1. Bradford, R.B. (1999) Drought Events in Europe, Institute of Hydrology, UK, for Space Applications Institute, DG Joint Research Centre, European Commission, Ispra, Italy, 41 p.
2. Arnell, N.W. (1997) The Impact of Climate Change on Hydrological Regimes and Water Resources in Europe, Final Report to EC-DGXII.
3. Bidwell, V.J. (1973) A Methodology for Analysing Agricultural Drought, in E.F. Schulz, V.A. Koelzer, and Khalid Mahmood (eds.), Floods and Drought, Proceedings of 2nd International Symposium in Hydrology, Fort Collins, Colorado, USA.
4. Bonacci, O. (1993) Hydrological Definition of Drought, Hydrol. Processes 7: 249–262.
5. Byun, H.R. and Wilhite, D.A. (1999) Objective Quantification of Drought Severity and Duration, J. Climatology 1: 2747–2756.