where N is the length of data, m is the duration of drought and m is the return period. After
quantifying the related risk of return periods of various drought events and with respect to the
severity and the longest duration, the corresponding probability of occurence to the amount
of risk was calculated. The available software in GIS environment such as ArcInfo and
ArcView were used to prepare the drought maps of the region under study. The ArcView
software was applied to draw the maps and iso-intensity curves of droughts. Furthermore,
ArcInfo Software was used to convert the geographical coordinates to UTM coordinate
system.