Ocean–Atmosphere Forcing of Summer Streamflow Drought in Great Britain

Abstract

roughts are high-impact events that have substantial implications for both human and natural systems. As such, improved understanding of the hydroclimatological processes involved in drought development is a major scientific imperative of direct practical relevance. To address this research need, this paper investigates the chain of processes linking antecedent ocean?atmosphere variation to summer streamflow drought in Great Britain. Analyses are structured around four distinct drought regions (defined using hierarchical cluster analysis) for the period 1964?2001. Droughts were identified using a novel regional drought area index. Composite analysis of monthly sea surface temperature (SST) prior to drought onset reveals a horseshoe- or tripole-shaped pattern of North Atlantic SST anomalies that is similar to patterns of SST anomalies associated with the North Atlantic Oscillation (NAO). Patterns in geopotential height, wind, moisture vapor flux, and precipitation prior to drought onset support the influence of the NAO but also demonstrate that the atmospheric bridge linking North Atlantic SST to drought development is too complex to be described solely by indices of the NAO. In revealing new information on the chain of processes leading to the development of hydrological drought in Great Britain, this paper has the potential to inform drought-forecasting research and so improve drought preparedness and management.