Changes in Central-European soil-moisture availability and circulation patterns in 1881-2005

摘要

Relationships between the soil moisture availability atmospheric and the atmospheric circulation in Central Europe were analyzed for the period 1881-2005. The analysis was based on the Hess-Brezowsky catalogue of circulation types and series of weekly self-calibrated Palmer Z-index (scZ-index) and Palmer Drought Severity index (scPDSI) at seven stations where high-quality daily data had recently become available. The results show that the large scale droughts during spring months (MAM) were associated with east (E), south (S), and south-east (SE) Grosswettertypen (GWT), whereas during summer (JJA) and the whole growing season, i.e., April-September (VEG), the Central Europe high pressure systems (HM) and east (E) GWT were conducive to drought. Statistically significant drying trends were noted at a majority of the stations, especially during MAM and JJA over the whole period for which the scPDSI and scZ-index series were available (1875-2005). Although almost no statistically significant tendencies were found prior to 1940, after this year a significant tendency towards more intense drought was present at all sites. The largest drying trend was noted during the VEG and AMJ seasons. The overall drying trend might be associated with shifts in the GWT frequency, especially during AMJ. Although the aggregate frequency Of Occurrence of drought conducive GWT (i.e. E, S and HM) remained stable at approximately 30% up to the 1940s, afterwards a steady increase to the present 55% is observed. Higher frequencies of S and HM types drove the observed increase of drought conducive GWT at the expense of N types that are associated with wet conditions. The long-term shifts in the frequency of circulation types conducive to drought explain more than 50% of the long-term variations of both scZ-index and PDSI values over the territory of the Czech Republic, and they are likely to affect neighboring regions as well.