A city that has no patience for leaves

Every April-May, I take out my infrared thermometer and run a small experiment in my garden. I point it at the paved slab in full sun, note the reading, then walk a few steps into the shade and take another. The difference has always been striking. In full sun, the slab reads 42 to 45 degrees Celsius. A few steps into the shade, it held at 25 or 26. It moved to 27 last year, and 29 this year. And I wonder how quickly the gap will close in the years to come.

Bengaluru summers were not always like this. There was a time before the nineties when the city’s heat was considered mild enough to attract people escaping the furnace of the plains. You could step out in the afternoon, run your errands, and come back home without feeling wrung out. Big, old, unhurried trees like Pongamia, Sampige, Margosa and Rain trees lined the avenues and rendered the pavements beneath them that much cooler. Walking under them on a hot afternoon, you felt the cool breeze play gently on your skin. They gave a few degrees of relief that no air conditioner can quite replicate. Today, many of them are gone. Some have fallen in storms, others have made way for wider roads and taller buildings.

The concretisation of city roads is one part of the story. But it is not just the main roads. Look around us. We have covered every inch of soil around our homes with concrete. Plastered floors are neat, easy to maintain, and clean. What this has created, though, is a problem we have not quite come to terms with. When the transition from winter to summer arrives, and trees shed their leaves, those leaves have nowhere to go. On soil, a fallen leaf stays put. It mats down, softens, and over weeks, disappears back into the ground. But with barely any exposed earth, they pile up on concrete, clog drains, and blow into corners. We have removed the very surface that knew what to do with them. And now we stand, broom in hand, baffled and irritated. We created this situation. The trees did not.

My neighbour has a grievance against trees. Specifically against any branch that drifts across the compound wall into their side. Their compound is neatly cemented, easy to sweep, and almost entirely sealed from the sky. A fallen leaf in their courtyard is cause enough for a conversation I do not want to have. They are not alone. There is a whole school of urban thought that treats falling leaves as a civic inconvenience, something to be engineered away.

In my garden, the canopy of bamboo and mango does what the avenue trees do to the city. It intercepts the sun before it reaches the ground. The fallen leaves add to this. They break down slowly, feed the soil, and help it hold moisture. Together, the tree and its leaves create a system. The shade keeps the ground cool. The soil, kept alive by what falls into it, does the rest. No drain is blocked. No broom is required.

When a city replaces trees and soil with concrete, it loses this system entirely. Hard surfaces absorb heat throughout the day and release it through the night, keeping temperatures elevated long after the sun has moved on. This is what is called an urban heat island. It is not the dramatic spike in peak summer temperatures that tells the story. It is the temperature of the floor that rises. Shaded areas and cool nights no longer bring the relief they once did, and the baseline creeps up degree by degree.

The difference between my shaded garden slab at 29 degrees Celsius and the sunlit slab three steps away at 45 degrees is 16 degrees. Multiply that across a city, across all those sealed, swept, leafless compounds, and you begin to understand why April in Bengaluru feels different from how it did 30 years ago. A city does not heat up all at once. It does so quietly, in increments that we barely notice, until one April, the thermometer tells us what we should have seen coming. We have built a modern city that has no patience for leaves. Now it has no comfort for us either.

Motley Garden is your monthly kaleidoscopic view into a sustainable garden ecosystem. The author believes gardens are shared spaces where plants and creatures thrive together. She can be reached at [e-mail] or on social media at @allthingsinmygarden