Sensitivity of Modeled Precipitation to Sea Surface Temperature in Regions with Complex Topography and Coastlines: A Case Study for the Mediterranean

An analysis of the effects of SST representation on precipitation in long-term continuous simulations was carried out for the Mediterranean peninsula of Calabria, Italy, which is characterized by complex coastlines and orography. A parameterization analysis was performed to find an optimal model configuration, using a method where SST fields are directly ingested from NCEP datasets into the Weather Research and Forecasting (WRF) Model lower boundary condition files. The results of the optimal configuration were used for a comparison with recorded precipitation patterns for a very wet period (from November 2008 to January 2009), adopting several interpolation options available in the WRF Preprocessing System. An additional comparison was made against a uniform variation of the original SST fields by epsilon = +/- 0.5 K. It was found that the interpolation options mainly affect near-coastline SSTs, where methods requiring fewer source data points have several advantages. Effects of SST representation on precipitation, accumulated over the whole 3-month period, are generally lower than +/- 2%, but a specific class of events (synoptic situations) with strong differences in precipitation patterns was identified. These events are connected to pressure systems moving from the African coast to the north and approaching the Sicilian and Calabrian coastlines. Two of these events, which occurred on 27-29 December 2008 and 9 January 2009, were analyzed in detail, highlighting that small variations of SST values induce slight shifts in the paths of the weather fronts. These slight shifts are important enough to determine whether or not wet air masses can reach the mountain ranges close to the coast, where rainfall intensity is enhanced by orographic effects.