The role of teleconnection patterns in the increased drought frequency in Mediterranean climate: Some hints from central Italy

Central Italy presents numerous factors potentially affecting the precipitation regime: 1) it includes both Tyrrhenian and Adriatic sides, the first exposed to Atlantic perturbation and generally more rainy, the second one possibly exposed also to Balkan streams; 2) due to the short distance between the two coasts (few tens of kilometres), also the more internal areas are prone to the influence of the sea; 3) at the same time, the highest reliefs of the Apennine chain are located in the region; 4) the Northern areas of the Adriatic side experience the influence of the continental climate, due to the Po Valley. The climate framework Central Italy sees in the last thirty years a tendency toward drier conditions and an increasing of drought events, mostly in frequency. To explore the variability in time and space of the precipitation regime in relation to the atmospheric patterns, land rainfall data collected and homogenised trough geostatistical approach over the period 1951-2019 in Central Italy have been analysed in relation to the following indexes: Winter NAO index, East Atlantic-West Russia index, Pacific/North America index, Polar/Eurasia index, Scandinavian index, Artic oscillation index, Western Mediterranean oscillation index. Focus of the analysis (1951-2019) is put on possible common signal between precipitation regime anomalies (on both Tyrrhenian and Adriatic side) and teleconnection patterns, sought through regression analysis and a wavelet and cross-wavelet decomposition. Results indicate that possible influence of some teleconnection patterns (particularly East Atlantic, East Atlantic/Western Russia and NAO) on the precipitation regime is limited to winter and early spring for the Tyrrhenian side, and to summer for the Adriatic side. Moreover, the analysis of the mean wavelet time series-period indicates an increasing in frequency of drought episodes for the last 20 years on both sides of the study area.