6 ms·

It should be relatively easy to calculate the max flood height and path of a area, with a given amount of rain on google maps. Anyone know such a tool?

rmah 5y ago
In the US, FEMA maintains flood maps for areas of the USA that are prone to flooding. Your tax dollars at work! You can access them here: https://www.fema.gov/flood-maps https://www.fema.gov/flood-maps
montalbano 5y ago
If there was such a tool, and it was accurate, do you think insurance companies would have insured the parts of Germany that recently flooded? I think you may be underestimating the complexity of both weather and climate modelling.
- Proven 5y ago
  But we can predict average temperatures decades into the future!
- PicassoCTs 5y ago
  Where i live, i know the whole water from a defined area flows through in a little stream. I know the areas watersheds and i know how much poured down in extreme cases. Thus i can mark the area on a topographic map, i can calculate the area and multiply it with the max amount of downpour. In my area thats 4490887(m^2) ×0,2(m^3 water) = 898 177.4 ^ m3 max rain water. Now all i want is a model of what areas would be reached on a stream if it received this much water. I know that some here are grumpy because there houses may loose value like a sinking ship very soon. But knowing is better then not knowing. Always. No fluid-simulations needed, just a basic Topographic map fill the pond.
  - woeirua 5y ago
    In the US at least the USGS builds floodplain predictions for most of the major streams/rivers using this exact method. The problem is that those maps typically underestimate the amount of water that falls during these extreme events.
    - bombcar 5y ago
      They are also sometimes based on assumptions about the land upon which the rain is falling - forests and meadows absorb way more water before runoff begins than concrete and asphalt do.
  - thehappypm 5y ago
    You're missing a key variable here: time. If you dumped that amount of rain water in one second, you'd have a Tsunami. Dump it over a 24 hour period, it might flow out smoothly out of a little stream. Dump it 10% in an hour, 50% in the next hour, 10% the next hour, 30% over the next 12? Um, that's harder.
- BitwiseFool 5y ago
  >"do you think insurance companies would have insured the parts of Germany that recently flooded" Many insurance companies will be happy to write you a policy for something high risk but they will absolutely charge you more to compensate. It's all a numbers and probability game for them.
- nine_k 5y ago
  I wonder if the insurance companied would insure them anyway, because they might be legally obliged, and might not be allowed to "unfairly discriminate". I can easily imagine a setup where an insurer either averages out the risk profiles and premiums over a large administrative area to offer basically the same deal to every resident, or loses the license to operate in that area.
baq 5y ago
It’s called your government’s weather forecasting center or equivalent. They have all the data, tools and compute needed to calculate that with any accuracy, and they do.
arethuza 5y ago
SEPA here in Scotland produce detailed flood risk maps - I'd have thought most countries would have something similar: https://map.sepa.org.uk/floodmap/map.htm https://map.sepa.org.uk/floodmap/map.htm
LeifCarrotson 5y ago
"Relatively easy" is brushing over an awful lot. https://xkcd.com/793/ https://xkcd.com/793/ You can get a rough approximation, and that's been done at great effort for the entire US at the FEMA website: https://msc.fema.gov/portal/home https://msc.fema.gov/portal/home. It's not a simple problem to solve. Some of the caveats are discussed in this Practical Engineering video: https://www.youtube.com/watch?v=EACkiMRT0pc https://www.youtube.com/watch?v=EACkiMRT0pc Volume of outflow through a stream is equal to rainfall times watershed area. Seems intuitive, right? Except what about water that gets absorbed into the ground, or captured in a temporary holding pond, slowed by vegetation, or accelerated in a storm drain...I think Grady put it well when he pointed out that the silly Imperial units of outflow in cubic feet per second, rainfall in inches per hour, and watershed area in acres multiply together to 1.008, which is off by about 1% but close enough that civil engineers just throw away the constant entirely because it's such an imprecise approximation that the error is irrelevant.
totetsu 5y ago
Local government in Japan publishes such maps.
LegitShady 5y ago
Time to get a degree in civil engineering.

rmah 5y ago

In the US, FEMA maintains flood maps for areas of the USA that are prone to flooding. Your tax dollars at work! You can access them here: https://www.fema.gov/flood-maps https://www.fema.gov/flood-maps

montalbano 5y ago

If there was such a tool, and it was accurate, do you think insurance companies would have insured the parts of Germany that recently flooded? I think you may be underestimating the complexity of both weather and climate modelling.

Proven 5y ago
But we can predict average temperatures decades into the future!
PicassoCTs 5y ago
Where i live, i know the whole water from a defined area flows through in a little stream. I know the areas watersheds and i know how much poured down in extreme cases. Thus i can mark the area on a topographic map, i can calculate the area and multiply it with the max amount of downpour. In my area thats 4490887(m^2) ×0,2(m^3 water) = 898 177.4 ^ m3 max rain water. Now all i want is a model of what areas would be reached on a stream if it received this much water. I know that some here are grumpy because there houses may loose value like a sinking ship very soon. But knowing is better then not knowing. Always. No fluid-simulations needed, just a basic Topographic map fill the pond.
- woeirua 5y ago
  In the US at least the USGS builds floodplain predictions for most of the major streams/rivers using this exact method. The problem is that those maps typically underestimate the amount of water that falls during these extreme events.
  - bombcar 5y ago
    They are also sometimes based on assumptions about the land upon which the rain is falling - forests and meadows absorb way more water before runoff begins than concrete and asphalt do.
- thehappypm 5y ago
  You're missing a key variable here: time. If you dumped that amount of rain water in one second, you'd have a Tsunami. Dump it over a 24 hour period, it might flow out smoothly out of a little stream. Dump it 10% in an hour, 50% in the next hour, 10% the next hour, 30% over the next 12? Um, that's harder.
BitwiseFool 5y ago
>"do you think insurance companies would have insured the parts of Germany that recently flooded" Many insurance companies will be happy to write you a policy for something high risk but they will absolutely charge you more to compensate. It's all a numbers and probability game for them.
nine_k 5y ago
I wonder if the insurance companied would insure them anyway, because they might be legally obliged, and might not be allowed to "unfairly discriminate". I can easily imagine a setup where an insurer either averages out the risk profiles and premiums over a large administrative area to offer basically the same deal to every resident, or loses the license to operate in that area.

baq 5y ago

It’s called your government’s weather forecasting center or equivalent. They have all the data, tools and compute needed to calculate that with any accuracy, and they do.

arethuza 5y ago

SEPA here in Scotland produce detailed flood risk maps - I'd have thought most countries would have something similar: https://map.sepa.org.uk/floodmap/map.htm https://map.sepa.org.uk/floodmap/map.htm

LeifCarrotson 5y ago

"Relatively easy" is brushing over an awful lot. https://xkcd.com/793/ https://xkcd.com/793/ You can get a rough approximation, and that's been done at great effort for the entire US at the FEMA website: https://msc.fema.gov/portal/home https://msc.fema.gov/portal/home. It's not a simple problem to solve. Some of the caveats are discussed in this Practical Engineering video: https://www.youtube.com/watch?v=EACkiMRT0pc https://www.youtube.com/watch?v=EACkiMRT0pc Volume of outflow through a stream is equal to rainfall times watershed area. Seems intuitive, right? Except what about water that gets absorbed into the ground, or captured in a temporary holding pond, slowed by vegetation, or accelerated in a storm drain...I think Grady put it well when he pointed out that the silly Imperial units of outflow in cubic feet per second, rainfall in inches per hour, and watershed area in acres multiply together to 1.008, which is off by about 1% but close enough that civil engineers just throw away the constant entirely because it's such an imprecise approximation that the error is irrelevant.

totetsu 5y ago

Local government in Japan publishes such maps.

LegitShady 5y ago

Time to get a degree in civil engineering.