The ‘cooling urban water environments’ concept: potential for application in practice

ABSTRACT

Research indicates that water in small water bodies has negligible cooling effects, but also that its surrounding environment can be designed to become cooler by applying the ‘cooling urban water environments’ concept. However, this concept was created for generic urban environments and not tested in practice. This study applies this concept to a specific urban environment, tests its micrometeorological performance and surveys how urban designers and landscape architects regard its usability. The results indicate that the ‘cooling urban water environments’ concept can lead to site-specific cooling effects and that there is willingness amongst practitioners to apply this concept.

KEYWORDS:

• Urban climate
• urban design
• urban water bodies
• climate-responsive design
• practice and implementation

Introduction

Cities worldwide are increasingly experiencing the impacts of climate change, of which heat waves, precipitation extremes, flooding, drought or storms are amongst the most widely described (IPCC 2021; Votsis, Ruuhela, and Gregow 2021). The heat-related impacts on human comfort and health are particularly serious (Rost et al. 2020; Ruuhela et al. 2021; Yang et al. 2020). Research on climate-responsive design, nested within the broader field of urban resilience (Therrien, Usher, and Matyas 2020), has been widely addressing heat-related challenges and opportunities with the goal of contributing to the liveability of urban areas and the well-being and health of their populations (e.g., Attia et al. 2019; Kleerekoper 2016).

Water is frequently employed in urban design and landscape architecture (henceforth referred to as spatial design) often fuelled by the assumption that water bodies deliver cooling effects in summer. However, research has been challenging the idea of water as a coolant. Regarding large water bodies, such as rivers or lakes, research revealed their limited daytime cooling effects and that they may eventually lead to night-time warming (Heusinkveld et al. 2014; Steeneveld et al. 2014). Relatively to small urban water bodies (Figure 1) such as ponds or canals embedded in urban profiles with varying dimensions and functions on and along the water, results from previous research point out different microclimatic effects.

Figure 1. Example of a small urban water body: canal in Aarhus, Denmark.

Source: João Cortesão.

While research indicates that small urban water bodies lead to negligible cooling effects during the day and to insignificant warming effects during the night (Jacobs et al. 2020; Solcerova, van de Ven, and van de Giesen 2019), previous research also reports cooling effects (Manteghi, Bin Limit, and Remaz 2015; Robitu et al. 2006) and that shading water, vaporizing water and proper ventilation around the water body can keep urban water bodies and their surroundings cooler (Coutts et al. 2013; Oláh 2012; Rinner and Hussain 2011). Fuelled by these opportunities for cooling, the concept of ‘cooling urban water environments’ has been proposed in the ‘REALCOOL’ research (Cortesão et al. 2019; Jacobs et al. 2020) as a combination of the water body itself with four design principles:

1. substantially increasing shading and evapotranspiration with trees near the water

2. not blocking wind

3. installing water evaporation features close to sojourn places

4. enabling physical access to the water body

This combination can lead to more cooling effects than the ones achieved by considering its components separately, in particular, the water body left alone. The ‘cooling urban water environments’ concept was developed for urban environments not specific to a site (Cortesão et al. 2020). Although this concept was targeted at assisting design practitioners, it is known that the practical application of urban climate knowledge can be challenging due to its common abstractness (Graça et al. 2022; Klemm, Lenzholzer, and van den Brink 2017). In the case of the ‘cooling urban water environments’ concept, it is unknown if it can lead to cooling effects when applied to a specific urban environment and, if so, how likely that this concept will be applied by spatial designers in practice.

To fill this knowledge gap, this study tested the applicability of the ‘cooling urban water environments’ concept focussing on: the micrometeorological performance of a site designed based on this concept and the way spatial designers regard its usability. Three questions (RQ) were defined:

• What are the micrometeorological effects of cooling urban water environments during a hot summer day when applied to a specific urban environment? (RQ1)

• Can the misconception about the cooling effects of water be changed amongst spatial designers? (RQ2)

• Are spatial designers willing to start applying the ‘cooling urban water environments’ concept? (RQ3)

Addressing these questions is relevant (1) with regards to testing the cooling effectiveness of the ‘cooling urban water environments’ concept when applied to a specific context; and (2) when considering the way urban designers and landscape architects in practice regard the usability of this concept.

This study contributes to the scholarly urban design literature by providing more robustness to the formerly theoretical concept of ‘cooling urban water environments’ through a practice-oriented research. For the professional community this study offers insights relevant to start implementing small urban water bodies tackling urban heat stress.

Materials and methods

To answer the questions above, this study employs numerical modelling with ENVI-met on the micrometeorological effects of the concept applied to a specific urban environment (RQ1) and a survey on the likelihood for its application by spatial designers (RQ2 and RQ3).

Modelling micrometeorological effectiveness

The ‘GreenQuays’ project was used as a case as it is a design-driven research for developing climate-responsive and nature-inclusive practical solutions for the river Mark, situated in the city of Breda (51.572 N, 4.768E, Köppen climate zone Cfb, the Netherlands). GreenQuays provided the suitable context to address RQ1 because its research outcomes fed the projected retrofitting of a small urban water body. Furthermore, this site represents a ‘cooling urban water environment’ defined in the REALCOOL project (which was taken as the theoretical framework of the present study): the river Mark fits in a street canyon matching the REALCOOL design prototype ‘Canal 2’: a 25 m wide canyon in a high-density urban area, with a central 9 m wide water body flanked by low quays with lined-up trees. Water at this spatial setting leads to very limited cooling effects (Jacobs et al. 2020).

The GreenQuays intervention area (Figure 2) is the 500 m-long stretch of the river Mark situated between the high-density commercial core of the city centre and the mid-density adjacent residential areas. The goal of the intervention is to refurbish the open-air segment of this stretch of the river and daylight the currently culverted segment, while bolstering climate adaptation, urban ecosystems and recreation. Regarding climate adaptation, heat stress is the focus as few conditions are on place for people to remain outside during summer and heat wave days. This results from the North-South orientation combined with low height-to-width ratio (meaning full exposure to sun in the midday), predominantly hard-paved surfaces, the absence of vegetation and trees planted inefficiently regarding the provision of shade.

Figure 2. The intervention area of the GreenQuays project: location of the stretch of the river Mark within the city centre of Breda, the Netherlands (a); the open-air and culverted segments of the river Mark (b).

Source: adapted from Google Earth.

A climate-responsive masterplan addressing these problems was developed by Wageningen University based on the ‘cooling urban water environments’ concept. This masterplan comprised introducing a number of deciduous trees (heights between 6 and 14 m) planted at intervals along the water body and positioned so as not to block the wind, and also de-paving and/or replacing pavement by grasses at specific spots and introducing water misting nozzles (water consumption of 18 liters/hour) at sojourn locations. These measures took into account accessibility and mobility needs, surrounding building functions, heritage values and were discussed with, and validated in terms of feasibility, by municipality members involved in GreenQuays. The masterplan was merged into the design schema developed in parallel by the GreenQuays design team, which was eventually the input for running the ENVI-met modelling (Figure 3).

Figure 3. The design schema developed by the GreenQuays design team, which incorporates the climate-responsive masterplan developed by Wageningen University. ‘GreenQuays project area’ denotes the stretch for which the ENVI-met modelling was performed.

Source: Municipality of Breda.

The micrometeorological modelling was performed with the ENVI-met 4 model for the open-air segment of the water body, as this stretch constitutes the first project’s implementation phase. ENVI-met was selected due to its widespread use in urban microclimate studies (Toparlar et al. 2017). Furthermore, compared to other models, ENVI-met enables the simulation of complex interactions between buildings, atmosphere, soil and vegetation processes (Simon 2016), necessary to assess the microclimate effects of the masterplan. Finally, ENVI-met enables a straightforward (graphical) assessment of thermal effects. ENVI-met has been validated by previous research, particularly for testing the effects of green and blue infrastructure (Alsaad et al. 2022; Liu et al. 2021; Tsoka, Tsikaloudaki, and Theodosiou 2018). The modelled Physiological Equivalent Temperature (PET) was used as the main indicator for the effectiveness of the design measures. PET was selected as it closely relates to the actual experience of people regarding physiological thermal stress (Lee, Mayer, and Chen 2016). Furthermore, PET uses a ‘temperature’ scale that alludes to people’s thermal perception in an easily understandable way, thereby deemed appropriate for communicating to spatial design practitioners (Matzarakis, Mayer, and Iziomon 1999). The PET analysis was generated for a level of 1.35 m above the ground surface, which lies between the average centre of gravity of the human being (1.1 m) (Matzarakis, Mayer, and Iziomon 1999) and the commonly used height of 1.5 m for meteorological observations. PET difference maps (between the proposed design and the existing spatial situation) were chosen as the output to analyse the data resulting from the modelling.

The modelling was conducted for the 1^st of July 2015, which was a hot day with a maximum air temperature of 34.9°C, a gentle breeze 3 ms⁻¹ (2 Bft.), mostly cloudless (some translucent high clouds, 0–2 octas) and 31% relative humidity at the nearby air base Gilze-Rijen (WMO code 06350). These conditions have been used in previous research (Koopmans, Heusinkveld, and Steeneveld 2020). The ENVI-met model was set to start at 6 a.m. CET (=UTC+2). The results analysed refer to the time range between 11 a.m. CET and 4 p.m. CET. A spin-up of two days was performed to correctly initialize the soil, water temperatures and soil moisture properties. The model was fed at the edges with weather data from the neighbouring KNMI station Gilze-Rijen. Wind direction was east as it is the prevailing direction during heat waves in Western Europe (Gromke et al. 2015).

The modelling was repeated for the 4^th of May 2015, selected as a contrasting cooler day in order to perform a broader evaluation of the results obtained and simulate the effects of the proposed design for cooler and windier circumstances. This date was characterized as a cloudy day with south-westerly winds (often causing wind nuisance). The maximum air temperature was 19.7°C and the imposed wind speed on the domain borders was 5 ms⁻¹ (3 Bft.).

Survey on applicability in practice

The survey consisted of two questionnaires built with the online tool Typeform. The first questionnaire was to inquire viewpoints of practitioners directly involved in discussing and applying the ‘cooling urban water environments’ concept. The sample entailed eight spatial designers of the GreenQuays design team. This small sample was the only option for receiving the feedback of practitioners directly involved in the application of the ‘cooling urban water environments’ concept, given the timeframe of the GreenQuays design project. The questionnaire included one close-ended statement and a question of relevance to the present study, namely to RQ2 and RQ3:

• Statement: ‘This project changed your perception about the cooling effects of water – namely that water does not necessarily cool its surroundings’

• Question: ‘If your perception about the cooling effects of water is now different, which changes will it bring to your design activity beyond this project?’

The statement was to examine whether the misconception about the cooling effects of water had been accepted. The answers were given on a seven-point Likert scale, ranging from ‘strongly agree’ to ‘strongly disagree’. The question was to understand whether the new knowledge provided with the research was likely to have short- or longer-term effects on design decisions. This question was answered with the following multiple-choice options: ‘you will use urban water bodies the same way you have been using so far (e.g., for aesthetics or recreation)’; ‘you will start designing urban water bodies based on a combination of water, shade, wind and water features (e.g., sprays)’; and ‘you will no longer use urban water bodies’. This question also included an optional open-ended possibility for giving respondents more answering latitude. The data obtained underwent a basic descriptive statistical analysis expressed as percentage distributions using Excel spreadsheets.

The second questionnaire was targeted at expanding the results of the first questionnaire with the feedback of a wider sample of practitioners. This questionnaire was presented at the end of a webinar held online in February 2022 on the negligible thermal effects of water and on the ‘cooling urban water environments’ concept. Sixty participants followed the webinar and 44 (73%) completed the questionnaire. The sample comprised practitioners from the fields of urban planning and urban design (20% and 23%, respectively) and ‘landscape architecture’ (57%). 61% of respondents worked in a design/planning office, followed by consultancy (21%), municipality/government (11%) and NGO (7%). 55% of participants were based in the Netherlands, 45% in other (non-disclosed) parts of the world.

The questionnaire comprised the statement and question of the first questionnaire, however slightly adapted to the scope of the webinar (not specific to GreenQuays):

• Statement: ‘This webinar changed your perception about the cooling effects of water – namely that water does not necessarily cool its surroundings’

• Question: ‘If your perception about the cooling effects of water is now different, which changes will it bring to your design activity?’

The answering format and options were the same as the first questionnaire, to ensure consistency in the comparison of the results. Three last questions allowed characterizing the sample: ‘what is your field of work/discipline?’, ‘in which sector are you employed?’ and ‘where are you based?’. ‘Other’ was offered as answering option for identifying participants eventually not working with spatial design. The data obtained was anonymous and also underwent a basic descriptive statistical analysis. This analysis excluded answers of respondents not working with spatial design and/or not in practice.

None of the questionnaires were subject to the need for ethics approval: the first was protected by the confidentiality terms of the GreenQuays project; the second operated in fully anonymous and undisclosed terms.

Results

The results of testing the ‘cooling urban water environments’ concept on micrometeorological effects and its applicability are herewith presented in the sequence of the research questions. Table 1 presents an overview of the main results obtained. All results are discussed in detail in the sub-sections below.

Table 1. Overview of the results obtained in this study.

Micrometeorological effectiveness RQ1 – what are the micrometeorological effects of cooling urban water environments during a hot summer day when applied to a specific urban environment?	Hot summer day (1^st of July, 11 a.m. CET)
	Applying ‘cooling urban water environments’ led to an increase of spots with relatively low PET values within a somewhat continuous previously sunlit area. This is mostly due to reduced air temperatures resulting from a larger area shaded with trees. Sunlit spots leeward of the trees present higher PET values due to slightly decreased wind speed values at these spots. The cooling effects of water evaporation are relatively small.
	Hot summer day (1^st of July, 4 p.m. CET)
	The shading pattern of trees is larger than at 11 a.m. but the relatively continuous area of lower PET values along the water is not as distinguishable as at 11 a.m. Evapotranspiration by the trees is lower than at 11 a.m. due to limited soil moisture availability in ENVI-met.
	Relatively cool and windy day (4^th of May)
	The PET differences between the proposed design and the existing situation are smaller than for the 1^st of July due to more ventilation and to partly cloudy skies. Some spots of lower PET are still noticeable although the extent of higher PET spots is larger than for the 1^st of July.
Applicability in practice RQ2 – can the misconception about the cooling effects of water be changed amongst spatial designers?	Questionnaire 1 (GreenQuays design team)
	All respondents indicate start perceiving water not necessarily as a coolant.
	Questionnaire 2 (broader sample of practitioners)
	Most respondents (78%) indicate start perceiving water not necessary as a coolant.
Applicability in practice RQ3 – are spatial designers willing to start applying the ‘cooling urban water environments’ concept?	Questionnaire 1 (GreenQuays design team)
	All respondents indicate willingness to start applying the ‘cooling urban water environments’ concept. No respondent indicates neither to keep using water bodies the same way, nor to no longer use urban water bodies.
	Questionnaire 2 (broader sample of practitioners)
	95% indicates willingness to start applying the ‘cooling urban water environments’ concept. 5% indicates using urban water bodies the same way they had been using. No respondent indicates to no longer use urban water bodies.

Micrometeorological effectiveness

The micrometeorological modelling for the hot summer day (1^st of July) at 11 a.m. CET shows that the application of the ‘cooling urban water environments’ concept to the river Mark resulted in an increase of spots with relatively low PET values, mostly below 31°C. Figure 4 shows the PET difference map originated with ENVI-met where these spots are depicted in dark blue. The lower PET spots can be found along a relatively continuous area of lower PET values depicted (Figure 4) in tints of green.

Figure 4. PET difference modelled in ENVI-met between the proposed design and the existing situation, at 11 a.m. CET of the 1^st of July 2015.

Source: ENVI-met.

The PET reductions are likely to result from reduced air temperatures, which were largest around the trees’ canopies introduced in the proposed design and with a magnitude of 0.5–1.3°C compared to sunlit areas in the existing situation (Figure 5). Evapotranspiration contributed ~30% to the air temperature reduction. Although practically the whole area presents lower air temperatures downwind from the trees, the modelled PET difference at 11 a.m. CET also exhibits higher PET values at sunlit spots leeward of the trees (Figure 4). The model results showed slightly decreased wind speed values at these spots leading to an increase in PET (Figure 5, lower panel). The cooling effects of water evaporation features reached a maximum reduction of air temperature between 0.2°C and 0.3°C. Due to these low values and the small size of the water nozzles, the PET difference maps (Figure 4) cannot depict the cooling effects of these water features.

Figure 5. Air temperature (a) and wind speed (b) difference between the proposed design and the existing situation modelled in ENVI-met, at 11 a.m. CET of the 1^st of July 2015.

Source: ENVI-met.

Regarding the PET differences at 4 p.m., the model results show that the shading pattern of trees is larger than at 11 am (Figure 6). However, at 4 p.m. the relatively continuous area of lower PET along the water body is not as clearly visible as at 11 a.m. The evapotranspiration provided by the trees at 4 p.m. is a factor 2–3 lower than at 11 a.m., which is related to limited soil moisture availability in ENVI-met.

Figure 6. PET difference modelled in ENVI-met between the proposed design and the existing situation, at 4 p.m. CET of the 1^st of July 2015.

Source: ENVI-met.

The model results obtained for the relatively cool and windy day (4^th of May) show that the PET differences between the proposed design and the existing situation are smaller than for the 1^st of July (Figure 7). The weather conditions on this date were less favourable for spatial variability in PET as there was more ventilation, therefore blending local PET differences. Furthermore, this was a partly cloudy day, which implies less differences in radiation between sunlit and shaded places. However, some spots of relatively low PET are still noticeable even though the extent of higher PET spots is larger than for the 1^st of July.

Figure 7. PET difference modelled in ENI-met between the proposed design and the existing situation, at 11 a.m. CET of the 4^th of May 2015.

Source: ENVI-met.

Applicability in practice

All respondents to the first questionnaire answered ‘yes’ to the initial statement (‘this project changed your perception about the cooling effects of water’). The responses were also unanimous regarding willingness to ‘start designing urban water bodies based on a combination of water, shade, wind and water features’. No respondent indicated neither to keep using water bodies the same way, nor to no longer use urban water bodies.

The results of the second questionnaire show that the webinar changed the perception of most respondents about the cooling effects of water (Figure 8), with a total of 78% of responses agreeing, compared with 13% disagreeing and 9% neutral.

Figure 8. Distribution of responses obtained for the statement of the second questionnaire: ‘this webinar changed your perception about the cooling effects of water – namely that water does not necessarily cool its surroundings’.

Regarding the question on which changes this new perception would bring to their practice of designing water bodies, the majority (95%) indicated to ‘start designing urban water bodies based on a combination of water, shade, wind and water features’ against a minority (5%) choosing ‘you will use urban water bodies the same way you have been using so far’ (Figure 9). No respondent chose ‘you will no longer use urban water bodies’.

Figure 9. Distribution of responses obtained for the question of the second questionnaire: ‘if your perception about the cooling effects of water is now different, which changes will it bring to your design activity?’.

Discussion

Micrometeorological effectiveness for a hot summer day

The results of the micrometeorological modelling for a hot summer day (1^st of July) show that positive cooling effects can be achieved around small urban water bodies when the ‘cooling urban water environments’ concept is applied to a specific urban environment (RQ1). This supports the results of the REALCOOL project (Jacobs et al. 2020) with site-specific data. The PET values observed in the cooler spots identified with the modelling for the 1^st of July at 11 a.m. correspond, in PET classes (Matzarakis, de Rocco, and Najjar 2009), to a thermal perception of ‘warm’ or ‘slightly warm’ and a ‘grade of physiological stress’ between ‘moderate heat stress’ to ‘no thermal stress’. Compared to the current situation, these PET classes represent reduced heat stress. This reduction is related to the larger area of shade provided by the deciduous trees comprised in the masterplan.

Regarding the first design principle of ‘cooling urban water environments’ (substantially increasing shading and evapotranspiration with trees near the water), the major influence on the PET and air temperature reductions observed was the increase in shade and evapotranspiration from trees with large crowns. This echoes the widely documented capacity of trees to regulate urban microclimates (e.g., Lenzholzer 2015; Ouyang et al. 2021) and confirms the adequacy of the first principle of ‘cooling urban water environments’ to a specific urban environment. The shade trees cast over the water is not likely to increase the cooling effects of water itself, which remain negligible (Jacobs et al. 2020). Also, the modelled cooling effects from trees require enough water availability. When heat waves are accompanied with drought, evaporative cooling can be hampered (Kabano, Lindley, and Harris 2021; Marchionni et al. 2021).

Regarding the second design principle (not blocking wind), the results confirm that increasing vegetation (design principle 1) should not block wind. This principle has also been described in the literature elsewhere (e.g., Manteghi, Bin Limit, and Remaz 2015; Saaroni and Ziv 2003) and sufficient ventilation can be provided by clustered, smaller tree canopies in strategic spots where many people circulate or stay. The locally increased PET values resulting from wind blocking do not necessarily mean undesirable microclimatic conditions as they are offset by significant PET reductions. It can be argued that the variety of cooler and warmer spots modelled for the proposed design provides people with a diversity of ways to meet their personal comfort requirements (e.g., Nikolopoulou 2011) throughout the day in different seasons. All in one, the second principle of ‘cooling urban water environments’ is confirmed for this specific urban environment. Although the importance of ventilation depends on the climate type, being relatively more important in hot and humid climates, the expected longer, more intense and frequent extreme heat periods render ventilation equally relevant to other climate types.

For the third design principle (installing water evaporation features close to sojourn places), despite their described effective cooling effects (Ulpiani 2019), water evaporation through fountains and misting nozzles could not be proven to contribute significantly to the PET reductions due to limitations of the ENVI-met model.

The fourth design principle (enabling physical access to the water body) deals with the benefits for mental health from being close to water (e.g., Völker and Kistemann 2011). The effects of this principle can only be assessed with an ex-post analysis of the environments created. This was, nevertheless, a topic discussed throughout the GreenQuays co-creation meetings and eventually included in the final design schema with stairs and ramps towards the water and with lowered quays (Figure 10).

Figure 10. Artist’s impression showing how accessibility to water was incorporated in the GreenQuays project.

Source: Municipality of Breda.

Micrometeorological effectiveness for a relatively cool and windy day

Regarding the results obtained for a relatively cool and windy day (4^th of May), the reason for the smaller PET and air temperature differences observed is that, compared to the relatively hot summer day, there is more ventilation and, as a result, local air temperatures are more effectively mixed. Another reason is that the cloud cover value in the situation modelled for May is higher (5/8 octas) than the one modelled for July, which results in lower incoming global radiation and smaller radiation differences between shadow and sunlit spots.

Since the radiation differences were less substantial on a relatively cool and windy day, wind is likely to have had a more important influence on the PET values obtained. While for the relatively hot and cloudless situation this wind effect might lead to higher PET values locally leeward of the trees, for the relatively cool and windy day wind reduction is desirable. The chilling effect of the wind, coupled with high wind speed and turbulent wind flows around buildings can lead pedestrians to experience discomfort (Lenzholzer 2015). Creating cooling urban water environments therefore calls, from the outset of the project, for an inter-seasonal understanding of the need for and the effects of the design interventions employed.

Applicability in practice

Despite some nuances in the distribution of votes, the responses obtained to the questionnaires indicate acceptance amongst practitioners that water is not necessarily a coolant (RQ2) and that they are willing to start applying the ‘cooling urban water environments’ concept (RQ3). Two factors related to the way knowledge was shared with practitioners are worthy of reflection regarding the disagreement in the responses obtained to the second questionnaire. The first aspect is the sharing of knowledge through the face-to-face, transdisciplinary contact between researchers and practitioners during the GreenQuays co-creation meetings. This might have led to a better understanding and acceptance of the ‘cooling urban water environments’ concept and, thus, explain the unanimity of responses obtained within the GreenQuays design team. The richness of this face-to-face process is recognized in previous research on employing co-creation/production (e.g., Lindquist and Campbell-arvai 2021). This knowledge transfer process is of a different nature than the webinar, which was an online, single-time, informative session that did not involve neither a co-creation process nor the systematic interaction between researchers and practitioners to produce a design product, as in GreenQuays.

The second aspect worthy of reflection is the time available for conducting the surveys. While researchers and practitioners cooperated within GreenQuays in the course of one year, the webinar had a duration of one hour only. This represents a substantial difference in the time available for sharing (researchers), discussing (researchers and practitioners) and processing knowledge (practitioners). The shorter time available for transferring knowledge during the webinar might have led to unclarity and, thus, to the neutral and disagreement responses on the initial statement of the second questionnaire.

These responses might also be explained with previous familiarity with the topic (n = 6), as the respondents choosing for neutrality or disagreement all answered the subsequent question with the same answer as the respondents on the agreement side of the scale (‘you will start designing urban water bodies based on a combination of water, shade, wind and water features’). Some attendees might have accessed information on the topic beforehand. In this case, it can be argued that the negligible cooling effects of water was not new information for them.

The face-to-face GreenQuays meetings and the online webinar engaged practitioners and transferred them the intended knowledge. Eventually the design principles of cooling urban water environments comprised in the climate-responsive masterplan could not be fully applied into the GreenQuays design schema due to underground infrastructure, mobility and budget issues. Although this type of constraints was also observed in the REALCOOL project (Cortesão et al. 2019), they are not specific to cooling urban water environments but recurrent feasibility issues in spatial design practice.

Limitations

This study was conducted in the Netherlands and, thus, its findings are only presumably suitable to locations in a similar climate zone (Köppen Cfb), latitude and soil type(s), where temperatures, solar angles, precipitation and evaporation patterns are comparable. Applying the ‘cooling urban water environments’ concept to other contexts requires new research and could also consider aspects such as local design culture or socio-cultural idiosyncrasies.

The Green Quays intervention area is a 500 m-long stretch of a river. Therefore, the implications of this study to other small urban water bodies should be critically assessed. The cooling effects herewith documented might substantially differ from those of, for instance, large but shallow urban water bodies.

ENVI-met has limitations that might have conditioned the results obtained. For example, the generally less significant cooling effects of trees modelled with ENVI-met for the 1^st of July at 4 p.m. are due to a lower evapotranspiration value induced by low soil moisture availability in ENVI-met.

While the willingness of practitioners in applying the ‘cooling urban water environments’ concept was observed at this point, it is difficult to know whether or not it will be followed through on. Also, a wider sample of respondents to the questionnaires could have led to different results regarding the applicability of the concept.

Conclusion

The goal of this study was to test the cooling effectiveness of the ‘cooling urban water environments’ concept when applied to a specific context. This concept was proposed by previous research on water-related climate-responsive urban design, but only for generic urban environments. In this study the concept was tested in a specific urban environment on its micrometeorological effects, and on the way spatial designers regard the usability of this generic and theoretical urban design concept in practice.

It is concluded that employing the ‘cooling urban water environments’ concept can lead to cooling effects during hot summer days when applied to a specific urban environment (RQ1). The results of the micrometeorological modelling supported previous research stating that the most effective principle in reducing PET is the increase of shading and evapotranspiration with trees strategically positioned along the water body. Intensifying tree coverage might, however, lead to increasing PET leeward of the trees due to wind blockage. Hence, it is recommended that planting trees follows patterns in which ventilation is also guaranteed.

The first main conclusion of this study is that the design principles comprised in the ‘cooling urban water environments’ concept are valid when applied to specific urban environments with regards to their micrometeorological effects.

It is also observed that the misconception about the cooling effects of water can be changed amongst spatial designers (RQ2) and that these professionals seem to be willing to start applying the ‘cooling urban water environments’ concept (RQ3). Therefore, the second main conclusion of this study is that water may no longer be regarded necessarily as a coolant and that the designing of small urban water bodies may start incorporating the ‘cooling urban water environments’ concept: placing the actual cooling interventions (shading, ventilation, evaporation features and access to water) in the direct vicinity of the water body. These conclusions imply that the ‘cooling urban water environments’ concept holds the potential to set the tone for a novel way of designing small urban water bodies.

The findings and discussion points above indicate the need for site-specific assessments of the ‘cooling urban water environments’ concept. It is recommended that future research develops more detailed micrometeorological quantitative assessments. These assessments can lead to refining the concept herewith presented. Furthermore, this concept should be tested on its validity in other climate zones, latitudes, natural and cultural conditions. It is essential to investigate the concept further on practice-related criteria, such as cost-effectiveness or maintenance costs. Likewise, future research should investigate whether or not this concept is actually followed through.

Acknowledgments

The authors would like to express their gratitude to the Wageningen University MSc thesis student Man Du, for her contribution to the GreenQuays climate-responsive masterplan.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The micrometeorological modelling was supported by the Netherlands Organisation for Scientific Research [Grant 864.14.007]. The GreenQuays project is supported (co-financed) by the European Regional Development Fund through the Urban Innovation Actions Initiative [Grant UIA04-139 GreenQuays].