In #9 we looked at trends in peak streamflow. As there isn’t a global database of floods this is the best proxy for flood risk from rivers and waterways. The result was a surprising decrease globally - the trend was down in some stations and up in others, but the down outweighed the up. This is
Not only dams, but levees also prevent flooding. That's a good thing, but a downside is that for major river deltas, the lack of periodic flooding experienced before the levees result in river deltas receding due to the sediment sinking once the river meets the sea. Could be water wells contribute to the sinking of the deltas too. A misconception is that deltas are being overtaken by the oceans primarily due to sea level rise. Of course the seas are rising, but not at the rate that the deltas are sinking.
I posted the first section of this article in the original blog site with a link to this full article. There's a comment there that reduced peak stream flow isn't always good news.
I'm pasting my reply here:
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Nathan,
I agree with you. I've oversimplified.
A few comments:
1. Brevity is not my strong point, and in this series I'm going for brevity. Over-simplification is the inevitable result.
2. This is from the section of the IPCC report on floods. The section is trying to assess recent trends in flood risk.
A reduction in flood risk can also be an increase in drought risk. Pluses and minuses in many aspects of climate.
I was struck reading one of the references on changes in snow melt, I think it was "Trends in snowmelt-related streamflow timing in the conterminous United States", R.W. Dudley et al 2017. There was less flooding from snow melt in the northwestern US, which led to greater fire risk.
Reduced flooding in some regions can be a negative - greater risk of droughts, greater forest fire risk due to drier ground.
But that idea isn't popular when you've just had floods in your region, especially if it was your house or your community.
3. Most people, even "very interested in climate" people, aren't going to read the 95 pages of the report on Extreme Weather (when you strip out the exec summary, the references and the tables at the end). It's hard to digest.
If there was a good summary of what was actually in the report, instead of just the negatives, it would be wonderful. My work would already be done. But we don't live in that world.
Anyway, I welcome your comment. I will endeavour to balance brevity and nuance.
Not only dams, but levees also prevent flooding. That's a good thing, but a downside is that for major river deltas, the lack of periodic flooding experienced before the levees result in river deltas receding due to the sediment sinking once the river meets the sea. Could be water wells contribute to the sinking of the deltas too. A misconception is that deltas are being overtaken by the oceans primarily due to sea level rise. Of course the seas are rising, but not at the rate that the deltas are sinking.
I posted the first section of this article in the original blog site with a link to this full article. There's a comment there that reduced peak stream flow isn't always good news.
I'm pasting my reply here:
---
Nathan,
I agree with you. I've oversimplified.
A few comments:
1. Brevity is not my strong point, and in this series I'm going for brevity. Over-simplification is the inevitable result.
2. This is from the section of the IPCC report on floods. The section is trying to assess recent trends in flood risk.
A reduction in flood risk can also be an increase in drought risk. Pluses and minuses in many aspects of climate.
I was struck reading one of the references on changes in snow melt, I think it was "Trends in snowmelt-related streamflow timing in the conterminous United States", R.W. Dudley et al 2017. There was less flooding from snow melt in the northwestern US, which led to greater fire risk.
Reduced flooding in some regions can be a negative - greater risk of droughts, greater forest fire risk due to drier ground.
But that idea isn't popular when you've just had floods in your region, especially if it was your house or your community.
3. Most people, even "very interested in climate" people, aren't going to read the 95 pages of the report on Extreme Weather (when you strip out the exec summary, the references and the tables at the end). It's hard to digest.
If there was a good summary of what was actually in the report, instead of just the negatives, it would be wonderful. My work would already be done. But we don't live in that world.
Anyway, I welcome your comment. I will endeavour to balance brevity and nuance.