River floods are among some of the costliest natural disasters(1), but their socio-economic impacts under contrasting warming levels remain little explored(2). Here, using a multi-model framework, we estimate human losses, direct economic damage and subsequent indirect impacts (welfare losses) under a range of temperature (1.5 degrees C, 2 degrees C and 3 degrees C warming)(3) and socio-economic scenarios, assuming current vulnerability levels and in the absence of future adaptation. With temperature increases of 1.5 degrees C, depending on the socio-economic scenario, it is found that human losses from flooding could rise by 70-83%, direct flood damage by 160-240%, with a relative welfare reduction between 0.23 and 0.29%. In a 2 degrees C world, by contrast, the death toll is 50% higher, direct economic damage doubles and welfare losses grow to 0.4%. Impacts are notably higher under 3 C warming, but at the same time, variability between ensemble members also increases, leading to greater uncertainty regarding flood impacts at higher warming levels. Flood impacts are further shown to have an uneven regional distribution, with the greatest losses observed in the Asian continent at all analysed warming levels. It is clear that increased adaptation and mitigation efforts-perhaps through infrastructural investment(4)-are needed to offset increasing risk of river floods in the future.