La Houille Blanche
Number 7-8, Novembre 1981
|Page(s)||537 - 540|
|Published online||01 December 2009|
Analyse quantitative du phénomène de pluie ponctuelle maximale sur une surface Coefficient d'épicentrage des averses de 1 h à 24 h
Quantitative analysis of the phenomenon of maximum spot rainfall over an area - Epicentric coefficient of showers from 1 h to 24 h
Division Hydrologie-Hydraulique Fluviale, CEMAGREF, Paris-Antony
The problem of estimating extraordinary rainfall usually arises in connection with a given location. In practice, meteorologists are very often confronted with the problem of estimating heavy rainfall, not in a given place, but over a whole section of space. For these practitioners, the problem is posed in the following terms : What is the probability of rainfall exceeding R over a zone within a region of Area A ? Consider a region whose area is S covered by p rainfall recorders (thus defining p sub-zones of average area S/p). Assume that rain for t hours follows the same statistical law at all points of the region. The investigation covers the maximum rainfall recorded by the p rainfall recorders for each time interval t. The problem consists of assessing the theoretical distribution of this rain. Denote by PL (T) local rainfall over a return period of T years and by PX (T) maximum rainfall (recorded on the p rainfall recorders) with the same return period. The coefficient (KX) is the ratio of the two quantiles. KX(T) =PX(T)/PL(T) Knowledge of KX(T) thus provides an estimate of PX(T) when local rainfall by site is known. A priori, KX(T) depends on the four variables listed below : - area S of the region under study (km2) ; - the number of rainfall recorders (or sub-zones) : p ; - the duration of rainy spells to (hours) ; - the return period T (years). We have proposed the following analytical expression for KX, taking account of limit conditions, based on rainfall data portraying the Orgeval area. KX = 1+[ln (S+1)/S+1/P][0.03+0.26 lnT +0,32e-t/20] This formula has been drawn up within the following limits: 7 ≤ S ≤ 104 (km2) 0.2 ≤ T ≤ 10 (year) 2 ≤ t ≤ 24 (hour) 5 ≤ p ≤ 21 Climatic conditions of the Paris basin The formula can reasonably be extrapolated beyond these limits, expecially for p. when the functions used make it possible to have p tend to infinity. The formula can be used to assess likely risks in a given small region : hydrical erosion in a sensitive agricultural zone, local overflow of a city sewage system, etc.
© Société Hydrotechnique de France, 1981
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.