Urban Water Storage Capacity Inferred From Observed Evapotranspiration Recession

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 14 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 and 28.4 mm, corresponding to e-folding timescales of 1.8-20.1 days. This makes the urban storage capacity at least five times smaller than all the observed values for natural ecosystems, reflecting an evaporation regime characterized by extreme water limitation.

Automated summary

Water storage plays a crucial role in mitigating heat and flooding in urban areas. A novel approach to estimating effective water storage capacity from observed evaporation rates during precipitation-free periods is introduced. The study reveals that urban storage capacities are at least five times smaller than those of natural ecosystems, indicating extreme water limitation in urban evaporation regimes.