Urban water storage capacity inferred from observed evapotranspiration recession 

Abstract

<p>The amount and dynamics of urban water storage play an important role in mitigating urban flooding and heat. Assessment of the capacity of cities to store water remains challenging due to the extreme heterogeneity of the urban surface. Evapotranspiration (ET) recession after rainfall events during the period without precipitation, over which the amount of stored water gradually decreases, can provide insight on the water storage capacity of urban surfaces. Assuming ET is the only outgoing flux, the water storage capacity can be estimated based on the timescale and intercept of its recession. In this paper, we test the proposed approach to estimate the water storage capacity at neighborhood scale with latent heat flux data collected by eddy covariance flux towers in eleven contrasting urban sites with different local climate zones, vegetation cover and characteristics and background climates (Amsterdam, Arnhem, Basel, Berlin, Helsinki, Łódź, Melbourne, Mexico City, Seoul, Singapore, Vancouver). Water storage capacities ranging between 1 and 12 mm were found. These values correspond to e-folding timescales lasting from 2 to 10 days, which translate to half-lives of 1.5 to 7 days. We find ET at the start of a drydown to be positively related to vegetation fraction, and long timescales and large storage capacities to be associated with higher vegetation fractions. According to our results, urban water storage capacity is at least one order of magnitude smaller than the known water storage capacity in natural forests and grassland.</p>