Accounting for elevation and distance to the nearest coastline in geostatistical mapping of average annual precipitation

Spatial distribution of precipitation in mountainous areas suggests strong control of surface orography on precipitation processes. Generally, quantifying orographic control of precipitation and identifying homogeneous areas are difficult because of the complex combination of factors, which could influence the precipitation process. The objective of this study was to account for morphometric attributes (elevations and distances to the nearest coastline) in geostatistical mapping of average annual precipitation in southern Italy. The study area was the Calabria Region, which has a spatially variable Mediterranean climate because of its high orographic variability. In this study, annual precipitation data collected by the former Italian Hydrographic Service for the 1916–2006 period were used. Elevations and distances to the nearest coastline were derived from a digital elevation model with 250 m × 250 m cell size in a geographic information system environment and used to delineate areas with homogeneous morphological features [landscape units (LU)]. The effectiveness of LU was assessed estimating the expected value of the average annual precipitation with polygon kriging and comparing their differences with the Mann–Whitney–Wilcoxon test. The average annual precipitation map showed that mountains areas receive more precipitation than low elevation areas and, in the Tyrrhenian side, it was also evident the orographic influence of Coastal chain on precipitation with high precipitation values. Results can help in understanding the differences among LU and the influence of surface orography on spatial patterns of annual precipitation in mountainous regions.