Mapping oxygen stable isotopes of precipitation in Italy

Study region: Italy. Study focus: The oxygen isotope composition from 266 pluviometers was used to study thespatial variability of delta-18O and its relationship with Italian orography. The local meteoricwater lines (LMWLs) of northern, southern and central Italy and Sicily are reformulatedand a new definition of isotopic variations with elevation is provided. New hydrological insights for the region: Altitude and, to a lesser extent, latitude are themain geographical factors affecting the isotopic signature of precipitation in Italy. A high-resolution map of the spatial distribution of18O content in precipitation was created usingthe identified relationship between delta-18O/Latitude-Altitude and the spatial distribution ofthe residuals. The general features of the delta-18O distribution map may be summarised asfollows: delta-18O distribution over the Alps clearly depends on latitude and altitude, whereasover the Apennines, which run down the whole peninsula from north-west to south-east,it is more affected by altitude, the contour lines roughly following the axis of the chain. Theisotope compositions on the western side of the peninsula are generally higher than thoseof the east at the same elevation and latitude; they are more or less uniform in the northernplain of Italy.