Nature-based solutions for hydro-meteorological risk reduction: a state-of-the-art review of the research area
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Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020
https://doi.org/10.5194/nhess-20-243-2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
Nature-based solutions for hydro-meteorological risk reduction:
a state-of-the-art review of the research area
Laddaporn Ruangpan1,2 , Zoran Vojinovic1,3 , Silvana Di Sabatino4 , Laura Sandra Leo4 , Vittoria Capobianco5 ,
Amy M. P. Oen5 , Michael E. McClain1,2 , and Elena Lopez-Gunn6
1 IHE Delft Institute for Water Education, Delft, the Netherlands
2 Department of Water Management, Faculty of Civil Engineering and Geosciences,
Delft University of Technology, Delft, the Netherlands
3 College for Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
4 Department of Physics and Astronomy, University of Bologna, Bologna, Italy
5 Norwegian Geotechnical Institute, Oslo, Norway
6 Icatalist S.L., Madrid, Spain
Correspondence: Laddaporn Ruangpan (l.ruangpan@tudelft.nl)
Received: 16 April 2019 – Discussion started: 30 April 2019
Revised: 29 November 2019 – Accepted: 15 December 2019 – Published: 20 January 2020
Abstract. Hydro-meteorological risks due to natural hazards ing and replication and to make them become mainstream
such as severe floods, storm surges, landslides and droughts solutions.
are causing impacts on different sectors of society. Such risks
are expected to become worse given projected changes in
climate, degradation of ecosystems, population growth and 1 Introduction
urbanisation. In this respect, nature-based solutions (NBSs)
have emerged as effective means to respond to such chal- There is increasing evidence that climate change and asso-
lenges. A NBS is a term used for innovative solutions that are ciated hydro-meteorological risk are already causing wide-
based on natural processes and ecosystems to solve different ranging impacts on the global economy, human well-being
types of societal and environmental challenges. The present and the environment. Floods, storm surges, landslides,
paper provides a critical review of the literature concerning avalanches, hail, windstorms, droughts, heat waves and for-
NBSs for hydro-meteorological risk reduction and identifies est fires are a few examples of hydro-meteorological hazards
current knowledge gaps and future research prospects. There that pose a significant risk. Hydro-meteorological risk is the
has been a considerable growth of scientific publications on probability of damage due to hydro-meteorological hazards
this topic, with a more significant rise taking place from 2007 and its interplay with exposure and vulnerability of the af-
onwards. Hence, the review process presented in this paper fected humans and environments (Merz et al., 2010). Some
starts by sourcing 1608 articles from Scopus and 1431 ar- of the main reasons for such risks are climate change, land
ticles from the Web of Science. The full analysis was per- use change, water use change and other pressures linked to
formed on 146 articles. The analysis confirmed that numer- population growth (Thorslund et al., 2017). The situation is
ous advancements in the area of NBSs have been achieved to likely to become worse given the projected changes in cli-
date. These solutions have already proven to be valuable in mate (see, for example, EEA, 2017). Therefore, effective
providing sustainable, cost-effective, multi-purpose and flex- climate change adaptation (CCA) and disaster risk reduc-
ible means for hydro-meteorological risk reduction. How- tion (DRR) strategies are needed to mitigate the risks of ex-
ever, there are still many areas where further research and treme events and to increase resilience to disasters, particu-
demonstration are needed in order to promote their upscal- larly among vulnerable populations (Maragno et al., 2018;
McVittie et al., 2018).
Published by Copernicus Publications on behalf of the European Geosciences Union.
244 L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction Since biodiversity and ecosystem services can play an im- 2 Overview of definitions and theoretical backgrounds portant role in responding to climate-related challenges, both mitigation and adaptation strategies should take into consid- There are several terms and concepts which have been used eration a variety of green infrastructure (GI) and ecosystem- interchangeably in the literature to date. In terms of the based adaptation (EbA) measures as effective means to re- NBSs, the two most prominent definitions are from the Inter- spond to present and future disaster risk (see also EEA, national Union for Conservation of Nature (IUCN) and the 2015). Such approaches are already well accepted within European Commission. The European Commission defines multilateral frameworks such as the United Nations (UN) nature-based solutions as “Solutions that aim to help soci- Framework Convention on Climate Change (UNFCCC), the eties address a variety of environmental, social and economic Convention on Biological Diversity (CBD) and the Sendai challenges in sustainable ways. They are actions inspired by, Framework for Disaster Risk Reduction (SFDRR). As such, supported by or copied from nature, both using and enhanc- they are recognised as effective means for CCA and DRR ing existing solutions to challenges as well as exploring more and for the implementation of the Sustainable Development novel solutions. Nature-based solutions use the features and Goals (SDGs). complex system processes of nature, such as its ability to In view of the points above, many countries are nowa- store carbon and regulate water flows, in order to achieve de- days developing adaptation and mitigation strategies based sired outcomes, such as reduced disaster risk and an environ- on GI and EbA to reduce their vulnerability to hydro- ment that improves human well-being and socially inclusive meteorological hazards (Rangarajan et al., 2015; EEA, green growth” (EC, 2015). The IUCN has proposed a defini- 2015). Nature-based solutions (NBSs) have been introduced tion of NBSs as “actions to protect, sustainably manage and relatively recently. The reason for their introduction is that restore natural and modified ecosystems that address societal NBSs offer the possibility to work closely with nature in challenges effectively and adaptively, simultaneously pro- adapting to future changes, reducing the impact of climate viding human well-being and biodiversity benefits” (Cohen- change and improving human well-being (Cohen-Shacham Shacham et al., 2016). Eggermont et al. (2015) proposed a et al., 2016). NBSs have been the focus of research in sev- typology characterising NBSs into three types: (i) NBSs that eral EU Horizon 2020-funded projects. Horizon 2020 offers address a better use of natural or protected ecosystems (no or new opportunities in the focus area of “Smart and Sustain- minimal intervention), which fits with how the IUCN frames able Cities with Nature based solutions” (Faivre et al., 2017). NBSs, (ii) NBSs for sustainability and multi-functionality of Some of these important projects are Nature4Cites, NATUR- managed ecosystems, and (iii) NBSs for the design and the VATION, NAIAD, BiodivERsA, INSPIRATION, URBAN management of new ecosystems, which is more representa- GreenUP, UNaLaB, URBINAT, CLEVER Cities, proGIreg, tive of the definition given by the European Commission. EdiCitNet, Regenerating ECOsystems with Nature-based A NBS is a collective term for innovative solutions to solutions for hydro-meteorological risk rEduCTion (RE- solve different types of societal and environmental chal- CONECT), OPERANDUM, ThinkNature, EKLIPSE and lenges, based on natural processes and ecosystems. There- PHUSICOS (nature4cities, 2019). Through these projects, fore, it is considered to be an “umbrella concept” cover- knowledge of NBSs has grown rapidly and been documented ing a range of different ecosystem-related approaches and in a considerable body of grey literature (project reports, for linked concepts (Cohen-Shacham et al., 2016; Nesshöver et example). On the other hand, the number of scientific stud- al., 2017) that provides an integrated way to look at differ- ies focused on NBSs to reduce hydro-meteorological risk is ent issues simultaneously. Due to the diverse policy origins, continuously increasing all over the world. NBS terminology has evolved in the literature to emphasise The aim of this article is to provide a state-of-the-art re- different aspects of natural processes or functions. In this re- view of scientific publications on hydro-meteorological risk gard, nine different terms are commonly used in the scien- reduction with NBSs to indicate some directions for future tific literature in the context of hydro-meteorological risk re- research based on the current knowledge gaps. The analy- duction: low-impact developments (LIDs), best management sis focuses on the following hydro-meteorological hazards: practices (BMPs), water-sensitive urban design (WSUD), floods, droughts, storm surges and landslides. The review sustainable urban drainage systems (SuDs), green infrastruc- addresses both small- and large-scale interventions and ex- ture (GI), blue–green infrastructure (BGI), ecosystem-based plores available techniques, methods and tools for NBS as- adaptation (EbA) and ecosystem-based disaster risk reduc- sessment while also providing a snapshot of the major socio- tion (Eco-DRR). The timeline of each term based on their economic factors at play in the implementation process. The appearance in literature is shown in Fig. 1, and their defini- key objectives and methods of this study are discussed in tions are given in Table 1. Sect. 3, while Sect. 2 provides a brief overview of concepts and definitions related to NBSs either in general or that are specifically linked to hydro-meteorological risk reduction. Results and conclusions are discussed in Sects. 4 and 5 re- spectively. Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020 www.nat-hazards-earth-syst-sci.net/20/243/2020/
L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction 245
Figure 1. Timeline and year of origin of each term (low-impact developments – LIDs, best management practices – BMPs, water-sensitive ur-
ban design – WSUD, green infrastructure – GI, sustainable urban drainage systems – SuDs, nature-based solutions – NBSs, ecosystem-based
adaptation – EbA, ecosystem-based disaster risk reduction – Eco-DRR – and blue–green infrastructure – BGI) based on their appearance in
publications.
Table 1. Glossary of terms and their geographical usage.
Terminology Definition, objectives and purpose Places where commonly used Reference
Low-impact “LID is used as a retro- fit designed to reduce the stress on urban – US Eckart et al.
development (LIDs) stormwater infrastructure and/or create the resiliency to adapt to climate – New Zealand (2017)
changes, LID relies heavily on infiltration and evapotranspiration and
attempts to incorporate natural features into design.”
Best management “A device, practice or method for removing, reducing, retarding or – US Strecker et
practices (BMPs) preventing targeted stormwater run-off constituents, pollutants and – Canada al. (2001)
contaminants from reaching receiving waters.”
Water-sensitive “Manage the water balance, maintain and where possible enhance water – Australia Whelans
urban design quality, encourage water conservation and maintain water-related consultants et
(WSUD) environmental and recreational opportunities.” al. (1994)
Sustainable urban “Replicate the natural drainage processes of an area – typically through – UK Ossa-Moreno
drainage systems the use of vegetation-based interventions such as swales, water gardens et al.
(SuDs) and green roofs, which increase localised infiltration, attenuation and/or (2017)
detention of stormwater.”
Green infrastructure “The network of natural and semi-natural areas, features and green – US Naumann et
(GI) spaces in rural and urban, and terrestrial, freshwater, coastal and marine – UK al. (2011)
areas, which together enhance ecosystem health and resilience, contribute
to biodiversity conservation and benefit human populations through the
maintenance and enhancement of ecosystem services.”
Ecosystem-based “The use of biodiversity and ecosystem services as part of an overall – Canada CBD (2009)
adaptation (EbA) adaptation strategy to help people to adapt to the adverse effects of climate – Europe
change.”
Ecosystem-based “The sustainable management, conservation, and restoration of – Europe Estrella and
disaster risk reduction ecosystems to reduce disaster risk, with the aim of achieving sustainable – US Saalismaa
(Eco-DRR) and resilient development.” (2013)
Blue–green “BGI provides a range of services that include; water supply, climate – UK Lawson et
infrastructure (BGI) regulation, pollution control and hazard regulation (blue services/goods), al. (2014)
crops, food and timber, wild species diversity, detoxification, cultural
services (physical health, aesthetics, spiritual), plus abilities to adapt to
and mitigate climate change.”
Nature-based “NBS aim to help societies address a variety of environmental, social and – Europe EC (2015)
solution economic challenges in sustainable ways. They are actions inspired by,
supported by or copied from nature, both using and enhancing existing
solutions to challenges as well as exploring more novel solutions.”
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246 L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction
The commonalities between a NBS and its sister concepts (EKLIPSE, 2017). Lafortezza et al. (2018) reviewed differ-
(i.e. GI, BGI, EbA and Eco-DRR) are that they take partic- ent case studies around the world where NBSs have been
ipatory, holistic, integrated approaches, using nature to en- applied from the micro scale to the macro scale. Further-
hance adaptive capacity, reduce hydro-meteorological risk, more, an overview of how different NBS measures can reg-
increase resilience, improve water quality, increase the op- ulate ecosystem services (i.e. soil protection, water quality,
portunities for recreation, improve human well-being and flood regulation and water provision) has been carried out by
health, enhance vegetation growth, and connect habitat and Keesstra et al. (2018).
biodiversity. More information on the history, scope, applica-
tion and underlying principle of terms of SuDs, LIDs, BMPs,
WSUD and GI can be found in Fletcher et al. (2015), while
the relationship between a NBS, GI–BGI and EbA is de- 3 Materials and methodology
scribed in detail by Nesshöver et al. (2017).
Although all terms are based on a common idea, which The methodology consisted of two phases as schematised in
is embedded in the umbrella concept of NBSs, differences Fig. 2. The first phase consisted of the identification of arti-
in definition reflect their historical perspectives and knowl- cles satisfying the search criteria discussed in Sect. 3.1. Next,
edge base that were relevant at the time of the research all articles were screened and filtered based on the selection
(Fletcher et al., 2015). The distinguishing characteristic be- criteria discussed in Sect. 3.2.
tween a NBS and its sister concepts is how they address so-
cial, economic and environmental challenges (Faivre et al., 3.1 Search strategy
2018). Some terms such as SuDs, LIDs and WSUD refer
to NBSs that specifically address stormwater management. The review analysis concerned articles from scientific jour-
They use the landscape feature to transform the linear ap- nals written in English. Two main concepts were used in the
proach of conventional stormwater management into a more search: nature-based solutions and hydro-meteorological risk
cyclic approach where drainage, water supply and ecosys- reduction. As the concept of nature-based solutions appears
tems are treated as part of the same system, mimicking more under different names (which more or less relate to the same
natural water flows (Liu and Jensen, 2018). GI and BGI focus field of research), articles related to LIDs, BMPs, WSUD,
more on technology-based infrastructures by applying natu- SuDs, GI, BGI, EbA and Eco-DRR were included in the
ral alternatives (Nesshöver et al., 2017) for solving a spe- identification of relevant articles (see Table 2) The review
cific activity (i.e. urban planning or stormwater). EbA looks of hydro-meteorological risk included literature on relevant
at long-term changes within the conservation of biodiversity, terms (i.e. disasters, risks, hydrology, etc.) and different types
ecosystem services and climate change, while Eco-DRR is of hazards (floods, droughts, storm surges and landslides; Ta-
more focused on immediate and medium-term impacts from ble 2).
the risk of weather, climate and non-climate-related hazards. During the construction of the queries, the strings were
EbA is often seen as a subset of NBSs that is explicitly con- searched only within index terms and metadata “titles, ab-
cerned with climate change adaptation through the use of na- stract, and keywords” in the Scopus database. The search
ture (Kabisch et al., 2016). From the above discussion, it can terms for the two concepts were linked with the Boolean op-
be concluded that EbA, Eco-DRR and GI–BGI provide more erator “AND”, while the Boolean operator “OR” was used
specific solutions to more specific issues. One key distinc- to link possible terms (Table 2). An example of a protocol is
tion is that unlike the sister concepts, the concept of NBSs shown below:
is more open to different interpretations, which can be use- “TITLE-ABS-KEY (“Nature-based Solutions” OR “Na-
ful in encouraging stakeholders to take part in the discussion. ture based solutions” OR “Nature Based Solutions” OR
Moreover, features of NBSs provide an alternative to work- “nature-based solutions” OR “Low impact development” OR
ing with existing measures or grey infrastructures. Therefore, “Sustainable Urban Drainage Systems” OR “Water Sensi-
it is important to note that very often a combination between tive Urban Design” OR “Best Management Practices” OR
natural and traditional engineering solutions (also known as “Green infrastructure” OR “Green blue infrastructure” AND
“hybrid” solutions) is likely to produce more effective results “flood”) AND (LIMIT-TO (DOCTYPE, “ar”) OR LIMIT-
than any of these measures alone, especially when their co- TO (DOCTYPE, “ch”) OR LIMIT-TO (DOCTYPE, “re”)
benefits are taken into consideration (Alves et al., 2019). OR LIMIT-TO (DOCTYPE, “bk”)) AND (LIMIT-TO (LAN-
An important advancement in the science and practice GUAGE, “English”))”.
of NBSs is given by the EKLIPSE Expert Working Group, The time window selected for the review process was
which developed the first version of a multi-dimensional im- from 1 January 2007 to 19 November 2019; 1608 arti-
pact evaluation framework to support planning and evalua- cles published in scientific journals were found in the Sco-
tion of NBS projects. The document includes a list of im- pus database, and 1431 were found in the Web of Science
pacts, indicators and methods for assessing the performance database. The articles from both databases were combined
of NBSs in dealing with some major societal challenges for a total of 3089 articles. Duplicate articles were removed,
Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020 www.nat-hazards-earth-syst-sci.net/20/243/2020/
L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction 247
Figure 2. Process of article selection with systematic review method on nature-based solutions for hydro-meteorological risk reduction. The
final number of fully reviewed articles is 146.
resulting in a total of 1439 articles to be considered for fur- 2. to review the use of techniques, methods and tools for
ther evaluation. planning, selecting, evaluating and implementing NBSs
for hydro-meteorological risk reduction;
3.2 Selection process
3. to review the socio-economic influence in the imple-
As stated in the Introduction, this study aims at reviewing mentation of NBSs for hydro-meteorological risk re-
the state of the art of the research on NBSs that specifically duction as well as their multiple benefits, co-benefits,
address hydro-meteorological risk reduction. In this regard, effectiveness and costs;
the key objectives of the present review work were carefully
formulated as follows: 4. to identify trends, knowledge gaps and proposed future
research prospects with respect to the above three ob-
1. to assess the state of the art in research concerning both jectives.
small- and large-scale NBSs for hydro-meteorological
risk reduction;
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248 L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction
Table 2. Selected concepts and terms used to search relevant literature on NBSs for hydro-meteorological risk reduction.
No. Research words
First concept Connection Second concept
(nature-based solutions) (hydro-meteorological risk)
1 “Nature-based solutions” OR AND “Flood”
2 “Nature-Based Solutions” OR AND “Drought”
3 “Low impact development” OR AND “Storm surge”
4 “Sustainable Urban Drainage Systems” OR AND “Landslide”
5 “Water Sensitive Urban Design” OR AND “Hydro-meteorological”
6 “Best Management Practices” OR AND “Disaster”
7 “Green infrastructure” OR AND “Review”
8 “Green blue infrastructure” OR AND “Hydrology”
9 “Ecosystem-based Adaptation ” OR AND “Coastal”
10 “Ecosystem-based disaster risk reduction” OR AND “Risk”
11 “Green and grey infrastructure”
These key objectives were defined for the review, with the at the urban or local scale (i.e. buildings, streets, roofs or
intention that the results could be both quantitative and qual- houses), while NBSs in rural areas, river basins and at the
itative. regional scale are referred to as large-scale NBSs (Fig. 3).
The 1439 articles resulting from the search query were
thus evaluated with respect to these objectives and those 4.1.1 Research on small-scale NBSs for
found of little or no relevance with the topic removed. hydro-meteorological risk reduction
This selection process involved a set of progressive steps
as schematised in Fig. 2. Initially, all articles were analysed Small-scale NBSs are usually applied to a specific location
on the basis of reading titles and keywords and evaluating such as a single building or a street. However, for some
their relation to the search terms. Articles were discarded if cases, a single NBS is not sufficient to control a large amount
their title and keywords were considered to be of little or no of run-off. Therefore, this review discusses the application
relevance to the key objectives. This step served to reduce and effectiveness of both individual NBSs and multiple-NBS
the number of articles from 1439 to 433. Secondly, a more combinations. There are 41 articles that have been reviewed
in-depth analysis was conducted, based on reading the ab- on the effectiveness of small-scale NBSs (Table 3). A major-
stract of each article selected in the previous step. The cri- ity of these (31 articles) discuss the effectiveness of a single
teria at this step was that the abstract should discuss hydro- or individual NBS site, while only 13 articles discuss the ef-
meteorological risk reduction. For example, if the abstract fectiveness of multiple-NBS sites (around 31 %). A summary
focused more on water quality than risk, that paper was ex- of the effectiveness, co-benefits and cost of NBS measures at
cluded. This step served to reduce the number of articles small scale is shown in Table 3.
from 433 to 205. Finally, articles were read in full to iden- To date, various types of single-NBS sites have been stud-
tify those that were relevant to the review objectives. Any ied with objectives such as reduction of the flood peak (Car-
studies appearing to meet the key objectives (dealing with penter and Kaluvakolanu, 2011; Ercolani et al., 2018; Liao et
subjects such as effectiveness of NBSs, techniques, method al., 2015; Mei et al., 2018; Yang et al., 2018), delay and at-
and tools for planning, and other subjects relevant to the key tenuation of the flood peak (Ishimatsu et al., 2017), reduction
objectives) were included in the review. As a result, the entire of volume of combined sewer overflows (Burszta-Adamiak
selection process resulted in a total of 146 articles relevant to and Mrowiec, 2013), and reduction of surface run-off volume
the objectives of the present review. (Lee et al., 2013; Shafique and Kim, 2018). The review found
just three articles that discuss the reduction of drought risk
by using NBSs. Lottering et al. (2015) used NBSs to reduce
4 Findings water consumption in suburban areas, while Radonic (2019)
showed that rainwater harvesting can help reduce household
4.1 Lesson from research on small- and large-scale water consumption. Finally, Wang et al. (2019) demonstrated
NBSs for hydro-meteorological risk reduction that forests can significantly mitigate drought impacts and
protect water supplies for crop irrigation.
In this review, NBSs for hydro-meteorological risk reduc- The most common NBS measures in urban areas appear
tion have been divided into small- and large-scale solutions to be intensive green roofs (Burszta-Adamiak and Mrowiec,
(Fig. 3). Small-scale NBSs are usually referred to as NBSs 2013; Carpenter and Kaluvakolanu, 2011; Ercolani et al.,
Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020 www.nat-hazards-earth-syst-sci.net/20/243/2020/L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction 249 Figure 3. Illustration of large and small-scale nature-based solutions (NBSs). Large-scale NBS A illustrates NBSs in mountainous regions (e.g. afforestation, slope stabilisation, etc.), large-scale NBS B illustrates NBSs along river corridors (e.g. widening river, retention basins, etc.) and large-scale NBS C illustrates NBSs in coastal regions (e.g. sand dunes, protection dikes and walls, etc.). Typical examples of small-scale NBSs are green roofs, green walls, rain gardens, permeable pavements, swales, bio-retention, etc. 2018), extensive green roofs (Cipolla et al., 2016; Lee et the aim of implementing both concepts and practices of LIDs al., 2013), rain gardens (Ishimatsu et al., 2017), rainwater and NBSs as well as various comprehensive urban water harvesting (Khastagir and Jayasuriya, 2010), dry detention management strategies (Chan et al., 2018). Nowadays, the ponds (Liew et al., 2012), permeable pavements (Shafique et concept (Sponge City) is widely used when a city increases al., 2018), bio-retention (Khan et al., 2013; Olszewski and resilience to climate change. It also combines several sys- Allen, 2013), vegetated swales (Woznicki et al., 2018) and tems, such as the source control system, urban drainage sys- trees (Mills et al., 2016). However, the authors of these stud- tem and emergency discharge system. ies investigated the performance of such measures individu- Porous pavement appears to be one of the most popular ally (i.e. at the specific, local and single site) without evalu- measures suitable to be combined with other NBSs for urban ating them in combination with other NBS sites or in hybrid run-off management. Examples of this are described in Hu combinations. et al. (2017), who used inundation modelling to evaluate the The literature to date acknowledges that the effectiveness effectiveness of rainwater harvesting and pervious pavement of NBSs greatly depends on the magnitude and frequency as retrofitting technologies for flood inundation mitigation of of rainfall events. Green roofs are recognised in reducing an urbanised watershed. Damodaram et al. (2010) concluded peak flows more effectively for smaller-magnitude frequent that the combination of rainwater harvesting and permeable storms than for larger-magnitude infrequent storms (see, for pavements is likely to be more effective than pond storage for example, Ercolani et al., 2018). There are also reports that small storms, while the pond is likely to be more effective to rain gardens are more effective in dealing with small dis- manage run-off from the more intense storms. charges of rainwater (Ishimatsu et al., 2017). Swales and per- Several studies argue that multiple-NBS measures can lead meable pavements are more effective for flood reduction dur- to a more significant change in run-off regime and more ef- ing heavier and shorter rainfall events. Zölch et al. (2017) fective long-term strategies than single-NBS measures (Web- suggested that the effectiveness of NBSs should be directly ber et al., 2018). For example, Wu et al. (2018) simulated linked to their ability to increase (as much as possible) the eight scenarios changing the percentage of combined green storage capacities within the area of interest while using open roof and permeable pavement in an urban setting. The results spaces that have not been used previously and/or while pro- show that when green roofs and permeable pavements are ap- viding benefits to other areas for urban planning. plied at all possible locations, a 28 % reduction in maximum Several studies evaluated the performance of multiple- inundation can be obtained. In comparison, scenarios imple- NBS (or combined-NBS) measures (i.e. a train of NBSs; see, menting either green roofs or permeable pavements alone at for example, Damodaram et al., 2010; Dong et al., 2017; all possible areas experienced a reduction of 14 %. One of Huang et al., 2014; Luan et al., 2017). One of the most suc- the main reasons for the superior performance of combined cessful international projects in combining several NBS mea- NBSs is that they work in parallel, each treating a different sures at the urban scale is the Sponge City Programme (SCP) portion of run-off generated from the sub-catchment (Pap- in China. The SCP project was commissioned in 2014 with palardo et al., 2017). For these combinations, the spatial dis- www.nat-hazards-earth-syst-sci.net/20/243/2020/ Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020
L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction
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Table 3. Summary of run-off volume and peak flow reduction effectiveness, co-benefits and costs of small-scale NBS measures.
Measures References Case Area or Effectiveness Co-benefits Cost per Remark
studies volume Run-off Peak flow square metre∗
covered volume reduction
by NBS reduction
Porous Shafique et al. Seoul, 1050 m2 ∼ 30 %–65 % – – Removing diffuse USD ∼ 252 – More effective
pavement (2018) South Korea pollution in heavier and
Damodaram et Texas, 2.99 km2 – ∼ 10 %–30 % – Enhancing recharge to shorter rainfall
al. (2010) USA groundwater events
Green roofs Burszta- Wroclaw, 2.88 m2 – ∼ 54 %–96 % – Reducing nutrient USD ∼ 564 – More efficient
Adamiak and Poland loadings in smaller storm
Mrowiec (2013) – Saving energy events than
Ercolani et al. Milan, Italy 0.39 km2 ∼ 15 %–70 % ∼ 10 %–80 % – Reducing air pollution larger storm
(2018) – Increasing amenity events
Carpenter and Michigan, 325.2 m2 ∼ 68.25 % ∼ 88.86 % value
Kaluvakolanu USA
(2011)
Rain gardens Ishimatsu et Japan 1.862 m2 ∼ 36 %–100 % – – Providing a scenic USD ∼ 501 More effective
al. (2017) amenity in dealing with
Goncalves et Joinville, 34 139 m2 50 % ∼ 48.5 % – Increasing the median small discharges
al. (2018) Brazil property value of rainwater
– Increasing biodiversity
Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020
Vegetated Luan et al. Beijing, 157 m3 ∼ 0.3 %–3.0 % ∼ 2.2 % – Reducing USD ∼ 371 – More effective
swales (2017) China concentrations in heavier and
Huang et al. Hai He 1500 m3 9.60 % ∼ 23.56 % of pollutants shorter rainfall
(2014) basin, China – Increasing biodiversity events
– Not suitable in
mountains areas
Rainwater Khastagir and Melbourne, 1–5 m3 ∼ 57.8 %–78.7 % – – Improving water USD ∼ 865
harvesting Jayasuriya Australia quality (TN – total nitrogen) was per m3
(2010) reduced around
72 %–80 %)
Damodaram et Texas, 1.5 km2 – ∼ 8 %–10 %
al. (2010) USA
Dry Liew et al. Selangor, 65 000 m2 – ∼ 33 %–46 % – Providing recreational Delaying the
detention (2012) Malaysia benefits time to peak by
pond 40–45 min
250Table 3. Continued.
Measures References Case Area and Effectiveness Co-benefits Cost per Remark
studies volume Run-off Peak flow square metre∗
covered volume reduction
by NBS reduction
Detention Damodaram et Texas, 73 372 m3 – ∼ 20 % – Providing biodiversity USD ∼ 60
pond al. (2010) USA benefits
Goncalves et Joinville, 9700 m3 55.7 % ∼ 43.3 % – Providing recreational
al. (2018) Brazil benefits
Bio- Luan et al. Beijing, 945.93 m3 ∼ 10.2 %–12.1 % – – Reducing total suspended solids (TSSs) USD ∼ 534 – Measure has a
retention (2017) China pollution better reduction
Huang et al. Hai He 1708.6 m3 9.10 % ∼ 41.65 % – Reducing TP (total phosphorous) pollution effectiveness in
(2014) basin, China various rainfall
Khan et al. Calgary 48 m3 ∼ 90 % – intensities
(2013)
www.nat-hazards-earth-syst-sci.net/20/243/2020/
Infiltration Huang et al. Hai He, 3576 m3 30.80% ∼ 19.44 % – Reducing water USD ∼ 74
trench (2014) China pollutant
Goncalves et Joinville, 34 139 m2 55.9 % ∼ 53.4 % – Improving surface
al. (2018) Brazil water quality
Green roof Damodaram et Texas, 4.49 km2 – ∼ 10 %–35 % – Saving energy – More effective in
and porous al. (2010) USA – Increasing amenity smaller events
pavement value
Swale and Behroozi et al. Tehran, – 5 %–32 % ∼ 10 %–21 % – Decreasing TSSs – More effective in
porous (2018) Iran pollution 50 %–60 % smaller events
pavement
Rainwater Damodaram et Texas, 4.49 km2 – ∼ 20 %–40 % – Removing diffuse – More effective in
L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction
harvesting al. (2010) USA pollution smaller events
and porous
pavement
Detention Goncalves et Joinville, 18 327 m2 70.8 % ∼ 60.0 % – Providing a scenic
pond and al. (2018) Brazil amenity
rain garden
Detention Goncalves et Joinville, 18 327 m2 75.1 % ∼ 67.8 % – Improving surface
pond and al. (2018) Brazil water quality
infiltration
trench
∗ Cost of each measure is based on CNT (2009), Nordman et al. (2018) and De Risi et al. (2018).
Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020
251252 L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction
tribution should be carefully considered because it can im- effectiveness, co-benefits and cost of large-scale NBS mea-
prove the run-off regime better when compared to centralised sures is shown in Table 4.
NBSs (Loperfido et al., 2014). Only few articles have addressed the combined behaviour
Further research on the use of combined NBSs and grey in- of NBSs at large scales. One of the possible reasons is that
frastructure (i.e. hybrid measures) is desirable, as only three large-scale systems are more complex than small-scale sys-
contributions were found in the review. Alves et al. (2016) tems. The most common large-scale NBSs are flood storage
presented a novel method to select, evaluate and place differ- basins (De Risi et al., 2018) and preservation and regener-
ent hybrid measures for retrofitting urban drainage systems. ation of forests in flood-prone areas (Bhattacharjee and Be-
However, only fundamental aspects were touched upon in hera, 2018), making more room for the river (Klijn et al.,
the methodology, and they suggested that future work should 2013), river restoration (Chou, 2016), wetlands (Thorslund
include the possibility of considering stakeholders’ prefer- et al., 2017) and mountain forestation (Casteller et al., 2018).
ences or flexibility within the method. In the work of Vo- A classic example of a large-scale NBS implementation
jinovic et al. (2017), a methodological framework that com- is the Room for the River Programme implemented along
bines ecosystem services (flood protection, education, art and the Rhine and Meuse rivers in the Netherlands. The Room
culture, recreation, and tourism) with economic analysis for for the River Programme consisted of 39 local projects
the selection of multi-functional measures and consideration based on nine different types of measures (Klijn et al.,
of small- and large-scale NBSs has been discussed for the 2013). These measures are floodplain lowering, dike reloca-
case of Ayutthaya in Thailand. Onuma and Tsuge (2018) tion, groyne lowering, summer bed deepening, water stor-
compared the cost and benefits and performance of NBSs age, bypassed and floodways, high-water channels, obstacle
and grey infrastructures, concluding that NBSs are likely to removal, and dike strengthening. The benefits that the pro-
be more effective when implemented through cooperation gramme achieved are more than just reducing flooding, also
with local people, whereas hybrid solutions are more effec- increasing opportunities for recreation, habitat and biodiver-
tive than a single NBS in terms of performance. sity in the area (Klijn et al., 2013). Another case study of
The first limitation of the above studies is that they only a large-scale NBS is the Laojie River project in Taoyuan in
assess the effectiveness of NBSs at urban scales. This may Taiwan. The study focused on changing the channelised, cul-
not be sufficient for large events, as climate change is likely verted, flood-control watercourse into an accessible green in-
to increase the frequency and intensity of future events (Qin frastructure corridor for the public (Chou, 2016). The land-
et al., 2013). A large-scale NBS could be a solution for storm scape changes resulting from this project have increased
events with large magnitude and long duration, which is usu- recreation activities and improved the aesthetic value in the
ally the case for disaster risk reduction applications, and area.
therefore research in this direction is highly desirable (Gi- NBSs may benefit people in coastal areas by reducing risk
acomoni et al., 2012). Although Fu et al. (2018) analysed from storm surges, wave energy, coastal flooding and ero-
variations in run-off for different scales and land-uses, the sion, as documented by several authors (see, for example,
impact of NBSs was only examined for the small urban scale. Van Coppenolle, 2018; Joyce et al., 2017; Ruckelshaus et al.,
Another limitation is that none of these contributions incor- 2016; Sutton-Grier et al., 2018). NBSs for coastal areas can
porated cost–benefit analyses (CBAs). CBAs can be used as a be implemented either at large or small scales. They include
tool to support the decision-making process, as they serve the dunes, beaches, oyster and coral reefs, mangroves, seagrass
feasibility of implementation costs and the potential benefits beds, and marshes. These measures can also provide habi-
of NBSs. tats for different species such as fish, birds and other wildlife
(Ruckelshaus et al., 2016). Schoonees et al. (2019) provided
lists of general recommendations, technical guidelines and
4.1.2 Research on large-scale NBSs for
policies, and design considerations for NBSs in coastal areas.
hydro-meteorological risk reduction
However, only a few articles of the 146 reviewed focused on
the potential benefits of NBSs in coastal areas.
Large-scale water balance, water fluxes, water management Casteller et al. (2018) concluded that native mountain
and ecosystem services are affected by future changes such forests could be used to reduce hydro-meteorological risk
as climate change, land use changes, water use changes and such as flash floods and landslides. Moreover, the use of
population growth. To address such challenges, large-scale NBSs in different forest ecosystems to reduce shallow land-
NBSs are needed to make more space for water to retain, de- slide impacts should be addressed (de Jesús Arce-Mojica
celerate, infiltrate, bypass and discharge (Cheng et al., 2017; et al., 2019). To reduce the impact of large-scale hydro-
Thorslund et al., 2017). Generally, a large-scale NBS com- meteorological events, more research is needed on large-
bines different NBSs within a larger system to achieve better scale NBSs and their hybrid combinations designed to at-
long-term strategies. There are some examples of NBS mea- tenuate flows and improve drainage. They should be imple-
sures for hydro-meteorological risk reduction summarised in mented to include improvements in solid waste management,
McVittie et al. (2018) and Sahani et al. (2019). A summary of
Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020 www.nat-hazards-earth-syst-sci.net/20/243/2020/L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction 253
Table 4. Summary of effectiveness, co-benefits and costs of large-scale NBS measures.
Measures References Case studies Area or volume Effectiveness Co-benefits Cost
covered
by NBSs
De-culverting Chou (2016) Laojie River, 3 km – It can reduce flood – Increasing landscape value EUR ∼ 16.92 million
(river Taiwan risk up to 100-year – Increasing recreational value
restoration) return period
Floodplain Klijn et al. Deventer 5.01 km2 – It can reduce water – Increasing nature area EUR ∼ 136.7 million
lowering (2013) Netherlands level 19 cm – Increasing agriculture value
Dike Klijn et al. Nijmegen- 2.42 km2 – It can reduce water – Increasing floodplain area EUR ∼ 342.60 million
relocation and (2013) Lent, level 34 cm – Increasing recreational value
floodplain Netherlands
lowering
Floodwater Klijn et al. Volkenrak- 200 × 106 m3 – It can reduce water – Increasing habitat and EUR ∼ 386.20 million
storage (2013) Zoommeer, Netherlands level 50 cm biodiversity in the area
– Increasing recreational value
Green Klijn et al. Veessen- 14.10 km2 – It can reduce water – Increasing floodplain area
floodway (2013) Wapenveld, Netherlands level 71 cm – Increasing recreational value
Wetlands Van Coppenolle – It can mitigate – Providing shoreline protection
(mangroves (2018), Gedan et storm surge 80 % services
and salt al. (2011) – It can protect
marshes) against tsunami
impacts
4.2.1 Selection of NBSs
It has been a well-accepted fact that not all NBSs are suit-
able for all conditions. Therefore, it is important to consider
the feasibility and constraints at the site at an early stage
in the selection process. The first consideration in select-
Figure 4. Evaluation process of nature-based solutions. The process ing NBSs is to define the objective such as the target area
includes selecting possible measures and evaluating and optimising
(i.e. urban or rural) and performance requirements such as
measures’ performance using available tools.
quantity and/or quality (Romnée and De Herde, 2015; Zhang
and Chui, 2018). For example, Pappalardo et al. (2017) chose
community-based river cleaning programmes and reforesta- permeable pavements and green roofs because they can de-
tion (De Risi et al., 2018). tain run-off or enhance infiltration to the subsoil. Another
approach is to consider both primary benefits and key co-
4.2 Techniques, methods and tools for planning, benefits. For instance, Majidi et al. (2019) developed a frame-
selecting, evaluating and implementing NBSs work to select NBSs to reduce flood risk and enhance human
thermal comfort (reducing heat stress). Many authors suggest
Figure 4 illustrates a typical process for the selection and restricting the choice of appropriate NBSs based on com-
evaluation of NBSs. The process starts by selecting possi- mon site constraints such as land use, soil type, groundwater
ble measures that correspond to the local characteristics and depth, catchment characteristics, political and financial reg-
project’s target. The next step is concerned with evaluating ulations, amenities, environmental requirements, and space
the measures’ performance using numerical models, cost– available (Eaton, 2018; Joyce et al., 2017; Nordman et al.,
benefit analysis and/or multi-criteria analysis. For more com- 2018; Oraei Zare et al., 2012). For example, Eaton (2018)
plex systems with a large number of scenarios and parame- selected bio-retention measures because they are more suit-
ters, optimisation can be used to maximise the benefits and able in low-density residential land use. Moreover, the study
minimise the costs. The techniques, methods and tools for of Reynaud et al. (2017) describes how the type of NBS
planning, selecting, evaluating and implementing NBSs are has an impact on individuals’ preference for ecosystem ser-
reviewed in the following section. vices. Therefore, a screening analysis is necessary for select-
ing the NBS measures that are best suited to local constraints
and objectives, providing decision makers with valuable in-
formation. The way forward in the selection of NBSs is to
consider spatial planning principles to locate the position for
www.nat-hazards-earth-syst-sci.net/20/243/2020/ Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020254 L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction
measures. Spatial planning principles can facilitate and stim- in large catchments. Yang et al. (2018) proposed relative per-
ulate discussion among local communities, researchers, pol- formance evaluation (RPE) methods, which use a score to
icymakers and government authorities. calculate the performance for all alternatives. This score is
calculated as the weighted sum of the scores of individual
4.2.2 Frameworks and methods for evaluation of NBSs indicators.
From the discussion above, it can be observed that there
There are several frameworks and methods that can be used are still challenges in evaluating intangible benefits of NBSs
to evaluate the performance indicators of NBSs discussed in and incorporating stakeholders’ preferences into the process.
this review. One of the most popular evaluation approaches For complex systems with a large number of scenarios and
is to analyse, simulate and model hydrology, hydraulics and parameters, simple trial-and-error methods may not be the
water balance processes. This information is then used to feasible approach. In such cases, an automated optimisation
support decision makers, planners and stakeholders in their method could be effectively applied to handle these tasks and
evaluation of performance and potential of NBSs by compar- to combine the above-mentioned methods. There is also a
ing modelled results against the current situation, baseline challenge in combining a range of aspects that can and cannot
scenario or targets (Jia et al., 2015). be expressed in monetary terms into the same framework of
In addition to hydrological and hydraulic analyses, cost– analysis.
benefit analyses are often used to select and evaluate NBSs
(Huang et al., 2018; Nordman et al., 2018; Watson et al., 4.2.3 Optimal configuration of NBSs
2016; Webber et al., 2018). The common benefits consid-
ered include prevented damage costs, omitted infrastruc- In order to implement NBSs, typical selection factors include
tures and prevented agricultural losses. One cost–benefit ap- the number of NBS measures, size, location and potential
proach is to evaluate NBSs by applying the whole life cycle combinations of NBSs. Optimisation of NBS strategies has
costing (LCC) approach, including construction, operation, been increasingly used in the context of urban stormwater
maintenance and opportunity costs (Nordman et al., 2018), management. Most of the studies focus on minimising water
and return on investment (ROI; De Risi et al., 2018). quantity and improving water quality by selecting the type,
Another method for the evaluation of NBSs is multi- design, size and location of NBSs (Behroozi et al., 2018; Gao
criteria analysis (MCA), which has the potential to integrate et al., 2015; Giacomoni and Joseph, 2017; Zhang and Chui,
and overcome the differences between social and technical 2018). Zhang and Chui (2018) systematically reviewed opti-
approaches (Loc et al., 2017). It can be used to structure com- misation models that have different structures, objectives and
plex issues and help find a better understanding of costs and allocation components. This section reviews some examples
benefits. Such analysis is useful for decision makers when of using optimisation to assess NBSs.
there are multiple and conflicting criteria to be considered A comprehensive modelling system typically refers to
(Alves et al., 2018b; Loos and Rogers, 2016). The MCA an optimisation package tool that integrates an “easy-
takes different criteria into account and assigns weights to to-use” user interface with physically based determinis-
each criterion. This process can produce a ranking of the dif- tic models. Examples include SUSTAIN (the System for
ferent measures that can be implemented on the site (Chow Urban Stormwater Treatment and Analysis IntegratioN;
et al., 2014; Jia et al., 2015). For example, Loc et al. (2017) Zhang and Chui, 2018) and best management practice de-
integrated the results from numerical modelling and social cision support (BMPDSS; Gao et al., 2015). The SUSTAIN
surveys into a MCA and ranked the alternatives based on the model was developed by the US Environmental Protection
evaluation criteria of flood mitigation, pollutant removal and Agency (US EPA) and aims to provide decision makers with
aesthetics. Loos and Rogers (2016) applied multi-attribute support in the process of selection and placement of NBS
utility theory (MAUT) to assess utility values for each al- measures and to optimise the hydrological performance and
ternative by assuming that preference and utility are indepen- cost-effectiveness of NBSs in the urban watershed (Leslie et
dent of each other. Petit-Boix et al. (2017) recommended that al., 2009; C. Li et al., 2018). There are several studies that ap-
future research combine the economic value of the predicted ply SUSTAIN with the aim of minimising the cost of NBSs
material and ecological damage, risk assessment models and for both run-off quantity (flow volume and peak flow) and
environmental impacts of NBSs. run-off quality (pollutant removal; Gao et al., 2015; N. Li et
Since not all assessments can be done with modelling al., 2018). It is, however, important to note that comprehen-
alone, interviews and fieldwork are often necessary. For in- sive modelling systems are not always easily modified to fit
stance, Chou (2016) used 18 open questions from six top- with the specific needs of users.
ics, namely accessibility, activities, public facilities, environ- Another optimisation tool approach is integrated model–
mental quality, ecological value and flood prevention. These algorithm tools, which combine numerical (hydrological–
questions are used to evaluate the qualitative performance of hydrodynamic) models with optimisation algorithms. A pop-
river restoration. However, some of the methods are only ap- ular optimisation method used to evaluate NBS perfor-
propriate for small-scale applications and cannot be applied mance is a multialgorithm, genetically adaptive multiobjec-
Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020 www.nat-hazards-earth-syst-sci.net/20/243/2020/L. Ruangpan et al.: Nature-based solutions for hydro-meteorological risk reduction 255 tive (AMALGAM) method using the multilevel spatial opti- two-dimensional models in the optimisation analysis. This is misation (MLSOP) framework (Liu et al., 2016). particularly important when considering estimation of flood In the reviewed articles, the non-dominated sorting ge- damages and other flood propagation-related impacts. netic algorithm II (NSGA-II) is used in most of the stud- ies to date. Wang et al. (2015) concluded that NSGA-II is 4.2.4 Tools for selection, evaluation and operation one of the most popular multiobjective evolutionary algo- of NBSs rithms (MOEAs) despite limited parameter tuning features and generally outperformed the other MOEAs in relation Recently, several selection and evaluation tools have been to the set of solutions generated. There are several exam- developed in order to assist stakeholders in screening, se- ples of the use of NSGA-II. Oraei Zare et al. (2012) min- lecting and visualising NBS measures. Examples of web- imised run-off quantity while maximising the improvement based applications developed to screen urban NBS measures of water quality and maximising reliability. Karamouz and are the green–blue design tool (atelier GROENBLAUW, Nazif (2013) minimised the cost of flood damage while min- 2019), PEARL KB (PEARL, 2019), climate adaptation app imising NBS cost in order to improve system performance (Bosch Slabbers et al., 2019) and Naturally Resilient Com- in dealing with the emerging future conditions under cli- munities solutions (Naturally Resilient Communities, 2019). mate change. Yazdi and Salehi Neyshabouri (2014) opti- These web-based tools allow the user to filter NBSs in rela- mised cost-effectiveness, which focused on land use change tion to their problem type, measure, land use, scale and loca- strategies including orchard, brush and seeding measures in tion. different parts of the watershed. All of the above-mentioned In addition to the above, there are also tools that combine studies coupled NSGA-II with the Storm Water Management both the selection and evaluation processes together to use Model (SWMM) developed by US EPA (Cipolla et al., 2016; as planning support systems tool. An example is the SuD se- J. Li et al., 2018; Mei et al., 2018; Tao et al., 2017; Wu et al., lection and location (SUDSLOC) tool, which is a GIS tool 2018; Yang et al., 2018; Zhu and Chen, 2017) to address the linked to an integrated 1-D hydraulic sewer model and a 2-D optimisation problems. surface model. UrbanBEATS (the Urban Biophysical Envi- There are two different optimisation methods of parti- ronments and Technologies Simulator) aims to support the cle swarm optimisation (PSO) which have been found in planning and implementation of WSUD infrastructure in ur- the course of this review. The modified particle swarm op- ban environments (Kuller et al., 2018). Other tools that can timisation (MPSO) is used by Duan et al. (2016) to solve be used to select and evaluate potential NBS interventions are the multi-objective optimal (MOO) of the cost-effectiveness Long-Term Hydrologic Impact Assessment-Low Impact De- of NBS-based detention tank design. Similarly, Behroozi et velopment (L-THIA-LID; Ahiablame et al., 2012; Liu et al., al. (2018) used the multi-objective particle swarm optimisa- 2015) and the GIS-based tool called the Adaptation Support tion (MOPSO) by coupling it with SWMM to optimise the Tool (AST; Voskamp and Van de Ven, 2015). Although these peak flow and mean total suspended solid (TSS) concentra- tools could be useful in assisting decision makers, some of tion reduction by changing the combinations of NBSs. them may not be suitable for every location and scale. For Another algorithm that is used for optimising the perfor- example, source data required into L-THIA-LID cover only mance of NBSs is simulated annealing (SA). SA is a gen- the US, and QUADEAU (Romnée and De Herde, 2015) is eral probability optimisation algorithm that applies thermo- only suitable for urban stormwater management on a public- dynamic theories in statistics. An example of a study with SA space scale. is given by Huang et al. (2018), who automatically linked In addition to the above, other models such as MIKE pack- SA with SWMM to maximise the cost and benefit for flood ages developed by DHI (Semadeni-Davies et al., 2008), the mitigation and layout design. The cost–benefit analysis is soil and water assessment tool (SWAT; Cheng et al., 2017), computed using annual cost, which includes both annual IHMORS (Herrera et al., 2017), and the urban water option- fixed cost and annual maintenance cost. Another study that eering tool (UWOT; Rozos et al., 2013) can be effectively applied SA is Chen et al. (2017), who combined SA with used in the analysis effectiveness of NBSs. SWMM to locate NBSs in Hsinchu County in northern Tai- To date, very few tools have been developed to calculate wan by considering three objective functions. These were multiple benefits of NBSs in monetary terms as well as to ad- minimising depths, durations and the number of inundation dress their qualitative benefits. Some examples are the Ben- points in the watershed. efits of SuDs Tool (BeST), which provides a structured ap- It can be observed that most of the optimisation models to proach to evaluating potential benefits of NBSs (Digman et date (both the comprehensive modelling system and model al., 2017; Donnell et al., 2018; Fenner, 2017), and the MU- algorithms) are coupled with SWMM for urban storm man- SIC (Model for Urban Stormwater Improvement Conceptu- agement. There is still a lack of research that uses optimi- alization) tool, which is a conceptual planning and design sation to maximise the efficiency of NBSs on a large scale tool that also contains a life cycle costing module for differ- as well as combining other co-benefits in optimisation (Ta- ent NBSs that are implemented in Australia (Khastagir and ble 3). Furthermore, there is a lack of research that employs Jayasuriya, 2010; Schubert et al., 2017). www.nat-hazards-earth-syst-sci.net/20/243/2020/ Nat. Hazards Earth Syst. Sci., 20, 243–270, 2020
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