NUS researcher develops model to help store rainwater underground, curb floods

Singapore could see more intense and frequent heavy rainfall events with rising global temperatures.
Singapore could see more intense and frequent heavy rainfall events with rising global temperatures.PHOTO: ST FILE

SINGAPORE - As the world prepares to deal with shifting weather patterns due to climate change, finding ways to harness rainwater to prevent floods and meet needs during dry periods becomes all the more important.

One option may lie underground. Parched aquifers - or bodies of rock beneath the surface that hold water - can be replenished when floodwaters flow through pipes or canals and are stored there.

Using drought- and flood-prone California as a case study, a researcher from the National University of Singapore (NUS) developed a computer model that can project the volume and location of floods under a changing climate till 2100.

The model also recommends investments in groundwater infrastructure for various parts of the state so that floodwaters can be optimally stowed underground.

California's volatile climate that switches between periods of drought and deluge is likely to turn more severe and erratic as the planet warms.

Heavier torrents and earlier snowmelt due to rising temperatures will drive up flood volumes, said Assistant Professor He Xiaogang of the civil and environmental engineering department at NUS, who led the study. He had pursued the project as a postdoctoral fellow at Stanford University.

"The tool can be customised and applied to regional and global scales to map the floodwater recharge potential of those areas," added Prof He.

During droughts, up to 60 per cent of California's water comes from groundwater.

Singapore does not depend on groundwater to meet its needs but instead relies on water from Malaysia, rainfall collected in its reservoirs, desalination and treatment of used water.

But Prof He said the tool and groundwater recharge could be a possible way for Singapore to mitigate floods.

A deluge on April 17 - that broke the record for the highest daily rainfall for that month since 1980 - caused flash floods that overwhelmed drainage systems, flooding pavements and causing high water levels in drains and canals.

The Centre for Climate Research Singapore has projected that the nation could see more intense and frequent heavy rainfall events with rising global temperatures.

But is channelling floodwaters underground a possible solution for Singapore?

Experts said more studies are needed in order to understand the groundwater systems here, starting with groundwater models.

Noting that Singapore has a complex geology, Dr Pang Chee Meng, national water agency PUB's chief engineering and technology officer, said it is data intensive to build a reliable groundwater model.

He added that the country's geology consists of top weathered soil and solid rock beneath, and the range and variation of soil and rocks in different areas are significant.

A small amount of rain seeps through the top weathered soil as groundwater and flows towards the nearest drains and into reservoirs.

In 2016, PUB said it is furthering its groundwater monitoring.

Dr Pang said: "We have installed monitoring wells and sensors to provide a better understanding of the presence of groundwater in Singapore... We will continue to build on the data collected."

Prof He's study was published in the journal Science Advances in April, and a policy brief was prepared by Stanford University this month.

Commenting on the study, Dr Cecilia Tortajada, an adjunct senior research fellow at the Lee Kuan Yew School of Public Policy's Institute of Water Policy, said: "The study in California, although very promising, would not be applicable for Singapore. Geological formations in Singapore are not favourable for groundwater occurrence."

"It would first be necessary to have a whole series of modelling studies," she added.