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[en] The knowledge of raindrop size distributions is of great interest to cloud physicists radar meteorologists and communication engineers. Beginning from the Winter 1986-87, the Precipitation Group of the Atmospheric Physics Institute installed on the roof of the Institute building in Roma-Eur a disdrometer RD-69. The sensor is an electromechanical device with surface of 50 cm2 able to measure the raindrop diameter with a precision of 5% and a resolution (delay between two drops hitting the sensor) of one millisecond. After the calibration, significant precipitations were recorded continuosly, with a sample period of 1 minute, during the whole life of the storms. It can be expected that a knowledge of the drop size distributions, and in particular of the differences between distributions, can be used to infer details of the storm and the environment. In the work the first results of the analyses are presented. Particular attention was conferred to the variation characteristics of the precipitation type (thunderstorm and widespread) as well as to the variations of the distributions in short time intervals, that may be caused by different effects, for example the growth and decay of a precipitation cell or the movement of a cell combined with the different fall velocities of small and large drops
[en] Rainfall thresholds for landslides occurrence derived in real applications tend to be lower than the ones one would obtain using exact data. This letter shows how the use of coarse temporal resolution rainfall data causes a systematic overestimation of the duration of the triggering rainfall events that directly contributes to thresholds underestimation. A numerical experiment is devised to quantify this systematic effect for the relevant case of power-law depth/intensity–duration thresholds. In the examined conditions, i.e., the frequentist method at 5% non-exceedance probability level, ~ 70% underestimation of the scale parameter and ~ 60% overestimation of the shape parameter of the thresholds is to be expected using daily resolution rainfall data, but the exact quantification depends on the specific characteristics of each study case. The underestimation increases as the temporal resolution becomes larger than the expected minimal duration of the triggering events. Under operational conditions, sensitivity analyses based on the methods and datasets of interest are advised.
[en] This article attempts to give a very detailed perspective to the challenge and advances associated to rainfall-triggered landslides, which are characteristic and very common in tropical environments, such as Colombia. Landslides are one of the most common hazards around the world. Economic losses caused by landslides are huge, and are often exaggerated due to urban sprawl. Recent findings in this topic around the world have been applied for determining critical thresholds by physical or statistical models, combined with rainfall forecasting and near real time monitoring as fundamental component of an early warning system. Landslides are caused by several phenomena, including geological, geomorphologic and anthropogenic dynamics; however, one variable - precipitation - has a uniquely strong capability to cause rapid, intense slope failure. A review of several studies of rainfall-triggered landslides is presented some of who have used statistical tools that define critical thresholds based on intensity and duration rainfall. Other authors have focused upon physical based models combining hydrological and geotechnical aspects of rainfall, water pore pressure and slope stability.
[en] An investigation was carried out to characterize some selected parameters which influence rainfall erosivity in southeastern Nigeria. Rainfall amount, distribution, duration, intensity, storm types, energy loads and frequency of rain events in the region were studied using data from stations located in three major agroecological zones. Raindrop size and detaching capacity were evaluated in one of the stations for two months. The mean annual rainfall erosivity values for southeastern Nigeria point to the fact that rainfall tend to be highly erosive. 25 refs, 6 figs, 8 tabs
[en] Annual and seasonal rainfall data taken in the period 1951-1986 have been spatially averaged over the region Friuli-Venezia Giulia and analysed with the aim of searching for the presence of trends. The results of the two rank tests recommended by the world meteorological organization support the hypothesis of a decreasing trend in the autumn rainfall and, with less probability, an increasing trend in spring
[en] Understanding the trend characteristics of design rainstorm and spatial heterogeneity of extreme precipitation is of great importance to reduce disasters induced by rare extreme precipitation. Using a high-resolution (0.5° × 0.5°) daily gridded data set of precipitation across mainland China from 1961 to 2013, this study investigated the historical changing trend and spatial heterogeneity of design rainstorm using the 30-year moving window method (30YM). Differences in the quantification of the design rainstorm were compared for the use of the 30YM and the 30-year-based increasing window method (30YBI). The results show that a significant increasing intensity but no spatially uniform trend of design rainstorm can be observed across mainland China based on the 30YM analysis. The south, east, and northeast China mainly showed an increasing trend, but the southwest and north China presented a decreasing trend. The spatial heterogeneity of the design rainstorm was greatly enhanced if the nonstationarity assumption was adopted on the national scale. The heterogeneity showed an increasing trend mainly in southeast, north, northeast, and northwest China, and a decreasing trend in southwest and west China, indicating significant regional variation in spatial heterogeneity. For most areas of mainland China, especially for southeastern, northeastern, and western China, use of the most recent precipitation sub-series to quantify the design rainstorm may weaken the potential nonstationarity and guarantee the safety of infrastructure in these areas where design rainfall increases.
[en] We present a method to estimate the beamfilling correction factor for rain rates calculated from SSM/I data at 19 GHz, horizontal polarization. An application to a tropical situation is presented, where brightness temperatures vary typically from 175 K to 235K. We show the quantitative dependence of this correction with the fraction of the field of view covered by rain. This leads to a correction factor in the range 1.5-3. (author)
[en] This precipitation station is designed to measure the rainfall and to offer the possibility to take samples for isotopic analyses of the total discharge during one month or any other pre-selected period. Precipitation measurement: Digital tipping bucket rain gauge with a time resolution from one minute up to some hours (free of scaling) and a quantity resolution (depending on the type of bucket) from 0.1 or 0.2 mm rainfall. Sampling application: For isotopic analyses it is necessary, that no part of the precipitation can re-evaporate. Therefore in this application the container where the precipitation is stored, can be opened and closed. This procedure is working automatically controlled by the data-logger. When the rainfall starts (=the moment of the first tipping), the container is opened. After the rainfall it is closed again. The time of delay can be chosen individually (for instance 1 till 10 minutes). To get correct samples of one month, a second valve is changing the flow path between the two containers exactly at the beginning of the month. Apart from precipitation also other parameters like temperature, wind speed, radiation and so on can be stored. The whole application can be mounted in existing measuring stations, without changing the existing collecting funnel (as shown in the picture). This is important for the continuity of the measurement at an existing station. On the other side, the whole measuring and sampling equipment can be mounted in a new station with any tipping bucket, which allows to gather the measured precipitation. To avoid large changes of temperature of the sampled water, the containers can be isolated. In cold areas the station must be heated in such a way, that the sample is not freezing. A simple funnel heating is not enough. The heating can be done with gas or electricity regulated by a thermostat. The described station is equipped with two separated electrical heating systems with thermostat control, as the hut is dived off in two parts. In the upper part are the tipping bucket, the data logger and one valve. In the lower part are the other valve and the containers. This allows an exact control of the temperature. The prototype of this station was erected for the Zentralwasserversorgung Hochschwab Sued, designed and rebuilt with the digital equipment from Joanneum Research, Graz. Outlook: In stage of development is a temperature controlling system for the collecting funnel. This is necessary during very cold and very hot spaces of time. There are two systems possible: a small cooling plant (perhaps powered with solar energy) or Peltier-elements, both with an electronic control system and an isolated collecting funnel. With Peltier-elements it is possible to heat and cool the funnel according to the temperatures of the surroundings but they need a lot of energy. In our alpine regions especially the cooling of the funnel during summertime will be an important step to optimise the sampling procedure. Especially the high temperatures before a thunderstorm brings problems with re-evaporation of raindrops at the beginning of a precipitation event. Therefore the cooling of the collecting funnel is a crucial element in the procedure of isotope sampling. The system (including the temperature controlled liquid gas heating) can be supplied with solar energy and supplemented with remote data transfer systems like LEO-satellites, GSM, dedicated radio or telephone
[en] In most urban areas in Europe and Northern American serious corrosion impacts on buildings and cultural monuments have been caused by emissions of pollutants. The rapidly increasing pollution levels in many of the developing countries also exert a serious threat to materials. Beside the very important role of SO2 also the direct or synergistic effect of NO2 and O3, the particulates and rain acidity may contribute in an important way to materials degradation. Results from extensive international field exposure programmes i. e. within the UN/ECE have enabled development of dose-response relations which describe the effect of dry and wet deposition of pollutants on corrosion of different material groups. In most of the industrialized countries decreasing trends of sulphur and nitrogen pollutants and of acidity of precipitation have resulted in decreased corrosion rates. The concept of acceptable levels of pollutants is a useful tool in planning of abatement strategies and for defining of conditions for a suitable development in the field of corrosion of construction in the atmosphere. (Author) 12 refs