Seasonal precipitation trends in the Mediterranean Iberian Peninsula in second half of 20th century

Abstract This is a study of the changes in annual and seasonal precipitation amounts and variability, during the period 1951–2000, using MOPREDA MES . This dataset includes 1113 complete and homogeneous monthly precipitation time series from the Mediterranean Iberian Peninsula (IP), and corresponds to the five official Spanish hydrological divisions which drain into the Mediterranean Sea. The time series of annual and seasonal precipitation were used to test for trends. The absolute value of the anomaly time series was also tested for trends to identify changes in interannual variability of precipitation. The significance of these changes was assessed using the non‐parametric Spearman rank test. The intensities of observed changes, both on mean values and variability, were estimated by using linear regression techniques. Finally, we analysed the area affected by different trends by using raster maps and spatial statistics, in addition to calculating the global balances for the five hydrological divisions. We detected high variability in precipitation regimes and conditions in the study area; nevertheless, a decrease in seasonal and annual precipitation has predominated in the east of the IP during the second half of the 20th century. On an annual scale, precipitation has diminished over 90.1% of the study area. Additionally, a high percentage of the territory was affected by diminishing precipitation at a seasonal level: 85% (of territory) in summer, 82% in spring, 64% during winter and 61% in autumn. Taking the study area as a whole, seasonal precipitation decreases are ranked as follows: summer (−22.5%), spring (−19.3%), winter (−7.3%), and autumn (−5.2%), with a decrease in the value of the global mean annual precipitation − 12.4%. We also detected an increase of precipitation variability in winter (+23.5%) and summer (+11.4%), and a decrease in autumn and spring (−14.9 and − 16.8%, respectively) with a global mean value of + 7.8%. Copyright © 2008 Royal Meteorological Society