Evolution of heating and cooling degree-days in Spain: Trends and interannual variability

Heating and cooling degree-days estimate the influence of meteorological variability on the domestic energy demand. Heating and cooling degree-day indices are obtained from daily mean temperatures that are weighted by the ratio of the local population that is experiencing such weather, to the total population of the region under study. In this paper we investigate the evolution of heating and cooling degree-days in the case of Spain, under present (1958–2005) and future atmospheric composition. The observed variability is obtained from temperature records at 31 stations through Spain and from the available census data. The evolution presents a trend and an interannual variability that are both found statistically significant. The North Atlantic Oscillation influences winter heating and autumn cooling needs. The influence of the Southern Oscillation is detectable only in the spring cooling degree-days. The observed winter and summer degree-day indices are used to validate the corresponding variability in Spain found in four simulations of the Mediterranean Region performed with high resolution Coupled Regional Climate Models, in the historical period, from 1950 to 2000. The future evolution of degree-days is estimated with four simulations performed with the same models under scenario A1B conditions, for the period 2001–2050. Both, trends found in the simulated and in the observed winter heating degree-days present a similar lack of significance. However, the observed and simulated trends in the case of the summer cooling degree-days are statistically significant. In the historical period, these trends are similar to the observed ones, roughly 5%/decade. Under the scenario conditions the cooling degree-days are increased by 50% with respect to their values in the historical period.

► Weather-conditioned energy demand for indoor cooling in Spain has increased lately.
► The North Atlantic and the Southern Oscillations also influence the degree-days.
► Projections for the middle of this century show an increase of summer degree-days by 50%.