Recent spatial and temporal variability and trends of sunshine duration over the Iberian Peninsula from a homogenized data set

This paper describes the construction of a new data set of sunshine duration over the Iberian Peninsula ( IP), based upon 72 monthly instrumental series covering the 1931 2004 period. Particular emphasis is placed upon the quality control, gap filling, and homogenization procedures. We also produced a gridded version (1 degrees x 1 degrees resolution, latitude, and longitude) of the homogenized data set covering the whole IP with 84 cells. We subsequently analyzed sunshine duration data in search of temporal variability, long-term trends, and spatial differences over the IP. The analyses were carried out on the mean series calculated for the whole IP and for four subregions, at annual, seasonal, and monthly resolution. We defined the subregions using a principal component analysis applied to the sunshine duration data. The temporal evolution of the mean annual series for the whole IP shows a decrease in sunshine duration from the 1950s to the early 1980s, followed by a positive trend up to the end of the 20th century, which matches the global dimming'' and the subsequent and recent brightening'' described for other regions in international scientific literature. The most interesting seasonal significant trend for the IP series was found for summer (-0.9% per decade, over the 1951-2004 period); this trend is influenced by the months of July and August in two subregions. In addition, important trends ranging from +2.8 to +3.8% per decade were observed for the March series for all Mediterranean climate subregions.