Media playback is unsupported on your device Media caption How weather forecasts are used to prevent cholera outbreaks

Cholera cases in Yemen have been slashed by a new system that predicts where outbreaks will occur.

Last year, there were more than 50,000 new cases in just one week - this year, the numbers plummeted to about 2,500.

The system has enabled aid workers to focus efforts on prevention several weeks in advance of an outbreak - by monitoring rainfall.

It comes as the UN says it is concerned about a possible "third wave" of the epidemic.

The deployment of the technology has been coordinated by the UK's Department for International Development.

Prof Charlotte Watts, the department's chief scientific adviser, said that the system had helped aid workers bring a rampant epidemic under control.

"We have thousands of people around the world that died from cholera each year," he said.

"And I think this approach could really help put a dent into that figure.

"What this technology enables us to do is really home in to where we're going to get new outbreaks, and respond really effectively."

Last year, there were a million cases of the waterborne disease in Yemen. More than 2,000 people died and many of them were children.

It was the largest and fastest-spreading epidemic on record - and its rapid spread was caused by the destruction of sewerage and sanitation systems during the country's civil war.

Although cases have reduced dramatically in 2018, the UN says it is concerned about a possible "third wave" of the epidemic.

The UK's overseas aid department has worked with the Met Office to develop a system that predicts where cholera will occur four weeks ahead of time.

How does it work?

The Met Office produces a rainfall forecast for Yemen. Using its supercomputers, it is to determine the specific amount of rain that will fall and pinpoint the areas it will hit within a 10km (six-mile) radius.

Image copyright MET OFFICE Image caption The system combines heavy rainfall forecasts, in red, with local cholera risk data

These are important because downpours overwhelm the sewerage system and spread the infection.

The forecasts are used in conjunction with a computer model developed by Prof Rita Colwell, at the University of Maryland, and Dr Antar Jutla, at West Virginia University.

It draws on a variety of local information such as:

population density

access to clean water

seasonal temperature

Together, this information enables scientists to predict the areas most likely to experience an outbreak, up to four weeks in advance.

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The information is passed on to the UN's children's charity, Unicef, which uses it to to deploy its limited resources on the ground.

It distributes hygiene kits, jerrycans and chlorine tablets to prevent the spread of disease. Most importantly, it coordinates local health education campaigns.

The information is simple sanitation advice, such as washing hands and drawing water from safe sources - but the early intervention has prevented tens of thousands of cases.

But the promising early impact of the cholera prediction system should be treated with caution, according to Prof Watts.

There are many factors that can influence the number of cases, such as local structures and geography.

But she believes that the reduction in cases and deaths has been so dramatic that the system must be having some effect and is keen to develop it further.

Image copyright UNICEF Image caption Yemen experienced the worst cholera outbreak on record, with more than one million cases last year

"We would like to extend the predictions from four weeks to eight weeks because that would enable us to not only plan prevention activities in terms of clean access to clean water and health education but also potentially deploy a vaccine campaign, which takes a little bit longer to plan and implement," she told BBC News.

Across the world, an estimated 30,000 people die of cholera each year - mostly in South Asia and Africa.

The new predictive system has the potential to slash that number, according to Helen Ticehurst, who is the Met Office's international development manager.

"The project is really exciting in understanding the application of forecasting to cholera prevention," she said.

"We can use what we have learned from this project and use it in other parts of the world where there is cholera prevention and also to prevent other diseases that are associated with temperature and rainfall, such as dengue fever and malaria".

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