Extreme weather events can be costly and usually difficult to predict, among which hail is especially a difficult one. Hailstorms come and go quickly on small scales (usually several kilometres) for a short period of time (usually within 10 minutes), but can cause great damage to aircraft, vehicles, houses, and crops, and can be deadly to livestock and people. Researchers from all over the world are working towards a better understanding of hail to improve the ability of hailstorm forecast and modification, to mitigate the environmental and financial impact.

A group of researchers from Peking University in China are studying the role of aerosol in the formation of hailstones, and they have involved citizens in the project since 2016 to help with the research by collecting freshly fallen hailstones across the whole country. The name of the citizen science project is Hailstone Hunting!

Hold on there for a second! You might be wondering: freshly fallen hailstones? Across the country? China is huge! Hailstones melt into water, and they can easily be contaminated! So how can it be done?

Here’s how the hunting goes!

The Hailstone Collection Citizen Science Project is led by Professor Qinghong Zhang from Peking University, China. The online communication platforms for their public engagement and project promotion are WeChat and Weibo, which are dominantly used by people in China. The project team share the initiative through a self-managed project social media account where they educate about hail, invite people to help, and keep people posted on the progress of the research. Besides a clear written instruction to tell people how to help, they also made a simple and brief video demonstrating how to collect fresh and clean hailstones without touching them directly. 

Screenshots from the demonstration video

After a hailstorm, in a safe environment, participants are asked to select at least 15 relatively clean hailstones of varied sizes using disposable gloves or plastic wraps and store them in the freezer immediately. They are also asked to document the specific time and location of the hailstones found on the ground. The researchers, as soon as possible, will travel to the location to collect the samples with a portable freezer. They use different means as necessary, travelling by plane, train, or car depending on the location.

A screenshot from a video documenting a hailstone collecting trip from the research group after being informed by participants

Collected hailstones are used in the lab to study the formation process to understand its growth mechanisms, so the more intact the ice particles the better. According to one of the researchers, a PhD student Haifan Zhang, around 60-90% of the collected samples can be effectively used in the study, and every hailstone is unique with quite a different shape, composition, colour and transparency. They will carefully store the rest of the hailstones even if they are not usable due to the current condition (too small or shattered) because it is believed that advanced equipment and technology can decipher the rest of the hailstones in the future, just like DNA evidence cracking numerous old cases. 

Hailstone samples. Images provided by the Research Group of Hail from Peking University

They started the Hailstone Hunting Citizen Science Project in 2016. The project team built the network by asking help from local acquaintances to participate and promoting the project on social media later on. Until this year, researchers have collected hailstone samples from 12 areas (provinces, municipality, autonomous regions) across China (circled on the map below).

Participants come from diverse backgrounds like agriculture, business, technology, and academia. Farmers, in particular, are willing to help because hail has a significant impact on their lives. Professor Zhang told us that one of the participants who took part before even upgraded her hail hunting skill by setting up a net outside of the window to better capture the hailstones this year. 

The researchers express their appreciation to the citizen scientists in a unique way: gift exchange! Reciprocity is an important etiquette in China, so people always try to return something to express their gratitude upon receiving a favour. In the case of the hailstone hunting project, citizen scientists are given an agate keyring and a thank you card for their contribution. Professor Zhang shared that the idea was inspired by the notion that things in nature are one of a kind: there’s a common saying that no two snowflakes are identical in the world! Similarly, no two hailstones nor two agates are the same. When promoting the initiative, the project team had a great approach by writing an article about how both hailstones and agates have similar natural experiences in their formation. Both have challenging journeys to form into something extraordinarily unique. The agate keyring gifted to the people also allows the citizens to learn something fascinating.

Photo credit: Alicia Cui

So, does the gift attract more citizen scientists? Professor Zhang observed that generally people did not care much about the gift but were eager to support the research because they wanted to contribute, and they understood the value.

There was no public call for hailstone collection during 2017 and 2020 since the team were focusing on lab work progress, but there were still people voluntarily collecting samples for them.

The research had progressed from studying collected hailstone samples and the findings have been published in three papers which can be found here: Water-soluble ions in hailstones in northern and southwestern China,  Chemical composition of a hailstone: evidence for tracking hailstone trajectory in deep convection and Notable Contributions of Aerosols to the Predictability of Hail Precipitation. 

The Hailstone Hunting Citizen Science Project has been reinitiated in 2021. There is more to collect, study, and learn due to the geographic diversity in China. If interested, please follow their official account on WeChat: PKU_Hail_Group. Let’s look forward to their future findings! And happy hunting!

--We hope to promote citizen science by showing the general public what’s happening in that world and encourage more people to get involved. We also want to create a platform for various citizen science projects to share their journeys.--

Joint Centre for Disaster Research

Massey University

New Zealand

In 2024, a questionnaire was conducted among the hail collection volunteers with 28 responses were received, to explore the motivation of volunteers and implication for Citizen Science projects. Please find the translated questionnaire and responses here: /Uploads/keditor/file/20240831/20240831190042_82761.pdf

Other data sources used in the following research in related to this project: /Uploads/keditor/file/20240831/20240831190504_37994.xlsx