Why Mumbai’s Trees are Collapsing Before Monsoon and How BMC’s ‘Hydration Blitz’ is Racing to Save Its Green Lungs from Heat Desiccation
Days after a tree collapse in Khar critically injured two girls, the Brihanmumbai Municipal Corporation (BMC) has launched a first-of-its-kind summer drive to water large, full-grown trees across Mumbai’s high footfall locations in a bid to reduce heat stress in trees and prevent their weakening. According to senior officials, the drive was initiated after an increasing trend of tree collapses across the city this summer, which was linked to lack of moisture in soil and weakening of branches amid extreme heat, due to tree ’embolism’.
Currently, the city is in the midst of a prolonged hot and humid spell with the India Meteorological Department (IMD) placing the city until a yellow alert till Friday. The burgeoning heat levels have also taken a toll on Mumbai’s mature trees with the civic officials recording an uptick in tree collapses across the city. On Friday, two girls were critically injured after a tree – surrounded with large stones at base – collapsed upon a moving auto rickshaw.
Typically, Mumbai experiences cases of tree falls and branch collapses during the monsoon season, triggered by heavy showers and strong winds. However, an unprecedented increase in tree collapses during summer nudged the civic body to investigate the root cause of the spike.
“When we conducted our survey to investigate the cause, we observed that extreme heating was leading to loss of soil moisture, thereby affecting tree stability, drying of branches and weakening of root systems. Inevitably, this was increasing the risk of large branch falls and uprooting of trees in many locations,” a senior BMC official from the civic garden cell told The Indian Express.
Scientifically, extreme dehydration in trees is a phenomenon associated with “Hydraulic Failure” and “Embolism” in trees. “During extreme heat, trees open their stomata (leaf pores) to cool themselves through evaporation. However, when soil moisture is insufficient, trees begin drawing water from their internal storage tissues. This creates intense suction within the xylem tissues, causing air bubbles or vapor pockets (embolism) to form, which obstruct water transport inside the tree. As a result, certain branches or sections of the trunk begin drying out while the tree may still appear alive externally,” a civic official explained.
(Graphic generated using AI)
With branches becoming brittle and soil drying, the risk of collapses have shot up even without windy atmosphere.
In a bid to prevent weakening, the BMC on Tuesday issued directives across departments to carry out watering of mature, adult trees across the city. For the drive, the BMC is eyeing to initially target trees in high footfall pockets like railway stations, hospital compounds, bus depots which witness huge crowding.
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According to officials, while trees within the garden and recreational spaces will be watered by the garden department, the Solid Waste Management (SWM) department will undertake watering of trees along roads while carrying out their regular road cleaning exercise.
Meanwhile, the civic officials have also instructed organisations who maintain plantations within road dividers through CSR funds to carry out watering around their premises. Additionally, the civic garden cell has also instructed citizens to carry out watering within private compounds like residential complexes and surrounding public spaces.
Generally, the civic body carries out plantation of new trees during the pre-monsoon period with the goal of providing them with sufficient watering when monsoon kicks in. While new saplings are watered during summers, mature trees are self-sufficient and as such are not watered.
“However, we are witnessing unprecedented levels of heat right now. Therefore, a decision to launch a watering drive for adult trees till the onset of monsoon was taken,” said an official, adding that each of the city’s trees will be watered at least once or twice a week.
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According to the garden department’s data until March 2025, Mumbai is home to 29.75 lakh trees of which 12.21 lakh trees are situated in the western suburbs, 10.34 lakh in the eastern suburbs and 7.18 lakh in island city.
Of these, over 1.90 lakh are roadside trees as per the last available census records.
Currently, the BMC is also undertaking tree trimming exercise as a part of its pre-monsoon preparedness for which 92,277 trees have been earmarked.
