The Rainiest Place On Earth

Summary

The world's largest rainfall simulator in Japan creates extreme weather conditions to study flooding and landslides. With 550 nozzles, it simulates record 300mm/hour rainfall that occurred in Missouri. Tokyo's infrastructure prevents $1.7 billion in flood damage but 200 died in 2018 floods. The building moves to test shallow landslides on model terrain. Landslides increase with deforestation and climate change makes extreme rain more common. The simulator also tests drones and self-driving cars to improve their rain/visibility functionality. As climate impacts worsen, the importance of this research facility grows.

Takeaways

• 😲 The world's largest rainfall simulator in Japan can simulate rainfall intensities up to 300mm per hour, equal to the most intense rainfall ever recorded.
• 🌧️ The facility is used to study flooding and landslides, which are major natural disaster threats in Japan due to its climate and topology.
• 😮 The entire facility can move on railway tracks to test landslides on sloped sections recreating real-world conditions.
• ⛈️ Smaller raindrops fall slower than larger ones due to differences in their weight to surface area ratio affecting terminal velocity.
• 🚜 Deforestation has increased landslides 10x in some areas as tree roots provide stability and absorb water.
• 🔬 The complexity of landslide physics makes large scale physical simulations important for research.
• 🚗 Self-driving cars are tested at the facility to improve detection in heavy rain which can decrease sensor visibility.
• ☔ Catchment zones, diversion channels and drainage pipes help protect from landslide damage.
• 🌡️ Climate change is increasing extreme rainfall events, underscoring the importance of this research.
• 😠 Addressing root causes of climate change is ultimately more important than mitigating negative impacts.

Q & A

Why is the rainfall simulator so important for Japan?

The rainfall simulator helps scientists in Japan study flooding and landslides, which are major natural disaster threats in the country due to its mountainous terrain and frequent typhoons dumping heavy rain.

What is the intensity of rain that the rainfall simulator can produce?

The rainfall simulator can produce rain with an intensity between 15 mm per hour up to 300 mm per hour, which matches the highest rainfall intensity ever recorded of 305 mm per hour in Holt, Missouri in 1947.

How does rain contribute to landslides?

Rainwater fills the pores in soil, increasing water pressure between soil grains. This decreases friction holding the soil together, making slopes more likely to slide.

How have extreme rain events in Japan changed over the past 30 years?

Over the past 30 years, rain events in Japan with intensity over 50 mm/hr have become 40% more common, while events with over 100 mm/hr intensity are 70% more common.

What are some solutions for preventing landslides?

Solutions include steel beams/mesh to anchor slopes, lowering slope angles, drainage pipes, catchment zones to divert landslides, and planting trees since their roots anchor soil and draw up water.

Why does raindrop size matter for rainfall intensity?

Larger raindrops fall faster due to higher weight/surface area ratio. Smaller 1 mm drops fall ~2 m/s while 3 mm drops fall 6 m/s, so drop size affects rate rain accumulates.

How are self-driving cars tested at the rainfall simulator?

The simulator provides a repeatable environment to test how rain impacts the cameras and LIDAR sensors in self-driving cars used to detect objects, improving solutions to weather-related visibility issues.

What was the economic damage from floods during a 2018 typhoon?

Typhoon Prapiroon in 2018 caused over $10 billion USD in property damage across Japan due to flooding after parts of the country received 2 meters of rain in 10 days.

How can deforestation increase landslide risk?

Trees anchor soil with roots and absorb water. In British Columbia, deforestation led to a 10x increase in landslides due to lack of trees to stabilize soil.

How do tunnels and tanks help mitigate flooding in Tokyo?

Tunnels under Tokyo divert floodwaters from 100+ rivers into a huge underground water storage tank to prevent overflow that would otherwise damage the city of almost 40 million.