阶段在不同降水保证率下的降水量，并选取25％、50％、75％和95％保证率作为典型的湿润年、平水年、干旱年和极枯水年，进行旱稻各生育阶段降水与作物需水的耦合度分析和补灌量估算。结果表明：旱稻出苗后总需水量平均为596.1 mm，需水强度平均为4.3 mm/d，需水强度峰值出现在孕穗-抽穗阶段。4种降水年型下旱稻出苗后降水和旱稻需水的耦合度分别为0.82、0.71、0.50和0.39，所需的补灌量分别为106.6、171.1、296.0和363.9 mm。     

Rainfall erosivity in Cape Verde

This paper presents rainfall erosivity values derived from a 7-year rainfall recording in the Cape Verde islands, Central East Atlantic. The data set consisted of 63 storm events, continuously registered in 15-min intervals. Kinetic energy of storm rainfall corresponded to established values in other tropical locations. Two algorithms to estimate erosivity, expressed as energy times intensity, using daily rainfall or storm depth and duration as predictor variables are derived. Erosivity of design storms for various return frequencies is calculated for some locations in Santiago island. An indicative range for the annual rainfall erosion R-index is given. Data analysis further showed the extreme seasonal concentration of precipitation and erosivity at this location, with a very high fraction of total annual erosivity contained in the annual maximum 24-h rainfall.     

Seasonal dynamics of soil–water pressure in a cracking clay soil

This paper describes the results of an investigation of changes in soil water pressure head (ψ) and its relationship to the macropore network in a cracking clay soil. Four vertical nests, each consisting of three tensiometers positioned at depths of 30 cm, 60 cm and 90 cm below the surface, were monitored continuously over a two-year period to study changes in ψ. On one occasion an anionic tracer (Br-) was applied to investigate the extent of macropore flow. The results revealed considerable temporal variation in ψ with consistent variations between adjacent tensiometer nests. Variations in ψ indicated the seasonal development of a soil macropore system, followed by its subsequent decay and demonstrated the significant effect of rainfall intensity, duration and timing on percolation pathways. Differences in ψ were examined for individual summer rain events which were characterised by differences in precipitation amount and intensity. A total of 79 rain events extending across the period of study were analysed to assess the degree to which time-invariant parameters can be used to describe changes in ψ at a depth of 30 cm below the surface. The results indicated that individual regression models had considerable success in predicting ψ, although the residuals in the regression models were high for the specific case of large summer rain events, and in particular for three events.     

Relationships between rainfall characteristics and ephemeral gully erosion in a cultivated catchment in Sicily (Italy)

Recent research has shown a lack of long-term monitoring for detailed analysis of gully erosion response to climate characteristics. Measures carried out from 1995 to 2007 in a wheat-cultivated area in Raddusa (Sicily, Italy), represent one of the longest series of field data on ephemeral gully, EG, erosion. The data set collected in a surface area of almost 80 ha, permits analysis of the influence of rainfall on EG formation and development. Ephemeral gullies formed in the study area were measured on a yearly scale with a Post-Processing Differential GPS for length and with a steel tape for the width and depth of transversal sections. Ephemeral gully formation was observed for 8 years out of 12, which corresponds to a return period of 1.5 years. The measurements show strong temporal variability in EG erosion, in agreement with the rainfall characteristics. The total eroded volumes ranged between 0 and ca. 800 m³ year⁻¹, with a mean of ca. 420 m³ year⁻¹, corresponding to ca. 0.6 kg m⁻² year⁻¹. Ephemeral gully erosion in the study area is directly and mainly controlled by rainfall events. An antecedent rainfall index, the maximum value of 3-days rainfall (H_max3_d), is the rain parameter which best accounts for EG erosion. This index is used here as a simple surrogate for soil water content. An H_max3_d threshold of 51 mm was observed for EG formation. The return period of the H_max3_d threshold is almost the same as the return period for EG formation. Although a mean of seven erosive rain events were recorded in a year, EG formation and development generally occur during a single erosive event, similarly to other semiarid environments. The most critical period is that comprised between October and January, when the soil is wetter and the vegetation cover is scarce. Empirical models for EG eroded volume estimation were obtained using the data set collected at this site. A simple power-type equation is proposed to estimate the eroded volumes using H_max3_d as an independent variable. This equation shows an R² equal to 0.67 and a standard error of estimation of 0.79.     

Chemical and biological relationships relevant to the effect of acid rainfall on the soil-plant system

This paper deals with problems concerning measurements of rainfall acidity and interpretation in terms of possible effects on the soil-plant system. The theory of acidity relationships of the carbon dioxide-bicarbonate equilibria and its effect on rainfall acidity measurements is given. The relationship of a cation-anion balance model of acidity in rainfall to plant nutrient uptake processes is discussed, along with the relationship of this model to a rainfall acidity model previously proposed in the literature. These considerations lead to the conclusion that average H+ concentration calculated from pH measurements is not a satisfactory method of determining H⁺ loading from rainfall if the rain is not consistently acid. Calculating loading from H⁺ minus HCO₃ ^? , strong acid anions minus basic cations, or net titratable acidity is suggested. The flux of H⁺ ions in soil systems due to plant uptake processes and sulfur and nitrogen cycling is considered. H⁺ is produced by oxidation of reduced sulfur and nitrogen compounds mineralized during decomposition of organic matter. Plant uptake processes may result in production of either H⁺ or OH^? ions. Fluxes of H⁺ from these processes are much greater than rainfall H⁺ inputs, complicating measurement and interpretation of rainfall effects. The soil acidifying potential due to the oxidation of the NH₄ ⁺ rainfall is examined, with the conclusion that acidity from this source is of a similar magnitude to direct H⁺ inputs common in rainfall.     

暴雨的判定方法和评价指标

 在分析暴雨特征的基础上,提出了以降雨量和降雨强度为参数的暴雨判别指标计算公式K=Pi,根据P=it得出K=P2/t=i2t,该表达式简单明了地反映了不同降雨历时的雨量大小,便于暴雨的分析和计算。同时,以日降雨量标准和时段降雨量或降雨强度标准为基础,定量化的确定了暴雨的判别指标和暴雨等级划分标准。对于暴雨2≤K>K<7,大暴雨7≤K<28,特大暴雨K≥28。在保持与日降雨量标准和时段降雨量或降雨强度标准基本一致的前提下,将二者有机地结合在一起,形成新的统一的暴雨判别和划分标准     

不同雨强条件下工程措施对坡地产流产沙影响

基于试验站不同坡地措施（坡耕地和坡改梯）2016年和2017年的逐日降水、产流产沙数据，研究不同坡地措施和雨强下产流产沙规律特征，定量揭示坡改梯和坡耕地对产流产沙的影响。结果表明：（1）7月平均雨强I、最大雨强I₃₀及坡地产流量最大，8月最大雨强I₆₀与坡地产沙量最大，表明坡地产流产沙高峰期与雨强高峰期一致。（2）春夏两季产流、产沙量与I、I₃₀和I₆₀相关性显著（超过95%置信度检验）。其中坡耕地产流产沙量与I、I₃₀、I₆₀的相关系数整体高于坡改梯。春夏季坡耕地产沙量分别是坡改梯的3.91，7.85倍。（3）降雨主要集中在I（1~3 mm/h）、I₃₀（3~29 mm/h）、I₆₀（2~27 mm/h）之间，且坡地产流产沙量与最大雨强I₃₀、最大雨强I₆₀在95%置信度水平呈现显著正相关。当I₃₀达到29.0 mm/h、I₆₀达到26.6 mm/h时，坡地产流产沙达到最大，坡耕地产流产沙峰值是坡改梯的2.43，7.52倍以上，并且坡耕地全年产流产沙变异系数总体高于坡改梯，因此坡改梯工程在一定程度上防治了水土流失，使产流产沙变化减小。