Short Duration Rainfall Intensity Research Articles

In situ measurements of post-fire debris flows in southern California: Comparisons of the timing and magnitude of 24 debris-flow events with rainfall and soil moisture conditions

[1] Debris flows often occur in burned steeplands of southern California, sometimes causing property damage and loss of life. In an effort to better understand the hydrologic controls on post-fire debris-flow initiation, timing and magnitude, we measured the flow stage, rainfall, channel bed pore fluid pressure and hillslope soil-moisture accompanying 24 debris flows recorded in five different watersheds burned in the 2009 Station and Jesusita Fires (San Gabriel and Santa Ynez Mountains). The measurements show substantial differences in debris-flow dynamics between sites and between sequential events at the same site. Despite these differences, the timing and magnitude of all events were consistently associated with local peaks in short duration (< = 30 min) rainfall intensity. Overall, debris-flow stage was best cross-correlated with time series of 5-min rainfall intensity, and lagged the rainfall by an average of just 5 min. An index of debris-flow volume was also best correlated with short-duration rainfall intensity, but found to be poorly correlated with storm cumulative rainfall and hillslope soil water content. Post-event observations of erosion and slope stability modeling suggest that the debris flows initiated primarily by processes related to surface water runoff, rather than shallow landslides. By identifying the storm characteristics most closely associated with post-fire debris flows, these measurements provide valuable guidance for warning operations and important constraints for developing and testing models of post-fire debris flows.

Technical Note: Proposed Standard for Automatic Calculation of Rainfall Erosivity

The universal soil loss equation (USLE) and its modifications have been globally accepted as a model to estimate water erosion. A rainfall erosivity index is a key part of this equation. This article describes a web-accessible method for the automatic summarization of short duration rainfall intensity and the USLE rainfall erosivity index. We propose that these methodologies be used as a standard for automatically calculating daily rainfall intensity percentage and daily rainfall erosivity.

Are extreme rainfall intensities more frequent? Analysis of trends in rainfall patterns relevant to urban drainage systems

The fact that climate change is affecting the intensity and frequency of rainfall is well accepted in the scientific community. This is backed by a multitude of reports on the basis of daily rainfall series analysis; however, little research is available for short duration intensities. Due to its significant influence on the behaviour of urban drainage, it is critical to investigate the changes in short duration rainfall intensities. In this study different intensities relevant for the urban drainage and the total rainfall per rain event are analysed. The trend is investigated using the Mann-Kendall test. The rainfall series analysed are from the alpine region Tyrol. The results present differences depending on the duration of the intensity and the series considered, however an increase in the number of extreme events is detectable for short durations for the most series.

ASSESSMENT OF POSSIBLE IMPACTS OF CLIMATE CHANGE IN AN URBAN CATCHMENT1

ABSTRACT: Stationarity of rainfall statistical parameters is a fundamental assumption in hydraulic infrastructure design that may not be valid in an era of changing climate. This study develops a framework for examining the potential impacts of future increases in short duration rainfall intensity on urban infrastructure and natural ecosystems of small watersheds and demonstrates this approach for the Mission/Wagg Creek watershed in British Columbia, Canada. Nonstationarities in rainfall records are first analyzed with linear regression analysis, and the detected trends are extrapolated to build potential future rainfall scenarios. The Storm Water Management Model (SWMM) is used to analyze the effects of increased rainfall intensity on design peak flows and to assess future drainage infrastructure capacity according to the derived scenarios. While the framework provided herein may be modified for cases in which more complex distributions for rainfall intensity are needed and more sophisticated stormwater management models are available, linear regressions and SWMM are commonly used in practice and are applicable for the Mission/Wagg Creek watershed. Potential future impacts on stream health are assessed using methods based on equivalent total impervious area. In terms of impacts on the drainage infrastructure, the results of this study indicate that increases in short duration rainfall intensity may be expected in the future but that they would not create severe impacts in the Mission/Wagg Creek system. The equivalent levels of imperviousness, however, suggest that the impacts on stream health could be far more damaging.

Estimating maximum expected short-duration rainfall intensities from extreme convective storms

Certain hydrological applications require estimates of maximum rainfall intensity values for short time durations, as it is the case of urban hydrology design among others. Short duration rainfall intensities are affected by a large uncertainty when durations under 10 or 5 minutes are considered, especially when they are produced during extreme convective rainfall events.In this paper, 408 rainfall events have been statistically analyzed for the period 1925–1992 in Alicante (Spain). Maximum intensities for durations ranging from 2 minutes up to 240 minutes were extracted from the series, and described in terms of a set of GEV-three parameter extreme value distributions. The resulting quantiles were plotted, and nine frequently used empirical functions imax(t) were fitted, including 2-parameter and 3-parameter functions.Considerable differences are found in the behaviour of the empirical functions for short durations (t < 10 minutes). A systematic comparison is performed in all cases, with return periods ranging from 5 to 500 hundred years, assessing reliability of the estimates of maximum rainfall intensities for short durations. The 3-parameter functions together with the Talbot function provide satisfactory goodness-of-fit, although in most cases, underestimation of maximum rainfall intensities for very short durations is observed. On the other hand, the postulated empirical Intensity-Duration-Frequency (idf) relationships are more suitable when data for larger durations (i.e., t<60 min) are considered. This result is consistent with the consideration of essentially different dynamics of the maximum rainfall intensities producing mechanisms at the different time scales.

Regional Analysis of Convective Storms

With the support of a dense hydrometeorological telemetric network of 24 stations over an area of 625 km² surrounding the metropolitan area of Mendoza city (central west Argentina) at 33° S, a detailed study of thunderstorm rainfall fields was carried out to obtain standard project storms for the area. In the region, precipitation-frequency relations for small arid basins that produce flash floods are difficult to estimate, basically due to the extreme temporal and spatial variability of precipitation. The high density and synchronized rain gauge network permits the detailed determination of rainfall fields in space and time for an arid zone of the southern hemisphere, where the lack of good-quality and highly resoluted rainfall data has been a major hindrance for operation, design, and research. To have a composite record for the area using the concept of station-storm, a regional analysis of convective storms was done on a sample of 140 events. First, precipitation zones were defined according to stations-elevations and then a grouping of stations was obtained by means of a statistical determination with the multivariate method of principal component analysis. Second, relations between the two lower zones were done using a comparison of the average slope of short-duration rainfall intensity curves between 10 and 5 years of time of return for durations of up to 30 and 60 min. The final aim of the study was to provide a procedure for the regional analysis of convective storms and produce practical tables for the standard project storm for the area.

Comment on short-duration rainfall intensity measured using calibrated time-of-tip data from a tipping bucket raingauge

Comment on short-duration rainfall intensity measured using calibrated time-of-tip data from a tipping bucket raingauge

Short duration rainfall intensity measured using calibrated time-of-tip data from a tipping bucket raingage

Laboratory testing of a tipping bucket raingage provided a calibration curve expressing the equivalent depth of rainfall per tip as a function of intensity. The time of each tip from the instrument was recorded during a 7 week period encompassing 20 rainfall events. A technique was presented to compute rainfall intensity for durations of 1 min to 1 h using the time-of-tip data and the calibration curve. Rainfall intensities computed using the proposed method were compared with intensities computed using several conventional recording schemes which used fixed recording intervals (from 15 s to 1 h) and the manufacturer's nominal calibration constant. Intensities measured using the conventional recording schemes were significantly lower than the proposed method. These differences were greatest when the recording interval exceeded the storm duration.

Rainfall intensity duration frequency analysis

In the present study the analysis of rainfall data compiled for eighty stations spread over several parts of India has been carried out for developing a general relationship for the estimation of short duration rainfall intensity.

Characterizing Short Duration Rainfall Intensities for Runoff Calculation

ABSTRACT INVESTIGATIONS of nonpoint pollution in rural areas involve the transport of pesticides and other chemicals from farm fields. The transport process, in turn, considers erosion and surface runoff as its major components. Determining the rate and volume of runoff for this problem frequently involves the rainfalls that cover the entire magnitude spectrum and not just the large rainfall events that hydrologists often use for the design of hydraulic structures. Because of the nature of the problem, this analysis involves relatively small hydrologic units; i.e., individual fields or small water-sheds where the spatial variability of rainfall can be con-sidered uniform. One major difficulty in analyzing the transport process arises from lack of adequate time definition of rainfall. In much of the United States and Canada, analysts are limited to using published clock-hour rainfall data as the shortest time increment. Yet, the critical factors affect-ing the transport of chemicals from a field often have time resolutions much less than 1 h. These critical fac-tors are the time of concentration or the equilibrium time of the runoff surface and the magnitude and time distri-bution of rainfall excess intensity. Use of hourly rainfall data would generally underestimate peak runoff rates for erosion and chemical transport. The objectives of this paper are to present an analysis that illustrates the size of the error that can be expected by using hourly rainfall data to calculate peak runoff and to develop a procedure for determining sequences of 5-min rainfall increments from published hourly rainfall data.

On the transposition of short duration rainfall intensity data in mountainous regions

Maximum rainfall amounts for various durations at low level and high level stations in an area exposed to the same general moisture inflow are compared. It is found that ratios between low level and high level values increase with durations. These ratios are used to obtain frequency analyses of maximum short duration rainfall for high level stations with a relatively short record from available long station records at the lower elevations.