SUMMER MOISTURE VARIABILITY ACROSS EUROPE, 1892-1991 - AN ANALYSIS BASED ON THE PALMER DROUGHT SEVERITY INDEX

Monthly Palmer Drought Severity Indices (PDSI) have been calculated fo r the period 1892-1991 over a 5-degrees latitude by 5-degrees longitud e grid covering Europe and south-west Asia from 35-degrees-N to 70-deg rees-N and 10-degrees-W to 60-degrees-E. These indices are used to des cribe the spatial and temporal details of relative moisture variabilit y during summer (June-August). The full series of mean summer PDSI map s are presented. Over Europe asa whole, there has been a consistent (b ut statistically insignificant) increase in moisture supply throughout the period of record. The 1930s and 40s were exceptionally dry. The s ummer of 1947 was the driest, both in terms of average PDSI but also i n terms of the spatial extent of moderate drought. However, the summer of 1921 was by far the most extreme when considering the spatial exte nt of severe drought conditions. Widespread drought conditions also pr evailed over many regions of Europe during the 1890s. The wettest summ ers occurred in 1987 and 1916. The total area of Europe experiencing e ither severe dry or severe wet conditions has increased noteably durin g recent years. Nine regions of coherent summer moisture variability a re objectively defined by orthogonal rotation of the principal compone nts of the summer PDSI. The nine rotated components, which explain 60 per cent of total variability of this data wt, represent moisture vari ability in north-western Europe (NWEUR), the north-west Mediterranean (NWMED), the lower Volga (LVOLG), central European Russia (CERUS), the north-east Mediterranean (NEMED), the southern Caspian Sea (SCASP), t he Pechora Basin (PECHB), the Danube Basin (DANUB), and northern Fenno scandia (NFENN). The last 3 years have been very dry in NWEUR and NWME D. The most recent summer in our analysis, 1991, was the wettest on re cord in both CERUS and NEMED. Preliminary spectral analyses provide li ttle evidence for a solar-moisture relationship in these European data over this period.