1. John: I think a good blog post, or maybe 1/3rd of a good book chapter, would be an explanation of how southwestern states — especially California, Arizona, and Mexio — adjusted to the historical overestimate of Colorado River water when it was originally partitioned out.

    I take it Mexico was a huge loser. Anyone else?

    Have you written anything about that?

  2. David Appell
    IF it wasn’t any dams and irrigation = would have being LESS rainfall in the Colorado river catchment areas!!! Clouds avoid dry areas, can you get that?!
    No wander why you Warmist are against building new dams; because dams / irrigation IMPROVE the climate! More moisture in the soil, water storages and WV = milder climate – reason the Warmist prefer everything opposite than normal. No dams for electricity -> cray about CO2 no enough food -> anarchy is what the Marxist prefer. shame, shame, shame!!!

  3. David –

    In a sense that’s one of the book’s central themes. The problem is that we haven’t yet adjusted. We only grew into the full utilization of the over-allocated amount in the 1990s, when Arizona finally was able to take its full share. Since then, the three states primarily impact by this – Nevada, Arizona and California – have largely gotten their full allocation by drawing down reservoir storage. The book is really an attempt to reckon with what we do next, now that we’re close to having exhausted that option.

    Stefan – The wettest period in the Colorado River Basin happened from 1900-1920, *before* we built all those dams and irrigation systems. It’s been getting generally drier since then. The last 15 years, when we had all those dams and continued all that irrigation, are among the driest such stretches in a thousand years. In other words, the data are available to test your hypothesis.

  4. Update: Over on the Twitters, Kevin Anchukaitis pointed to some literature that’s looked more closely at this question in terms of precipitation on more localized scales around reservoirs. Basically within 100 km of the big reservoirs, there’s maybe a slightly positive impact on rainfall, though difficult to detect. Kevin’s words: “At the mesoscale (<100km), a small signal, difficult to confidently detect. Lots of other factors. Climate still dominates.”

  5. Update 2: Tom Meixner (like Kevin, University of Arizona water/climate) points out on the Twitters that the total evaporative loss from the reservoirs is likely to be greater than the amount of subsequent rain that falls nearby. So, overall, net loss to the regional system.

  6. jfleck, I’m pointing that: clouds avoid areas where is no water vapor, no topsoil moisture and water storages; lots of examples on the planet.
    In other words: if it wasn’t for those dams – would have being even much dryer! #2: ”dry agriculture” is not good / you had ”the dust bowl” People irrigate when is hot and dry and, that increases humidity; without ”humidity” in the air -> evaporation increases from crops and forests! B] swamps and rice paddies are magnet for clouds from the sea AND they bring the clouds ”lower” to drop the rain – dry land even if clouds come -> they get very high, and no rain; until the clouds go back somewhere close to the sea; they are they rules

    bottom line: dams prevent floods and droughts!

  7. jfleck
    usually I don’t read articles, where cannot ask questions, or make comment; but: those guys on the link have a bit narrow vision, for obvious reasons. b] it’s the ”indirect effects” they ignore or most probably don’t understand. c] in a comment is impossible to explain, needs many pages, will try to condense it:

    By opening Gibraltar -> Mediterranean started stilling all warmed surface water from Mexican gulf -> Texas ”and west” climate started deteriorating = Nevada, Arizona ”started producing dry heat” that dry heat was spreading even to Colorado catchments – then Bosporus opened 560BC, bad effect increased; gradually climate southern half of US keep deteriorating (shonks blame Maya irrigators)
    When opened Suez canal – some of water evaporated deficit in Mediterranean started coming from Red sea = that was a good benefit for US, BUT: Sahara expending -> more dry heat produced to destroy WV in Atlantic, bad! c] before 4000y ago, Sahara was savanna – mongrels by rubbing two sticks, made it desert. So: the indirect influences are most important. example: for last 4000y southeast Asia climate kept improving.
    Good climate is, when is not much difference between day and night! Climate is not what shonky climatologist call the phony global warming! For them Sahara and Brazil have SAME climate; because both places is SAME amount of CO2.
    To explain all details, need a thick book… BUT: if you want to see the whole picture; step back, encompass the lot and will start noticing the important factors, that are conveniently overlooked by the propaganda machine for the last 25years. cheers!

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