Hydroclimatology of extreme river flows

Floods and droughts are recurrent events with characteristics of frequency, magnitude, duration and timing occupying the opposing extremes of natural river flow regimes. This hydrological variability, driven by climate and meteorology and modified by river basin processes, is a key determinant of physicochemical river habitat influencing the structure and function of freshwater communities. A changing (warming) climate is projected to alter water and heat inputs to river systems that drive river flow, and thus, hydrological processes may be subject to unprecedented future change, resulting in potentially unprecedented river flow extremes. We review the hydroclimatology of extreme river flows in changing climates and draw case studies from the European temperate regions. Specifically, we adopt a catchment perspective', in which an understanding of meteorological and hydrological processes is used to (i) conceptually define extreme river flows, (ii) explain the (natural) climatic and catchment processes that drive extreme river flows, (iii) discuss future potential changes driven by an anthropogenically modified climate and (iv) identify uncertainties associated with projections of future climate-driven hydrological shifts.