Bayesian hazard analysis of heavy precipitation in eastern Spain

The hazard due to heavy daily rainfall in the Valencia region (eastern Iber ian Peninsula) is analysed by using 30-year records at 72 rain gauge statio ns. The proposed method is a Bayesian version of the commonly used point ov er threshold or exceedance methods. For each site, the occurrence of events in time are assumed to be Poisson distributed and the excesses over a sele cted high threshold are assumed to follow some generalized Pareto distribut ion. A large uncertainty about the type of distribution for the excesses is observed for each station and the preferred distribution changes from stat ion to station. The large uncertainty in estimated occurrence probabilities or return periods suggests the use of Bayesian predictive occurrence proba bilities as the main parameters describing the hazard. Two stations are sel ected for a detailed analysis. The whole database has been used to obtain p redictive exceedance probability spatial distributions for thresholds of 15 0, 300 and 500 mm of daily precipitation. These maps confirm the most hazar dous sites are placed at the northeast of the main mountain range of the re gion, where it is speculated that deep convection develops when humid north easterly flows cross the coastal range. Copyright (C) 2001 Royal Meteorolog ical Society.