Sudden storms called “guerrilla downpours” have been hitting with increasing frequency over the past five decades and are now considered a growing disaster threat.

As municipalities struggle to deal with the increase in floods, companies are proposing new technology based on what they say is their only useful lead in predicting flood risk — manhole covers.

Attaching communication chips to their backs turns manhole covers into real-time monitoring devices that can show the water levels in sewers, and hence the places most likely to flood when heavy rain strikes.

One of the companies, Tokyo-based Meidensha Corp., makes electrical equipment, including motors, for pumping facilities that discharge rainwater from sewer system into rivers.

“Given the increasing trend of unexpected strong rain, there’s a need now to see the image of the amount and flow of rainwater before it comes into the pumping facilities,” said Kazuyuki Hirai, general manager of the water processing and environmental engineering business unit at Meidensha.

According to the Meteorological Agency, Japan used to get heavy rain, defined as more than 50 mm per hour, an average of 176 times a year from 1976 to 1988. That surged to 232 times from 2002 to 2014.

Teaming up Tokyo-based waterway expert Nihon Suido Consultants Co., Meidensha started marketing manhole-based flood monitoring systems in July. The systems work by installing water gauges in the manholes themselves and equipping the covers with communication devices and batteries and antennas, so data on underground water levels can be sent to its computer servers.

This gives clients, including municipalities, access to real-time water data. By combining maps of the sewage system with the land ministry’s real-time rainfall monitoring system, called Xrain (extended radar information network), city officials will be able to determine areas at risk of flooding.

“Using these data, municipalities will know what kind of measures they need to prepare” to mitigate the adverse effects of sudden, torrential rain, said Hirai.

In Japanese cities, rainwater flows into either dedicated drain pipes or sewer pipes.

In response to growing concern over the risk of sudden downpours and floods, the government revised the Flood Control Act in 2015 to require that prefectural governments obtain images of water levels in sewerages.

However, a land ministry survey in October 2015 showed that only 63 municipalities had installed water gauges to check the water levels in their sewer lines. Only 21 said they had five or more gauges.

But for a scientific pursuit, why focus on manhole covers?

Manhole covers are the only infrastructure links to pipes underground, said Hirai, adding that they are “simple and compact.”

Using the backs of manhole covers can save space and accommodate batteries, which last about two years, doing away with the need to attach power cables, he said.

Hirai said the Tokyo Metropolitan Government came up with the idea of using manhole covers to monitor sewer levels about 15 years ago, but it was tough to make a compact device with the technology available at the time.

Installment costs might also turn out to be about half of what is costs to install existing water-gauging systems, which are more bulky, he added.

Tokyo-based Fujitsu Ltd. is proposing a similar product. Fujitsu’s system can provide updates on sewer water levels every five minutes with batteries that last as long as five years.