Why trees fall and what we can do

Photo: CHAN BOON KAI/The Star

HEAVY rain can cause urban trees to fall due to a confluence of factors, two of which are soil saturation and root instability. When the soil becomes waterlogged, it loses its structural integrity and ability to anchor tree roots. This can result in trees being uprooted easily during storms.

Wind load on wet trees is another critical factor. Wet foliage increases the overall weight of the tree and the wind load it experiences during heavy rain. Tree canopies can store 2%-40% of the rainfall, which roughly translates to an additional weight of 40kg-1,300kg for every 10mm of rain, depending on the tree type and size. This combination of added weight and strong winds can cause trees to topple.