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Growing and shrinking regions are experiencing increased vulnerability to urban flooding because of climate change. While traditional stormwater runoff mitigation policies, such as regulating total impervious areas (TIA) and enhancing green infrastructure (GI) connectivity, have been widely adopted, their effectiveness remains uncertain in the face of divergent patterns of land use change and population shifts. To address this uncertainty, this research examines the impacts of impervious composition and GI connectivity on runoff within the Chicago-Naperville and Detroit-Warren-Ann Arbor combined statistical areas over time, representative growing and shrinking regions in the Midwestern US, respectively. The impervious composition is quantified using TIA and hydraulic connectivity, while GI connectivity is measured using FRAGSTATS. Ordinary least squares and panel data regression models are employed, controlling for socio-demographic, climate, and biophysical variables. The results indicate that regulating both TIA and hydraulic connectivity decreases stormwater runoff. The impact of GI connectivity on runoff depth varies by region. In Chicago, a less linearly connected and more clumped GI configuration decreases runoff depth. Conversely, in Detroit, a less clumped but more linearly connected GI layout is more effective. The findings highlight the importance of developing tailored stormwater runoff management and flood mitigation plans in association with development trends. • Besides limiting TIA, controlling hydraulic connectivity reduces runoff depth. • The impact of green infrastructure connectivity on runoff depth varies by region. • Less linearly connected and more clumped GI connectivity in Chicago reduces runoff depth. • Less clumped but more linearly connected GI connectivity in Detroit reduces runoff depth. [ABSTRACT FROM AUTHOR]

Urbanization increases directly connected impervious area (DCIA), the impervious area that is hydraulically connected to downstream drainage by closed pipelines. Although the benefits of low-impact development (LID) have been examined in other studies, its effect on alleviating DCIA levels has seldom been assessed. This study measured the DCIA of urban watersheds in Houston, TX, USA. Five land-use types were categorized and the contribution of LID facilities to reducing DCIA in each type was estimated by using Sutherland's equations. The results showed (1) DCIA in commercial areas was greater than that in residential areas, especially for big-box retailers; (2) the percentage of DCIA reduction by LID varied by land-use type; and (3) optimal combinations of LID application could maximize the effectiveness of DCIA reduction. The results contribute to prioritizing land-use type for implementing LID practices and providing local governments with a useful measure to estimate runoff volume. [ABSTRACT FROM AUTHOR]

The impacts of flooding can be devastating. Huge financial burden often follows major storm events to recover from structural damage. Well-designed drainage systems allow for effective discharge of stormwater, reducing property losses and expenditures on recovery. However, a lack of empirical studies on the topic has impeded the determination of which drainage method might be the most effective in preventing or minimizing property losses from flooding. This study assessed the economic impacts of three drainage systems − storage-, conveyance-, and infiltration-based facilities – on reducing flood damage recorded from 2009 to 2012 by Federal Emergency Management Agency in the Buffalo Bayou watershed in Houston, Texas, USA. Ordinary least squares and spatial autoregressive models were developed with a group of variables featuring drainage system, housing structure, geophysical environment, and storm characteristics. The results show that storage-based systems outperform conveyance-based mechanisms. Infiltration-based facilities are found to be less effective in reducing property damage because green spaces disconnected from sewer systems are rapidly inundated after being saturated while excessive overflow is not properly drained. This study confirms that the performance of a drainage system varies by facility type and environmental setting. The results encourage the recovery of wetlands and integration of retention/detention basins into community development in flood-prone areas to prevent potential future economic losses. • Storage-based drainage mechanisms are most effective for flood mitigation. • 92% of flood damage cost can be saved by using storage-based facilities. • Installing conveyance-based systems on property roads reduces flood damage by 19%. • Directing runoff to green spaces causes undesirable effects on property losses. [ABSTRACT FROM AUTHOR]

• TIA and DCIA positively affect the probability of runoff yield. • DCIA contributes far more than TIA to generating far-above-average runoff depth. • The contributions of TIA and DCIA to far-above-average peak flow are comparable. • The impacts of TIA and DCIA are subject to climate variability. • TIA and DCIA control is effective within a specific range of rainfall depth. Total impervious area (TIA) is one of the most common measures for predicting runoff yield in hydrologic studies and regulating urbanization in land use policy. Directly connected impervious area (DCIA), a subset of TIA, represents the hydraulic connection between development and underground sewer systems. Which indicator to use in runoff prediction has been subject to debate. The effectiveness of TIA and DCIA in the face of climate variability also remains unclear. The present study empirically assessed the impacts of TIA and DCIA on urban runoff in three metropolitan statistical areas (MSAs) in the U.S. state of Texas. The total monthly runoff depths of 92 watersheds and peak flows of 43 watersheds were computed using streamflow monitored by the U.S. Geological Survey from 2010 to 2017. A series of ordinal logit regression models were developed to determine which imperviousness indicator better predicted probable runoff yield. Additionally, an average marginal effect analysis was performed to investigate how TIA and DCIA responded to changing precipitation depths. The results demonstrate that DCIA outperformed TIA in runoff depth prediction, whereas TIA predicted peak flow better than DCIA. However, for far-above-average runoff, the contribution of DCIA to runoff depth was far greater than that of TIA, but no difference was found for peak flow. The effectiveness of TIA and DCIA also varied by total and 24-hour peak depths of monthly precipitation. After reaching their maximum capacity, both TIA and DCIA became less effective in predicting runoff and did not correlate with rainfall depth in extremely wet months. Meanwhile, the control of TIA and DCIA for runoff volume reduction was most effective for monthly rainfall of a 5% to 10% probability of exceedance in all MSAs, whereas that of peak flow reduction was most effective if the 24-hour peak storm in a month had a 2% to 5% probability of exceedance. The findings of this study demonstrate the hydrologic significance of regulating DCIA over TIA for high-risk runoff under certain rainfall depths and return periods. The study expands the current knowledge of urban hydrology for effective stormwater management and mitigation of future flooding risk. [ABSTRACT FROM AUTHOR]