To validate the WRF model upon updating the land-use categories for the Maltese Islands

Abstract

The WRF model is a numerical weather prediction model which uses real observed data to formulate a forecast for future weather. An input for the model are the land-use categories and these are defined according to the latest United States Geological Survey. These are important because they act as a definition to the surface of the model with which the atmosphere interacts. This interaction leads to various and distinct atmospheric systems which are encountered in our daily weather. The Maltese Islands, within the WRF model, at standard highest resolution of 30 second (1 km x 1 km), the terrain is listed mainly as shrubs and pasture land with no urban areas. In this project, these categories were updated to a higher 3 second (100 m x 100 m) resolution using Coordination of Information on the Environment data collected by the European Environment Agency. The update of the land-use is important because real data is used to define correctly the islands' surfaces. Different surface parameter values are attributed for every land-use category, and this will affect the simulation accordingly. The purpose of this project is to re-define and update these land-use categories for the above-mentioned resolution. The interactions of wind and temperature should be mostly affected; the expected values for wind speed and temperature are to decrease and increase respectively. These effects are mostly pronounced in the urban mappings of the model. The wind decreases because the surface roughness, a parameter affected by the change, is increased; this is a resistance and inhibits the formation of wind flow. The temperature increases because the change varies the surface albedo to a much lower value. The wind speed, when compared to the simulation results which excludes the update, resulted in an overall partial decrease following the expected observed data. The temperature also managed to follow the expectation and to increase in its minimal values when compared. Taking into account that the islands are very small when compared to the surrounding waters, only minor changes were recorded.