Living Lab Demonstration of GBGI’s Multiple Co-Benefits for Multi-Hazard Risk Reduction
The LivGBGI project stands for “Living Lab Demonstration of GBGI’s Multiple Co-Benefits for Multi-Hazard Risk Reduction”. It is funded by Reclaiming Forgotten Cities - Turning Cities from Vulnerable Spaces to Healthy Places for People (RECLAIM Network Plus) under the 'Urban Greenspace and People Call.'
The LivGBGI project is led by teams from the University of Surrey and the Centre for Ecology & Hydrology (UKCEH). Its objective is to gather evidence for the direct benefits of Green-Blue-Grey Infrastructure (GBGI) for heatwaves and co-benefits for managing drought and flood risks, noise pollution and associated human health impairments.
The project expands the existing Guildford Living Lab (GLL) network of strategically located heat sensors at key sites, including ponds, grasslands, woodlands, and built environments. It further extends to three additional natural areas: a green wall, a pocket park, and a mixed area with a river and riparian trees. The aim is to assess the multifaceted benefits of GBGI in reducing risks associated with heatwaves, droughts, floods, and traffic noise. This assessment is achieved through monitoring environmental parameters and numerical modelling. Since the project's inception, various activities have been carried out by the project teams.
Notably, the project has produced robust results and built evidence showcasing the multifunctional benefits of GBGI against cascading hazards such as drought and flood risks, noise pollution, and associated human health impairments. These results were presented in the RECLAIM Network Plus, as illustrated in Figure 1. Additional activities and milestones achieved since the project's kickoff are highlighted below.
Figure 1. Dissemination and communication of project results at RECLAIM Network Plus Conference, Guildford, Surrey, September 2023.
Monitoring the efficiency of GBGI
The efficacy of various GBGI types in mitigating the harmful effects of rising temperatures in urban areas is of paramount importance. The LivGBGI project contributes to evaluating the effectiveness of different GBGI types by providing real-time data on their performance across Guildford, UK. For this purpose, an existing network of temperature and RH sensors (HOBO MX2301A) installed at four different types of GBGI expanded to seven GBGI types covering waterbody, park, woodland, green wall, pocket park, mixed green and blue infrastructure, and built environment to demonstrate their benefit, in terms of heat mitigation. The network of sensors was expanded in the summer of 2023, and the data started logging on the 1st of June 2023. The data was utilised to assess temporal (seasonal and diurnal) variation in the mean or peak daytime local temperatures, heatwave risk, Urban Heat Island (UHI) effect, and cooling efficiency of GBGI.
Figure 2. Location of temperature monitoring sensors.
Perception and awareness of multi-hazard and risk
Understanding residents' perceptions and responses to increasing heatwaves, particularly in urban areas, is vital for effective policies and interventions to mitigate heat-related risks. LivGBGI addresses knowledge gaps by examining participant attributes, behaviours, and concerns related to the UK heat waves through a co-designed survey. The survey provides insights into behaviours and perceptions, informing policies to address urban heat concerns. Participants from Guildford (37%) and the broader UK (52%) took part, with females constituting 53%, and the largest age group being 20 to 40 years (54%). Flats were predominant (31%), with a preference for the ground floor (57%), and outdoor Nature-Based Solutions (NBS) features like trees (23%) and green areas (44%) were significant. Participants spent an average of 15 hours at home, with 35% engaging in moderate activity. Daily commuting was common (38%), often by cars/taxis (38%) or walking (26%). Concerns about heatwaves (54%) prompted mitigation strategies such as fans (22%), ventilation (228%), and shading (18%). Support came from family/friends (53%) and neighbours (25%). Vulnerable individuals were absent in many households (56%). Salary ranges varied, with 55% willing to pay for heat mitigation measures. Respondents displayed concern, as evidenced by attention to weather forecasts (79%). The findings highlighted an interplay between urban residents' behaviours and environmental factors, underscoring the importance of green spaces for well-being. Mitigation strategies indicated awareness and proactive measures, but tailored support might be needed for vulnerable households. The willingness to pay underscored the severity of heatwave challenges, emphasising the need for targeted policies prioritising green infrastructure, health awareness, and community resilience to address urban heat concerns.
GBGI performance assessment based on severity, heatwave, and multi-hazard duration
Heatwave duration and intensity without and with GBGI
To extract the extremes (heatwaves) from the rest of the temperature time series, we identified temperature values exceeding the 28°C threshold (Sahani et al., 2023). For a detailed methodology, we refer to Sahani et al. (2023). The methodology employed in this study aimed to quantify heat duration and intensity from a time-series dataset of temperature values using the R programming language. Heat duration was determined by summing the calculated time intervals. This cumulative duration provided insights into the overall period under consideration, representing the temporal scope of the temperature dataset. Average temperature, a descriptive statistic, was computed to capture the central tendency of the temperature values throughout the dataset. The mean function was applied to the temperature column, offering a representative measure of the prevailing thermal conditions.
The calculation of heat intensity involved a nuanced approach. Multiplying each time interval by its corresponding temperature value, we aimed to quantify the combined impact of temperature and time. The product of these values was then summed and divided by the total heat duration, resulting in a comprehensive measure of heat intensity. Finally, the results were displayed in Figure 4, which included heat duration and heat intensity.
Figure 4. Heatwaves duration and intensity of summer 2021 (a) and 2022 (b).
Figure 4a shows that in 2021, a better temporal cooling efficiency of GBGI is observed with less heatwave intensity ranging from 28.6°C (woodland) to 29.0°C, occurring for 3 to 5 days. In contrast, the built-up area exhibited a heatwave intensity of 34.7°C for 8 consecutive days, commencing on 2021-07-16 and lasting until 2021-07-23. Similarly, in 2022, where record heatwaves were recorded, areas equipped with GBGI produced lower heatwave intensity (Woodland = 30.1°C to Lake = 33.0°C) and shorter duration (3 to 5 days). Meanwhile, areas without GBGI (built-up) showed extensive and longer heatwave intensity (35.3°C) and duration (14 days), as shown in Figure 4b. Overall, during the heatwaves, GBGI reduced heatwave intensity and duration by up to 6.1°C and 5 days in 2021, and 5.2°C and 11 days, respectively, compared to areas without GBGI (built-up).
Estimating potential evapotranspiration with and without GBGI
In adherence to the hydrological data processing guidelines established by the UK National River Flow Archive, a water/hydrological year spans from October 1 to September 30. Therefore, to characterise multi-hazards and assess the effectiveness of GBGI, we conducted evaluations over three distinct periods—3 months (June to August), 6 months (April to September), and 12 months (October to September). For estimating evapotranspiration, we have used empirical methods mainly based on temperature, which became very popular due to their limited data requirements. Therefore, the Hargreaves method is considered for the calculation of PET.
The effectiveness of GBGI in reducing extreme PET is illustrated in Figure 5. The results indicate that during peak heatwave months, such as July to August, the average PET is approximately 141 mm/day in areas equipped with GBGI and 209 mm/day in built-up areas (with no natural elements). Consequently, over the three peak heatwave months, GBGI can, on average, reduce PET by up to 68 mm/day of water from the surroundings, thereby maintaining lower temperatures compared to the grey (built-up) areas, as shown in Figure 5.
Figure 5. Time series of monthly potential evapotranspiration (PET) and heatmap estimated for the years 2021 and 2022.
The role of GBGI in reducing compound and cascading multi-hazards
Heatwaves and droughts, collectively referred to as 'dry' hazards in this context, share common antecedents such as prolonged periods of below-normal precipitation and elevated temperatures. These hazards may manifest concurrently, compound or sequentially, with one event following another in a cascading fashion. In this context, compound hazards are the simultaneous occurrence of two or more extreme events on the same day and within the same region. Cascading events, on the other hand, are described as the successive or cumulative occurrence of two or more extreme events, either as single hazards or compound hazards, over time without interruption by a hazard-free day (Sutanto et al., 2020).
Figure 6. The 3, 6, and 12 months heatwaves (a) and drought Reconnaissance Drought Index (RDI) (b) were calculated for the years 2021 and 2022.
The drought severity is assessed through the computation of the Reconnaissance Drought Index (RDI). RDI is expressed in both the initial and standardised forms. The initial value of RDI is usually calculated for the i-th year on a time basis of k consecutive months. The results of RDI drought intensity are presented in Figure 6. The results show that heatwaves impact triggering drought conditions in soil moisture, specifically agricultural drought. For instance, in 2022, the three-month heatwave intensity averaged 32.3°C in areas with GBGI, compared to 37.9°C in built-up areas, representing an efficiency of 5.6°C reduction in heat intensity. Simultaneously, this heatwave intensity triggered an extreme drought in soil moisture, where the GBGI reduced the drought intensity from 8-20% or on average up to 0.19 compared to areas without natural elements (Figure 6).
GBGI for River and Urban Flood Risk Reductions
The simulations for the efficiency of seven GBGI types are shown in Figure 7. To evaluate the performance of the GBGI, simulations were run with seven GBGI types by spatially varying Manning’s coefficient (n). The River Wey catchment in Guildford is considered a case study. The Hydraulic Engineering Center’s River Analysis System (HEC-RAS) was set up as a coupled 1D-2D model (1D and 2D hydraulic model), in which river flow structures (e.g., bridges) are modelled in one dimension, and floodplain flow is modelled in two dimensions.
Figure 7. Guildford land use and type classification (a) and digital elevation map (DEM) and geographical location of the Wey River (blue lines) for flood modelling.
Acknowledgements
LivGBGI is supported by the UKRI (EPSRC, NERC, AHRC) funded RECLAIM Network Plus (Grant No. EP/W034034/1)) project.
by Dr Sisay E Debele, Jeetandra Sahani, Soheila Khalili (all from the University of Surrey), David Fletcher, Prof. Laurence Jones (both from UKCEH), Prof. Prashant Kumar (University of Surrey)
Reference
Sahani, J., Kumar, P., Debele, S.E., 2023. Efficacy assessment of green-blue nature-based solutions against environmental heat mitigation. Environment International, 179, p.108187.
Sutanto, S.J., Vitolo, C., Di Napoli, C., D’Andrea, M. and Van Lanen, H.A., 2020. Heatwaves, droughts, and fires: Exploring compound and cascading dry hazards at the pan-European scale. Environment International, 134, p.105276.