Climate Variability for a 150‐Year (1862–2011) Meteo‐Hydrological Series in the Italian Alps at Different Time Scales

ABSTRACT

This paper reports the analysis of climate variability, including water balance components, over one and a half centuries of meteorological observations (1862–2011) for the Adige River basin in the Italian Alps. A water balance model was applied to a dense grid in the basin and the data were aggregated as a single series, representative of the whole 9763 km ² ‐wide basin. Monthly series of precipitation, temperature, evapotranspiration and water deficit were analysed to assess time trends, climate variability, cyclicity and coherence spectra with possible forcings: astronomical cycles (sunspots), atmospheric circulation (North Atlantic Oscillation) and sea surface temperature (Atlantic Multidecadal Oscillation). Temperature increase was confirmed to be stronger in the more recent period (over 2°C in the last 50 years), but varied between seasons, whereas precipitation only displayed some seasonal patterns that did not change significantly in the observation period. The annual and monthly climate variability showed signals not always directly attributable to a climate change forcing; in particular, precipitation regimes showed a prevailing trend of decreasing interannual variability and persistence, whereas temperature showed predominantly opposite trends in the long term. Evapotranspiration and water deficit long‐term trends are consistent with those of temperature, significantly increasing in the last decades (0.33 and 0.36 mm year ⁻¹ , respectively). Statistical links with astronomic, atmospheric and sea‐temperature forcings suggest a weak influence of these drivers on the climate of the region. This study fills a gap of knowledge of long‐term climatology in an important region of the Alps, and highlights its features in terms of quantifying the effects, either ascertained or not, of atmospheric and solar teleconnections on its hydro‐climatological regimes at the catchment scale, also with respect to the climate‐change signal.