Las rachas secas en el sector central de la cuenca del Duero

Abstract

The aim of this work is to characterize the climate of the most arid area in the Duero basin. It has been paid attention to periods without precipitation (dry spells) and the estimation of probability and frequency of these periods using statistical methods of easy application. Average annual precipitation is below 400 mm and the annual number of dry days is high. Using a rainfall threshold of 0'1 mm in the definition of a dry day, the mean of dry days is 291 and the mean length of dry spells is 9'6 days. If the threshold is increased to 10 mm, the annual number of dry days is 356 and the mean length of dry spells is 40'1. Although the study area is located in the northern part of Iberian Peninsula, the analysis of the previous data and the length, intensity and probability of the maximum annual dry spells, confirm that its climatic characteristics are more similar to data from Mediterranean observatories than those from Atlantic area. Finally, as much the first-order Markov chain as the Gumbel distribution of extremes are suitable to estimate the probability and frequency of dry spells respectively.