Predisposition of drought occurrence in selected arid areas of the Czech Republic

Abstract

Predisposition of drought occurrence is based on combined evaluation of
above-normal temperatures and below-normal precipitation. According to the weight
of the individual categories of extremity, the five degrees of predisposition to drought
were determined (degree 1 is the lowest risk, degree 5 is the highest risk). Evaluation
of temperature extremity is based on the determination of abnormality in comparison
with average value and standard deviation. Individual categories of extremity of precipitation
are determined by comparing the individual monthly data with percentile values.
Monthly data of homogenized technical series of the Czech Hydrometeorological Institute
were evaluated for the years 1961–2010 in two climatologically dry areas (Břeclav and
Kladno county in the Czech Republic). Fourty-two months were rated risky in Břeclav
county and fourty-four in Kladno county. The evaluation shows an increase of predisposition
to drought, especially after 1990. The highest incidence of degree 5 was recorded
in 2001 to 2010 in vegetation season. Subsequently the drought variability as a mean
variance of years/season and drought severity as a sum of degree of predisposition to
drought of years/season were assessed. A gradual increase of variability and severity from
1961–1970 to 2001–2010 is visible. The lowest values of variability (maximum 2) and
severity (maximum 3) in both counties were recorded in winter.