Inferring the influence of urban vegetation on urban water storage capacity from evapotranspiration recession

Increasing the effective urban water storage capacity is one of a range of solutions to mitigate heat issues and flooding in urban areas and vegetation plays an important role in it. In this study, the regional-scale water storage capacity of four city clusters in China during the period 2009-2018 was estimated based on a four-source evapotranspiration (ET) model incorporated with urban water storage capacity (S) estimated on the basis of daily ET recession. Our results showed that simulated ET was consistent with four flux towers (R2 = 0.57, RMSE = 1.45 mm/d). The spatial distribution of S was similar to that of ET, and ranged from 2 to 28 mm. The influence of environmental drivers on the spatial pattern of S was explored using a machine learning technique, and the relative contribution of LAI (leaf area index) to the spatial pattern of S ranged from 11.59% to 27.56%. The effect of vegetation change on S in urban and non-urban areas showed an opposite relationship to the LAI change. However, the effect on S in urban and non-urban areas was reversed when vegetation was expanded to 1.25 times the existing mean, owing to the increase in vegetation dominating the change in urban Eb (soil evaporation) to a greater degree than for non-urban Eb. Urban areas in Beijing-Tianjin-Hebei, the Yangtze River Delta, Pearl River Delta, and Chengdu-Chongqing would need to increase existing vegetation by 10%, 32%, 32%, and 28%, respectively, to store additional precipitation (above the mean annual precipitation) in high-precipitation years. This study provides a new mechanistic understanding of the effects of vegetation change on water consumption in urban ecosystems, allowing the role of urban ecological planning in urban flood mitigation to be quantified.

Automated summary

Vegetation plays an important role in mitigating heat issues and flooding in urban areas, and its effect on water storage capacity was evaluated in four city clusters in China from 2009 to 2018. The study found that the spatial distribution of water storage capacity was influenced by vegetation, and increasing vegetation was necessary to store additional precipitation in high-precipitation years. This study provides a mechanistic understanding of the effects of vegetation change on water consumption in urban ecosystems and quantifies the role of urban ecological planning in urban flood mitigation.