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THREE years ago, siblings Priscilla Matanhura (4), and her brother Matthew (3), were swept away as torrential rain hit Shambakumanja village in Muzarabani near the border with Mozambique in the north-east.

Rain of over 300mm within days had turned the low-lying lands of Muzarabani into a sea.

Rivers overflowed, homes and crops were washed away, and 13 bridges were completely destroyed.

Matthew and Priscilla were later found dead by fellow villagers.

Before tragedy struck, the two had been left playing under a tree, as their parents were out working in the fields..

As climate-linked events such as floods, drought and hailstorms worsen, Zimbabwe has endured an in-ordinate amount of loss of human life.

Financial and asset losses run into tens of millions of dollars, experts say.

Now, climate scientists at the University of Zimbabwe (UZ) have developed a satellite-based technology that they hope will help communities and policymakers prepare better for extreme events, particularly flooding.

How it works

According to Professor Amon Murwira, a geo-information science and earth observation specialist with the university, who is leading the project, the tool tracks water-flow following a rainfall event using satellite, predicting with some precision the likelihood of a flood within a day or so.

“When using satellites, they tell us where exactly it is raining,” Professor Murwira told The Herald Business Thursday, by telephone.

“But our challenge is, if the rain is falling, how much of that rain will be runoff (flowing water that does not soak into the ground).

“This is the water that constitutes a flood,” he said of the flood monitoring technology, which has taken a year to develop.

“Our job is to be able to interpret satellite rainfall using intelligent methods to convert that rainfall into runoff, and secondly, to determine the runoff above which a certain threshold, it now constitutes a flood.”

The “threshold” is the level at which a river is said to have filled up, its banks bursting and allowing water to flood surrounding areas.

From river to river, the threshold changes depending on the characteristics of each catchment area, he said.

But through specialised computer programmes, UZ scientists have managed to calculate and predict the probability of floods, or lack thereof, of different catchments based on the information they already know about those specific areas.

“Look at Gwai River, for example,” Professor Murwira explained.

“We know that it flows into areas where most of the soils are deep Kalahari sands. The time it will take for that water to start running off is much longer than the water running off from a hill slope.

“These are the characteristics that we use, through specific computer programmes that translate rainfall into runoff. As soon as that runoff leave the banks of a river, it becomes a flood.”

Precision

One of the major concerns with meteorological information and data in Zimbabwe is its perceived weaknesses in terms of accuracy and reliability.

Local meteorologists tend to produce vague and generalised information for entire provinces, such as Mashonaland Central, which consists of several vast districts with differing climates.

This has not endeared them with communities, mostly farmers.

Not so with the new flood tracking technology, stressed Professor Murwira.

As far as lead times are concerned, communities are now more likely to know of impending floods a day or more before the flood actually occurs, boosting preparedness.

Professor Murwira said: “For water (in the Manyame river) to flow from Marondera to Muzarabani, we know that it takes 24 hours to 36 hours.

“So, if there is a lot of rain say in Chinhoyi, we know approximately what time it will start reaching Muzarabani, and if it is the kind of runoff that will cause floods, we will know precisely at what time it will literally start flooding the ‘bani.’”

The tool’s precision is remarkable, he said. “If you pour water on top of the hill and you want to establish how much time it will take to get to the bottom of the hill, the system we have developed is able to calculate that.”

No silver bullet

Studies show that rainfall patterns in Zimbabwe are no longer as predictable.

Since the early 1900s, rainfall has dropped sharply in November, January, February and March, with the onset periods becoming erratic.

Rains in October and November and December have become “more violent and destructive,” leading to frequent flash flooding, according to a 2013 paper by Meteorological Services Department director Dr Amos Makarau.

Strong winds like tornadoes are now common place, he said, blaming the changes on climate change.

The new flood forecasting service will ease some of those impacts by equipping people with crucial information that helps them prepare and respond better to extreme events, says Terrence Mushore, a climate change expert with the Bindura University of Science Education.

God is faithful.

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