Exploratory statistical analysis of heating and cooling degree days in Bulgaria

Climatic conditions are critical in shaping the necessity for cooling and heating to maintain comfort within residential and commercial buildings. Degree day indexes, with their modifications for cooling and heating, serve as an essential measure of the external temperature conditions. This study aims to identify patterns in the time series dynamics of cooling and heating degree days in Bulgaria based on exploratory statistical analysis. We review the most commonly referenced methods for calculating cooling and heating degree days indexes in the literature, with a focus on the approach applied across European Union countries. Eurostat database, as an official data source, forms the basis of our analysis. We conduct visual inspections and autocorrelation analyses to explore the dynamics of these indices. Furthermore, we apply the Mann-Kendall test and its modifications to identify the presence of trends. We conclude that there is an upward trend for the cooling degree days and a downward trend for the heating degree days.