Future estimations of precipitation in the Balkan Peninsula with the use of a Regional Climate Model

During the last decades there were a lot of discussions regarding climate changes. Many climatological studies have focused on precipitation and drought due to their important role for many human activities. South Europe and especially the Balkan Peninsula is a prominent and vulnerable area, mainly due to its complex topography. This study aims to estimate the changes in the precipitation regime at the Balkan Peninsula through the end of the 21^st century using a Regional Climate Model (RCM).
   The daily precipitation data used are derived from an updated Regional Climate Model, the RACMO2, developed by the Royal Netherlands Meteorological Institute (KNMI) with the GCM ECHAM5 as a «parent» model. For the future climate projections the SRES A1B scenario is used. The spatial resolution of the model is 25x25 km and the data cover the whole European area. Of the 14136 grid points of the domain, those corresponding to the Balkan Peninsula have been chosen and their precipitation daily time series were analyzed. Also, three extreme indices were calculated and their trends were analysed over the entire time period (1960-2100). The selected indices were: the heavy rainfall threshold (the 95^th percentile of rainday amounts (mm/day), the greatest 5-day rainfall (greatest 5-day total rainfall (mm)), and the longest dry days (maximum number of consecutive dry days (days). It is to be noted that the first index is based on thresholds defined using percentile values rather than fixed values. This makes the pq95 index transferable in different regions with different climatic regimes. The greatest 5-day rainfall amount is an important measure of extreme from the point of view of flooding in a region.
   The first results of the study showed that heavy rainfall conditions will become more intense in the future mainly in the western part of the Balkan Peninsula. On the other had, the model “predicted” a general shift to drier conditions. In the case of the summer period a persisting absence of rainfall is expected in the future, since the length of dry spells approaches 90 days. Finally, extreme precipitation tends to decrease during the warm part of the year by the end of the 21^st century, while intense precipitation episodes should be more often expected in autumn.
   In the last part of the study, the relationship between extreme indices of precipitation and the atmospheric circulation was analysed. More specifically, the North Sea-Caspian teleconnection index is identified as an upper level (500hPa) atmospheric teleconnection between grid points 0^o to 55^oN; 10^oE to 55^oN (North Sea) and 50^oE to 45^oN; 60^oE to 45^oN (northern Caspian). During the negative phase of the NCP index there is an increased southwesterly anomaly circulation towards the study area, while during its positive phase there is an increased northeasterly circulation towards the Balkans. After calculating the daily calendar of the index, until the end of the 21^st century, the statistical relationship between the teleconnection index and the extreme rainfall was estimated for both the present time and future period.