Blue-Green Infrastructure (BGI) is an integrated, nature-based approach to urban planning. The concept combines the natural water cycle (water bodies, infiltration areas) with green elements such as green spaces, green roofs and trees, in order to manage water sustainably and promote biodiversity. In contrast to traditional, grey infrastructure (concrete channels and pipes), BGI utilises natural processes to collect, store and filter rainwater. This reduces the risk of flooding, improves water quality and, at the same time, cools the city. Researchers at Eawag are conducting interdisciplinary projects to investigate how effective blue-green infrastructure can make our cities more climate-resilient and liveable.
Green roofs, like the one on the Ethnographic Museum in Budapest, are havens of biodiversity and contribute positively to the urban climate. (Photo: Kilian Perrelet)
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authors => protected'Perrelet, K.; Cook, L. M.; Reji Chacko, M.; Altermatt,&n bsp;F.; Moretti, M.' (100 chars)
title => protected'Food webs on green roofs are unique but less robust than their ground‐leve l counterparts' (90 chars)
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categories => protected'biodiversity; blue-green infrastructure; ecological networks; environmental DNA; herbivores; metaweb; predators; urban ecology' (126 chars)
description => protected'1. Green roofs are increasingly acknowledged as novel habitats capable of su staining diverse species assemblages. Due to their distinct abiotic conditio ns and stochastic colonization pathways, they are hypothesized to support ec ological communities that differ from those of ground-level habitats, yet th e capacity of these habitats to sustain coherent and robust food webs is har dly known.<br />2. Combining environmental DNA metabarcoding from soil sampl es with a metaweb approach, we compared the composition, structure and robus tness of ground-level and green roof food webs across 52 paired green roof a nd ground-level sites along an urban densification gradient in Zurich, Switz erland.<br />3. Food webs on green roofs were compositionally and structural ly distinct from those at ground level. These networks were denser (higher c onnectance), more diffuse (greater omnivory) and less structured (increased trophic incoherence) than ground-level webs. Together, this made the food we bs on green roofs more prone to secondary extinctions. These patterns were l argely driven by the predominance of predators and a lack of basal consumers , such as detritivores.<br />4. Variation in food web properties was mediate d by green roof design. Specifically, older roofs with deeper substrates sup ported sparsely connected, vertically diverse food webs that exhibited great er robustness to secondary extinctions than more recently built green roofs. <br /><em>5. Synthesis and applications</em>. Green roofs operate as distinc t habitats, offering novel environmental conditions, thus increasing urban h abitat diversity and supporting denser but less robust food webs compared wi th ground-level habitats. Increasing substrate depth and allowing for long-t erm development can promote trophic diversity and robustness, informing stra tegies for urban biodiversity conservation and ecosystem management.' (1892 chars)
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authors => protected'Perrelet, K.; Moretti, M.; Inglard, O.; Altermatt, F.; C ook, L. M.' (96 chars)
title => protected'Green roofs harbor different and non-substituting invertebrate communities t han surrounding ground-level habitats' (113 chars)
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description => protected'Green roofs are increasingly promoted to support urban biodiversity, potenti ally mitigating habitat loss from urban growth. Given their standardized des ign, however, green roofs are expected to differ ecologically from the groun d-level habitats they are intended to substitute. Yet the extent of this div ergence remains unclear, especially for taxa with varying dispersal abilitie s, including low-mobility invertebrates that are less often associated with green roofs. To quantify this divergence, we used environmental DNA metabarc oding to assess invertebrate diversity and identify environmental drivers af fecting species with different dispersal abilities across 52 pairs of extens ive green roof and ground-level sites in Zurich, Switzerland. We found that green roofs shared around 10 % of species with ground-level sites, regardles s of how spatially isolated they were. Instead, green roofs harbored unique communities, albeit marginally poorer in number of species. However, this pa ttern varied by species mobility, with soil-dwelling species forming more he terogeneous communities, likely due to dispersal limitations between roofs. Additionally, green roof design choices, including substrate type and depth, as well as vegetation cover, emerged as key drivers of species richness, re gardless of species dispersal abilities. Although green roofs do not structu rally or ecologically replicate the ground-level habitats they would substit ute, they provide complementary habitats that enhance urban biodiversity whe n designed with ecological considerations. While further research is require d to evaluate the capacity of green roofs to sustain viable populations desp ite their spatial isolation, this study highlights practical design interven tions, such as deepening the substrate, to improve their role as complementa ry habitats in cities.' (1846 chars)
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authors => protected'Dietzel, A.; Moretti, M.; Perrelet, K.; Cook, L. M.' (76 chars)
title => protected'Urban heat exacerbates climatic risks to urban biodiversity' (59 chars)
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description => protected'Urban climates typically exhibit high local variability and diverge markedly from mesoclimate conditions. Yet, urban microclimate data needed to assess the impacts of urban heat on biodiversity are lacking. We present a scalable modeling approach to generate high-resolution projections of urban bioclima tic conditions using Zurich, Switzerland, as a case study. We demonstrate th at globally available land use and remote sensing data can effectively predi ct spatial patterns in urban bioclimatic conditions. Our findings show that mean annual temperatures can deviate by up to 2 °C from mesoclimate conditi ons, and that uncorrected mesoclimate data substantially underestimate risks to 182 species of amphibians, birds, butterflies, dragonflies, grasshoppers and trees. By the end of the century, up to half of these species are expec ted to exceed their climatic tolerance across all habitat patches. Our appro ach is transferable to cities globally using existing data, marking a major step forward for urban microclimate and biodiversity research.' (1050 chars)
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Food webs on green roofs are unique but less robust than their ground‐level counterparts
1. Green roofs are increasingly acknowledged as novel habitats capable of sustaining diverse species assemblages. Due to their distinct abiotic conditions and stochastic colonization pathways, they are hypothesized to support ecological communities that differ from those of ground-level habitats, yet the capacity of these habitats to sustain coherent and robust food webs is hardly known. 2. Combining environmental DNA metabarcoding from soil samples with a metaweb approach, we compared the composition, structure and robustness of ground-level and green roof food webs across 52 paired green roof and ground-level sites along an urban densification gradient in Zurich, Switzerland. 3. Food webs on green roofs were compositionally and structurally distinct from those at ground level. These networks were denser (higher connectance), more diffuse (greater omnivory) and less structured (increased trophic incoherence) than ground-level webs. Together, this made the food webs on green roofs more prone to secondary extinctions. These patterns were largely driven by the predominance of predators and a lack of basal consumers, such as detritivores. 4. Variation in food web properties was mediated by green roof design. Specifically, older roofs with deeper substrates supported sparsely connected, vertically diverse food webs that exhibited greater robustness to secondary extinctions than more recently built green roofs. 5. Synthesis and applications. Green roofs operate as distinct habitats, offering novel environmental conditions, thus increasing urban habitat diversity and supporting denser but less robust food webs compared with ground-level habitats. Increasing substrate depth and allowing for long-term development can promote trophic diversity and robustness, informing strategies for urban biodiversity conservation and ecosystem management.
Perrelet, K.; Cook, L. M.; Reji Chacko, M.; Altermatt, F.; Moretti, M. (2026) Food webs on green roofs are unique but less robust than their ground‐level counterparts, Journal of Applied Ecology, 63(2), e70306 (14 pp.), doi:10.1111/1365-2664.70306, Institutional Repository
Green roofs harbor different and non-substituting invertebrate communities than surrounding ground-level habitats
Green roofs are increasingly promoted to support urban biodiversity, potentially mitigating habitat loss from urban growth. Given their standardized design, however, green roofs are expected to differ ecologically from the ground-level habitats they are intended to substitute. Yet the extent of this divergence remains unclear, especially for taxa with varying dispersal abilities, including low-mobility invertebrates that are less often associated with green roofs. To quantify this divergence, we used environmental DNA metabarcoding to assess invertebrate diversity and identify environmental drivers affecting species with different dispersal abilities across 52 pairs of extensive green roof and ground-level sites in Zurich, Switzerland. We found that green roofs shared around 10 % of species with ground-level sites, regardless of how spatially isolated they were. Instead, green roofs harbored unique communities, albeit marginally poorer in number of species. However, this pattern varied by species mobility, with soil-dwelling species forming more heterogeneous communities, likely due to dispersal limitations between roofs. Additionally, green roof design choices, including substrate type and depth, as well as vegetation cover, emerged as key drivers of species richness, regardless of species dispersal abilities. Although green roofs do not structurally or ecologically replicate the ground-level habitats they would substitute, they provide complementary habitats that enhance urban biodiversity when designed with ecological considerations. While further research is required to evaluate the capacity of green roofs to sustain viable populations despite their spatial isolation, this study highlights practical design interventions, such as deepening the substrate, to improve their role as complementary habitats in cities.
Perrelet, K.; Moretti, M.; Inglard, O.; Altermatt, F.; Cook, L. M. (2025) Green roofs harbor different and non-substituting invertebrate communities than surrounding ground-level habitats, Journal of Environmental Management, 392, 126630 (10 pp.), doi:10.1016/j.jenvman.2025.126630, Institutional Repository
Urban heat exacerbates climatic risks to urban biodiversity
Urban climates typically exhibit high local variability and diverge markedly from mesoclimate conditions. Yet, urban microclimate data needed to assess the impacts of urban heat on biodiversity are lacking. We present a scalable modeling approach to generate high-resolution projections of urban bioclimatic conditions using Zurich, Switzerland, as a case study. We demonstrate that globally available land use and remote sensing data can effectively predict spatial patterns in urban bioclimatic conditions. Our findings show that mean annual temperatures can deviate by up to 2 °C from mesoclimate conditions, and that uncorrected mesoclimate data substantially underestimate risks to 182 species of amphibians, birds, butterflies, dragonflies, grasshoppers and trees. By the end of the century, up to half of these species are expected to exceed their climatic tolerance across all habitat patches. Our approach is transferable to cities globally using existing data, marking a major step forward for urban microclimate and biodiversity research.
Dietzel, A.; Moretti, M.; Perrelet, K.; Cook, L. M. (2026) Urban heat exacerbates climatic risks to urban biodiversity, npj Urban Sustainability, 6, 4 (12 pp.), doi:10.1038/s42949-025-00309-6, Institutional Repository
Cover picture: Blue-green infrastructure, such as this example here in Zurich, can significantly improve the urban climate. Among other things, it mitigates the effects of heatwaves and helps to protect against flooding. It also creates habitats for plants and animals, thereby promoting urban biodiversity. (Photo: Kilian Perrelet, Eawag)
