A very high spatial resolution database for heating and cooling degree-days in Catalonia (1971-2100): observations and climate projections.

Future climate projections for the Mediterranean area point out to an important increase in temperature during this century, independently on the considered emission scenario. This projected increase will have a significant impact on temperature-related climate indices, such as heating and cooling degree-days, and also, the economic costs to maintain climate comfort within buildings, especially for summer. These indices are key outside temperature-based indices to evaluate the energy consumption of buildings. 

In this work, a very high spatial resolution database for heating (HDD) and cooling degree-days (CDD) has been performed from different temperature data: The network of automatic weather station from the Meteorological Service of Catalonia from 2006 to 2015 (138 stations in 32,000 km2), and non-automatic weather station data from 1971 to 2015. It has been taking as a baseline 15 and 18 °C for HDD, and 21 and 25 °C as thresholds for CDD. 

Data from automatic weather stations allow us to compute these indices with a high temporal accuracy (hourly or sub-hourly time scales), but they are only available with a highly-dense network for the last few 15 years. Otherwise, data from non-automatic weather stations allows us to analyse a wider temporal coverage, but only with daily-mean temperature data. Thus, in areas with a complex topography, as it is the case of Catalonia, important differences at annual scale can appear when computing HDD and CDD from daily or hourly-mean values, especially for zones prone to thermal inversion situations. Hourly data leads to increase HDD and CDD for each considered threshold. The differences among them reach annual-mean values higher than 200 ºC-days for heating degree-days and 150 ºC-days for cooling degree-days. 

Taking into account statistically downscaled climate projections at 1-km spatial resolution from 3 IPCC-AR5 global climate simulations forced by RCP4.5 and RCP8.5 emission scenarios, it is expected a significant decrease in HDD for the Pyrenees, up to 2000-2400 ºC-days in 2100, for 15 and 18 ºC thresholds, respectively. Meanwhile, it is projected an important increase in CDD for the Ebro Valley, up to 400-600 ºC-days in 2100, for 25 and 21 ºC thresholds, respectively.