Jagdish Krishnaswamy remembers the barn owls that began nesting in his apartment complex after a long gap during the pandemic. “Some people complained about them. They can be screechy and make a lot of noise,” he agrees. However, other people in the same complex came to the defence of these birds, including a nature-loving resident who told folks that owls are the vahan of Goddess Lakshmi, recalls Krishnaswamy, the Dean of the Indian Institute for Human Settlements’ School of Environment and Sustainability. “They said that we were anyway exposed to a lot of noise from residents and children and asked why we couldn’t put up a little bit of noise from the owls,” he recalls.

When it comes to biodiversity, we are more likely to foster the plants and animals we are familiar with, so acquainting people with the flora and fauna in their vicinity plays a crucial role in biodiversity conservation. “If citizens get to know a magnificent tree, a bird that keeps coming to nest in a particular place in your neighbourhood or a place where bats are roosting, it will help in fostering first-hand natural history-based conservation attitudes in the city,” he says in an interview following his recent talk, “Bengaluru in Blue, Green and Grey: The Ecological and Environmental Dimensions of Blue-Green Infrastructure.”

At this illustrated talk, held at the Science Gallery in Bengaluru, Krishnaswamy, who is working on building a long-term urban ecological observatory in Bengaluru, also mentions that in India, which has committed to the Global Biodiversity Framework, 30% of land is supposed to come under some form of conservation and restoration regime by 2030. “In a couple of decades, 50% of Indians will be living in some form of urbanisation,” he says. “To meet the 30 % target, urbanising areas must play a role in biodiversity conservation.”

Sustaining urban biodiversity

Krishnaswamy also provides an overview of Bengalaru’s blue, green, and grey infrastructure and how the three can be integrated to sustain urban biodiversity and improve the quality of the lives of its citizens. Green infrastructure comprises urban green spaces, including public parks, private gardens, and wooded university campuses, while blue infrastructure refers to all water bodies that are part of an urban environment. The human-engineered parts of a city, such as roads, pipes, wastewater treatment plants, and sewers, come under grey infrastructure.

Over the last century of urbanisation, our cities, including Bengaluru, have been drastically altered, hydrologically and topographically, making the need for grey infrastructure more crucial than ever. “We have completely transformed the city’s hydrology, and we can no longer aspire to the original hydrology of 150 to 200 years ago.”

This means that the green and blue infrastructure now have to depend on the grey infrastructure, such as drains, pipelines and sewage treatment plants, with constructed wetlands also playing a role. In a city that faces both acute water shortages and flooding hazards, “Our water resource management must cope with both a lack of water in some years and excess water in parts of the city due to runoff from impervious built areas,” explains Krishnaswamy. “You need the grey infrastructure to convey this water out of harm’s way into somewhere it can be stored or help recharge groundwater and rejuvenate water bodies or tanks. Isolated green and blue infrastructure by themselves cannot help that.”

Bhadrappa layout flooded due to heavy rains on October 22. Fire personnel ferry residents in and out of their houses to buy daily supplies. | Photo Credit: MURALI KUMAR K

Challenges in water management

Krishnaswamy elaborates on various water-related global crises, undoubtedly exacerbated by climate change, that make this need for effective water resource management more pressing. For starters, the Indian monsoon has seen a moderate decline since the 1950s. “Some of our climate scientists attribute the decline in the Indian monsoon to the weakening of the thermal gradient between land and sea,” he says.

Additionally, a warmer atmosphere can hold higher moisture, and higher temperatures have increased evaporation rates, accelerating the hydrologic cycle. “You may end up getting more rain in more intense events over fewer rainy days,” he says, pointing out that since the 1950s, we have seen rainfall exceeding daily totals of 150-200 mm more frequently. However, the latter process may trump the former at some point, and we may end up with higher annual totals in some parts of the country but in more intense rain events, he also says. “We need to plan and help our cities and citizens adapt to these changes.”

This means there will be more rainless days, and rainy days will be fewer but more intense. “This is going to be a huge challenge for us,” he says, pointing out that most Indian cities in their current state simply cannot handle such unprecedented amounts of rainfall because of the nature of the built infrastructure and loss of their ability to absorb rainfall in green spaces that have dwindled and store moisture as ground-water or in surface water bodies. Due to the rapid transformation of surfaces permeable to rainfall and massive changes in water bodies, “urban flooding is becoming increasingly frequent and severe due to the intense and improper modification of natural topography and drainage patterns,” he says, drawing on the Varthur Lake watershed and its sub-watersheds, which were severely affected by the 2022 flood to illustrate this point.

Krishnaswamy also expands on the three types of water — green, blue, and grey — into which the precipitation we receive globally is partitioned. Green water is the rainfall that infiltrates the soil and is accessed by plants, including rain-fed crops, while blue water is the water that flows and is in groundwater, a reservoir, or a river. “This is the water we depend on for drinking, washing, everything else… even construction of buildings.”

Human appropriation has already exceeded the blue water limits in many areas, leading to the loss of aquatic ecosystems, he says, which has irreparable impacts on our rivers and wetlands. “If we can shift some of the water requirements for agriculture through changes in cropping patterns and other measures and treat our cities’ wastewater so that it goes from black to blue or bluish, we may be able to divert some of the saved water into our blue infrastructure, rivers, lakes, and wetlands,” he says.

Additionally, in the cities, he believes, we take a lot of the blue water and convert it to grey (wastewater from sinks, washing machines, showers) and black water (wastewater from toilets), a precious potential water source if recycled. “Bangalore has made some strides in doing that (recycling). It can be a part of the urban transformation, the sustainable transformation we all are interested in,” he says.

Hesaraghatta grass land, Lake and manmade reservoir created across Arkavathy river at Hessarghatta 18 kms from Bengaluru. | Photo Credit: MURALI KUMAR K

Biodiversity and the city

Earlier this month, Hesaraghatta, an area housing a grassland ecosystem located on the northwestern fringes of Bengaluru, was declared a conservation reserve by Bengaluru’s State Board for Wildlife, a move that Krishnaswamy is delighted by. “Hesaraghatta’s grassland has fortunately now received some protection.”

While cities do not have the scope for large reserve forests except on the peripheries — like the Bannerghatta National Park — urban green spaces, whether a campus, a garden, or even a small neighbourhood park, can harbour native biodiversity if best practices are adopted. “As cities have the double trouble of heat island effects from their built infrastructure as well as climate change-based warming on top of it, we will increasingly need a good network of green and blue spaces throughout the city so that citizens can benefit from their cooling potential and shade during hot spells,” he says.

He brings up the concept of Other Effective Area-Based Conservation Measures, or OECMS, a new category of conservation that recognises “any type of land and water which is being used for some other purpose but where biodiversity can co-benefit.” The Aravalli Biodiversity Park (ABP) in Gurgaon is the first such OECM in the country, he says. “Bengaluru has the potential of having several OECMs if, along with the integration between blue, green and grey, we can get our act together and find and manage many of these places.”

Exotic species

Krishnaswamy goes on to offer insights into how to manage our urban biodiversity better. For instance, a pressing issue in urban environments is how we deal with the exotic species of plants and animals found in many cities today, including Bengaluru.

Not all exotic species are invasive or harmful, and, of course, “if they don’t spread too much at the cost of native biodiversity, they are fine, and a few provide habitat and resources for native species of birds or bats. But there are other exotic species -- both plants and animals -- that become invasive and harming or displacing native biodiversity,” he says. He feels that we should not club all the exotics under a single umbrella. Not all exotic species are dangerous, of course, “if they don’t spread too much at the cost of native biodiversity, they are fine. But there are other exotic species, both plants and animals, that have become invasive,” he says.

Krishnaswamy also highlighted other aspects of urban ecology and its management: the high species diversity of bees in the city, how urban and peri-urban farming can have a positive effect on both people and fauna, how green spaces can mitigate heat stress, something cities are more prone to because of its built-up infrastructure, why we need to be cautious in our approach to lake rejuvenation, and the need to adopt a scientific approach while creating sustainable urban ecosystems.

A little help

“Green spaces come in all types of shapes, sizes, and functionality, but the ones that truly contribute to native biodiversity conservation in the city must allow for key ecological mechanisms like plant-animal interactions including pollination, predation and nutrient cycling and the entire life cycles of diverse sets of organisms to be completed,” he believes. “If you provide the habitat, plus a little help, then nature can thrive in the city. “