How Can Green Roofs Help Protect Against Flooding?

Green roofs provide a number of benefits for homeowners and business owners. For example, they can help protect against flooding, reduce urban runoff, and retain rainwater. In addition, they can improve public health.

Reduce urban runoff

The use of green roofs can significantly reduce urban runoff. Stormwater is retained on the green roof, which filters pollutants from the atmosphere. This enables the stormwater to recharge groundwater. 

A green roof is also beneficial because it provides a shaded area for the building and acts as a sponge to absorb the rain and gradually release it into the environment. However, there is an important risk of pollution of water bodies and aquatic ecosystems.

Runoff from green roofs depends on the depth, duration and duration of the rainfall event. There are two factors that influence the probability of runoff: evapotranspiration rate and retention capacity. If the retention capacity is high, the probability of runoff is higher than if it is low.

The maximum retention capacity of a vegetated platform is relatively small. For a typical platform, the retention capacity may be as little as a few millimetres. On the other hand, the effect of the green roof on runoff is stronger during storms of smaller duration.

Retain rainwater

The amount of rainwater retained on green roofs to protect against flooding depends on a variety of factors. Retention is dependent on the type of roof, the drainage layer, and the vegetation cover over the roof catchment. Moreover, the intensity of rainfall and duration of the rain are also important.

Compared to bare roofs, the amount of rainwater retained on a green roof can be calculated and modelled. It is estimated that 40% to 100% of the rainfall falling on a green roof can be retained over a period of one year. During the growing season, little runoff occurs.

This study was conducted to determine how well a 3.5-inch intensive green roof performed during extreme storm events. Runoff quantities from 69 rainfall events were analyzed. Results showed that runoff from green roofs was much less than the runoff from adjacent paved roofs. In addition, the runoff from the green roof was less than the rainfall recorded on the bare roof.

Improve public health

The use of green roofs has been touted as a way to mitigate the effects of urbanisation. This has come at the cost of introducing pernicious effects such as pollution, temperature rise and biodiversity loss. To combat these effects, a green infrastructure scheme is in order. While this may sound like a no-brainer, the implementation of such an initiative can be a herculean task.

In a recent study, the research team at the University of Chile looked at the benefits and limitations of installing green roofs in the central region of the country. As a result, the researchers found out that, a., there is a limited amount of data on the effectiveness of this technology to date. b., installing green roofs is a daunting task. So they looked for the elusive secret ingredient to the best green roofing solution. They identified the following as prerequisites.

Among them, the most notable is the ability to capture rain where it falls. Taking into account the unique weather conditions of Central Chile, a hydrological model was created and put to the test. Several commercial green roofs were tested for the purpose of this exercise.