Extreme point rainfall temporal scaling: a long term (1805-2014) regional and seasonal analysis in Spain

This paper presents a regional and seasonal study of extreme point rainfall scaling from 10 min to 2 years. To do this, the highest point-based rainfall list based on these temporal periods was calculated from the Spanish Meteorological Service (AEMET) precipitation databases with more than 11000 rain-gauge stations, with the longest series ranging from 1805 to 2014 (209years). This list constitutes the register of single station largest amounts of precipitation in Spain ever recorded for selected periods, including for example the values for 2h (193mm), 24h (817mm) or 1 year (5503mm). Rainfall extremes for 10min periods are evenly distributed in coastal and inland areas. Daily precipitation extremes are mostly concentrated over the Mediterranean coast while from durations from one month to two years, extremes are located in southern and northwest Spain. Extreme data obtained were compared with existing worldwide rainfall records for equivalent periods. Results indicate that Spanish extreme rainfall scaling relating R depth (in mm) against D duration (in minutes) may be expressed as a potential law R=21.8 D-0.422 (R=43.6 D-0.507 for worldwide data). We propose the upper envelope line (greater or equal to extreme rainfall values) parallel to the potential fit law as a simple method to estimate possible extreme records for different time scales. Using this method, worldwide envelope may be expressed as R = 60.5 D-0.507 and the Spanish envelope as R = 39.3 D-0.422. Further analysis stratifying results by season and region show that seasonal scaling has more variability than regional scaling. The methodology described can be readily applied to other regions for which detailed rainfall databases exist. Applications of the results include using the scaling found as a reference for classification of heavy precipitation events for temporal scales.