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Venice may be not more flooded in 21st century

Discussion in 'Environmental Discussion' started by tochatihu, Jun 10, 2011.

  1. tochatihu

    tochatihu Senior Member

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    For our Environmental Good News Section (we should have one I think)

    New research suggests that Venice (the one in Italy) may be less inundated than we'd suppose from global sea level projections:

    Venice to suffer fewer storm surges (Media Release)

    The work was published in Climatic Change, and not too hard to get access there in case anyone's interested.

    As often the case, for those who suppose that nothing can be predicted by climate models, this is all fluffer nutter and won't cheer them up at all. But I'm happy because maybe I can visit (stinky :eek:) Venice in the coming decades.
     
  2. bisco

    bisco cookie crumbler

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    i'll bet the venisians are happy.
     
  3. chogan2

    chogan2 Senior Member

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    Well, I've seen that expressed differently. No storm surges? Great, won't be anybody living on the Mediterranean coast anyway.

    [​IMG]

    FWIW, that's the Palmer Drought Severity Index, modified to account for a greater than -10 to +10 range (the range that suffices for the world as it is now). Minus seven-ish is US 1930's Dust Bowl territory. The purple areas are like-onto-uninhabitable, short of desalinization of ocean water or somehow-inexhaustable supplies of fossil water to be pumped out of the ground.

    The overview is here:
    Climate change: Drought may threaten much of globe within decades | UCAR

    This is, in large part, why I am concerned about global warming. This is the mainstream prediction for drought in 2100. For the U.S., it's a fair match to the recent historical data (the Holocene thermal maximum corresponded to desert-like conditions in the US midwest),, so it's not like you have to rely exclusively on model predictions to have a pretty good idea of what's in store for North America. Europe? Not my problem. The Americas? There will not be a country called Mexico in 2100. And it's doubtful there will be one called the USA at that time. Combine that with Googling "Canadian Shield" and ... there ain't much left in the eastern North American continent that will be able to grow food.
     
  4. tripp

    tripp Which it's a 'ybrid, ain't it?

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    Southern England will be a desert? That seems unimaginable. Wales gets an insane amount of rainfall every year. What are the mechanics for a hotter, drier planet. Colder and drier I get, but not warmer and drier (given that most of the planet is covered with water, and much warmer water presumably be 2090).

    BTW, it looks like Bangladesh's flooding problems will be a thing of the past.
     
  5. sipnfuel

    sipnfuel New Member

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    At least we have Alaska. Time to crush Canada so we can have the Great Lakes. Bye Canada, hello 51st state... *evil laugh*
     
  6. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    As you know since you are in a semi-arid desert, deserts flood easily. That's why in Colorado where there has been a drought in the majority of the state, everytime it rains the water just floods over the ground and fills the streets. Dry ground doesn't take lots of water well. Moist ground takes more water easily. So when it drizzles, that is good for deserts. When it rains, most of that water causes flash flooding, sort of like what it is already happening...
     
  7. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Wales and Ireland do and will still get loads of rain. Western Scotland and England will too, but the East of the Country (London :D ) will and ARE getting much less rain than they used to.

    It's only June and parts of the South East of England are already in drought conditions - hardly any rain all year and the driest year since records began hundreds of years ago (apparantly).

    BBC News - Parts of England officially facing drought conditions
     
  8. chogan2

    chogan2 Senior Member

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    England, I couldn't say. But that's the third such study I've seen saying more-or-less the same thing for North America. Maybe in part they agree because the underlying models they rely on overlap. And there is a lot of uncertainty and significant disagreement among models. But if you'll read up on it even a bit, it seems like there's pretty good agreement about the underlying mechanism.

    As the earth warms up, two things happen.

    First, as meteorologists measure it, drought is a measure of soil moisture. It's the net difference between precipitation and evaporation/transpiration. As the earth warms, you get more rain (total) but also more evaporation/transpiration. So there are offsetting factors. Of all the water that falls on land across the globe, on average, something like 1/3 runs off, 2/3rds evapotranspires off. You can find maps for the tendency for evaporation alone (so-called pan evaporation, literally how many inches of water would evaporate off an open pan), and the correlation between temperature and evaporation is clear.

    [​IMG]


    So as the climate zones move northward,

    Hardiness Zone Changes at arborday.org

    evapotranspiration will increase as well. And you'll need more rain to keep the same average soil moisture that you have now.

    Second, as the earth warms, the equatorial Hadley cell expands to higher latititudes. This is the air circulation pattern whereby air rises at the equator (and so it rains a lot at the equator, despite being very warm), moves north (and south) to about 30 degrees latitude or so, then sinks (so most of the worlds major deserts are concentrated at that latitude, because the air has no moisture left but it warms as it sinks.) (This is, by the way, the same mechanism that drives the trade winds, the doldrums/horse latitudes, and the equatorial jet stream -- it's the Hadley cells plus conservation of angular momentum.)

    The expansion of the equatorial Hadley cells moves the dry zone (the deserts) north (in the Northern Hemisphere) and moves the rain northward. The corresponding mid-latitude and polar cells move toward the poles as well. You'll note that the top of the world is blue, meaning very wet conditions for that temperature zone (large excess of precipitation over evapo-transpiration.)

    This is what drives the drying out of the middles of the continents. Obviously this is broad brush, and it's not the explanation for the prediction for England, but it's a significant driver of the drying out of the interior of North America.

    Obviously, the boundary of the Hadley cell is not some firmly fixed place, it's where the air sinks on average. But the best estimates show that the Hadley cells have expanded between 2 and 5 degrees of latitude since the 1970s.

    Papers on Hadley Cell expansion « AGW Observer

    A degree of latitude is only about 70 miles, so that's not a huge event, and clearly that has to be pretty hard to measure well. But it appears to be happening pretty much in line with predictions. And it's a basic feature of atmospheric circulation -- this is one of those things where there's pretty good agreement this will happen.

    A third factor -- that you'll get your rain as more intense storms, as noted above -- that's plausible, but I don't think that's a significant driver of that drought map. But I don't know enough about the details to be able to say.

    The other evidence to bear in mind is archeological. The holocene thermal maximum, for example, was a period about 8000 years ago when the earth's tilt produced warmer summers nearer the poles than we have now. At that point, the interior of North America was much dryer than present. The Great Plans maybe weren't a desert, exactly, but they were much dryer than present. That's not exactly analogous to what's happening now, but I think it's a pretty strong clue that as it warms up, we're going to lose most of our Midwest farm land.
     
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  9. tochatihu

    tochatihu Senior Member

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    Chogan2's ref is a review following the Dai and Running drought paper, which was a very impressive study says I. Anybody needs copies?

    This certainly does not fall in the category of Env. Good News, but I still think we should have such a category here. Otherwise it's kinda gloomy. Another recent buzzkill was mapping areas of food insecurity over these drought projections. Would have to look to see where that was published, but if somebody is interested...
     
  10. austingreen

    austingreen Senior Member

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    I think it should be clear from the link sent

    These models are extremely poor at actually getting precipitation correct, so I would caution that stronger agreement could just be a symptom of group think. All the rating agencies thought mortgage backed securities and thus their derivatives were low risk, until they collapsed. Let's wait until the models at least match real rain patterns before we get all depressed and think of only gloom. Then again there is great uncertainty so it is almost certain that although some places will do better others will get worse.

    Local climate models like that given in the first link are much better at predicting local results. Again everyone should be cautioned that although these are better at prediction than global climate models their track record is also bad.

    Climate variability can be quite scary, and is what is not modeled well. The uncertainty should be looked upon as an opportunity for more and better research, which may help us mitigate damaging weather.
     
  11. richard schumacher

    richard schumacher shortbus driver

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    Storm surges in Venice and floods in Bangladesh will not be problems because both places will be permanently under 6 to 20 feet of sea water.

    On the bright side, Germany will be able to depend entirely on Solar energy.
     
  12. chogan2

    chogan2 Senior Member

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    To each his own.

    I look at figures 7, 8, 9 in the article,

    http://onlinelibrary.wiley.com/doi/10.1002/wcc.81/abstract

    and my conclusion, just by eye, is that the fit regionally and over time, for the past half-century, is good enough to work from.

    Add in the known US Midwest droughts at the Holocene thermal maximum, and I think the evidence is sufficient for a prudent person to be worried.
     
  13. tochatihu

    tochatihu Senior Member

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    Ok well if this simply must be a global hydrology thread...

    I am very simpathetic to the notion that the predictability of precipitation is still low, especially at smaller scales of time and space.

    Not at all, with the notion that we require perfection in these predictions (or any others) as a prerequisite for a serious global discussion of monetizing carbon emissions.

    If someone were not aware of the successes that Aiguo Dai and collaborators have had comparing their models with global records of river flow during second half of 20th century, they might be forgiven for tossing it into the groupthink bin.

    If.

    What I called Dai and Running is actually Zhao and Running ('scuse me) and you can snag your free copy here:

    http://physics.indiana.edu/~brabson/p310/Drought.pdf

    And if anyone can't get enough of Aiguo Dai's pubs, I'll steal you a copy.
     
  14. austingreen

    austingreen Senior Member

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    Let's first take my remarks as it relates to your original thread. I quoted dai about the impression as to a local area like venice. It would be great if dai, zhao, and running would review this study, but we can expect if it passes review that it would trump using global climate models to examine venice. I don't think there is anyway to get around that.

    I'll get to your and chogan's other criticism in my next post. That would apply to global hydrology.
     
  15. austingreen

    austingreen Senior Member

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    It must be remembered that models are calibrated on past data, and we can expect correlation from past data. If these models failed on the data sets they were calibrated on they would not have made it into dai. We must remember earlier global climate models did not correctly predict today's rainfall patterns. I further expect the new models to also fail, but they may succeed. The test comes when we see how well they do when tested with new data.

    If you look at mbh's temperature reconstruction the model looks greatly correlated with current temperatures, but when you dig down in the paper and data you realize the data was actual temperature after 1980, and not the model, as model diverged from the data set it was tested against. The global climate models do not use this method, but there are other calibration techniques that can make the models look better than they actually are.

    Dai then does a composite model. This removes even some of the variability of the current models, and only does his calculations on one set of emissions projections. He clearly states this, and acknowledges the possible problem. I think it is well to take this uncertainty and not pretend that we should have confidence in the composite model.

    I did not mean to imply that this was not a possible case. Things should be kept in perspective. The Holocene records are only one possibility. Things may be better or worse than dai. I would think there is much mitigation possible. This includes planting different crops that are drought resistant in dry places, and that adapt to floods in wet places. Stanford recently complete a survey of grain crops in the US and found no warming impact from 1980 until today. This is not what was predicted in 1990 or even 2000. 2009 had the best productivity on two of the crops. Bad policies implemented created the dust bowl and famine during the great leap forward. This is independent of actual climate. Its important to not just look at data that we know is suspect, but look into the scientific questions and devise experiments that can improve and validate models.
    I'm not sure how that comes into this discussion. There was not a model proposed that showed droughts at different co2 levels. That would be needed to monetize costs. I don't think we need a perfect model for that, but we do need a good model.

    Thank you for that information. My criticism is on the composite model that dai is based on, not on dai's use of the model. I don't think we can determine that convergence of the models means anything until the models actual predict precipitation. I am positing the possibility that the models are converging simply because the model makers are talking, only when the models are tested do we know if they are more accurate. I was suggesting the possibility of group think in the creation of the models, not dai's use of them. Until the new models are tested we should assume that there is still a large amount of climate variability not modeled. I know the idea of testing of an hypothesis before assuming it is correct is uncomfortable for many politicians and the media, but that is scientific method. In other words, I am not saying dai or zhao or running is wrong, only that we should take their own doubts into account, and not declare them right until we have enough information.
     
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  16. tochatihu

    tochatihu Senior Member

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    Dai's 'big hits' (published in 2008 and 2009) were the correspondence between model and the observed decadal trends in global river flows. The models of course were not parameterized by the river data. I'll hazard to guess that's why people are paying attemtion to his PDSI projections.

    Austingreen I much appreciate the fact that you are scrutinizing Dai's models and the others. More than most 'civilians' do, to be sure. Might this be related to your line of work? In any case, we can certainly agree to the current (and perhaps long-lasting) veil of unpredictability at smaller spatial and temporal scales. Heck, while we're at it, let's throw in ENSO and the Asian monsoon - both are still doing a great job at eluding modeling. I set up a soil-water manipulation experiment in local mountains (one of many such, globally). Some models say 20% increase, others 20% decrease, so I had to include both treatments :)

    So, we are not in excellent shape anticipating global hydrology of the future. But I'd suggest that we are confident that, smoothed over decades, many of the wet areas will become wetter and likewise dry ares will become drier. And I think that Dai has contributed substantially to that.

    If I seem to be over-reaching to connect this to carbon control efforts, so be it. Many people feel that way! But many other people find that we have enough evidence now to justify increasing our efforts to limit CO2 growth. Many efforts cost money, so in we go...

    Frustration remains on both 'sides' as well. Frustration at an apaprent inability to recognize the current situation as a clear and present danger, and that earlier actions could be cheaper than waiting. And in the other corner, frustration at calls to act before our understanding is better (this is not a complete list...)

    As I've said before, it won't get settled in this chat. But looks like I'll persist in bringing in ideas that interest me, both good news and bad. When somebody else brings up the latest publication that seems to (or is regarded as) bringing down the climate-change edifice, I seem to get drawn into those discussions as well.

    But they're all just discussions here, OK? None shall be tried and convicted based on what they think is so.
     
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  17. tripp

    tripp Which it's a 'ybrid, ain't it?

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    Excellent discussion, lads. Between work, family, and piping I don't have the time to dig in and understand these issues. I very much appreciate all of your efforts to create a synthesis followed by reasoned debate.
     
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  18. austingreen

    austingreen Senior Member

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    Yes, I only wanted to bring up these limitations in our knowledge. I think dai also asked for better modeling of volcanic eruptions. We also need to know the impact of damn, buildings, and agriculture on soil dryness. I'm glad some good people are looking into, and lucky for us computing power is getting faster and cheaper.:eek:

    I find the evidence compelling, but would like more years of supporting data before I am fully convinced. Part of my skepticism on the regional level may have something to do with the great natural variability in rainfall where I live. We are in extreme drought with the lake levels looking very low for this time of year. Last year was normal rain, but 2009 was so exceptionally hot and dry no one my age had seen anything like it here. But if you look at the records, we were in drought from 1947-1957 (3 years being close to normal by one year less than 30% normal the rain). So we can see the pictures of when it was dryer for a long period of time. The climate record also shows the climate getting slightly wetter over time. rains in 1980 had water levels rise to 100 year flood level.

    I wasn't trying dispute that. I was only saying that in order to know how much co2 efforts will save you must run the models with those lower co2 levels. If the US say drops co2 in 2030 to 40% bellow 1995 levels (which happen to be today's levels) I don't think it changes dai's predictions much at all. Now if the whole world drops the 2050 co2 levels to 80% bellow 1995 levels, that may make an impact, but is there any possibility that it happens? Things should be tried though, including planning for floods and droughts.

    I appreciate your comments.
     
  19. SageBrush

    SageBrush Senior Member

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    Call me a pessimist, but I think it is clear that the US will squander it's economic resources on disaster relief and ignore mitigation until it is far too late. As the disasters become more severe and numerous, the ability to mitigate AGW will decrease and the skeptics/denialists will argue that the limited social resources not be spent on mitigation until more proof is available.

    Rinse, wash, repeat until no mitigation is possible. People like AG are the forefront of the stall armada, since they know enough science to be a danger to themselves and the people who listen to them.
     
  20. cyclopathic

    cyclopathic Senior Member

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    tochatihu!

    I am not sure the title of your post reflects the findings described in article.

    Article talks about less favorable conditions for surge floods, not flooding in general. Granted surge flooding is the biggest issue for Venice, but rising sea levels will be still a threat, and damps may still fail.

    Also semantically "may be not more flooded" could be the equivalent to "there will be no floods", which is not the case and was not your intent.