Abstract

In the paper, the aridity is defined on the basis of four climate indices: De Martonne's index of aridity, Lang’s Rain Factor and Gračanin’s Rain factor for the vegetation period and hydrothermal coefficient of Seljaninov. While the annual value of the drought index (IDM) shows humid characteristics, the monthly values show the variability of the conditions. The summer months (July and August) are classified as semi-arid months, while the winter months (December- February) are extremely humid. The spatial distribution of the isoarids indicates that the northern part of the basin has the characteristics of a semiarid climate, while the southeastern parts are more humid. The analysis of mean annual values of the drought index indicates in semiarid conditions (1990 and 2000), but also the humid conditions (2005 and 2009). A positive linear trend indicates that there is a tendency towards humid conditions. The significance test confirms the existence of a statistically significant trend. During the vegetation period, semi-arid conditions are present (July- August). April is slightly humid, and October is moderately arid. The Lang’s Rain Factor (KFg) characterizes basin climate as semiarid, while the Gračanin rain factor for the vegetation period (KFm) indicates a moisture deficit in the summer months. Hydrothermal coefficient Seljaninova (HTC) indicates a lack of moisture in July and August. Vegetation period is characterized as insufficiently humid. Irrigation is one of the most important measures for solving drought problems, since the yield varies from year to year.