Geostatistics is a branch of geomathematics that deals with the analysis of spatial data for the purpose of quantifying and modeling their spatial correlation. In geostatistics, and sometimes with certain adjustments in meteorology, computer programs such as Surfer, ArcGIS, etc. are used to analyze the spatial distribution of meteorological elements. The spatial distribution of meteorological elements can be displayed graphically by creating variograms and contour maps in the Surfer computer programme.. The main goal of this research is to study the variability of mean annual air temperatures in two 30-year-long periods: 1961 – 1990 and 1991 – 2020 in the territory of the Republic of Croatia. The data on mean daily air temperatures at 30 observed meteorological stations were taken from the Croatian Meteorological and Hydrological Service (CMHS). A variographic analysis of annual average air temperatures in the Republic of Croatia's coastal, lowland and mountainous regions was carried out in the Sufer computer programme. Contour maps were created to determine whether there was an increase or decrease in annual average air temperatures between the two mentioned periods. The results of the geostatistical model created in Surfer were compared with the Regional Climate Model (RegCM) results. Also, a hypothesis about the statistical significance of the trend for an average daily increase in an air temperature at the meteorological station in Ogulin in the period from 1961 to 2021 was tested.