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Recent large-scale European droughts do not reach the severity of past extreme droughts

European droughts in the early 21st century are generally considered to be exceptionally significant, with extensive impacts in various regions. Speaking about extremes in the context of drought implies events that are repeated at most once in decades. However, the period in which we determine the magnitude of recent drought events is limited by the availability of observed data and thus is relatively short. For the whole Europe, the estimates of significance of current droughts are in most cases based on hydroclimatic observations since 1950.

Therefore, a team of scientists from the Czech University of Life Sciences in Prague and the Helmholtz Centre for Environmental Research in Leipzig has dealt with the assessment of the extent and severity of individual drought events in Europe during the period 1766-2015, i.e., the last 250 years. Based on the reconstruction of precipitation and temperature for this period, a simulation of the hydrological balance was carried out and periods with lack of precipitation (meteorological drought), soil moisture (agricultural drought) and/or streamflow (hydrological drought) were identified. In general, the most severe were the dry periods of 1858-59, 1921-22 and 1953-54. The exceptional nature of these events lies above all in the spatial extent of areas where drought can be considered extreme. For instance, more than a half of continental Europe was under severe drought conditions in 1921 while it was approximately one fifth in 2003 and 2015.

The extreme events in 1858-59, 1921-22 and 1953-54 belong to the so-called "wet-to-dry season" droughts, i.e., periods in which the lack of precipitation begins to appear at the end of summer or autumn and persists in the next year, when it reveals itself as soil water and streamflow decreases. On the other hand, drought events in 2003 and 2015 are associated with rise in evapotranspiration and a lack of precipitation in the summer months; the so-called "vegetation period" droughts, which are sometimes called "flash droughts". Taking into account only this type of droughts, we can say that the 2003 and 2015 droughts were two of the most serious during the whole period considered.

This is a direct consequence of the increase in temperature observed since the 1990s. The reason that their intensity is quite lower than the corresponding droughts observed in 1858-59, 1921-22 and 1953-54, is the partial compensation for rainfall, snow and soil water deficit during the winter. However, in the absence of winter precipitation we can expect that the drought events can reach or overpass the past ones, due to the effect of the rising temperature. Since there is a big confidence in the climate model projected temperature increase, it is likely that the impacts of drought events will be larer compared to the past ones, at least for the less extreme droughts.

The paper was published in Scientific Reports (https://rdcu.be/1qvZ). The interactive viewer is available at www.fzp.czu.cz/apps/drought250.

Reference:
Hanel, M., Rakovec, O., Markonis, Y., Máca, P., Samaniego, L.,Kyselý, J., Kumar, R. (2018) Revisiting the recent European droughts in a long-term perspective. Scientific Reports, 8(9499).

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