HISTORICAL AND RECENT FLOODS IN THE CZECH REPUBLIC: CAUSES, SEASONALITY, TRENDS, IMPACTS

摘要

The fluctuation of the climate and changes in the anthropogenic activity in the cultural landscape influenced the variability of floods in the Czech Lands during the past millennium. The existing chronology of floods compiled from documentary data and from systematic hydrological measurements presents a picture about long-term fluctuations from the view of the frequency of occurrence, seasonality, synoptic causes, intensity and impacts. The main points from the documented research can be summarised into the following points: a) In the period of systematic water-gauge observations (i.e. since about the mid-19th century) the total number of floods in the Czech Republic has been dropping, as has the extremity expressed by the N-annual culmination discharge rates. This drop can be ascribed to less frequent occurrence of floods of the winter synoptic type due to global warming, when, as a consequence of a later onset of winters and a lower accumulation of snow cover, the total number of floods from February to April is decreased. b) Documentary data about floods in the Czech Lands enhances understanding about flooding to centuries prior to the onset of systematic water-gauge observations. This knowledge can be useful in the study of the frequency of floods, their seasonality, synoptic typology and impacts. As a result, it is possible to document with relative reliability the occurrence of disastrous floods in the Czech Republic for the last eight or nine centuries. Analysis shows that with respect to the occurrence of destructive floods, the 20th century can be seen somewhat positively (with the exception of the July 1997 flood in the eastern part of the Czech Republic). c) The most disastrous, well documented floods affected the Czech Lands in September 1118, March 1272, February 1342, July 1432, August 1501, March and August 1598, February 1655, June 1675, February 1784, March 1845, February 1862, May 1872, September 1890, July 1897, July 1903, July 1997 and August 2002. From the May 1872 flood up to the present, that is to say during the period of global warming, floods have been only of the summer synoptic type (i.e. rain floods). The disastrous floods of the winter synoptic type of February 1784, March 1845 and February 1862 fall into the latter part of the so-called Little Ice Age, whose onset was in the early 14th century. d) Available data do not yet permit one to render an opinion as to what extent the disastrous floods of 1997, 1998 and 2002, which came after a relatively very quiet period, are a possible consequence of anthropogenic conditioned process of global warming and whether similar disasters will be repeated in the coming years with greater intensity and frequency.