Precipitation seasonality in eastern and southern coastal Spain

The nature of the seasonality of precipitation in eastern and southern coastal Spain (including both the Mediterranean and the far southwestern Atlantic provinces) is examined using monthly precipitation values available for 410 sites for the period 1964–1993. Important contrasts are illustrated between eastern (Mediterranean) and southern (Atlantic) areas. In the east, seasonality 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 almost completely dry, but the period October–February is wet due to incursions of active Atlantic frontal systems. In central areas (Almeria, Murcia, Alacant, Valencia and the Illes Balears) the significance of extensive severe thunderstorm development during September and October produces an autumn peak in precipitation amount. The spatial variation of precipitation seasonality is further examined using the seasonality index derived by Walsh and Lawler (Walsh PD, Lawler DM. 1981. Rainfall seasonality: description, spatial patterns and change through time. Weather36: 201–208). Trends of this index through the 30-year period are identified for some areas using linear regression on 5-year running means of the index, and indicate that seasonality 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 south, the increase in seasonality is due to a greater concentration of precipitation during the cooler part of the year, so that the period January–March is becoming drier, but October–December, wetter. The overall cool season precipitation remains much as for the present, though some evidence for drying is indicated for Malaga, Jaen and Granada. Precipitation in the normally dry month of July is also increasing. In upland Catalunya, there are indications of a greater concentration of cool season precipitation, with, notably, higher amounts in October and some evidence of warm season drying, notably in June. Copyright © 2001 Royal Meteorological Society