Significant rainfall decreases and variations of the atmospheric circulation in the Mediterranean (1950-2000)

• Published in: Regional environmental change 2014-10, Vol.14 (5), p.1724-1741
• Main Authors: Douguédroit, Annick, Norrant-Romand, Caroline
• Format: Article
• Language: English
• Subjects: Environmental Sciences
• ISSN: 1436-3798; 1436-378X

This paper aims to identify the link between significant rainfall decreases detected between 1950 and 2000 in the Mediterranean Basin and the 500hPa height atmospheric circulation. The subregions and timeframes over the 50-year period covered are Mediterranean Iberia (October), Atlantic Iberia (March), Greece (January, winter) and the Near East (winter). Monthly and daily data records from 62 rainfall stations and 138 grid points at the 500hPa height over a Euro-Atlantic window were used in Canonical Correlation Analyses to determine the Teleconnection Patterns explaining regional rainfall. Only six among them best explain significant rainfall decreases in the four subregions. The minimum and maximum rainy Weather Types at the 500hPa height (ZWTs) associated with each pattern in each subregion were studied. Disturbances from Atlantic reach directly Iberia when they are regenerated, or generated locally in Greece and the Near-East. Significant rainfall decreases and the corresponding 500hPa pressure increases appear to be non-linear phenomena. In all the studied subregions a break during the 1970s separates two half-series differing significantly from each other. The rainfall decrease is due to the higher frequency of maxima rainfall ZWTs over minima rainfall ZWTs during the first period and respectively the contrary during the second period. Such inversion could be partially linked with the prevailing NAO+ phase during the last quarter of the century.