The comparative study on the effects of NAO and GBO on the Hydroclimate in Southeastern Europe

The present investigation refers to the teleconnections of two climate indices with the observational data of the precipitation along the Danube River and of the Lower Danube Basin discharge.  Besides the well-known climate index associated with the North Atlantic Oscillation (NAO), a relatively new index was considered that reflects the baric contrast between the Balkan and the Greenland zones, the so-called the Greenland–Balkan Oscillation (GBO). This index was calculated as the difference of the normalized sea level pressure (SLP) at Nuuk and Novi Sad.

The influence of the GBO on the climate in southeastern Europe is stronger than that of the NAO. The comparative analysis was carried out for the entire 20th century, separately for each season.

The analysis of the effects of the two modes of variability was performed for precipitation, both punctually considering data from 15 meteorological stations along the Danube basin, as well as through the first principal component of precipitation (PC 1), and with regard to the discharge, the data were considered from the Orsova station located at the entrance of the Danube River in Romania.

For the precipitation in the middle and lower basin, as well as for the discharge of the Danube in the lower basin, the GBO signal is higher than that of the NAO. The intensity of this signal depends on the season. The highest difference between the GBO and NAO signals was evident in the winter season. The GBO is by construction almost complementary to the NAO, and considered together they can be good predictors for larger areas in Europe.