Empirical study of extreme rainfall intensity in a semi-arid environment at different time scales

Mediterranean environments are typical of semi-arid regions, dominated by episodes of torrential rain in which the critical variable is not the total rainfall, but the intensity. This paper studies the maximum rainfall intensities at different observation time scales, from 5 min to 24 h, over eastern Spain from 1994 to 2007. The statistical rainfall characteristics for each time scale are analysed and the effects of specific geographical factors - altitude, aspect and distance to the sea - for each observation interval are tested. The results show that extreme intensities are heavily dependent on the time scale. There are two important turning points in this trend, at I h and 6 h. With regard to the influence of geographical factors, distance from the sea is particularly important as it is significant for almost all observation time scales. Altitude is only significant between time scales of 30 min and 6 h. Aspect is not significant. Two intensity patterns are also observed: the first includes the highest intensities, at altitudes from 200 to 400 m and at locations 20-30 km from the sea, while the second is related to lower intensities, higher altitudes (900-1000 m) and longer distances to the sea (90-100 km). (C) 2013 Elsevier Ltd. All rights reserved.