European Water 49: 43-63, 2015. © 2015 E.W. Publications Short-term drought forecasting combining stochastic and geo-statistical approaches C. A. Karavitis 1* , C. G. Vasilakou 1 , D. E. Tsesmelis 1 , P. D. Oikonomou 2 , N. A. Skondras 1 , D. Stamatakos 1 , V. Fassouli 1 and S. Alexandris 1 1 Department of Natural Resources Development & Agricultural Engineering, Agricultural University of Athens, 11855 Athens, Greece 2 Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, Co. 8o523, USA * e-mail: ckaravitis@aua.gr Abstract: The current work presents the application of the seasonal Auto Regressive Integrated Moving Average Model (ARIMA) using the Standard Precipitation Index (SPI) as a drought indicator and then depicting the spatial distribution through geo-statistical methods. Greece is very often facing the hazardous impacts of droughts, hence presenting an almost ideal case for such an application. The applied methodology used precipitation data from 55 meteorological stations in two sets distributed throughout the country. To assess the drought, SPI was calculated for a variety of temporal steps. The statistical analyses of the examined temporal step parameters were performed and the Seasonal ARIMA model was employed. Then based on such link, forecasting attempts were derived and presented. The effort may lead to a further understanding of drought duration, magnitude and spatial extend in semi-arid areas. It is believed that such a methodology may provide some useful anticipatory information on the area’s vulnerability to drought and thus portraying the system’s susceptibility to change, damages and losses. In this context, drought contingency planning may be included in the decision making arsenal in order to also widen existing perceptions of the area’s inherent weaknesses and limited resilience to both anthropogenic and natural hazards, serving at the same time as an early warning mechanism. Key words: Standardized Precipitation Index, meteorological drought, statistical analysis, seasonal ARIMA model, forecasting, contingency planning, Greece 1. DROUGHT DEFINITIONS AND CHARACTERISTICS The equitable water use as an integral part of the quest for integrated water resources management confronts incessant multifaceted difficulties due to changes in human systems values, societal structural transformations and environmental aggravations. Such basic and evolving changes have created a context of high uncertainty and complexification as access to adequate water resources is generating conflicts and competing interests, further intensified by historical factors, traditional values and customs, religious considerations, and geographical peculiarities (Vlachos, 2004; Barraque et al. 2008; Karmarkar, 2012; Karavitis, 2008; Karavitis et al. 2014). Under such circumstances, the reoccurring drought events – mainly due to changes in precipitation patterns, duration and intensity – may accelerate the rise of water related social-ecological crises, particularly in areas of high drought susceptibility such as the subtropics and mid-latitudes, including the Mediterranean area. The area is already one exhibiting high vulnerability to drought due to socioeconomic (e.g. irrigated agriculture, fragile economies) and natural conditions, such as semi- dry environment with dry long summers (Gleick, 1993; Karavitis and Kerkides, 2002; IPCC, 2007; 2013). Therefore, drought analysis may be considered as a crucial fraction of any integrated water resources management approach. The pertinent literature clearly indicates that drought is a normal, recurring feature of any climatic zone, although often perfunctorily envisaged as an exceptional and unanticipated one (Hagman, 1984; Bruce, 1994; Grigg, 1996; Karavitis, 1999; Bordi et al. 2006; Karavitis et al.