Zürich residents water city trees as heat and drought intensify

Residents are watering trees outside their homes as heat and drought put pressure on urban greenery in Zurich, SRF reports. The city is currently watering more than 5,000 young trees, while Basel has expanded its stock of irrigation bags to about 4,000.

Every evening, Angelina carries litres of water to five trees on her street in Zurich’s District 4. She uses large containers with small holes drilled into them so the water seeps slowly into the soil, a task that takes about two hours each night. She began watering the trees several weeks ago out of concern for their condition.

Many people in Zurich have noticed trees with drooping or curled leaves, or leaves falling prematurely. Some tree crowns already look autumnal in August.

However, these signs do not necessarily mean that the trees are at immediate risk of dying, says Axel Fischer, head of the parks and green spaces division at Grünstadt Zürich. When water is scarce, trees reduce evaporation by curling their leaves or shedding some of them. What looks alarming is often a natural response to drought stress.

Young trees need support

Young trees are particularly vulnerable because their roots do not yet reach deep enough to access water reserves. Zurich is therefore watering more than 5,000 young trees, giving each between 50 and 70 litres of water up to three times a week.

Drought presents cities with a growing challenge. Trees provide shade, cool overheated streets and help reduce the effects of heatwaves. At the same time, they are increasingly exposed to stress. Zurich plants well over 1,000 new trees each year, Fischer says.

The public’s view of urban trees is also changing. Once seen as an ordinary part of the streetscape, they are increasingly regarded as something that needs protection. This is reflected in requests to the city and in private efforts such as Angelina’s watering initiative.

Grünstadt Zürich says private initiatives cannot replace professional watering, but it welcomes the commitment. Such efforts show that residents identify with the trees in their neighbourhood, Fischer says.

Basel expands use of irrigation bags

In Basel, the city’s gardening department has doubled its stock of irrigation bags to about 4,000. The green plastic bags, which hang around the trunks of young trees, were first used on Basel’s Allmend five years ago.

The bags are particularly useful where water from hoses cannot seep into the ground quickly enough, says Simon Leuenberger, head of green-space maintenance at Basel’s city gardening department. Each bag holds 75 litres, which drain through small holes in the underside over roughly half a day and keep the soil around the tree roots moist.

The system helps save tap water and distribute it according to each tree’s needs. Some trees have several bags attached, which are refilled several times a week.

Normally, Basel waters urban trees until their fourth or fifth year after planting. Because of the heat and drought, the city is now watering trees up to 10 years old. Older trees can have roots extending more than 10 metres deep and draw on groundwater, making the bags ineffective. A single large tree would need 30 irrigation bags to meet its water needs.

The bags are collected and cleaned before winter. Vandalism also occurs, Leuenberger says. Recently, all the bags along one street were slashed, although their low unit price limited the damage.

Zurich is expected to continue examining how cities can cope with longer dry periods. Fischer says the city has for years followed the so-called sponge city concept, which aims to store rainwater locally rather than sending it directly into the sewage system.