An earth scientist on Wednesday said that Hong Kong has to do more to guard against the effects of climate change, as more frequent and intense weather events are expected to occur.

The black rainstorm warning was in force twice on Tuesday, one of which for more than 11 hours – the second longest on record.

The Observatory recorded more than 360 millimetres of rain on the same day as the SAR saw its highest daily rainfall in August since records began.

Speaking on RTHK's Backchat programme, Benjamin Horton, Dean and Chair Professor of Earth Science at City University, said the record was an "incredibly powerful statement".

"You're [the Observatory] able to state that yesterday was the wettest day in August since 1884, since records began, and that is an incredibly powerful statement," he said.

"That means that nobody, nobody that's living in Hong Kong has ever experienced an August day like that since they were born, and that is staggering to actually think about."

While the government has made sure that infrastructure can withstand floods and other extreme weather events, Horton said more needs to be done.

"Invest in the science. Listen to the experts. Try to have the best possible predictions of what's going to happen on a granular scale. So what's going to happen in Asia? What's going to happen in Hong Kong? What's going to happen in Kowloon? So you know where the most at risk regions are," he said.

"And then you have to have very adaptive engineering, because climate change is a very wicked problem. We know it will occur, but we don't know when, and we don't exactly know how severe it's going to be. So you've got to have engineering solutions that allow you to be adaptive immediately when you're aware of the threat. And then finally, and the key thing is education."

Meanwhile, Leung Wing-mo, a spokesman from the Meteorological Society, told another RTHK show that the Observatory would not necessarily downgrade a rainstorm signal even if the amount of rainfall does not meet the threshold.

He went on to say that the weather forecaster does this to avoid public confusion, and the rainstorm warning thresholds are for guidance.

"When it comes to operation, we might not always stick to the threshold. Let's say it's now very heavy rain, where there is 70 millimetres of rain per hour, then we must issue the black rainstorm warning," he said.

"But even if we expect the rain to stop for awhile and not reach the threshold, the Observatory might not immediately downgrade the black rainstorm warning to red or amber. The reason being is that the Observatory does not want to be too confusing."