1. Beersma JJ, Buishand TA (2004) Joint probability of precipitation and discharge deficits in the Netherlands. Water Resour Res doi: W12508, 1029/2004WR003265.
2. Bonaccorso B, Bordi I, Cancielliere A, Rossi G, Sutera A (2003) Spatial variability of drought: an analysis of the SPI in Sicily. Water Resour Manag 17:273-296.
3. Cordery I, McCall M (2000) A model for forecasting drought from teleconections. Water Resour Res 36:763-768. Domonkos P (2003) Recent precipitation trends in Hungary in the context of larger scale climatic changes. Nat Hazards 29:255- 271.
4. Dracup JA, Lee K, Paulson EG (1980) On the definition of droughts. Water Resour Res 16:297-302. Guttman NB (1998). Comparing the Palmer drought index and the Standardized Precipitation Index. Journal of the American Water Resources Association, 34: 113–121.
5. Hayes M, Wilhite DA, Svoboda M, Vanyarkho O (1999). Monitoring the 1996 drought using the Standardized Precipitation Index. Bulletin of the American Meteorological Society, 80: 429– 438. Karl TR (1983). Some spatial characteristics of drought duration in the United States. J. Clim. Appl. Meteorol, 22: 1356–1366. Lana X, Serra C, Burgue˜no A (2001) Patterns of monthly rainfall shortage and excess in terms of the Standardied Precipitation Index for Catalonia (NE Spain). Int J Climatol 21:1669-1691.