Climatological Analysis of the Synoptic Situations Causing Torrential Precipitation Events in Bulgaria over the Period 1961–2007

Abstract

Variations in heavy and extreme precipitation are interesting to study as these events cause considerable damage and loss of life worldwide each year. The upward tendency of damages caused by natural disasters supports the idea that extreme events associated with the effects of climate change, such as torrential precipitation, are occurring with greater frequency. The same tendency is being observed in Bulgaria over the last decade of the twentieth century. Namely, there have been negative trends in annual and seasonal precipitation totals, but an increase in the contribution of heavy rainfall events to total precipitation. This pattern has also been observed for other Mediterranean countries.

In this chapter, a comparative analysis of some very extreme precipitation events is carried out using all available data for torrential precipitation (considered to be rain events totaling ≥ 100 mm/24 h at one station) from the meteorological network of the National Institute of Meteorology and Hydrology (NIMH) for the period 1961–2007. An increase of about 30% in the mean annual number of days with torrential precipitation is found for the period 1991–2007 versus the period 1961–1990. NIMH’s historical archive of synoptic maps and NCEP/NCAR reanalysis data files are used for analysis and classification of synoptic situations causing torrential precipitation over the country. Respective fields of air pressure and wind velocity are also considered.