Blue-green roofs with forecast-based operation to reduce the impact of weather extremes

Tim Busker*, Hans de Moel, Toon Haer, Maurice Schmeits, Bart van den Hurk, Kira Myers, Dirk Gijsbert Cirkel, Jeroen Aerts

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Conventional green roofs have often been criticised for their limited water buffer capacity during extreme rainfall events and for their susceptibility to droughts when additional irrigation is unavailable. One solution to these challenges is to create an extra blue water retention layer underneath the green layer. Blue-green roofs allow more stormwater to be stored, and the reservoir can act as a water source for the green layer throughout capillary rises. An automated valve regulates the water level of the system. It can be opened to drain water when extreme precipitation is expected. Therefore, the water buffer capacity of the system during extreme rainfall events can be maximised by integrating precipitation forecasts as triggers for the operation of the valve. However, the added value of this forecast-based operation is yet unknown. Accordingly, in this study, we design and evaluate a hydrological blue-green roof model that utilises precipitation forecasts. We test its performance to capture (extreme) precipitation and to increase evapotranspiration and evaporative cooling under a variety of precipitation forecast-based decision rules. We show that blue-green roofs can capture between 70 % and 97 % of extreme precipitation (>20 mm/h) when set to anticipate ensemble precipitation forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF). This capture ratio is considerably higher than that of a conventional green roof without extra water retention (12 %) or that of a blue-green roof that does not use forecast information (i.e., valve always closed; 59 %). Moreover, blue-green roofs allow for high evapotranspiration rates relative to potential evapotranspiration on hot summer days (around 70 %), which is higher than from conventional green roofs (30 %). This serves to underscore the higher capacity of blue-green roofs to reduce heat stress. Using the city of Amsterdam as a case study, we show the high upscaling potential of the concept: on average, potentially suitable flat roofs cover 13.3 % of the total area of the catchments that are susceptible to pluvial flood risk. If the 90th percentile of the ECMWF forecast is used, an 84 % rainfall capture ratio can translate into capturing 11 % of rainfall in flood-prone urban catchments in Amsterdam.

Original languageEnglish
Article number113750
Pages (from-to)1-12
Number of pages12
JournalJournal of Environmental Management
Volume301
Early online date28 Sep 2021
DOIs
Publication statusPublished - 1 Jan 2022

Bibliographical note

Funding Information:
This work is based on data from ECMWF and TIGGE, retrieved using the Meteorological Archival and Retrieval System (MARS). TIGGE (The Interactive Grand Global Ensemble) is an initiative of the World Weather Research Programme (WWRP). The research is funded by RESILIO; RESILIO is an acronym for ?Resilience nEtwork of Smart Innovative cLImate-adapative rOoftops?, a collaboration between the Municipality of Amsterdam, Waternet, MetroPolder company, Rooftop Revolution, HvA, VU, Stadgenoot, de Alliantie and De Key. This project is co-financed by the European Regional Development Fund through the Urban Innovative Actions Initiative. We would like to thank MetroPolder company, in particular Merle van der Kroft and Joost Jacobi, for their help and support during this research project. In addition, we would like to thank ECWMF User Services for the excellent support on the use of ECMWF ensemble forecasts.

Funding Information:
This work is based on data from ECMWF and TIGGE, retrieved using the Meteorological Archival and Retrieval System (MARS). TIGGE (The Interactive Grand Global Ensemble) is an initiative of the World Weather Research Programme (WWRP). The research is funded by RESILIO ; RESILIO is an acronym for ‘Resilience nEtwork of Smart Innovative cLImate-adapative rOoftops’, a collaboration between the Municipality of Amsterdam, Waternet, MetroPolder company, Rooftop Revolution, HvA, VU, Stadgenoot, de Alliantie and De Key. This project is co-financed by the European Regional Development Fund through the Urban Innovative Actions Initiative. We would like to thank MetroPolder company, in particular Merle van der Kroft and Joost Jacobi, for their help and support during this research project. In addition, we would like to thank ECWMF User Services for the excellent support on the use of ECMWF ensemble forecasts.

Publisher Copyright:
© 2021 The Authors

Keywords

  • Blue-green roof
  • Climate adaptation
  • Flood risk
  • Green roof
  • Heat stress
  • Stormwater management

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