Soil macroporosity affects field-scale water-cycle processes, such as infiltration, nutrient transport and runoff(1,2), that are important for the development of successful global strategies that address challenges of food security, water scarcity, human health and loss of biodiversity(3). Macropores-large pores that freely drain water under the influence of gravity-often represent less than 1 per cent of the soil volume, but can contribute more than 70 per cent of the total soil water infiltration(4), which greatly magnifies their influence on the regional and global water cycle. Although climate influences the development of macropores through soil-forming processes, the extent and rate of such development and its effect on the water cycle are currently unknown. Here we show that drier climates induce the formation of greater soil macroporosity than do more humid ones, and that such climate-induced changes occur over shorter timescales than have previously been considered-probably years to decades. Furthermore, we find that changes in the effective porosity, a proxy for macroporosity, predicted from mean annual precipitation at the end of the century would result in changes in saturated soil hydraulic conductivity ranging from - 55 to 34 per cent for five physiographic regions in the USA. Our results indicate that soil macroporosity may be altered rapidly in response to climate change and that associated continental-scale changes in soil hydraulic properties may set up unexplored feedbacks between climate and the land surface and thus intensify the water cycle.