1. A. Pankratz, Forecasting with Dynamic Regression Models (John Wiley & Sons, New York, 1991).
2. A. Pankratz, Forecasting with Univariate Box-Jenkins Models: Concepts and Cases (John Wiley & Sons, New York, 1983).
3. S. Pavlova and L. Nenova, “Peculiarities in climate variations during last 30ty years at the region of “Obraztsov chiflik” – Rousse,” Scientific Works, University of Ruse, issue 4, series 1.2 (2008), pp. 75–80. [in Bulgarian]
4. National report on the status and protection of the environment in Bulgaria in 2012, Executive Environment Agency, Ministry of Environment and Water, available at www.eea.government.bg.
5. Atmospheric characteristics statistic study of Ruse region, Bulgaria