A HYDROCLIMATOLOGICAL MODEL OF AREAL DROUGHT

A stochastic hydroclimatological model is developed to characterize areal droughts. Statistical properties of drought indices are described by conditioning monthly drought indices on large-scale atmospheric circulation patterns (CP). The methodology is applied to an area of about 110 000 km2 in eastern Nebraska, USA where the dry continental climate often produces severe droughts. In this example, the Bhalme-Mooley drought index (BMDI) illustrates the methodology. Five monthly classes of CP are derived using cluster analysis. Time series of BMDI are conditioned on monthly CP classes; BMDI is strongly related to these classes. A climate change may alter the structure of monthly CP classes; thus the impact of climate change on drought can be predicted.