Rainfall Rescue: 5 years on

A citizen science success story

Five years ago, on 26th March 2020, we launched the Rainfall Rescue project, just after the UK had just entered the first covid-related lockdown.

The idea was simple: ask for online volunteers to help transcribe millions of hand-written monthly rainfall amounts from 66,000 images. Each image represented a unique piece of paper recording rainfall for a single location for each month during a particular decade, stretching from the 1800s to the 1950s.

We expected the process to take months…

… but the response from the public was extraordinary. Within hours of launch we had 6000 volunteers helping. Within days we had 16,000 volunteers transcribing numbers. And, just 16 days after launch every single one of 5.3 million rainfall amounts had been transcribed by at least 4 different volunteers, along with all the location information. Around 100 million keystrokes had been typed. The data had been rescued and made available to scientists.

But, why was this information important? If you examine the number of monthly rainfall observations that were available before Rainfall Rescue then you can see that the data before 1961 was largely missing.

After Rainfall Rescue, the situation is very different - there are now thousands of locations with rainfall data back to the 1870s, and hundreds back to the 1840s. There are now more observations available in the 1880s than today.

But, just transcribing the observations was not the end of the process. Each sheet had to be checked and collated with sheets from other decades for the same location. Sometimes the location information was incomplete.

Eight dedicated volunteers helped for around 18 months to finalise the dataset, doing quality control, searching old maps, ancestry and census information, using the clues on the sheets to track down the missing locations.

Two years after the project launched we published the dataset, and the Met Office updated their official rainfall statistics back to 1836.

After these efforts, we can now map out the rainfall across the UK in extreme years and extreme months. The driest year on record is now 1855, and the wettest is 1872.

We can also see trends in rainfall in the wettest month of the year. The trend is towards wetter conditions - a 20% increase in the past 175+ years. This type of information is invaluable to learn about how we might adapt to rainfall changes, and to better understand extreme events and how they are changing.

October 1903 is the wettest month on record but, being a shorter month, February 2020 has the most rain per day of any month. It was during that very wet February that we decided to launch Rainfall Rescue.

We also need to recognise the efforts of the original observers, many of whom collected rainfall observations for decades, often on a voluntary basis, even continuing today.

Thank you to every one of the volunteers who transcribed the data and took the original observations. We note the efforts of George Symons who created the British Rainfall Organisation in the 1860s, without which none of this data would be available today.