European degree-day climatologies and trends for the period 1951-2011

The global increase of temperature, together with more frequent severe winters and summer heat waves may lead to a change in energy consumption and agricultural production. Cooling, heating, and growing degree-days (CDD, HDD, and GDD), respectively, are used to quantify the energy needed to condition or heat buildings, and to study the growing season. Using a new dataset made of 4023 daily T-N-T-M-T-X series for the period 2001-2011 and 3897 monthly T-M homogenized series for the period 1951-2011, we computed CDD, HDD, GDD, and Winkler Index (WI) for Europe. We developed a model that correlates degree-days calculated with daily T-N-T-M-T-X data with degree-days obtained by monthly T-M data, in the overlapping period 2001-2011. A set of parameters for each station was then applied to the corresponding 1951-2011 monthly records. We interpolated the parameters and the reconstructed degree-day series onto a European 0.25 degrees x 0.25 degrees grid: with these gridded parameters, one can estimate the degree-days for any European location if only monthly T-M is available. We present maps of HDD, CDD, GDD, and WI for the period 1951-2010. To validate them, we run a comparison in the Carpathian area using an independent dataset (from the CARPATCLIM project). The regional records show high correlations, especially for HDD (r > 0.99) and WI (r > 0.98). Subsequently, we performed a linear trend analysis on European and regional basis. HDD showed a significant decrease almost everywhere in Europe, whereas CDD, GDD, and WI showed a significant increase in particular in the last 30 years in the Mediterranean region. Moreover, WI indicated that new areas in France and central Europe became suitable for grape cultivation in the last decades.