Spatial and temporal variability of rain-spells characteristics in Serbia and Montenegro

Rain spells are a key parameter in examining rainfall regime. A rain spell is defined as a series of consecutive days above a certain daily rainfall threshold (DRT). For each rain spell, its duration (RSD), yield (RSY) and average intensity (RSI), as well as their total number (NRS) in each year, were calculated. The present study analyses daily rainfall series from 22 stations representing the different regions of Serbia and Montenegro in the period 1949-2007. This study highlights the temporal variability (both inter- and intra-annual) and the complexity of the rainfall regime in both countries. In each station, all years were divided into three categories: wet, normal and dry according to their standard scores. Then, on the basis of these scores, the entire year was categorized accordingly. The various rain-spell parameters were calculated and are presented for each of these three categories. The relationships between NRS (exponential), RSY (linear) and RSI (power) with the RSD were calculated for each station and their coefficients were plotted. The entire study area was divided into three sub-regions in terms of similar annual behaviour, using the factor analysis. The regions are as follows: northern and central Serbia, eastern and southern Serbia and Montenegro. All years were grouped into several clusters, each representing a different spatial distribution. Their characteristics and probabilities are presented. Overall, Montenegro is much rainier than Serbia, having longer and more intense rain spells. Serbia, on the other hand, has more short rain spells than Montenegro and demonstrates no real summer dryness such as in Montenegro. Intra-annual variability is relatively high in both countries, slightly higher in Montenegro.