Bayesian hazard analysis of heavy precipitation in eastern Spain

The hazard due to heavy daily rainfall in the Valencia region (eastern Iberian Peninsula) is analysed by using 30-year records at 72 rain gauge stations. The proposed method is a Bayesian version of the commonly used point over threshold or exceedance methods. For each site, the occurrence of events in time are assumed to be Poisson distributed and the excesses over a selected high threshold are assumed to follow some generalized Pareto distribution. A large uncertainty about the type of distribution for the excesses is observed for each station and the preferred distribution changes from station to station. The large uncertainty in estimated occurrence probabilities or return periods suggests the use of Bayesian predictive occurrence probabilities as the main parameters describing the hazard. Two stations are selected for a detailed analysis. The whole database has been used to obtain predictive exceedance probability spatial distributions for thresholds of 150, 300 and 500 mm of daily precipitation. These maps confirm the most hazardous sites are placed at the northeast of the main mountain range of the region, where it is speculated that deep convection develops when humid northeasterly flows cross the coastal range. Copyright (C) 2001 Royal Meteorological Society.