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"A new formulation to estimate of rainfall kinetic energy from daily rainfall. Application in the estimating the R factor to Spain"

Año:2007
Edita:5th International Congress of the European Society for Soil Conservation: “Changing soils in Changing World: the Soils of Tomorrow
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Resumen:

This paper presents a study on the quantitaive characterization of a very important property of the rainfall, the kinetic energy, and its application in order to obtain R factor (KE*I30) which determines rainfall erosivity. In the erosion studies the kinetic energy of the rainfall, necessary to calculate the erosivity, has been estimated by using empirical formulae taking part rainfall intensity. For this, it is necessary the availability of registered data of rainfall intensity in stations with pluviographs.

In this research, it has been obtained a relationship between the daily kinetic energy (KE24h ) and the daily rainfall (P24h ) with registered data. Therefore, the kinetic energy may be calculated with the registered daily rainfall in a normal meteorological station with only pluviometers.

The data were obtained with the disdrometer (Joss and Waldvogel, 1967) which provides information on the rainfall and allows the characterization of the distribution of raindrop size according to intervals of diameters of raindrop. The sampling equipment of data was installed in School of Forestry Engineering at Universidad Politécnica of Madrid. The equipment recorded rainfalls from two years, minute after minute, day and night.

From the obtained results it is deduced that the better relationship between the KE24h and P24h is a potential equation in which both top and low limits of the kinetic energy appear. That is, it seems reasonable to think that kinetic energy associated to daily rainfall has an upper limit for determined latitude and it does not grow indefinitely and thus neither does kinetic energy. And it also seems reasonable to think that below a determined value of daily rainfall its associated kinetic energy is so low that can be considered “no erosive”.

The equations that provided the best fits and correlation coefficients were the following:

 KE24h=

                  for 1<P24h=140mm, usual P24h

                          for P24h>140mm, unusual P24h

KE24h is the kinetic energy in J/m2 caused by the daily precipitation P24h in mm.

Combined potential equations were validated with pluviographs data and with observed data. The mentioned potential equations have been implemented for the estimation of the R factor (KE*I30). The maximum 30-min intensity (I30) was obtained by using the Intensity-Duration-Frecuency law (I-D-F law).

The use of these equations presents some advantages, mainly, a good interpretation of the phenomenon of relationship between KE24h and P24h , facility the obtention of data and simplicity and rapidity in the estimate of the R factor.

Palabras clave:Rainfall Kinetic Energy; Daily Rainfall; Disdrometer
 
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