Precipitation seasonality in eastern and southern coastal Spain

The nature of the seasonality of precipitation in eastern and southern coas tal Spain (including both the Mediterranean and the far southwestern Atlant ic provinces) is examined using monthly precipitation values available for 410 sites for the period 1964-1993. Important contrasts are illustrated bet ween eastern (Mediterranean) and southern (Atlantic) areas. In the east, se asonality is more subdued due to incursions of fronts from the north at all times of the year. In the far south, the months of July and August are alm ost completely dry, but the period October-February is wet due to incursion s of active Atlantic frontal systems. In central areas (Almeria, Murcia, Al acant, Valencia and the Illes Balears) the significance of extensive severe thunderstorm development during September and October produces an autumn p eak in precipitation amount. The spatial variation of precipitation seasona lity is further examined using the seasonality index derived by Walsh and L awler (Walsh PD, Lawler DM. 1981. Rainfall seasonality: description, spatia l patterns and change through time. Weather 36: 201-208). Trends of this in dex through the 30-year period are identified for some areas using linear r egression on 5-year running means of the index, and indicate that seasonali ty is increasing in the south (Andalucia), around the uplands of Catalunya (near Lleida) in the east, and in a few smaller areas in between. In the so uth, the increase in seasonality is due to a greater concentration of preci pitation during the cooler part of the year, so that the period January-Mar ch is becoming drier, but October-December, wetter. The overall cool season precipitation remains much as for the present, though some evidence for dr ying is indicated for Malaga, Jaen and Granada. Precipitation in the normal ly dry month of July is also increasing. In upland Catalunya, there are ind ications of a greater concentration of cool season precipitation, with, not ably, higher amounts in October and some evidence of warm season drying, no tably in June. Copyright (C) 2001 Royal Meteorological Society.