Spatial and temporal variability of aridity indices in the region of Southern and Eastern Serbia

The study analyzed spatial and temporal patterns and trends of aridity indices in southern and eastern Serbia from 1971 to 2022. Temperature and precipitation data from eight meteorological stations were used to quantify five aridity indices: the de Martonne Aridity Index, Lang Rain Factor, Pinna Combinative Index, Lobova Aridity Index, and Selyaninov hydrothermal coefficient. Calculations for the de Martonne Aridity Index were performed on annual, seasonal, and monthly scales, while the Lang Rain Factor was calculated on an annual scale and during the vegetation period (April to October). Selyaninov hydrothermal coefficient is calculated on the monthly scale and for the vegetation period, with the other indices calculated annually. The results reveal notable regional differences in the de Martonne Aridity Index, distinguishing between two, three, and five climate types on an annual, seasonal, and monthly basis, respectively. The Lang Rain Factor characterizes semiarid and temperate warm climates at an annual scale, while at a monthly level (the Gračanin Rain Factor), an arid and semiarid climate predominates. The Pinna Combinative Index indicates humid conditions, whereas the Lobova Aridity Index reflects arid conditions across the study area. Selyanin’s hydrothermal coefficient shows its lowest values ​​in August at all meteorological stations. During the vegetation period, this index indicates slightly dry climate conditions at two stations (Negotin and Niš) and slightly humid and moderately humid conditions at other stations. During the vegetation period, this index indicates slightly dry conditions at two stations (Negotin and Niš) and slightly to moderately humid conditions at other locations. The Pearson correlation coefficient reveals a statistically significant positive correlation between the indices, with particularly strong correlations between the de Martonne Aridity Index and both the Lobova Aridity Index and Lang Rain Factor. The inverse distance weighted (IDW) interpolation method was applied to visualize the results of the aridity indices across the study area. The Mann-Kendall test showed that aridity trends at all meteorological stations were not statistically significant.