Identifying keystone meteorological factors of green-roof stormwater retention to inform design and planning

Green roofs have received considerable attention for multiple ecosystem services which include stormwater amelioration. Offering sustainable stormwater source-control, green roofs utilize otherwise unused impervious urban surfaces to restore pre-development hydrologic functions such as infiltration and retention. Its ability to retain stormwater is related to external and internal factors. Meteorological conditions prior to a rainfall event can influence antecedent evapotranspiration, the only water-exit pathway of the green-roof system besides discharge. Whereas evapotranspiration may be difficult and costly to measure directly, other common meteorological conditions can be monitored conveniently and inexpensively even prior to actual green-roof installation. Identifying salient on-site meteorological factors may provide valuable insights into hydrologic dynamics, and inform green-roof design and planning decisions. A statistical regression approach identified potential antecedent meteorological factors and moisture indicators of extensive green-roof retention. Continuous field-monitoring data revealed the combined effects of rainfall depth, wind speed, solar radiation, and antecedent dry weather period to explain the measured stormwater retention under a humid subtropical rainfall regime. Amongst the studied environmental factors, solar radiation and wind speed contributed notably to green-roof stormwater retention and may provide a dependable basis to assist green-roof site selection when resources are limited. It is important to incorporate site-specific planning and assessment prior to green infrastructure design and implementation to maximize hydrologic and evaporative cooling services in cities with complex topographical features.