Short Rainfall Duration Research Articles

Comparison of Climatology of Precipitation Diurnal Cycle in Kalimantan Deduced from Rain Gauge and IMERG Data

Abstract The diurnal cycle is repetitive pattern of changes in weather factors on land and oceans due to the Earth rotation. Kalimantan Island as the largest island in the Maritime Islands region has a complex rainfall pattern that is influenced by local factors and global circulation. The research was conducted to find out the climatological comparison of the diurnal cycle of rain in Kalimantan based on rain gauge data and Integrated Multi-SatellitE Retrievals for GPM Version 07 (IMERG V07) data for the period 2016 - 2022. Data validation using rain gauge data to validate and calibrate IMERG satellite data, improving the accuracy and reliability of satellite rainfall estimates. The diurnal cycle is evaluated through a Precipitation Amount (PA), Precipitation Frequency (PF), and Precipitation Intensity (PI) every hour. The results show that the maximum rainfall occurs in the afternoon and evening along the coast, and in the middle of the night and morning on the Kalimantan plains. Kalimantan has high rainfall intensity values at short rainfall durations, i.e. rain lasting less than 3 hours. This is expected to improve the quality of hydrometeorological disaster mitigation in Kalimantan.

Variations of Runoff-Sediment Processes at Flood Event Scale at a Typical Catchment in the Loess Plateau of China

The flood season is the main period for runoff and sediment yield, and understanding the variations of runoff and sediment of flood events is of great significance for distinguishing the runoff-sediment processes in the Loess Plateau. In this study, we analyzed the variations of runoff and sediment at the flood event scale in the Qiaogou catchment and investigated the influencing factors. The results showed that runoff and sediment of flood events were mainly produced by rainfall with short rainfall duration and heavy rainfall intensity in the study area. Based on the 28 flood events and corresponding precipitation data from the reference period (P-I, 1986–1989) and the revegetation period (P-II, 2001–2009), we analyzed the variations of runoff-sediment processes at the flood event scale in the Qiaogou catchment, a typical catchment of the Loess Plateau. The results showed that the flood variables were lower in the revegetation period than those in the reference period, except for the flood peak discharge time and the flood duration. The sediment transport capacity per unit runoff depth in the revegetation period was weaker than that in the reference period. The hysteresis analysis indicated that the patterns of the hysteretic loop were dominated by the figure-of-eight pattern and the compound pattern, respectively, in the reference period and revegetation period. Compared to the reference period, runoff and sediment-related variables for flood events of counter-clockwise, figure-of-eight, and compound patterns were less in the revegetation period. With similar rainfall conditions, the main reason for the noticeable difference in runoff and sediment of flood events for the two periods was the variations in vegetation cover. The mentioned results indicated that revegetation performed a critical function in the variations of runoff and sediment at the flood event scale. This study revealed the variations of runoff-sediment processes of flood events and their responses to rainfall and revegetation in a typical catchment of the Loess Plateau, which can provide a basis for decision-making on soil erosion management and sustainable development of the ecological environment in the Loess Plateau.

Use of multifractal parameters to determine soil particle size distribution and erodibility of a physical soil crust in the Loess Plateau, China

Understanding the knowledge of multifractal analysis on particle size distribution (PSD) of soil physical crusts is indispensable for progressing soil surface erosion mode. In this study, hoeing tillage (20 cm long × 15 cm wide × 5 cm deep) were conducted to simulate classic tillage mode in Yangling, China to obtain physical crusts under artificial rainfall (60 mm h−1 intensity with three durations (5, 15, and 30 min)). We defined crusts formed in ridges as structural crust (Cst), formed by infiltration of runoff in hoes as sediment-containing depositional crust (Cscd), and formed by the extraction of runoff as sediment-free depositional crust (Csfd). Soil stratification methods were used to explore physical crust particle sorting. Results represented that the sand content of Cst, Cscd, and Csfd decreased, whereas clay and silt contents increased after rainfall compared to undisturbed soil. There was no significant difference between Cscd and Csfd under short rainfall duration. Three crust types became gradually concentrated in areas with higher density with increasing rainfall duration according to six common parameters in the generalised dimension spectrum (D0, D1, D2, D1/D0, Dv(D-10–D0), and Ds(D0–D10)). Multifractal singularity spectrum (α0, Av, Fv) showed that PSD was most symmetrical in Csfd, followed by Cscd and Cst. Erodibility index KEPIC was largest for Cst, followed by Csfd then Cscd. The relationship between KEPIC and multifractal parameters were significant. Spatial difference caused by tillage activities and rainfall events determine the heterogeneous formation mode, particle size distribution and erodibility of physical crust.

Intraseasonal Change in Diurnal Cycle of Precipitation over Sumatra from IMERG Observation

This study investigates the intraseasonal change in the diurnal cycle of rainfall over Sumatra in terms of Madden Julian oscillation (MJO) phases. Change in the peak time of mean accumulation (PA), frequency (PF), and intensity (PI) of precipitation from Integrated Multi-Satellite Retrievals of GPM (IMERG) final run product version 06 data during 2016-2019 was investigated. Data were classified into active (2,3,4, and 5) and inactive (1,6,7 and 8) MJO. Rainfall in the Sumatra region is generally dominated by short rainfall duration, as found by a previous study. During the active MJO, the increase the number of rain events over the mainland Sumatra is dominated by rain lasting less than 6 h. In the Indian Ocean region, the increase in rain events is dominated by short and long-duration rain. The means of PA and PF during the active MJO showed a significant increase (0.4 mm/h and 10%), especially in the western part of Sumatra. On the other hand, the average PI during the active MJO tends to decrease (~ 1.5 mm/h), especially in the southern mainland of Sumatra. Finally, we found no significant change in the peak time of PA, PF, and PI during the active MJO and inactive MJO.

Deadly floods and their causal factors: A case-control study in Iran between 2005 and 2018

Flood hazard characteristics play a key role in flood-induced mortality. Therefore, it is crucial to evaluate the associations between these factors and flood fatalities. This case-control study was performed in the flood-prone regions of Iran with recorded flood-induced mortality rates during 2005–2018. In total, 369 subjects completed the survey (123 cases and 246 controls); they were selected from 12 provinces and 30 cities.In this study, descriptive and analytical analyses were carried out to measure flood hazard characteristics. Afterward, the correlation of flood hazard characteristics with flood-induced mortality was measured. According to the descriptive analysis, most deaths occurred in summer, during hours of darkness, in areas with one- and five-year flood return periods, and in floods with short rainfall durations. In addition, the spatial analysis demonstrated that most deaths occurred in flash floods, floods accompanied by bad weather, and floods with floating debris. The results of Chi-square and Fisher's exact test also indicated significant correlations between darkness, flood return periods, flood behavior, floods with floating debris, bad weather, other hazards, and flood discharge with flood-induced mortality. According to the regression analysis, the variables of flood discharge over 500 m3/s, flash floods, nighttime floods, and floods with floating debris increased the risk of flood-induced mortality 3.64, 1.62, 3.34, and 1.06 times, respectively. Although changing flood hazard characteristics seems to be impossible, damages caused by floods can be decreased and the lives of people can be protected through appropriate preventive and managerial solutions, planning, training, promotion of preparedness, and timely warnings.

Temporal and spatial variation of rainfall characteristics under high urbanization in the Lake Taihu Plain

随着人类活动和气候变化影响的加剧，降雨特征变化引发的洪水问题日益突出，探讨其时空演变特征对保障高度城镇化地区洪涝安全有较大理论和实际意义.本研究以高度城镇化的太湖平原地区为例，选取降雨强度、降雨历时、降雨集中程度和降雨峰值程度为降雨类型特征指标，以高分辨率短历时加权集合降水资料MSWEP （multi-source weighted-ensemble precipitation）为基础探讨了快速城市化发展下（1979—2016年）不同降雨历时-强度-类型的时空演变规律及其演变机制.研究结果表明：①研究区的降雨频次呈现出强度小、历时短、雨量集中于中期和高峰型降雨发生的频次高的特征；同时历时较短、集中于前期和后期的降雨频次趋于增加，而历时较长、集中于中期且中峰型降雨的频次趋于减少.②城镇化对降雨雨型的影响分析发现，高城镇化水平地区较低城镇化水平地区的降雨量更大，其中降雨强度大于25 mm/d的大雨和暴雨事件更易发生；并且更倾向于发生前期型和高峰型的极端分布降雨.随着城镇化发展研究区更易于遭受因降雨量过于集中而导致的雨涝灾害.;Under the intensification of human activities and the impact of climate change, the flood problem caused by the change of rainfall characteristics is becoming increasingly prominent. This article takes the highly urbanized regions of the Lake Taihu Basin as an example. According to multi-source weighted-ensemble precipitation (MSWEP) precipitation data, the rainfall intensity, rainfall duration, rainfall concentration degree and rainfall peak degree are selected. The rainfall data from 1979 to 2016 are divided into events to analyze the evolution characteristics of different rainfall duration-intensity-type and its mechanism in the research area. The results are as follows:① The rainfall frequency in the core regions of Lake Taihu under elevated urbanization shows that rain with low rainfall intensity, short rainfall duration, concentrated in mid-term and with higher peaks occurs more commonly. The number of short duration rainfalls, early- and late-term rainfalls show an upward trend, and the number of long and extra-long duration rainfalls, medium-term rainfalls, and moderate peak rainfalls show a downward trend. ② Based on the analysis of the impact of urbanization on rainfall patterns, the rainfall in areas with high urbanization levels is larger than that in the areas with low urbanization levels. It is more likely to occur heavy rainfall events with rainfall intensity greater than 25 mm/d in high urbanization level areas. Compared with the low urbanization level area rainfall, the high urbanization level area rainfall is more inclined to occur the extreme distribution rainfall such as early and high peak rainfall. Suffering a flood event caused by excessive concentration of rainfall is more possible with the development of urbanization in the study area.

Responses of Runoff and Soil Loss to Rainfall Regimes and Soil Conservation Measures on Cultivated Slopes in a Hilly Region of Northern China.

Cultivated land plays an important role in water and soil loss in earthy/rocky mountainous regions in northern China, however, its response to soil conservation measures and rainfall characteristics are still not fully understood. In the present study, 85 erosive rainfall events in 2011–2019 were grouped into three types, and the responses of runoff and soil loss to soil conservation measures and rainfall regimes on five cultivated plots with different slopes in the upstream catchment of the Miyun Reservoir were evaluated. Results found that mean event runoff depths and soil loss rates on the five plots ranged from 0.03 mm to 7.05 mm and from 0.37 t km−2 to 300.51 t km−2 respectively, depending on rainfall regimes, soil conservation measures, and slope gradients. The high frequency (i.e., 72.94%) rainfall regime A with a short rainfall duration (RD), low rainfall amount (P), and high mean rainfall intensity (Im) yielded a lower runoff depth and higher soil loss rate. Rainfall regime B with a longer RD, and a higher P and Im, however, produced higher a runoff depth and lower soil loss rate. Terraced plots had the highest runoff and soil loss reduction efficiencies of over 96.03%. Contour tillage had comparable sediment reduction efficiency to that of the terraced plots on gentle slopes (gradient less than 11.0%), while its runoff reduction efficiency was less than 13.11%. This study implies that in the Miyun Reservoir catchment and similar regions in the world, contour tillage should be promoted on gentle slopes, and the construction of terraced plots should be given ample consideration as they could greatly reduce water quantity and cause water shortages in downstream catchments.

A computationally efficient system for assessing near-real-time instability of regional unsaturated soil slopes under rainfall

The objective of this paper is to obtain an applicable assessment method and a Web-GIS-based prediction system for regional landslides. The traditional Richards function is reconstructed using the soil-water characteristic curve (SWCC) and the coordinate transformation technique. The analytical pore pressure for a slope model is derived by solving the modified Richard equation via the Green function and Fourier transformation. The obtained transient pore pressure field is then incorporated with Brakensiek’s matric suction theory, to build a conceptual model for rainfall-induced shallow landslides. The safety factor is obtained by solving the limit equilibrium equation of the conceptual model. The method is then implemented in a Web-GIS system, considering influence of slope geometry features, geology parent material, and near-real-time rainfall intensity of the study area. It is verified that this method is computationally efficient and reliable for gentle slopes and short rainfall durations. Moreover, an extensive parameter study shows that the two commonly used coefficients in the intensity-duration equation are both correlated to rainfall inter-event time via exponential functions, and rainfall event time via power functions. The primary influential factor for regional landslides is the initial water content, followed by the rainfall duration and intensity, and least by soil thickness.

Quantification of the effect of soil erosion factors on soil nutrients at a small watershed in the Loess Plateau, Northwest China

PURPOSE: This research aimed to quantitatively assess the effect of soil erosion factors on soil nutrients under similar rainfall conditions at a small watershed in the Loess Plateau, China, with emphasis on quantification of each factor’s contribution to soil nutrients. MATERIALS AND METHODS: Forty-five soil samples were collected and the soil texture and nutrients were analyzed. The integrated fertility index (IFI) was quantified with laboratory-measured available phosphorus, available potassium, total nitrogen, and soil organic matter based on principal component analysis and the soil erosion factors were computed. The feature importance of soil erosion factors that affect soil nutrients was estimated based on the gradient-boosting decision tree (GBDT) method. RESULTS AND DISCUSSION: The GBDT optimized model revealed that the feature importance of soil erosion factors soil erodibility (K), slope length (L), slope steepness (S), vegetation cover (C), and mechanical erosion control (P) was 0.41, 0.11, 0.03, 0.39, and 0.06, respectively. The K and C factors occupied 80% of the importance and were the two predominant soil erosion factors affecting the soil comprehensive nutrients. The Pearson correlation coefficient between K, L, S, C, or P, and IFI was − 0.387, − 0.23, − 0.25, − 0.479, and − 0.532, respectively. The different order of factors between the Pearson correlation and feature importance may indicate that linear relation cannot be used to indicate the significance of each factor. CONCLUSIONS: The soil erodibility and the vegetation cover could basically determine the quality of soil nutrients in the small watershed under similar rainfall conditions. The soil property itself and associated effects on the amount and rate of runoff under a certain rainfall erosivity had a dominant impact on the soil nutrients. Factor C greatly contributed to runoff resistance and protection of nutrients from erosion. The L, S, and P factors had weak effects on the IFI because of the generally low rainfall intensity, short rainfall duration, and other factors that may counteract the effects in the area.

Storm event-based frequency analysis method

Abstract In this study, a storm event-based frequency analysis method was proposed to mitigate the limitations of conventional rainfall depth–duration–frequency (DDF) analysis. The proposed method takes the number, rainfall depth, and duration of rainstorm events into consideration and is advantageous in estimation of more realistic rainfall quantiles for a given return period. For the purpose of hydraulics design, the rainfall depth thresholds are incorporated to retrieve the rainstorm events for estimating design rainfalls. The proposed method was tested against the observed rainfall data from 1961 to 2010 at Seoul, Korea and the computed rainfall quantiles were compared with those estimated using the conventional frequency analysis method. The study results indicated that the conventional method was likely to overestimate the rainfall quantiles for short rainfall durations. It represented that the conventional method could reflect rainfall characteristics of actual rainstorm events if longer durations (like 24 hours) were considered for estimation of design rainfalls.

Landslide and debris flow initiated characteristics after typhoon Morakot in Taiwan

Typhoon Morakot brought extreme rainfall and initiated numerous landslides and debris flows in southern Taiwan in August of 2009. The purpose of this study is to identify the extreme rainfall-induced landslide frequency-area distribution in the Laonong River Basin in southern Taiwan and debris flow-initiated conditions under rainfall. Results of the analysis show that debris flows were initiated under high cumulative rainfall and long rainfall duration or high rainfall intensity. The relationship of mean rainfall intensity and duration threshold could reflect debris flow initiation characteristics under high rainfall intensity in short rainfall duration conditions. The relationship of cumulative rainfall and duration threshold could reflect debris flow initiation characteristics under high cumulative rainfall in long rainfall duration. Defining rainfall events by estimating rainfall parameters with different methodologies could reveal variations among intermittent rainfall events for the benefit of issuing debris flow warnings. The exponent of landslide frequency-area distribution induced by Typhoon Morakot is lower than that induced by the Chi-Chi earthquake. The lower exponent of landslide frequency-area distribution can be attributed to the transportation and deposition areas of debris flow that are included in the landslide area. Climate change induced high rainfall intensity and long duration of precipitation, for example, Typhoon Morakot brought increased frequency of debris flow and created difficulty in issuing warnings from rainfall monitoring.

A simplified physically based coupled rainfall threshold model for triggering landslides

A number of rainfall threshold models for triggering landslides have been developed in either empirical or physical manner. The objective of an empirical rainfall threshold model is to establish a relationship between rainfall intensity and duration, which is a line on a log–log diagram, although the mechanism of the relationship following the power law is not yet well understood. The sufficiency of rainfall and landslide data is also a significant concern for empirical models. A simplified physically based rainfall threshold model is developed by coupling the Mohr–Coulomb law and Darcy's law based on the assumptions that the slope has an infinite length and that discrete water diffusion is physically based. The power-law mechanism for the relationship between rainfall intensity and duration for the initiation of a landslide is investigated using this physically based model. The rainfall threshold calculated with the model shows that the threshold follows the power law for short rainfall durations whereas it gradually tends towards a constant value for long rainfall durations. Case studies have shown that a plausible threshold for regions that lack sufficient landslide and rainfall data can be obtained via the model. The model is also applied to cases which occurred in regions geologically typical of Fujian Province, southeast China. The landslide distribution predicted by our model accords with the interpretation of high resolution satellite imagery, and this suggests that the proposed physically based model also effectively determines rainfall thresholds for triggering regional landslides.

연최대치 계열과 연최대치 독립 호우사상 계열의 비교

본 연구에서는 강우 지속기간이 짧은 경우와 긴 경우에 대한 연최대치 계열과 연최대치 독립 호우사상 계열의 차이를 살펴보았다. 연최대치 독립호우사상은 1961년부터 2010년까지의 서울지점 시강우 자료에 다양한 IETD와 절단값을 적용하여 추출하였다. 결정된 연최대치 독립호우사상 계열은 기존의 연최대치 계열과 비교하였다. 그 결과를 요약하면 다음과 같다. 첫째, IETD와 절단값의 영향은 예상할 수 있는 수준을 벗어나지 않았다. 예를 들어, IETD의 증가에 따라 짧은 지속기간 및 긴 지속기간을 갖는 독립 호우사상의 발생 빈도는 유사한 감소비율을 갖으나, 절단값의 증가에 따라서는 특히 지속기간이 긴 호우사상의 발생빈도가 급격히 감소하는 것으로 나타났다. 둘째, 추출된 독립 호우사상의 평균 강우강도는 강우 지속기간에 관계없이 거의 일정한 것으로 나타났다. 이는 연 최대치 강우강도가 주로 지속기간이 긴 호우사상에서 결정될 가능성이 크다는 것을 의미한다. 마지막으로, 강우지속기간이 짧은 경우, 연 최대치 계열과 연 최대치 독립 호우사상 계열의 차이가 매우 큰 것으로 확인되었다. 그러나 이러한 차이는 강우 지속기간이 증가함에 따라 현저히 줄어들었다. 이러한 결과는 특히 매우 짧은 집중시간을 고려하는 작은 유역의 경우, 전통적인 자료 분석방법을 통해 결정된 설계강우가 실제 발생 가능성이 없는 비현실적인 경우가 될 가능성이 매우 큼을 의미한다. This study investigated the differences between annual maximum series and annual maximum independent rainfall event series with relatively short and long rainfall durations. Annual maximum independent rainfall events were selected by applying various IETDs and thresholds to the hourly rainfall data in Seoul for the duration from 1961 to 2010. Annual maximum independent rainfall event series decided were then compared with the conventional annual maximum series. Summarizing the results is as follows. First, the effect of IETD and threshold was not beyond the expected level. For example, as the IETD increases, the frequencies of independent rainfall events decreased similarly in their rate for both with short and long durations. However, as the threshold increases, the frequency of those with rather long durations decreased much higher. Second, The mean rainfall intensity of the independent rainfall events was found to remain constant regardless of their duration. This indicates that the annual maximum rainfall intensity could be found in a rainfall event with longer durations. Lastly, the difference between the annual maximum rainfall series and the annual maximum independent rainfall event series with rather short rainfall durations was found significantly large, which decreases with longer durations. This result indicates that the conventional data analysis method, especially for small basins with short concentration time, could lead an unrealistic design rainfall with little possibility of occurrence.

Numerical simulation of laboratory experiments in detention pond routing with long rainfall duration

This paper establishes a numerical detention pond volume model based on the hydrological continuity equation and the Runge-Kutta numerical method. Experiments for the conditions of both steady and unsteady flow have been used to verify the model. In unsteady flow cases, the outflow hydrograph by numerical simulation are fairly consistent with experimental value. Both experimental and numerical results indicate that wider rectangular sharp-crested weirs or larger rectangular slot tend to induce greater outflow discharges, which undesirably cut down the detention volume. Experiments show that the necessary detention volume of rectangular slot is smaller than that of the rectangular sharp-crested weir for a constant flood peak reduction. That is, the rectangular slot is the recommended outflow device when flood peak reduction is the design criteria. The study also shows that necessary detention volume of the short rainfall duration is less than that of the long rainfall duration under constant allowable maximum discharge.

Behavior of Unsaturated Layered Soil Columns during Infiltration

This paper presents the laboratory test results of vertical infiltration on two soil columns of finer over coarser soils subject to simulated rainfalls under conditions of no-ponding at the surface and constant head at the bottom. The main objectives were to evaluate the effect of rainfall intensity and duration; and to provide experimental evidence for soil water redistribution and hysteresis. The results show that rainfall intensity had a major effect on infiltration in the finer layer but had limited effect in the coarser layer due to the large difference of saturated permeability between the two layers. A relatively short rainfall duration resulted in a delayed response of pore pressure and water content to the rainfall after its cessation, while a relatively long duration did not result in such a delayed response. The delayed response indicated the redistribution of soil water in infiltration. Different paths of water content versus matric suction were followed during the tests indicating the apparent hysteretic behavior of soil water. In addition, the coarser layer restricted the increase of pore pressure in the finer layer. A minor variation of saturated soil permeability had minimal effect on infiltration.

PREDICTION OF COMBINED SEWER OVERFLOWS CHARACTERIZED BY RUNOFF

Pollution loading of Combined Sewer Overflows (CSOs) is frequently over the capacity of a wastewater treatment plant (WWTP) receiving the water. The objectives of this study are to investigate water quality of CSOs in Anmyun-ueup, Tean province and to apply Storm Water Management Model to predict flow rate and water quality of the CSOs. The capacity of a local WWTP was also estimated according to rainfall duration and intensity. Eleven water quality parameters were analyzed to characterize overflows. SWMM model was applied to predict the flow rate and pollutant load of CSOs during rain event. Overall, profile of the flow and pollutant load predicted by the model well followed the observed data. Based on model prediction and observed data, CSOs frequently occurs in the study area, even with light precipitation or short rainfall duration. Model analysis also indicated that the local WWTP’s capacity was short to cover the CSOs.