A sub-regional approach for the analysis of atmospheric teleconnection influence on precipitation in Calabria (southern Italy)

Due to the importance of precipitation as a climatic and meteorological variable, it is paramount to detect the relationships between teleconnections and precipitation at different temporal and spatial scale. In fact, large-scale systems can i) influence precipitation directly, ii) establish a favourable environment to deep moist convection, and thus extreme precipitation, but also iii) help triggering dry conditions and drought.

In this study, developed within the INDECIS EU project, the teleconnection influence on precipitation in the Calabria region has been evaluated over the 1981-2010 time period, by means of a database of 79 rain gauge stations and seven teleconnections indices. Calabria, the southernmost region of peninsular Italy, was chosen as a valuable test bed mainly because it is located in the centre of the Mediterranean region, which constitutes a hot spot for climate change. Moreover, Calabria has a high-density, long-time network of precipitation gauges, recently validated and homogenized.

Statistical relationships between teleconnection indices and precipitation are often developed through well-known correlation analyses techniques, e.g. Pearson, Spearman and Kendall, where a teleconnection index is compared to cumulated precipitation values. In this study, three types of correlation analysis were performed: i) seasonal indices vs seasonal cumulated precipitation; ii) three-month indices vs monthly cumulated precipitation; iii) monthly indices vs monthly cumulated precipitation. These analyses have been performed in five Rainfall Zones (RZs) of the study area, characterised by different climatic conditions: the North-Eastern Zone (I1), the Central-Eastern Zone (I2) and the South-Eastern Zone (I3) on the Ionian side of Calabria and the North-Western Zone (T1) and the South-Western Zone (T2) on the Tyrrhenian part.

Results showed that the Mediterranean Oscillation and the North Atlantic Oscillation are the most important large-scale contributors to the precipitation regime of Calabria. Moreover, seasonal Eastern Atlantic pattern influenced seasonal precipitation in the RZs I1 and T1; three-monthly East Atlantic/Western Russian pattern influenced monthly precipitation in the RZs I2 and T1; three-monthly Western Mediterranean Oscillation influenced monthly precipitation in the RZs I3 and T1; while three-monthly El Nino-Southern Oscillation influenced monthly precipitation in the RZ T2.

Investigating changes in the response of local precipitation and teleconnections throughout the 1951-2010 and 1951-1980 time periods, a change in precipitation response to teleconnection patterns emerged, i.e., in the impact that the Mediterranean Oscillation has on the East coast precipitation (RZs I1-I3), a possible result of natural variation or climate change. In addition, these results have been compared to those obtained with the classical correlation analyses between teleconnection indices and single-station precipitation.

The approach developed for this study is a general method that, in principle, can be reproduced for any variable for any region and for every teleconnection.

Acknowledgments:

The Project INDECIS is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462).