IF PENANG WANTS to maintain its status as one of the most liveable cities in the region, investing in quality green spaces is a given path to take—they have multiple co-benefits, from acting as places of respite to encouraging physical activity, while offering natural habitats for other living things. It is also well established that proximity to nature has a positive effect on mental health; one study suggests that a 90-minute nature walk reduces depression.[1] One other benefit that is gaining attention is the impact of greening on climate-induced urban heat, which is becoming a growing concern in Malaysia.

There are multiple international and local benchmarks to decide the appropriate level of green space. These include standards such as dedicating 10% of total area into green space based on square metres per capita. The benchmark for green space per capita in Malaysia (set by PlanMalaysia) is 20m2 per person. In Penang, this figure is 8.3m2 per person. In 2021, Cecil Konijnendijk from the Nature Based Solutions Institute[2] proposed the 3-30-300 rule, which states:

“Everybody should be able to see three large trees from their home, live in a neighbourhood with at least 30% tree canopy (or vegetation) cover and be no more than 300metres from the nearest public green space that allows for multiple recreational activities.”

Who can disagree with this as an aspiration? As a metric, this captures the mental health, physical health and climate values of urban green space, while retaining a level of simplicity that anyone can understand and relate to. It also moves us beyond an aggregated measure (e.g. square metres per person) to a more localised view, which considers real life experiences in different neighbourhoods in different parts of a given district.

While the premise is simple, trying to measure if a place meets this rule is not a walk in the park. Firstly, there are a host of definitional issues to address. It may sound silly, but how do we define a “tree”, how do we define a “neighbourhood” and what counts as an “urban green space”? Does a green roundabout count? Probably not.

The next challenge is the quality of the data—calculating this metric for individual buildings for a whole city is not straightforward; quantifying sightlines from individual buildings to trees, at scale, is quite a computational task. At what point do you consider a tree too far away to be in “view”? So, should this be a goal that Penang should aspire to achieve? Can we measure it? If so, how far are we from meeting the target?

Three Large Trees

According to Merriam-Webster, a tree is “a woody perennial plant having a single usually elongated main stem generally with few or no branches on its lower part.” Brandon Bennett[3] suggests that even such definitions are imprecise and vague. Which species count as trees? Is a palm tree a tree? We need to offer contextualised definitions of what qualities suffice for a plant to be termed a tree. The City Council of Penang Island (MBPP) has been attempting this. It has established the Penang Tree Inventory System (PeTIS) to catalogue data on trees. This, in combination with Penang Smart Island Digital Twin (SmIDaT), is moving in the right direction towards having the ability to run urban simulations that can support improved planning (and greening) strategies.

30% Tree Canopy

Canopy coverage (determined by extracting the lower bandwidth of surface temperature data) and its relationship to heat is abundantly evident (see Figures 1 & 2). We can readily feel the cooler tree-lined streets in Pulau Tikus and along Sungai Pinang.

We calculate that George Town has a 27% canopy coverage, close to reaching Konijnendijk’s rule. However, this aggregate for the city masks the neighbourhood variations—the George Town World Heritage Site canopy coverage is less than 12%.

300M From Public Green Space

There are 925ha of public open space in Penang. Overlaid with residential land use, we conclude that 56.2% of residential premises are within 300m of a public open space, which increases to 60% when forests are included. However, this aggregated figure hides marked differences between the island and mainland, with 79.8% of residential areas meeting the criteria on Penang Island, compared to just 47.4% in Seberang Perai (see Figure 3).

A Useful Rule?

Measuring the 3-30-300 rule is not simple, but not impossible; after all, our tools and data sets are developing rapidly. Croeser et al. (2024)[4] attempted to measure the rule for eight cities (Amsterdam, Buenos Aires, Seattle, Denver, New York, Singapore, Melbourne and Sydney), and experienced similar data challenges. Most buildings fail the 3-30-300 rule due to them having inadequate tree canopy, and while the “3” standard was met more often, achievement of the “300” standard was patchy.

Whether Penang should adopt (or even firmly quantify) the 3-30-300 rule is open for debate. However, it does serve as a useful starting point for a conversation around the value of urban green space. The Penang Nature-Based Climate Adaptation Programme and Green Connectors Initiative, being delivered by UN-Habitat, Think City, MBPP and the Department of Drainage and Irrigation, for example, is working to build climate resilience through initiatives such as urban greening.

MBPP is currently finalising plans for a major greening initiative of Lebuh Pantai and Pengkalan Weld, while Think City is offering grants to green buildings and façades, and is working to create a network of green connectors, converting rivers into blue corridors with recreational amenities, and greening streets and coastal parklands. A similar initiative is proposed for the mainland where street trees and parklands are much needed.

Greenery is one of Penang’s premier attributes. It is important that what we have is protected and enhanced to multiply its beneficial effects on lifestyle—and property prices. Without doubt, the urban heat island effect, now exacerbated by climate change, has to be addressed, achieving, along the way, the positive physical and psychological health benefits that proximity to nature brings.

FOOTNOTES

[1] G.N. Bratman, J.P.Hamilton, K.S. Hahn, G.C. Daily, & J.J. Gross, Nature experience reduces rumination and subgenual prefrontal cortex activation, Proc. Natl. Acad. Sci. U.S.A. 112 (28) 8567-8572, https://doi.org/10.1073/pnas.1510459112 (2015).

[2] https://nbsi.eu/

[3] Bennett, B. What is a Forest? On the Vagueness of Concepts, Topoi 20: 189–201, 2001

[4] Croeser, T., Sharma, R., Weisser, W.W. et al. Acute canopy deficits in global cities exposed by the 3-30-300 benchmark for urban nature. Nat Commun 15, 9333 (2024). https://doi.org/10.1038/s41467-024-53402-2