Water storage plays an important role in mitigating heat and flooding in urban areas. Assessment of the water storage capacity of cities remains challenging due to the inherent heterogeneity of the urban surface. Traditionally, effective storage has been estimated from runoff. Here, we present a novel approach to estimate effective water storage capacity from recession rates of observed evaporation during precipitation-free periods. We test this approach for cities at neighborhood scale with eddy-covariance based latent heat flux observations from fourteen contrasting sites with different local climate zones, vegetation cover and characteristics, and climates. Based on analysis of 583 drydowns, we find storage capacities to vary between 1.3-28.4 mm, corresponding to e-folding timescales of 1.8-20.1 days. This makes the storage capacity at least one order of magnitude smaller than the observed values for natural ecosystems, reflecting an evaporation regime characterised by extreme water limitation.

Understanding the response of extreme precipitation (EP) at a city scale to global warming is critical to protect a city from the risks of urban flooding under climate change. Yet, current knowledge on this issue is limited. Here, focusing on an urban agglomeration in the tropics, Singapore, we reveal that future global warming enhances both frequency and intensity of EP, based on simulations with a state-of-the-art convection-permitting regional climate model. EP intensification can reach maximum “super” Clausius-Clapeyron ( +7% per K warming) rate, consistently for both Representative Concentration Pathways (RCPs) 8.5 and 4.5. The intensification is lower for moderate and light precipitation, implying a situation of “wet gets wetter and dry remains dry”. EP enhancement is attributed to the increased atmospheric moisture and, more importantly, the enhanced lifting force, which directly strengthens the precipitation-making processes.