HESS Opinions: Floods and droughts – are land use, soil management, and landscape hydrology more significant drivers than increasing CO ₂ ?

Abstract. Floods, droughts, and heatwaves are increasing globally. This is typically attributed to CO2-driven climate change. However, at the global scale, CO2-driven climate change neither reduces precipitation nor adequately explains droughts despite the modest increase in evapotranspiration due to temperature rise. Past land-use changes, particularly soil sealing, compaction, and drainage, are likely to be more significant for water losses resulting from runoff and leading to flooding and water scarcity. The importance of these processes is generally poorly addressed in modelling because hydrological models rarely reflect lateral fluxes in the atmosphere, on the soil surface, and in the soil. Land use is only considered in coarse categories, and neighbourhood effects and feedback mechanisms are neglected. However, even if models fail and we cannot create landscape experiments, there is sufficient evidence that land use is a key driver of the problem and of the solution to mitigate floods, droughts, and heatwaves. Addressing land-use changes is imperative as they persist even with zero net CO2 emissions, making the world more vulnerable.