Critical Rainfall Values Research Articles

Analysis of the formation mechanism of debris flows after earthquakes – A case study of the Legugou debris flow

By means of the Graphic Method, Gray Correlation Method and Frequency Method, the total amount of loose solid materials, the amount of loose solid materials per unit area in the source area, and the risk degree and critical rainfall of the study area are determined, respectively. On the basis of the calculation results, the total amount of loose solid materials is 57.2 × 104 m3, the amount of loose solid materials per unit area is 0.13 m3/m2 (greater than 0.1 m3/m2), which better meets the initiation conditions for dilute debris flow. The Hazard Evaluation Model of Debris Flow in earthquake areas is established by the gray correlation method and the hazard index H = 0.725 is determined. According to the hazard classification standards for debris flows in earthquake areas, the debris flow in Lecugou was moderate after the earthquake. The critical rainfall value of 1H, calculated by the frequency method, ranged from 17.45 to 22.21 mm (Re = 25 mm) and 8.17 to 13.01 mm (Re = 50 mm). The critical rainfall value at 10 min ranged from 6.23 to 8.44 mm (Re = 25 mm) and 2.92 to 5.13 mm (Re = 50 mm), respectively. The maximum rainfall intensity of 45.5 mm/h was reached between 10:00 and 11:00 on July 29, 2019 and the cumulative rainfall reached 144 mm, far exceeding the critical rainfall of Legugou. Under the influence of earthquakes and human activities, the loose solid source amount and loose solid source amount per unit area increased greatly, and the critical rainfall for debris flow after earthquakes decreased sharply, which induced debris flows under the influence of heavy rainfall. This research will be helpful for the establishment of monitoring and early warning systems based on artificial intelligence methods, and can greatly improve the effectiveness of disaster prevention and mitigation.

A parsimonious post-processor for uncertainty evaluation of ensemble precipitation forecasts: an application to quantitative precipitation forecasts for civil protection purposes

Abstract In this study, we present a post-processing technique designed to assess conditional predictive uncertainty for quantitative precipitation forecasts (QPFs) that extends to the multivariate predictor case. The theoretical foundation of the mixed binary-continuous precipitation process representation for a single predictor is coupled with the univariate version of the model conditional processor (MCP) that allows considering ensemble forecasts while maintaining a parsimonious approach. The experiment set-up is based on a weather vigilance zone (WVZ) of the national warning system in southern Italy and the relative QPFs issued by the Italian Civil Protection Department. Various aspects of the quality of the probabilistic forecast from the uncertainty processor were evaluated. The results indicate that post-processed forecasts can provide improved performances in terms of accuracy and reliability, tend to correct bias and are generally less under-dispersive than raw forecasts for the investigated area. Furthermore, we explored the possibility of issuing warnings employing the full predictive distribution and moving to the use of probabilistic thresholds here identified through a receiver operating characteristic (ROC) analysis. Considering the probability of exceeding a critical rainfall value allowed successful discrimination between events and non-events for critical precipitation occurrences and proved to be a valuable approach to decision-makers and information providers.

Estimation of Critical Rainfall for Flood Disasters in the Qinghai-Tibet Plateau

According to the results of The Second Comprehensive Scientific Expedition on the Qinghai-Tibet Plateau, the balance of solid and liquid water on the Qinghai-Tibet Plateau is disturbed, and a large amount of solid water, such as glaciers and perpetual snow, is transformed into liquid water, which aggravates the risk of flood disasters in the Plateau. Based on the historical flood disaster records of the Qinghai-Tibet Plateau, this paper analyzed the temporal and spatial distribution characteristics of the flood disasters in the Plateau, and estimated the critical rainfall for the flood disasters combined with precipitation data from the meteorological stations in each basin of the Qinghai-Tibet Plateau. The results show that most of the flood disaster events in the Plateau are caused by precipitation, and the average annual occurrence of flood disasters is more than 30 cases and their frequency is on the rise. The high frequency areas of flood disasters in the Qinghai-Tibet Plateau are mainly in the Hehuang Valley and the Hengduan Mountains area; the secondary high frequency areas are located in the valley area of South Tibet and the peripheral area of the Hehuang valley. Finally, we found that the highest critical rainfall value of flood disasters in the Qinghai-Tibet Plateau is in the southern area of the plateau, followed by the eastern and southeastern parts of the plateau, and the lowest values are in the central, western and northern parts of the Plateau.

Rainfall Warning Model for Rainfall-Triggered Channelized Debris Flow Based on Physical Model Test—A Case Study of Laomao Mountain Debris Flow in Dalian City

Debris flows are among the most frequent and hazardous disasters worldwide. Debris flow hazard prediction is an important and effective means of engineering disaster mitigation, and rainfall threshold is the core issue in debris flow prediction. This study selected the Laomao Mountain debris flow in Dalian as the research object and explored the relationship among the percentage of coarse sand content of soil, rainfall conditions and the critical rainfall values that induce debris flows on the basis of field investigation data, combined with the results of a flume test, soil suction measurement and geomechanical analysis. The new multi-parameter debris flow initiation warning models were obtained through the mathematical regression analysis method. The critical rainfall values of debris flows in this area were calculated by the previous research on the mechanism of hydraulic debris flow initiation (HIMM). Lastly, the multi-parameter debris flow initiation warning models were compared and analyzed with the critical rainfall values obtained using the HIMM method and the rainfall information available in historical rainfall data, and the reliability of the models was verified. The comparison results showed that the new multi-parameter debris flow initiation warning models can effectively modify the traditional intensity–duration model and have certain reliability and practical values. They can provide an effectual scientific basis for future work on the monitoring and prediction of debris flow disasters.

Slope stability models for rainfall-induced lahars during long-lasting eruptions

In this study we analyse the spatial distribution of potential lahar sources during long-lasting eruptions using two slope stability models (SHALSTAB and TRIGRS). The analysis is based on observed deposit grain-size and thickness, rainfall data and slope angle of the lahar events, in the area surrounding the Cordón Caulle volcano, Chile, that occurred during the 2011 eruption. The main phase of the eruption (4–7 June) was characterized by eruptive plumes from 7 to 11 km high which dispersed most of the tephra eastward toward Argentina, with a total estimated volume of about 1 km3. Tephra-fallout blanketed the region from ESE to ENE of the volcano with the thickness of the tephra-fallout layers between approximately 1 m (15 km from vent) and 0.06 m (240 km from the vent). On 10 June 2011, a major lahar occurred close to the Argentina-Chile border that reached the National road 231 (28 km from the vent). Three field campaigns were undertaken to collect samples and data from tephra-fallout deposits and triggering mechanisms in the lahar source area. Model input parameters were obtained from geotechnical tests and field measurements. Several metrics were used for model evaluation and best fit to the data were obtained for simulations considering non-cohesive ash layers for SHALSTAB and a cohesion of 0.5 kPa for TRIGRS. Both models are sensitive to the physical properties of the tephra-fallout deposit and the hydraulic and materiel strength properties of the study area. They both also show good agreement with field data but provide different information: TRIGRS provides an estimate of the timing (based on a storm event) and location of a potentially unstable area, while SHALSTAB simulations result in landslide susceptibility classes based on critical rainfall value. These outcomes provide fundamental insights into lahar triggering during long-lasting volcanic eruptions and are crucial to the compilation of lahar hazard maps and emergency management plans in the South Andes volcanic region.

Research on the Critical Rainfall of Debris Flow in Beijing, China

Debris flow is the most serious and destructive geological disaster in the mountainous areas of Beijing. Statistical data on some antecedent and triggering rainfall for the occurrence of debris flow were collected, and the correlation between various rainfalls was analyzed in this research. The linear regression equations of rainfalls at different time periods were derived. Based on the statistical data of debris flow and rainfall from 1950 to 2012, the critical rainfall of debris flow in each districts of the mountainous areas in Beijing were computed by analyzing disaster and rainfall frequency, and the critical rainfall values of debris flow in Beijing were calculated and recommended in this research. The research results have important application value for the early warning and forecast of geological disaster in Beijing.

Analyzing temporal–spatial characteristics of drought events in the northern part of Cyprus

Drought in the northern part of Cyprus has become a recurrent phenomenon. In the last few decades, Cyprus has experienced significantly severe drought events occurring periodically, and this trend is now continuing. With rainfall distribution varying considerably across the region and frequent drought conditions, the water resources, agriculture, economy and the environment have been adversely affected. This study aims to investigate spatial–temporal characteristic of drought using Standardized Precipitation Index (SPI) at multiple timescales (3, 6 and 12 months). Monthly time series of 36 years (1977–2013) rainfall data from nine weather stations are used to derive SPI values. Based on different drought categories, this study focuses on propagation of drought from one timescale to another and estimating critical rainfall values during moderate, severe and extreme drought conditions. The analysis revealed that there is a strong correlation among different timescales in detecting drought events. On average, 79 and 78% of 3-month timescale drought propagated into 6- and 12-month drought events, respectively, while 90% of 6-month timescale drought events propagated into 12-month drought events. The derived critical rainfall value for extreme droughts over a 12-month timescale was less than 255 mm/year in the town of Alsancak, while for Guzelyurt, a major citrus growing city, this figure was less than 135 mm/year. The results are validated through drought events detected at various regions of the Mediterranean basin and local flood occurrences during the wet periods and decline in water tables at drought seasons.

Characteristic rainfall for warning of debris flows

A characteristic rainfall is introduced to overcome the difficulties encountered in determining a critical rainfall value for triggering debris flow. The characteristic value is defined as the rainfall at which debris-flow occurrence probability shows a rapid increase, and can be used as a warning rainfall threshold for debris flows. Investigation of recorded debris flows and 24-hour rainfall data at Jiangjia basin, Yunnan Province, in southwestern China, demonstrates the existence of such a characteristic rainfall. It was found that the characteristic rainfall corresponds to the daily rainfall of 90% cumulative probability by analyzing the basin’s daily rainfall histogram. The result provides a simple and useful method for estimating a debris-flow warning rainfall threshold from the daily rainfall distribution. It was applied to estimate the debris-flow warning rainfall threshold for the Subaohe basin, a watershed in the 2008 Wenchuan earthquake zone with many physical characteristics similar to those of the Jiangjia basin.

Estimation of rainfall thresholds triggering shallow landslides for an operational warning system implementation

The Piemonte regional warning system service, managed by the Environmental Protection Agency of Piemonte (“ARPA Piemonte” as official Italian acronym), is based on an advanced meteo-hydrological automatic monitoring system, and it is integrated with forecasting activities of severe weather-related natural hazards. At present, a meteo-hydrological chain is operated to provide flood forecasting on the main river pattern. The development of a forecasting tool for shallow landslides triggered by heavy rainfall is presented. Due to the difficulties in modelling shallow landslides triggering in a large and complex area like the Piemonte region, an empirical model is developed on the basis of the correlation between rainfall and previous landslides in historical documents. The research focuses on establishing rainfall thresholds for landslides triggering, differentiating the critical rainfall values through a geological characterisation of the different territories. The period from 1990 to 2002 is considered. A total number of 160 landslides with hourly information and time of triggering are used to calibrate the system. As a first outcome, two different zones have been identified: (1) zones in alpine environments, principally characterised by a bedrock composed of metamorphic rocks, igneous rocks, dolostones or limestones that require high values of critical rainfall and (2) zones in hilly environments, principally characterised by sedimentary bedrock that require low values of critical rainfall. Verification has been performed on a total number of 429 landslides with known date of occurrence. The results show a good agreement with the model with no missed alarms and a very low number of false alarms, thus suggesting an effective operational implementation.

<b>ANALISIS HUBUNGAN CURAH HUJAN DENGAN KEJADIAN BANJIR DAN KEKERINGAN PADA WILAYAH DENGAN SISTIM USAHATANI BERBASIS PADI DI PROPINSI JAWA BARAT</b><br> (ANALYSIS OF RELATIONSHIP BETWEEN RAINFALL AND FLOOD AS WELL AS DROUGHT EVENTS ON AREA WITH RICE ...

There are significantly decreasing of rainfall in wet season and dry season, and changed in onset of early season, that all of them can make crouded in plan of planting date, field actifity especially for food crops africulture. In the other side, climate is one of condition that has been ready and can not change, where probability of climate change will be reality that should be happened every time. Increasing frequency of climate extrem will give high impact in agriculture, especialy in rice-based farming system. This paper describes the climate risk based on statistical approaches. The climate risk is focused on flood and drought event. The analysis used was a chance occurrence based on time series data of rainfall and flood/droughts (affected and puso) based on median value from time series data. The goal of this research are : (1) to know rainfall critical value that can be influence flood and drought event in some of central food crops i West Java, (2) to know probability of flood and drought event in some of central food crops in West Java. The result of this research show that critical value of the rainfall that can be influence flood and drought event is very variety. Average of for flood event for paddy field near coastal based on median approach is 140 mm/month with probability 0,6. For another location, 166 mm/month with probability 0,68. Average of critical value of the rainfall for drought event is 64 mm/month for paddy field near coastal with probability 0,73. For another location, critical rainfall value is 119 mm/month with probability 0,76. For spesific research or detail scale (district or sub distric) we can use rainfall critical value and probablity based on data in that specific location because the data is more representative local riil condition.

Modelling landslide hazard, soil redistribution and sediment yield of landslides on the Ugandan footslopes of Mount Elgon

In this study, the LAPSUS-LS landslide model, together with a digital terrain analysis of topographic attributes, is used as a spatially explicit tool to simulate recent shallow landslides in Manjiya County on the Ugandan slopes of Mount Elgon. Manjiya County is a densely populated mountainous area where landslides have been reported since the beginning of the twentieth century. To better understand the causal factors of landsliding, 81 recent landslides have been mapped and investigated. Through statistical analysis it was shown that steep concave slopes, high rainfall, soil properties and layering as well as human interference were the main factors responsible for landslides in the study area. LAPSUS-LS is used to construct a landslide hazard map, and to confirm or reject the main factors for landsliding in the area. The model is specifically designed for the analysis of shallow landslide hazard by combining a steady state hydrologic model with a deterministic infinite slope stability model. In addition, soil redistribution algorithms can be applied, whereby erosion and sedimentation by landsliding can be visualized and quantified by applying a threshold critical rainfall scenario. The model is tested in the Manjiya study area for its ability to delineate zones that are prone to shallow landsliding in general and to group the recent landslides into a specific landslide hazard category. The digital terrain analysis confirms most of the causal topographic factors for shallow landsliding in the study area. In general, shallow landslides occur at a relatively large distance from the water divide, on the transition between steep concave and more gentle convex slope positions, which points to concentration of (sub)surface flow as the main hydrological triggering mechanism. In addition, LAPSUS-LS is capable to group the recent shallow landslides in a specific landslide hazard class (critical rainfall values of 0.03–0.05 m day − 1 ). By constructing a landslide hazard map and simulating future landslide scenarios with the model, slopes in Manjiya County can be identified as inherently unstable and volumes of soil redistribution can yield four times higher than currently observed. More than half of this quantity can end up in the stream network, possibly damming rivers and causing major damage to infrastructure or siltation and pollution of streams. The combination of a high population density, land shortage and a high vulnerability to landslides will likely continue to create a major sustainability problem.

Reconstructing high-magnitude/low-frequency landslide events based on soil redistribution modelling and a Late-Holocene sediment record from New Zealand

A sediment record is used, in combination with shallow landslide soil redistribution and sediment-yield modelling, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part. Eleven sediment cores were obtained from a dune-impounded wetland at Te Henga, west Auckland, northern New Zealand. Sediment stratigraphy and chronology were interpreted by radiocarbon dating, foraminiferal analysis, and provisional tephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, a physically based landslide model was used to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide-soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material, sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga Wetland during the last c. 1000 years. The spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard. The magnitude of the sediment pulses represented in the wetland can be back-calculated to critical rainfall thresholds representing a shallow landslide model scenario.

Regional test of a model for shallow landsliding

Landslides mapped in 14 watershed analyses in Oregon and Washington provide a regional test of a model for shallow landsliding. A total of 3224 landslides were mapped in watersheds covering 2993 km2 and underlain by a variety of lithologies, including Tertiary sedimentary rocks of the Coast Ranges, volcanic rocks of the Cascade Range and Quaternary glacial sediments in the Puget Lowlands. GIS (geographical information system) techniques were used to register each mapped landslide to critical rainfall values predicted from a theoretical model for the topographic control on shallow landsliding using 30 m DEMs (digital elevation models). A single set of parameter values appropriate for simulating slide hazards after forest clearing was used for all watersheds to assess the regional influence of topographic controls on shallow landsliding. Model performance varied widely between watersheds, with the best performance generally in steep watersheds underlain by shallow bedrock and the worst performance in generally low gradient watersheds underlain by thick glacial deposits. Landslide frequency (slides/km2) varied between physiographic provinces but yielded consistent patterns of higher slide frequency in areas with lower critical rainfall values. Simulations with variable effective cohesion predicted that high root strength effectively limits shallow landsliding to topographic hollows with deep soils and locations that experience excess pore pressures, but that low root strength leads to higher probabilities of failure across a greater proportion of the landscape. © 1998 John Wiley & Sons, Ltd. Language: en

A risk estimation method of railway embankment collapse due to heavy rainfall

Slope collapses of embankments and cut slopes along railways are often triggered by heavy rainfall of a typhoon, etc., and have much influence on the running safety of trains. It is of vital importance to find out the risky sites along the railway to control railway operations. For this purpose, it is desiable to develop a practical damage estimation method which can accurately predict the risks of slope collapse and can be simply applied by many railway workers. This paper deals with a method of estimating the railway embankment collapse in times of heavy rainfall based on a multivariate analysis. The critical rainfall is proposed to be defined as a product of the amount of accumulated rainfall and the maximum hourly rainfall. This value is also determined by a function whose variables include information on the embankment such as soil and structural properties, the surface ground geotechnical characteristics, the catchment and seepage, and the empirical rainfall. Therefore, the risk evaluation for embankments can be performed with the critical rainfall value.

A physically based model for the topographic control on shallow landsliding

A model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near‐surface through flow and slope stability models. The hydrologic model TOPOG (O'Loughlin, 1986) predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries. The slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity. The steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding. The spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high‐resolution digital elevation data are available: Tennessee Valley in Marin County, California; Mettman Ridge in the Oregon Coast Range; and Split Creek on the Olympic Peninsula, Washington. Model predictions in each of these areas are consistent with spatial patterns of observed landslide scars, although hydrologic complexities not accounted for in the model (e.g., spatial variability of soil properties and bedrock flow) control specific sites and timing of debris flow initiation within areas of similar topographic control.

Four types of relationships between rainfall and paddy production in Sri Lanka

Due to the absence of marked thermal differences in Sri Lanka, the paddy-climate relationship has been confined to rainfall alone in this study. Increase in total paddy production is highly attributed by the increase in paddy lands rather than yields, particularly in the drier parts, called Dry Zone. The effective rainfall period for the two principal cropping seasons in Sri Lanka, Maha and Yala, were determined according to the crop calendar of the Districts. The deviation values from the trend lines of 20 years (1961–1980) observations in sown, harvest and yield were well correlated with the deviations from the mean rainfall. The effects of rainfall on paddy production are well pronounced in the Dry Zone during the Maha season and in the Wet Zone during the Yala season. From the statictical analyses, four types of relationship, were observed: (1) Type I is the positive relationship, (2) Type II is the negative relationship, (3) Type III is the no realtionship and (4) Type IV a complex one which has a positive relationship below certain critical rainfall value and no or negative relationship above the critical rainfall value. The combination of Types I and IV shows the areas which need irrigation facilities with proper water management while the combination of the Types II and III indicates the areas which are prone to frequent floods and waterloggings.

The Reliability of Rainfall Over the Sudan

The paper attempts to throw some lights on the variability and the reliability of rainfall over the Sudan. Twenty stations are used to calculate the standard deviations and the coefficients of variations. The latter indices give a more realistic impression of the rainfall variability.Also an attempt is made to measure the reliability of rainfall as a means for determining the extent and the reliability of rain-cultivation in the country. The magnitude of the risk involved in the transitional areas is indicated by the percentage probability of receiving critical rainfall values.