Green spaces, including parks, urban forests, gardens, and green rooftops are crucial for cities. This note will discuss the primary reasons for having green spaces in cities at greater length, i.e., micro-climate regulation, and will briefly mention other reasons for having such spaces.
MICRO-CLIMATE REGULATION
Green spaces reduce the urban heat island effect by lowering temperatures through evapotranspiration and by providing shade. The lack of green spaces results in the expansion of the urban heat island phenomenon. Consequently, Hyderabad will experience higher temperatures and its population will experience higher heat stress, particularly during the summer months. This will result in a higher incidence of all-cause mortality that may exceed 10% during the summer months.
Raised temperatures: An urban heat island is a phenomenon where large urban centres experience significantly higher temperatures than their surrounding peripheries, rural areas and natural landscape. The temperature difference between the city centre and its periphery can range from 4-5oC. The temperature difference is usually larger at night than during the day and is most apparent when winds are weak.
Heat island effects are caused by the absorption and retention of heat by hard, dark surfaces in cities such as asphalt and concrete, and the reduced amounts of vegetation and open spaces that would otherwise help to regulate temperatures. Trees provide shade, thereby keeping street and building surfaces cooler; and trees use evapotranspiration to cool themselves and the surrounding air.
Higher temperatures and air pollution can result in the formation of smog in cities. Smog is the result of pollutants in the air acted upon by the sun’s light, this is known as a photochemical reaction. These pollutants are such things as nitrogen oxide, hydrocarbons and other particulates in the air.
Leaves help reduce air pollution by capturing airborne particles, such as nitrogen dioxide (NO2), nitrogen oxide (NO), and sulphur dioxide (SO2), while at the same time, they release oxygen (O2). Trees intercept and absorb rain through their leaves and roots, thus reducing the amount of water falling on the pavement and hard surfaces and subsequently being removed via stormwater drains.
The heat island effect can have various impacts, including increased energy consumption from air conditioning, compromised air quality, and most importantly, negative effects on human health, particularly for vulnerable populations such as the elderly, children, and those with pre-existing health conditions. It can also exacerbate the effects of climate change by contributing to rising temperatures in urban areas.
Heat stress: The Heat Index (HI) is a measure of how hot humans perceive it feels when relative humidity is factored with the actual air temperature. The heat index is also referred to as the apparent temperature. Higher concentrations of relative humidity make the same temperature feel hotter and more unbearable, e.g., at 35oC and a relative humidity of 30%, the apparent temperature feels like 36oC, but if the relative humidity doubles to 60%, the apparent temperature feels like 46oC
The chart below can also be used to obtain the HI from air temperature
and relative humidity values. A heat index of less than 33oC poses a minimal risk, 33-39oC a moderate risk, 39-46oC a high risk, and above 46oC a very high risk.
* Note: The above chart is based on NOAA’s chart and computations made from NOAA’s website. Apparent temperatures rounded off to the nearest integer.
Heat stress-related illnesses: Elevated core body temperatures may cause the following illnesses:
Heat rash is a skin irritation caused by excessive sweating. It is worsened in hot and humid weather. Heat syncope (fainting) or dizziness usually occurs after prolonged standing or sudden rising from a sitting or supine position. Dehydration and inadequate acclimatization often contribute to heat syncope.
Heat cramps are caused by the body’s depleted salt and water levels from excessive sweating resulting in muscle cramps or spasms. Heat cramps may also be a symptom of heat exhaustion.
Rhabdomyolysis is a medical condition associated with heat stress and prolonged physical exertion, resulting in the rapid breakdown, rupture, and death of muscle. If left untreated, it can lead to kidney damage, seizures, irregular heart rhythms, and death.
Heat exhaustion is the body’s response to an excessive loss of water and salt, usually through excessive sweating. Persons most prone to heat exhaustion are the elderly, those with high blood pressure, and those working in a hot environment. Heat exhaustion is often a precursor to heat stroke.
Heat stroke is the most serious heat-related illness and should be treated as a medical emergency. Heat stroke occurs when the body becomes unable to adequately dissipate heat, losing the ability to regulate core body temperature. The core body temperature rises rapidly, the sweating mechanism may fail, and the body is unable to cool down. When heat stroke occurs, the body temperature can rise to 41oC or higher within 10 to 15 minutes. Thinking clearly, reality perception, ability to plan, and other mental processes become impaired, and the person may be unable to recognize dangerous situations. Heat stroke can cause death or permanent disability if emergency medical treatment is not given.
Higher mortality and morbidity related to heat stress: Extreme heat stress is known to cause a higher incidence of all-cause mortality. A study[i] done in Hyderabad of a total of 122,117 deaths for 1,220 summer days (2006 to 2015) showed that there was an increase of all-cause mortality of 16% per day when maximum temperatures were 40oC or above, and an all-cause mortality increase of 17% per day for extreme danger days (Heat Index >54oC). The mean daily all-cause mortality shows a significant association with maximum day temperatures and Heat Index.
Another study[ii] on heat stress and mortality done in Surat concludes that “There is an increase of 11% all-cause mortality when temperature crossed 40oC. There is a direct relationship between mortality and HI (high heat index). Mean daily mortality shows a significant association with daily maximum temperature and HI.”
Exposure to higher temperatures has other health effects. A recent study[iii] established a correlation between high temperatures and chronic kidney disease (CKD) in rural areas by reviewing studies done in several continents—Asia, North and South America and Africa. The study found study sites in India, Sri Lanka, Costa Rica, Nicaragua, El Salvador and Guatemala as confirmed sites where CKD correlated with heat stress, and found other study sites in India, Thailand, Saudi Arabia, Sudan, Mexico and the United States where it suspects that CKD incidence is suspected to be associated with heat stress. The study concludes, “One of the consequences of [climate-related] extreme heat exposure is dehydration and volume loss, leading to acute mortality from exacerbations of pre-existing chronic disease, as well as from outright heat exhaustion and heat stroke. Recent studies have also shown that recurrent heat exposure with physical exertion and inadequate hydration can lead to CKD which is distinct from that caused by diabetes, hypertension, or GN. Epidemics of CKD consistent with heat stress nephropathy are now occurring across the world.” The necessity for green spaces in cities.
Green spaces are particularly important for hawkers and street vendors as these spaces reduce heat stress for workers who work under the hot sun all day.
Climate change will exacerbate heat stress: Global warming has raised the average global temperature by1.2-1.3oC above pre-industrial times, and, in India by 0.7-0.8oC. Greenhouse gas emissions are not declining fast enough to keep warming <1.5oC, and the average global temperature rise by 2100 is expected to be closer to 3oC. This means peak summer temperature rise will exceed 5oC above what it is today. Such a warming will put millions of Indians at risk from severe heat stress. The need to increase urban green spaces as part of urban heat action plans becomes all the more important.
OTHER BENEFITS OF GREEN SPACES
Improving Air Quality: Trees and plants absorb pollutants (CO₂, NO₂) and release oxygen, reducing urban smog.
Noise Reduction: Vegetation in green spaces acts as a natural sound barrier, minimizing traffic and industrial noise pollution.
Flood Prevention: Green spaces absorb rainwater, reducing runoff and the risk of urban flooding.
Biodiversity Conservation: Urban green spaces provide habitats for birds, insects, and small wildlife.
Carbon sequestration: Urban green spaces sequester a small amount of carbon dioxide (CO2), a greenhouse gas.
Physical and mental health: Green spaces encourage walking, jogging, cycling, and other forms of physical activity. Access to green spaces helps reduce stress, anxiety, and depression.
Social well-being: Green spaces foster social interaction, inclusivity, and community cohesion.
Leisure activities: Parks provide safe and open spaces for play, sports, picnics, and gatherings.
Environmental education: Urban green spaces can serve as outdoor classrooms and for learning about nature.
City aesthetics: Green spaces enhance urban aesthetics, making cities more visually appealing.
Cultural events: Parks often host festivals, performances, and community celebrations.
Tourism and microbusiness: Green spaces draw visitors and boost microbusiness.
CRITERIA FOR GREEN SPACES
There is no standard criteria for the extent of green space in a city. Various organizations have defined the extent of green space required in a city.
The World Health Organization[iv] (WHO) recommends that ideally 10-15 m2 but a minimum of 9 m2 of urban green space is required per person. WHO also recommends that 0.5 ha of green space be accessible within 300 meters. WHO links access to green spaces with reduced stress, improved mood, and lower rates of obesity, heart disease, and respiratory conditions. More green space means cleaner air and more space for exercise, reducing non-communicable diseases. Green spaces reduce anxiety and depression, especially in high-stress urban environments.
The 3-30-300 rule[v] recommends that a) every citizen should be able to see at least three trees (of a decent size) from their home, b) every neighbourhood have 30% canopy cover for cooling, better micro-climates and physical and mental health, c) the maximum distance of a green space of at least 1 ha for any urban resident be not more than 300 m.
The United Nations Habitat and European Environment Agency[vi] also recommend a 30% green space for urban areas.
GREEN SPACES IN HYDERABAD AND OTHER CITIES
Hyderabad’s green space is 10-11%
The above image indicates that green spaces in Hyderabad occupy only a small fraction of the city space.
Land use in Hyderabad 2001-2021vii
The table above indicates that the percentage of land under forest has declined since 2001. The land under forest in 2021 was about 7%. If we were to consider land under forest and vegetation, the land they covered together in 2021 was about 10-11%.
The green space in Hyderabad does not meet the 3-30-300 rule,
Green spaces in other cities
Hyderabad green space compares poorly with other large Indian cities. The green space in Delhi is ~20% (contributed significantly by the Ridge forest and parks), Bengaluru—15%, and Mumbai 12-13% (contributed significantly by the Sanjay Gandhi National Park).
Many cities outside India have significantly more green spaces than Indian cities, e.g., Singapore (~47% green cover, aims for 50% by 2030), Vienna, Austria (~50% green areas), Oslo, Norway (~68% forested and green space), Curitiba, Brazil (~52 m² green space per capita, New York City (~27% green space), London (~33% green space), Tokyo ~20% green space).
CONCLUSIONS
- The Kancha Gachibowli and other green spaces should be conserved.
- Green space in Hyderabad should be gradually increased to 30% over some time.
- Modern cities are unsustainable. In the long run, they should be shrunk to make human society sustainable.
Sagar Dhara is a Male; Upper class & caste; College-educated; City-slicker; Member of the most ferocious predator that stalked Earth—humans. Email: [email protected]
[i] Rathi SK, Sodani PR. Summer temperature and all-cause mortality from 2006 to 2015 for Hyderabad, India. Afri Health Sci. 2021;21(3). 1474-1481. Accessed from https://dx.doi.org/10.4314/ahs.v21i3.59 on 31 May 2023.
[ii] Desai, V.K., Wagle, S., Rathi, S.K., Patel, U., Desai, H.S., Khatri, K., 2015. Effect of ambient heat on all-cause mortality in the coastal city of Surat, India, Current Science, 109(9), 10 November 2015. Accessed on 1 February 2020 from https://www.currentscience.ac.in/Volumes/109/09/1680.pdf
[iii] Glaser, J., Lemery, J., Rajagopalan, B., Diaz, H.F., Garcı´a-Trabanino, R., Taduri, G., Madero, M., Amarasinghe, M., Abraham, G., Anutrakulchai, S., Jha, V., Stenvinkel, P., Roncal-Jimenez, C., Lanaspa, M.A., Correa-Rotter, R., Sheikh-Hamad, D., Burdmann, E.A., Andres-Hernando, A., Milagres, T., Weiss, I., Kanbay, M., Wesseling, C., Sa´nchez-Lozada, L.G., Johnson, R.J., 2016. Climate Change and the Emergent Epidemic of CKD from Heat Stress in Rural Communities: The Case for Heat Stress Nephropathy, Clin J Am Soc Nephrol 11: 1472–1483, 2016. doi: 10.2215/CJN.13841215. Accessed on 1 February 2020 from https://cjasn.asnjournals.org/content/clinjasn/11/8/1472.full.pdf.
[iv] World Health Organization, 2016. Urban green spaces and health, Copenhagen: WHO Regional Office for Europe, Document number: WHO/EURO:2016-3352-43111-60341
[v] Konijnendijk, C., 2021. The 3-30-300 Rule for Urban Forestry and Greener Cities. 4. Accessed on 10 Apr 2024 from https://www.researchgate.net/publication/353571108_The_3-30-300_Rule_for_Urban_Forestry_and_Greener_Cities.
[vi] European Environment Agency, 2011. Green infrastructure and territorial cohesion, EEA Technical report No 18/2011
[vii] Appala, K.R., Sivakumar, V.L., 2023. Hyderabad City Land Use/Land Cover Changes Multi-spatio Temporal Comparison Using Spectral Angle Mapper with Maximum Likelihood Classification, Journal of Survey in Fisheries Sciences 10(1S) 1748-1759.
