Rainstorm Characteristics Research Articles

Characterization and indexing of heavy rainstorms in Hong Kong

ABSTRACTHeavy rain events or rainstorms of various scales often occur in Hong Kong from April to September. In extremes cases, they lead to serious landslides and flash floods resulting in loss of life, and damage to property and infrastructure. With climate change, extreme rain events are projected to be more frequent and more intense in this region. A system to gauge and label the severity of rainstorms would be useful for identifying and communicating extreme conditions in warning and disaster prevention operations. In parallel, a better understanding of the characteristics of rainstorms would also be important for impact assessments and engineering design purposes. This paper formulates a practical framework to index the magnitude and severity of rainstorms in Hong Kong. An index termed as the Severity Index combining the magnitude of different rainstorm attributes is devised for quantifying the overall severity of rainstorms. This index is flexible to allow tuning for specific applications.

Research on Rainstorm and Flood Characteristics of YunNan Base on WebGis

The climatic and geographic characteristics in the Yunnan basin are introduced and characteristics of precipitation，runof and silting in the river basin are analyzed．The regulation of rainstorm and flood within the river basin is analyze according to the statistic data of previous rainstorm and flood.

A numerical study of the rainstorm characteristics of the June 2005 flash flood with WRF/GSI data assimilation system over south-east China

The evolution and structure of rainstorms associated with a flash-flood event are simulated by the Advanced Weather Research and Forecasting (WRF-ARW) model of the National Center for Atmospheric Research and the Gridpoint Statistical Interpolation (GSI) data assimilation (DA) system of the National Oceanic and Atmospheric Administration (NOAA) of the United States. The event is based on a flash flood that occurred in the central Guangdong Province of south-east China during 20–21 June 2005. Compared to an hourly mixed rain-gauge and satellite-retrieved precipitation data, the model shows the capability to reproduce the intensity and location of rainfall; however, the simulation depends on three conditions to a large extent: model resolution, physical processes schemes and initial condition. In this case, the Eta Ferrier microphysics scheme and the initialization with satellite radiance DA with a fine 4-km grid spacing nested grid and coarse 12-km grid spacing outer grid are the best options. The model-predicted rain rates, however, are slightly overestimated, and the activities of the storms do not precisely correspond with those observed, although peak values are obtained. Abundant moisture brought by the south-westerly winds with a mesoscale low-level jet from the South China Sea or Bay of Bengal and trapped within the XingfengJiang region encompassed by northern Jiulian, southern Lianhua and eastern small mountains are apparently the primary elements responsible for the flood event. All simulated rainstorms were initiated over the southern slopes of the Jiulian Mountain and moved south or north-eastward within the Xingfengjiang region. Meanwhile, the Skew-T/Log-P diagrams show that there is a fairly high convective available potential energy (CAPE) over the active areas of the rainstorms. The higher CAPE provides a beneficial thermodynamic condition for the development of rainstorms, but the higher convective inhibition near the northern, eastern and southern mountains prohibits the storms from moving out of the region and causes heavy rainfall that is trapped within the area. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of Severe Rainstorm Characteristics of the Godavari Basin in Peninsular India

AbstractThe analysis of rainstorms is of prime importance for the planning and design of water resources of any region. In the absence of actual records of streamflow data, analysis of rainstorms is useful for assessing flood potentialities as well as the runoff of river catchments. This study provides pertinent information on the spatial distribution characteristics of severe rainstorm events that occurred over the Godavari and its subbasins on the basis of 110 yr (1891–2000) of available rainfall data. The analysis showed that the August 1986 rainstorm had its areal extension over more than a 150 000 km2 area. It is also seen that the August 1913 rainstorm was the most efficient rainstorm over the basin. The rain depth data of severe rainstorms given in this paper can provide a reliable set of information to assess water resource planning on a probability basis. The relationship between the point to areal rainfall and area of the rainstorms from 1- to 3-day durations is also determined.

Stochastic generation of hourly rainstorm events

Occurrence of rainstorm events can be characterized by the number of events, storm duration, rainfall depth, inter-event time and temporal variation of rainfall within a rainstorm event. This paper presents a Monte-Carlo based stochastic hourly rainfall generation model considering correlated non-normal random rainstorm characteristics, as well as dependence of various rainstorm patterns on rainfall depth, duration, and season. The proposed model was verified by comparing the derived rainfall depth–duration–frequency relations from the simulated rainfall sequences with those from observed annual maximum rainfalls based on the hourly rainfall data at the Hong Kong Observatory over the period of 1884–1990. Through numerical experiments, the proposed model was found to be capable of capturing the essential statistical features of rainstorm characteristics and those of annual extreme rainstorm events according to the available data.

Characteristics of rain events at an inland locality in northeastern Borneo, Malaysia

Understanding the intensity and duration of tropical rain events is critical to modelling the rate and timing of wet-canopy evaporation, the suppression of transpiration, the generation of infiltration-excess overland flow and hence to erosion, and to river responsiveness. Despite this central role, few studies have addressed the characteristics of equatorial rainstorms. This study analyses rainfall data for a 5 km2 region largely comprising of the 4 km2 Sapat Kalisun Experimental Catchment in the interior of northeastern Borneo at sampling frequencies from 1 min-1 to 1 day-1. The work clearly shows that most rainfall within this inland, forested area is received during regular short-duration events (<15 min) that have a relatively low intensity (i.e. less than two 0·2 mm rain-gauge tips in almost all 5 min periods). The rainfall appears localized, with significant losses in intergauge correlations being observable in minutes in the case of the typical mid-afternoon, convective events. This suggests that a dense rain-gauge network, sampled at a high temporal frequency, is required for accurate distributed rainfall-runoff modelling of such small catchments. Observed rain-event intensity is much less than the measured infiltration capacities, and thus supports the tenet of the dominance of quick subsurface responses in controlling river behaviour in this small equatorial catchment.

Characteristics of rainstorms over a temperate region derived from multiple time series of weather radar images

Weather radars provide invaluable data to characterize rainstorms spatially and temporally. A correct description of rainfall in space and time contributes to improvements in hydrological modeling and design, and ultimately to a better water management. To provide a stochastic rainfall model with an accurate parameterization, frontal rain systems over Belgium (Western Europe) are analyzed. In this paper different structures within rainstorms and their relative spatial positions are studied, the movement of rainstorms is analyzed and distribution functions are constructed to characterize several features of rainstorms statistically. A correlation technique is applied to determine the direction and velocity of the translation of storms. Well developed rainstorms are isolated in radar images and their dimensions and shape are investigated. To describe the dimensions of the rainstorms three methods are proposed and compared. Statistical analyses provide probability distributions for the dimensions, the perimeter, the area, the velocity and the direction of the movement for rainstorms. Furthermore, the spatial distribution of clusters in a rainstorm is studied. It is shown that a simple Poisson process performs well in the representation of this spatial distribution. Two methods to calculate the single parameter in a Poisson process (in 1D and in 2D) are proposed and compared.

A linear system model of dynamic throughfall rates beneath forest canopies

This paper describes a black box, linear system model to predict time‐varying throughfall rates using only data of time‐varying rainfall and storm total throughfall. For two forest stands in the Pacific Northwest the model predicted throughfall with mean efficiency of 0.84 when calibrated individually to 48 rainstorms and mean efficiency of 0.82 when calibrated to all storms simultaneously. The median of mean hydraulic residence times of precipitation in the canopy averaged across all storms ranged from 8 to 30 min by location within the two stands (overall median 12 min). Model predictions and performance were approximately equivalent for transfer functions based on either published equations describing storage and drip or of the form of exponential or gamma distributions. The model was insensitive to characteristics of rainstorms, so that calibrated models of water transfer through canopies were similar for storms of all sizes and intensities.

Analysis of beginning, end, and length of the rainy season along a Mediterranean–arid climate transect for geomorphic purposes

Geomorphic processes are controlled by rainfall, particularly in Mediterranean semi-arid and the arid regions. From a geomorphological aspect the characteristics of rainstorms and dry spells in these regions should be analysed as they might explain these processes. As a part of such analysis the beginning, end, and length of the rainy season should be determined. Eleven stations along a climatic transect extending from Judean Mountains with a Mediterranean climate to the Dead Sea arid region in Israel were studied. The beginning, end, and length of the rainy season, based on rainfall data for 30 years, are presented for daily rainfall and for accumulated rainfall within a rain spell (ARWS), and for different thresholds that might be used for different geomorphic processes. The results show that: (1) a close linear relationship exists between the beginning and end dates, as well as the rainy season's length, and the various rainfall thresholds; (2) as rainfall threshold increases the rainy season begins later, ends earlier, and consequently it is shorter in length; (3) likewise, as aridity increases the rainy season begins later, ends earlier, and it is shorter in length; and (4) the differences increase as the threshold increases. The regression line slopes emphasized a distinction between the two climatic regions, the Mediterranean and the arid region.

Distributed simulations of landslides for different rainfall conditions

AbstractA physically based distributed slope stability model is described that utilizes a combined surface–subsurface kinematic wave module to assess groundwater fluctuations related to slope stability. A total of 82 major rainstorms from 1972 to 1990 in Carnation Creek, British Columbia, were examined to determine the influence of different characteristics of rainstorms (such as mean and maximum hourly intensity, duration, and rainfall amount) on the slope stability. These rainstorms vary in mean intensity from 1·6 to 11·2 mm h−1, storm duration from 11 to 93 h, and maximum hourly intensity from 3·4 to 35 mm h−1. Four synthetic ‘uniform intensity’ rainstorms were also tested against real storms to assess the effect of short‐term hourly rainfall intensity peaks on landslide occurrence. Altogether, 602 simulations were conducted. The combined influence of mean and maximum hourly intensity, duration, and total rainfall amount of rainstorms were important in generating landslides. The temporal distribution of short‐term intensity also influenced the landslide occurrence. When saturated hydraulic conductivity of the soil was lowered or soil depth was raised, most rainstorms produced larger numbers of landslides. For the most part, actual rainstorms produced less stable conditions than their synthetic ‘uniform intensity’ counterparts. For all landslide‐producing storms, slope failure usually occurred after some threshold of cumulative rainfall and maximum hourly rainfall intensity. These simulations provide insights into the distributed behaviour of landslide occurrence during large rainstorms with varying characteristics. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Étude de stationnarité des caractéristiques des événements pluvieux de la station de Niamey sur la période 1956–1998

The stationarity of the rainstorm characteristics recorded since 1956 in Niamey is studied by statistical tests. Form and intensity variables are defined from hyetographs (graphs of rainfall versus time) with a five-minute time step. These variables show a significant change especially for the events between 20 and 35 mm of rainfall, before and after 1969.

SIZING OF SURFACE WATER RUNOFF DETENTION PONDS FOR WATER QUALITY IMPROVEMENT1

ABSTRACT: Historically, storm water management programs and criteria have focused on quantity issues related to flooding and drainage system design. Traditional designs were based on large rainfall‐runoff events such as those having two‐year to 100‐year return periods. While these are key criteria for management and control of peak flows, detention basin designs based on these criteria may not provide optimal quality treatment of storm runoff. As evidenced by studies performed by numerous public and private organizations, the water quality impacts of storm water runoff are primarily a function of more frequent rainfall‐runoff events rather than the less frequent events that cause peak flooding. Prior to this study there had been no detailed investigations to characterize the variability of the more frequent rainfall events on Guam. Also, there was a need to develop some criteria that could be applied by designers, developers, and agency officials in order to reduce the impact of storm water runoff on the receiving bodies. The objectives of this paper were three‐fold: (1) characterize the hourly rainfall events with respect to volume, frequency, duration, and the time between storm events; (2) evaluate the rainfall‐runoff characteristics with respect to capture volume for water quality treatment; and (3) prepare criteria for sizing and designing of storm water quality management facilities. The rainfall characterization studies have provided insight into the characteristics of rainstorms that are likely to produce non‐point source pollution in storm water runoff. By far the most significant fmdings are the development of a series of design curves that can be used in the actual sizing of storm water detention and treatment facilities. If applied correctly, these design curves could lead to a reduction of non‐point source pollution to Guam's streams, estuaries, and coastal environments.

Micromorphological and mineralogical components of surface sealing in loess soils from different geographic regions

Mineralogy of clay sized particles and rainstorm characteristics are among the major factors that determine the nature of soil sealing. This research was designed to further our knowledge about the role of clay mineralogy and rainstorm characteristics on crust formation. Four loess soils from different geographic locations (Canada, USA, China, and Belgium) were used in this study. Preliminary studies were carried out on Grenada Bt (USA), Lishi (China), and Bierbeek Bt (Belgium) horizons. Detailed infiltration and microscopic studies were performed only on the Bm1 horizon of the Saskatchewan soil, Canada and the Ap horizon of the Grenada soil, Mississippi, USA. Two levels of rainstorm were applied (∼ 40 and 80 mm h −1). While smectite was the major component in the Saskatchewan Bm 1 horizon, vermiculite and illite were found to be the dominant clay minerals in the Bt horizon of the Grenada soil. Formation of the washed layer together with thin lamellar crust coincided with the preferential movement of clay sized particles through runoff in both the Saskatchewan Bm1 and Grenada Ap horizons. The higher initial infiltration rate with higher rainfall intensity in both soils were likely due to higher matric suction, but rapid reduction in infiltration in this treatment was due to rapid aggregate destruction and a dense packing of the fundamental soil particles. No washed-in zone could be observed in the Bm1 horizon of the Saskatchewan soil in both rainstorm intensities. However, drastic reduction in infiltration, especially with high rainstorm intensity (after 7–8 min), was attributed mainly to the swelling of smectite in this soil material. Washed-in materials were visible in the Ap horizon of Grenada under high rainstorm intensity. Due to the presence of iron oxides and clay coatings, aggregates were stable and no sealing could be observed in the Grenada Bt and Bierbeek Bt materials. The degree of seal development in the Lishi soils was low. This was due to low clay and high carbonate contents. This study shows clearly that higher and continuous rainstorm intensity causes rapid seal development and as a result more erosion would occur, especially in the soils with high smectite content.

On some characteristics of severe rainstorms of India

Detailed examination of daily rainfall data for India (and other relevant publications regarding severe rainstorms) show that during the last 110 years, the Indian region recorded 231 severe rainstorms. Of these, 27 were of 2-day duration and the rest (204) were of 3-day duration. Within a rainstorm, maximum rain fell on the 2nd day on 63% of occasions. It was also observed that the average raindepths obtained from slow moving rainstorms were greater in magnitude than those of fast moving rainstorms. All these rainstorms, during their movement through the country, had their rain centres at about 308 locations. This study has shown that only 19 locations recorded severe rainstorm centres on five or more occasions. Maximum number of rain centres recorded for one location was 13.

Predicting soil-surface seal conductance from incipient ponding and infiltration data

The objectives of this study were to determine: (1) the degree of seal development at incipient ponding, and (2) the relationship between the hydraulic conductance of developing seals and rainstorm characteristics, i.e. the rain intensity and kinetic energy rate. Laboratory columns of an Atwood soil (Typic Paleudalf) were subjected to rainstorms with different combinations of duration, intensity, and kinetic energy rate. Seal conductance was determined from measured infiltration data and a solution of the Richards' equation for vertical infiltration through an infinitely thin seal. The results show that the hydraulic conductance of the sealing zone decreased rapidly during early stages of rainfall commencing before incipient ponding. The analyses indicate that for storms of relatively brief duration (less than 2 h) the hydraulic conductance of the sealing zone depends on the cumulative rainfall energy and on the rainstorm intensity.

Flood hydrograph estimation from arid catchment morphology

AbstractData on performance of a geomorphologic rainfall‐runoff model in simulating observed flash flood hydrographs in 32 arid catchments have been analysed. The catchments, which are located in the southwest region of Saudi Arabia, vary in their size, slope of land, and characteristics of soils, and are in zones of different rainstorm characteristics. The sensitivity of the model accuracy with various catchment and rainfall characteristics has been investigated. Size, followed by rate of infiltration and slope of land, are the most effective catchment characteristics affecting the accuracy. In addition, the accuracy varies with spatial and temporal rainfall variation, total rainfall depth, and length of the dry period between two successive rainstorms over catchment. It is sensitive to temporal rainfall variation more than spatial rainfall variation, and to the dry period more than total rainfall depth. Generally, the model did not display an accuracy approaching that of the observations, especially in simulating peak flowrates in large size infiltrating catchments having high temporal rainstorm variation. Guidelines on the best use of the model in arid catchments were proposed.

Climatological Characteristics of Summertime Extreme Rainstorms in Minnesota

Abstract Each year flash floods cause considerable property damage and loss of life, yet the heavy precipitation events responsible for flash floods remain extremely difficult to forecast, especially during summer. This paper presents synoptic analog models for use in the short-range prediction of summertime extreme rainstorms in Minnesota. To develop these analog models, forty-three heavy rain events that occurred from 1974–78 first were classified into four similar categories on the basis of the spatial properties of their rainfall distributions. Next, composite fields of surface and upper-air parameters were prepared for each of the four categories, and features on the composite maps that contributed most to the occurrence of heavy rainfall were incorporated into synoptic analog models. The analog models reveal that the typical circulation patterns for the four rainfall types vary significantly and that the spatial characteristics of extreme rainstorms are determined by the synoptic-scale circulation r...

Rainstorm and sediment yield characteristics at Ibadan

Ibadan experiences violent, tropical convectional storms of small areal extent. Hence, it is common observation that whilst very heavy rainfall can occur in one part of the city, another part can be totally dry. The annual average rainfall among stations in Ibadan do not differ significantly.

Recent developments on the probable maximum precipitation (PMP) estimation in China

Abstract This paper deals with regional and seasonal characteristics of rain storms in China which are introducing the most intensive rainfall occurrences. The paper further summarizes the techniques and practices involved for estimating the probable maximum precipitation (PMP). In consequence of inadequate streamflow data and abundance of heavy storms in China, it would be very difficult and dubious to extrapolate a frequency curve to the long return periods required for a spillway of a major structure. Apart from this, there are often dense populated areas downstream from reservoirs. Thus, in the design criterion of earth dams and/or rockfill dams (embankment) for reservoirs of major significance and also for important small dams, whose failure could result in fatalities as well as catastrophic damages, the probable maximum precipitation and probable maximum flood should be used. Thus, generalized charts of 24-hr. point-PMP have been developed.

Rainsplash as a mechanism for soil contamination of plant surfaces.

We characterized the physical transport of soil, and therefore contaminants attached to the soil, onto vegetative surfaces due to rainsplash. Soil accumulation by tomato plants (Lycopersicon esculentum) was investigated as a function of soil particle size, rainstorm characteristics, foliage height, surface area and canopy cover of the plants. No soil particles greater than 105 micron in diameter were detected on the plants. Most of the soil was splashed no higher than 40 cm above the ground surface. Linear relationships were observed for concentrations of less than 53 micron soil on vegetation and certain rainfall characteristics. Data from this study, as well as ancillary calculations, provide evidence that a significant fraction of surficial contamination of foliage may be attributed to the rainsplash mechanism.