Impact of the Rainfall Intensity and Seepage on Slope Stability in Loess Plateau

In recent years,with the increase of traffic construction in mountainous areas in China,road slope traffic accidents have become more and more common.In addition,natural disasters such as landslides,collapses and subgrade settlements caused by rainfall,driving load,seasonal variation and groundwater distribution are frequent.In particular,rainfall is one of the most common factors leading to slope instability(landslide).Therefore,this paper proposes the seep module based on the application software Geo-studio,and analyzes the slope soil parameters and slope stability under five types of rainfall conditions:light rain(10 mm/d),moderate rain(25 mm/d),heavy rain(50 mm/d),rainstorm(100 mm/d),and torrential rain(250 mm/d).The critical safety factor under rainfall intensity is fitted with nonlinear curve by sine function.The results show that the fitting curve of rainfall intensity and safety factor on the upper slope is excellent.The residual points are evenly distributed in the belt area of±0.1,and the data basically conform to the nonlinear sine model,indicating that the curve plays an essential role in slope health diagnosis.

Impacts of Rainfall Intensity on Soil Solute Loss in a Small Basin

[Objective] The study aimed to analyze the impacts of rainfall intensity on soil solute loss. [ Method] Hydrus-1D model was used to sim- ulate surface runoff process and soil solute loss process under different rainfall intensities in Meilin basin, Yixing City, and its reliability was verified. Afterwards, the model was used to simulate the movement of total nitrogen （TN） in the soil under various rainfall intensities. [Result] Hydrus-1D model had a good effect in the simulation of soil moisture and TN content in surface soil. During the rainfall, TN loss from surface soil （0 -20 cm） accounted for above 95% of total loss from the whole soil （0 -100 cm）. In addition, TN loss increased with the enhancement of rainfall intensities. However, TN loss tended to be stable when rainfall intensity exceeded 0.030 0 cm/min. [Conclusion] The research could provide theoretical refer- ences for the control of agricultural nonpoint source pollution in future.

Evaluation of rainfall threshold models for debris flow initiation in the Jiangjia Gully,Yunnan Province,China

Systematically determining the discriminatory power of various rainfall properties and their combinations in identifying debris flow occurrence is crucial for early warning systems.In this study,we evaluated the discriminatory power of different univariate and multivariate rainfall threshold models in identifying triggering conditions of debris flow in the Jiangjia Gully,Yunnan Province,China.The univariate models used single rainfall properties as indicators,including total rainfall(R_(tot)),rainfall duration(D),mean intensity(I_(mean)),absolute energy(Eabs),storm kinetic energy(E_(s)),antecedent rainfall(R_(a)),and maximum rainfall intensity over various durations(I_(max_dur)).The evaluation reveals that the I_(max_dur)and Eabs models have the best performance,followed by the E_(s),R_(tot),and I_(mean)models,while the D and R_(a)models have poor performances.Specifically,the I_(max_dur)model has the highest performance metrics at a 40-min duration.We used logistic regression to combine at least two rainfall properties to establish multivariate threshold models.The results show that adding D or R_(a)to the models dominated by Eabs,E_(s),R_(tot),or I_(mean)generally improve their performances,specifically when D is combined with I_(mean)or when R_(a)is combined with Eabs or E_(s).Including R_(a)in the I_(max_dur)model,it performs better than the univariate I_(max_dur)model.A power-law relationship between I_(max_dur)and R_(a)or between Eabs and R_(a)has better performance than the traditional I_(mean)–D model,while the performance of the E_(s)–R_(a)model is moderate.Our evaluation reemphasizes the important role of the maximum intensity over short durations in debris flow occurrence.It also highlights the importance of systematically investigating the role of R_(a)in establishing rainfall thresholds for triggering debris flow.Given the regional variations in rainfall patterns worldwide,it is necessary to evaluate the findings of this study across diverse watersheds.

Relationships between Rainy Days,Mean Daily Intensity and Seasonal Rainfall in Normal,Flood and Drought Years over India

here are limitations in using the seasonal rainfall total in studies of Monsoon rainfall climatology. A correlation analysis of the individual station seasonal rainfall with all India seasonal mean rainfall has been made. After taking the significance test (strictly up to 5% level) the stations which are significantly correlated have been considered in this study in normal, flood and drought years respectively. Analysis of seasonal rainfall data of 50 stations spread over a period of 41 years suggests that a linear relationship fits better than the logarithmic relationship when seasonal rainfall versus number of rainy days is studied. The linear relationship is also found to be better in the case of seasonal rainfall versus mean daily intensity.

Critical rainfall intensity for safe evacuation from underground spaces with flood prevention measures

Underground space in urban areas has been expanding rapidly during recent decades, and so has the incidence of fatal accidents and extensive damage to facilities resulting from underground flooding. To evaluate the safe evacuation potential of individual underground spaces in flood-prone urban areas, the hydraulic effects of flood prevention measures, e.g., stacked flashboards or sandbags and elevated steps, were incorporated in a proposed formula for estimating the depth of inundation of an underground floor. A mathematical expression of the critical rainfall intensity for safe evacuation from underground space was established and then evaluated for two types of underground spaces, an underground shopping mall and a building basement. The results show that the critical rainfall intensity for any individual underground space can be determined easily using the proposed analytical or graphical solution. However, traditional underground flood prevention measures cannot improve safety if people refuse to evacuate immediately once water intrudes into the underground space.

Incorporating a rainfall intensity modification factorγinto the I a-S Relationship in the NRCS-CN method

The Natural Resources Conservation Service runoff curve number(NRCS-CN)method is widely used to simulate direct runoff,but the impact of rainfall intensity has not been considered.In this study,a rainfall intensity modification factor(γ)was incorporated into the Ia-S relationship of the NRCS-CN method,and the modified method(NRCS-CN-γ)was compared with the NRCS-CN method withλ=0.2 andλ=0.05 in three watersheds of the Walnut Gulch Experimental Watershed(WGEW).The results showed that for 2016-2018 period,the simulation performance of the NRCS-CN-γmethod was close to the NRCS-CN(λ=0.05)method and better than the NRCS-CN(λ=0.2)method.When the new data(2009 data with high variance)was added,the significant improvement was observed by NRCS-CN-γmethod with all the evaluation parameters being the best in the three watersheds,indicating a more adapted capa-bility of the modified method with highly uneven rainfall intensities.The covariance between rainfall intensity and the simulated runoff were 19.01,15.14,and 16.35 for the three methods,respectively.When the optimal CN changed,the relative errors representing CN sensitivity were 6.25,6.49 and 17.39 for the methods,respectively.It is suggested that the NRCS-CN-γmethod outperformed the other two methods and could contribute to a more accurate estimation of direct runoff where rainfall intensity greatly varied,especially in monsoon region or under the context of climate change.

Determination of a Mathematical Model of Erosion Taking into Account the Intensity of Rainfall and Soil Slopes from the Global MNT Model

Our study is being carried out in the Wouri Estuary more precisely in the Nylon area, Douala. This area is influenced by abundant rainfall which promotes the phenomenon of rain erosion. This erosion contributes to the degradation of structures and soils. To better understand and predict this phenomenon of rainfall erosion, we set out to establish a mathematical model that takes into account precipitation and topography. To this end, the data collected in the field and in the laboratory made it possible. First, we graphically modeled the variation of the potential as a function of the intensity of rainfall and the slope of the ground. Next, we identified a mathematical model from cubic spline surface interpolation. Finally, we obtained the mathematical model which makes it possible to evaluate and predict the erosion potential. The results obtained allowed to have an erosion potential of 153.67 t/ha/year with field data and 153.94 t/ha/year with laboratory data. We compared the results obtained with those existing in the literature on the same study site. This comparison made it possible to validate the established mathematical model. This mathematical model is a decision support tool and can predict problems related to water, erosion and the environment.

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China. Understanding the composition, distribution, and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion. In this study, based on laboratory rainfall simulation experiments, we analyzed rainfall-induced erosion processes on sand-covered loess slopes （SS） with different sand cover patterns （including length and thickness） and uncovered loess slopes （LS） to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion. The grain-size curves of eroded sediments were fitted using the Weibull function. Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS. The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed. The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS. Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes. The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage. Sand cover on loess slopes aggravates loess erosion, not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess, compared with the loess slopes without sand cover. The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount. Furthermore, given the same sand cover pattern, a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion. This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.

Characteristics of run off and sediment generation of forest vegetationon a hill slope by use of artificial rainfall apparatus

We studied the impact of forest vegetation on soil erosion, surface runoff, and sediment generation by using field simulated rainfall apparatus. We measured runoff and sediment generation of five 4.5 × 2.1 m runoff plots （a bare soil as a control; two Pinus tabulaeformis forest plots and two Platycladus orientalis forest with row spacing of 1 m × 1 m and 1.5 m× 1.5 m, respectively） in Beijing Jiu Feng National Forest Park under three rainfall intensities （0.42, 0.83, 1.26 mm per minute）. Forest vegetation significantly reduced soil erosion and sediment yield. Mean total runoff volume in the four tree stand plots was 93% of that in the control plot, demonstrating the limited effectiveness of forest vegeta- tion in runoff control. With increasing rainfall intensity, runoff reduction in forest plots declined from 28.32% to 2.1%. Similar trends in runoff coefficient and the relationship between runoffvolume and rainfall duration was observed. Mean total sediment yield and mean sediment yield reduction rate under different treatments was 55.05% and 43.17% of those in the bare soil control plot, respectively. Rainfall intensity played an important role in runoff and sediment generation processes, and had a greater impact on runoff than on soil erosion and sediment generation. When considering several factors in runoff and sediment transport processes, the P. tabulaeform plot with row spacing at 1 × 1 m had a greater effect on soil and water conservation than did other forested plots.

Numerical Simulations of Intense Meiyu Rainfall in 1991 over the Changjiang and Huaihe River Valleys by a Regional Climate Model with p-σ Incorporated Coordinate System

Based on the primitive equation model with p- σ incorporated coordinate system originally developed by Qian et al., a one-way nested fine mesh limited area model is developed. This model is nested with ECMWF T42 data to simulate the extra-intensive rainfall event occurring in the Changjiang and Huaihe River valleys in summer of 1991. The results show that the model has certain capacity to fairly reproduce the regional distribution and the movement of the main rainfall belts. Therefore it can be used as a regional climate model to simulate and predict the short-range regional climate changes.

The Extraordinary Rainfall over the Eastern Periphery of the Tibetan Plateau in August 2020

A large amount of accumulated precipitation was recorded over the Eastern Periphery of the Tibetan Plateau(EPTP)in August 2020.Using hourly rain gauge records and the ERA5 reanalysis dataset,we analyzed the unique characteristics of rainfall in August and the accompanying circulation conditions and conducted a comparison with previous data.This record-breaking amount of accumulated rainfall was centered on the northern slope of the EPTP.This location was in contrast with the historical records of the concentration of rainfall over the middle and southern slopes.The hourly rainfall in August 2020 was both more frequent and more intense than the climatological mean rainfall.An amplification effect of the topography was observed,with the precipitation over the EPTP showing a more significant change with terrain height in August 2020.A circulation analysis showed that cold(warm)anomalies existed over the north(south)of approximately 35°N compared with those in the years when the southern EPTP received more rain.The western Pacific subtropical high was more intense and extended to the west,and the low-level cold air from the north was more active.The enhanced low-level southerly winds on the periphery of the subtropical high injected warm,moist air further north than the climatological mean.These winds became easterly near the northern EPTP and were forced to ascend by the steep terrain.

Radiative Effects on Torrential Rainfall during the Landfall of Typhoon Fitow(2013)

Cloud microphysical and rainfall responses to radiative processes are examined through analysis of cloud-resolving model sensitivity experiments of Typhoon Fitow（2013） during landfall.The budget analysis shows that the increase in the mean rainfall caused by the exclusion of radiative effects of water clouds corresponds to the decrease in accretion of raindrops by cloud ice in the presence of radiative effects of ice clouds,but the rainfall is insensitive to radiative effects of water clouds in the absence of radiative effects of ice clouds.The increases in the mean rainfall resulting from the removal of radiative effects of ice clouds correspond to the enhanced net condensation.The increases（decreases） in maximum rainfall caused by the exclusion of radiative effects of water clouds in the presence（absence） of radiative effects of ice clouds,or the removal of radiative effects of ice clouds in the presence（absence） of radiative effects of water clouds,correspond mainly to the enhancements（reductions） in net condensation.The mean rain rate is a product of rain intensity and fractional rainfall coverage.The radiation-induced difference in the mean rain rate is related to the difference in rain intensity.The radiation-induced difference in the maximum rain rate is associated with the difference in the fractional coverage of maximum rainfall.

Characteristics of Caragana korshinskii and Hippophae rhamnoides stemflow and their significance in soil moisture enhancement in Loess Plateau, China

Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system and influences water utilization of plant roots at the stand scale,especially in water-scarce semi-arid ecosystems.The stemflow of two semi-arid shrubs(Caragana korshinskii and Hippophae rhamnoides)and its effect on soil moisture enhancement were evaluated during the growing season of 2011 in the semi-arid loess region of China.The results indicated that stemflow averaged 12.3%and 8.4%of the bulk precipitation for C.korshinskii and H.rhamnoides,respectively.Individual stemflow increased in a linear function with increasing rainfall depth.The relationship between funneling ratios and rainfall suggested that there existed a rainfall depth threshold of 11 mm for both C.korshinskii and H.rhamnoides.Averaged funneling ratios were 156.6±57.1 and49.5±30.8 for C.korshinskii and H.rhamnoides,respectively,indicating that the canopy architecture of the two shrubs was an effective funnel to channel stemflow to the root area,and C.korshinskii showed a greater potential to use stemflow water in the semi-arid conditions.For individual rainfall events,the wetting front depths were approximately 2 times deeper in the rooting zone around the stems than in the bare area outside canopy for both C.korshinskii and H.rhamnoides.Correspondingly,soil water content was also significantly higher in the root area around the shrub stem than in the area outside the shrub canopy.This confirms that shrub stemflow conserved in the deep soil layers may be an available moisture source for plant growth under semi-arid conditions.

Triggering mechanism and dynamic process of water-rock flow in Nanfen waste dump in 2010

Water-rock flow is a kind of debris flow with more coarse particles and low viscosity, which occurs in many areas of the world. In this work, the water-rock flow that occurred on May 24, 2010, at Nanfen’s open-pit mine of China was investigated by combining field investigation, meteorological and hydrological survey with numerical simulation to understand its triggering mechanism and dynamic process. The field data shows that the short-term high-intensity rainfall is the most direct inducement to trigger water-rock flow in the waste dump. The loose shallow gravel soil and the V-shaped valley with a certain slope provide the necessary conditions of the occurrence of water-rock flow in the waste dump. Moreover, the possibility criterion of water-rock flow is presented by analyzing the historical rainfall data. In addition, the smoothed particle hydrodynamics(SPH) method was employed to simulate the waterrock flow under the conditions of Newtonian fluid with uniform distribution of water and coarse-grained materials. The simulating results show that the flow distance, velocity, shape, and deposition profile of water-rock flow are in good agreement with the field observation. The present work is beneficial to the risk assessment and mitigation design of water-rock flow disaster in the waste dump.

An improved numerical model of ski-jump flood discharge atomization

Atomizing rainfall caused by flood discharge of high dams poses a great threat to the safety of powerhouse and ecological environment.As an indispensable means,numerical calculation is widely used in the safety design of discharge structures.The distribution of rainfall intensity is closely related to the trajectory nappe shape,jet trajectory distances,the splashed water droplet diameter and its velocity,and the spatial distribution of downstream nappe wind.In this paper,an experimental result is used to verify the improved stochastic splash mathematical model under different bucket types and discharge conditions,and the sensitivity of downstream rainfall intensity distribution to the shape of trajectory nappe,discharge flow,spatial distribution of downstream nappe wind,and the corresponding relationship between the droplet diameter and its splashing velocity is analyzed.The results show that the calculation accuracy of downstream rainfall intensity distribution is significantly improved when the above factors are taken into consideration.It is found that the bucket type and flood discharge rate play the greatest role in the rainfall intensity distribution,followed by the downstream nappe wind distribution,and finally the corresponding relationship between the diameter and velocity of splash droplets.Therefore,these factors should be considered comprehensively when the rainfall intensity distribution of flood discharge atomization is calculated.This study can help us to understand the influence factors of flood discharge atomization more deeply and predict the distribution of flood discharge atomization rainfall intensity more accurately.

Influence of Sedum Spectabile on Cd Concentration in Soil and Runoff

To research how planting Sedum spectabile affects Cd loss, in this experiment, the impact of soil pollution level (low, medium, high), rainfall intensity (30, 60, 90 mm·h-1), and slope (6°, 12°, 18°, 24°) on Cd concentration in soil and runoff after planting Sedum spectabile are investigating using an indoor artificial rainfall simulation method. The results showed that: 1) The mean values of agricultural soils in the study area reached 38.52 and 1073.28 mg·kg-1 for Cd and Zn, respectively, which were 176.70 and 11.96 times higher than the background values of soil environment in southern Yunnan. 2) The decrease of total Cd in the soil after planting Sedum spectabile ranged from 17.52% to 31.09%, and the decrease of effective state Cd ranged from 14.36% to 21.81%. The higher the pollution level, the more significant the decrease of effective state Cd. 3) After 120 days of planting, the Cd concentration in runoff decreased between 22.40% and 89.23% compared to 15 days, with the more significant decrease in low Cd pollution, 90 mm·h-1 rainfall, medium Cd pollution, 30 mm·h-1 rainfall, and high Cd pollution, 90 mm·h-1, reaching 81.14% - 87.43%, 82.21% - 89.00%, and 37.57% - 89.23%. 4) The pollution level and rainfall intensity were significantly and positively correlated with Cd concentration in runoff at 15 and 120 days of planting Sedum spectabile, with correlation coefficients of 0.498, 0.641, and 0.435, 0.464. Research shows that planting Sedum spectabile can reduce the Cd concentration in soil and runoff, which is essential for the remediation of Cd-contaminated farmland.

Effects of rainfall patterns on runoff and soil erosion in field plots

Soil erosion processes during a storm are strongly affected by intra-storm variations in rainfall characteristics.Four storm patterns,each with a different rainfall intensity variation were separated.The storm patterns were:(1)increasing rainfall intensity(2)increasing then decreasing intensity(3)decreasing intensity(4)decreasing then increasing intensity.After each erosive rainfall(12 events),Runoff and suspended sediment samples were collected in each plot's tank which is located on hillslopes of the basin of Khamsan.Main storm characteristics and soil losses were plotted and equation of the line of best fit were selected.Analysis of variance(ANOVA)was used to determine response of runoff and soil erosion to storm patterns.Results showed that in lower rainfall intensities a linear function fits the relationship between soil loss and rainfall intensity whereas this function tends to be non-linear at higher intensities.Also a strong non-linear relationship was found between different quartiles of storm and soil loss.Statistical analysis revealed significant differences in total runoff,soil loss and sediment concentration across four storm patterns(P<0.001)but no differences in the runoff coefficient.In particular,storms with increasing rainfall intensity yielded highest quantities of eroded sediments,total runoff and highest sediment concentrations followed by increasing then decreasing,decreasing then increasing and decreasing intensity,respectively.

Effects of Rainfall and Underlying Surface on Flood Recession——The Upper Huaihe River Basin Case

The effects of rainfall and underlying surface conditions on flood recession processes are a critical issue for flood risk reduction and water use in a region.In this article,we examined and clarified the issue in the upper Huaihe River Basin where flood disasters frequently occur.Data on 58 rainstorms and flooding events at eight watersheds during 2006–2015 were collected.An exponential equation(with a key flood recession coefficient)was used to fit the flood recession processes,and their correlations with six potential causal factors—decrease rate of rainfall intensity,distance from the storm center to the outlet of the basin,basin area,basin shape coefficient,basin average slope,and basin relief amplitude—were analyzed by the Spearman correlation test and the Kendall tau test.Our results show that 95%of the total flood recession events could be well fitted with the coefficient of determination(R2)values higher than 0.75.When the decrease rate of rainfall intensity(Vi)is smaller than 0.2 mm/h2,rainfall conditions more significantly control the flood recession process;when Vi is greater than 0.2 mm/h2,underlying surface conditions dominate.The result of backward elimination shows that when Vi takes the values of0.2–0.5 mm/h2 and is greater than 0.5 mm/h2,the flood recession process is primarily influenced by the basin’s average slope and basin area,respectively.The other three factors,however,indicate weak effects in the study area.

Effects of rainfall intensities and slope gradients on nitrogen loss at the seedling stage of maize(Zea mays L.)in the purple soil regions of China

Loss of soil nitrogen has been reported to reduce soil productivity and result in eutrophication.The objective of this work was to understand the mechanisms of nitrogen loss at the maize seedling stage from purple soil in the sloping farmlands of southwest China.The characteristics of nitrogen loss were explored in experiments simulating rainfall conditions during the maize seedling stage at different rainfall intensities(60 mm/h,90 mm/h,and 120 mm/h)and slope gradients(10°,15°,and 20°).The results showed that the runoff and sediment yield increased with time.The surface runoff and sediment yield increased with the rainfall intensity and slope gradient.Nitrogen losses increased in the surface runoff and sediment but decreased in the interflow as the rainfall intensity and slope gradient increased.Dissolved total nitrogen(DTN)was the main form of nitrogen in the surface runoff and interflow,and nitrate nitrogen(NO3-N)was the main form of DTN.The surface runoff and sediment accounted for less than half of the TN losses.Thus,interflow was the main pathwayfor nitrogen loss.The regression lines between the surface runoff and forms of nitrogen losses in the runoff and interflow were linear.The results indicated that an increasing rainfall intensity and slope gradient generally increased the surface runoff,sediment,andnitrogen losses.However,the opposite trend was observed for the interflow and its nitrogen losses.

Effects of rainfall on the weekday traffic flow in major cities of the Beijing-Tianjin-Hebei region, China, in 2021

Rainfall can bring uncertainties to the traffic flow and influence the normal function of urban transportation systems.The impact of precipitation on the urban traffic flow,especially the different impacts among cities and areas within a city,is worth investigating.Here,we analysed the impact of precipitation on the traffic flow in the urban areas of the Beijing-Tianjin-Hebei region by comparing the traffic flow in non-precipitation and rainy weather with different hourly precipitation intensities in 2021.The increase in the travel time index(TTI)is chosen to represent the influence of precipitation on the transportation system.The results show that the maximum of the average TTI increases on the city scale under various rainfall intensities by 3.3%,6.6%and 10.8%in Beijing,Tianjin and Shijiazhuang,respectively.In general,the increase in the TTI contributed by precipitation is the greatest at morning and afternoon peak hours,and the traffic congestion degree increases with the rainfall intensity.However,in the morning peak,afternoon peak and midday hours in Beijing and Tianjin,the influences of the weak rainfall intensity on the traffic flow are generally great,whereas the traffic congestion degree caused by heavy precipitation is relatively low.Particularly,in morning peak hours,the congestion reduction reaches approximately 2%,which may be related to the spatial difference in the impacts of precipitation on the traffic flow and the changes in people's travel intention under different rainfall intensities.The findings can help better understand the relationship between rainfall and urban traffic flow characteristics and also potentially contribute to the development of impact-oriented climate predictions.