The effect of observation timescales on the characterisation of extreme Mediterranean precipitation

This paper analyses the behaviour of five rainfall indicators (maximum intensity, cumulative rainfall, irregularity, probability of rain and persistence of rain) over different observation timescales ranging from 5 min to 24 h. It covers a large area on the Mediterranean side of the Iberian Peninsula (River Jiicar Water Authority, 43 000 km2) on a continuous basis over a period of 14 years (1994-2007). The results show that the behaviour of extreme Mediterranean rainfall is heavily dependent on the observation timescale. There are a number of turning points in the indicator trends which occur on different timescales (1 and 6 h in the case of rain intensity and irregularity, 6 h for cumulative rainfall and between 15 and 30 min for the persistence of rain) and may be relevant for the determination of thresholds used in water management.