Climate Science Defied…Extreme Rainfall Events In Arizona Have Decreased Over The Past 50 Years

I lived in Arizona for a few years and I remember flash floods occurring regularly during the rainy summer season. Good to see things are getting less extreme there. Thanks, global warming! -PG

Researchers surprised: extreme rainfall in Arizona has decreased over the past 50 years despite climate warming

By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(German text translated and edited by P Gosselin)

Climate change leads to more extreme rainfall events and worse flooding. That’s the common claim that gets made before one looks at the data.

Bit by bit, however, researchers are filling in the data gaps and finding one surprise after another. For example the University of Bristol put out a press release last October on the extreme rainfall trends in Arizona: In summary: Extreme rainfall has decreased over the past half century despite climate warming.

Moreover, total rainfall fortunately has risen. The alarmist general assumption of increased extreme rainfall events has failed to materialize. The press release follows:

Rainfall trends in arid regions buck commonly held climate change theories
The recent intense hurricanes in the Atlantic have sharply focused attention on how climate change can exacerbate extreme weather events. Scientific research suggests that global warming causes heavier rainfall because a hotter atmosphere can hold more moisture and warmer oceans evaporate faster feeding the atmosphere with more moisture. However, this link between climate warming and heavy rainfall has only been examined in particular regions where moisture availability is relatively high. Until now, no research has been undertaken that examines this relationship in dryland regions where short, sharp rainstorms are the dominant source of precipitation and where moisture availability on land is extremely limited.

To explore the links between climatic warming and rainfall in drylands, scientists from the Universities of Cardiff and Bristol analysed more than 50 years of detailed rainfall data (measured every minute) from a semi-arid drainage basin in south east Arizona exhibiting an upward trend in temperatures during that period. The analysis demonstrated a decline in rainfall intensity, despite an increase in total rainfall over the years. Interestingly, the study shows that there is a long-term decline in heavy rainfall events (greater than 25 mm/h) and an associated increase in the number of smaller storms each delivering less rainfall. This result is contrary to commonly held assumptions about rainfall trends under climate change.

Lead author, Dr Michael Singer from School of Earth and Ocean Sciences at Cardiff University, said: “In drylands, convective (or short, intense) rainfall controls water supply, flood risk and soil moisture but we have had little information on how atmospheric warming will affect the characteristics of such rainstorms, given the limited moisture in these areas.” Co-author, Dr Katerina Michaelides, from the School of Geographical Sciences and Cabot Institute at the University of Bristol, said: “Our findings are consistent with previous research in the Colorado Basin which has revealed a decline in runoff in the upper part of the Basin. “Our work demonstrates that there is a more regional decline in water resources in this dryland region, which may be found in other dryland regions of the world.”

Since trends in convective rainfall are not easily detected in daily rainfall records, or well-simulated by global or regional climate models, the researchers created a new tool to assess the effects of climate change on rainfall patterns and trends in dryland areas. Their new model, STORM, simulates individual rainstorms and their expression over a river basin, and it can represent different classes of climate change over many decades. Drs Singer and Michaelides employ STORM to show that the historical rainfall trends likely resulted in less runoff from this dryland basin, an effect they expect to have occurred at many similar basins in the region. Dr Singer added: “We see this model as a useful tool to simulate climate change in regions and cases where traditional models and methods don’t capture the trends.”

Paper: Deciphering the expression of climate change within the Lower Colorado River basin by stochastic simulation of convective rainfall by M. Bliss Singer and K. Michaelides in Environmental Research Letters.”

In May 2015 extensive flooding occurred in Texas and Oklahoma due to heavy rainfall. This was not caused by a hurricane, but rather by an El Nino, which indeed leads to extreme rainfall events, according to a study by Wang et al. 2015.

In another study by Wang et al. 2014, researchers found a flooding pattern in the region of the Missouri River which happened to follow a Pacific Ocean cycle. Knowledge of this link now allows better forecasts to be made and preventive efforts to be taken. Washington University in St. Louis reminded that not everything can be attributed in knee-jerk fashion to climate change. Extreme rain at the end of 2015 in Missouri led to terrible flooding. Part of the blame here was assigned to the changes in building in flood-prone areas of the river which led to an obstruction of the outflow.

In another study the University of Colorado in Denver was able to show that also the state of Colorado is poorly prepared for flooding. Important bridges and infrastructure urgently need to be upgraded. Damage that occurred in a flood in 2013 would have been much less had the structures been strengthened and better taken care of.

24 responses to “Climate Science Defied…Extreme Rainfall Events In Arizona Have Decreased Over The Past 50 Years”

  1. Bitter&twisted

    Good that papers that show real observations are now being published.
    It comes as no surprise that the observations are different from the Mosel predictions.
    In fact it is odds on that GCM predictions are completely wrong.

    1. SebastianH

      The paper this blog article is about ( a model. One of their results is:

      In summary, rainstorms in WGEW declined in intensity and in total amount of water delivered per storm over the multi-decadal period, but higher intensity storms became longer, delivering more water to the land surface per storm (even under declining intensity). Cumulative rainfall characteristics at WGEW show that PTotal has increased over the decadal period, along with the number of storms occurring each year (figures 2(k) and (l)).

      Besides this being just about a small region in NA, it also does show a change. Not the one globally anticipated, but nevertheless the observation/model is not the opposite of “weather becoming more extreme”.

      1. AndyG55

        Weather around the world has been becoming more benign, thanks to the slight and highly beneficial warming in the higher northern latitudes.

        Unfortunately, with the AMO and PDO turning and a sleepy sun, we can expect cooling of those higher latitudes, and more differential to drive extreme events.

        1. SebastianH

          AndyG55, so if it continues to warm in the next 5 years, you’ll consider that you could have been wrong and that the CO2 forcing observed by Feldmann is real?

          Or will you, like Pierre, forever proclaim the coming ice age?

          1. AndyG55

            Only warming has come from El Nino events.

            No warming for 33 or the last 39 years.

            A drop next month of only 0.2C will take us back to below the zero trend pre-2016/17 El Nino.

            A strong La Nina is forming

            So your “continues to warm” clause is a load of baloney.

          2. AndyG55

            forgot the link


            Feldman did not find any CO2 warming.


            If CO2 cause the warming from 2000-2010,

            …what caused the cooling from 2010 to 2012.

            You are, as always, working from a strong position of ignorance.

          3. Kenneth Richard

            So if temperatures warm during a 5-year period, CO2 caused it. If temperatures don’t warm, CO2 didn’t cause it. So what happened during the many 5-year periods in the last 150 years when there has been no warming, but a cooling instead? What was the mechanism causing the cooling?

  2. Newminster

    I thought the basic theory was that a warmer world would mean a smaller temperature gradient which would result in fewer extremes.

    So a more benign world and less in the way of floods and drought and severe storms.

    What changed?

    1. John F. Hultquist

      Just read that what you say is for the Northern Hemisphere only, as the Arctic area is warming faster than any other place.
      Southern Hemisphere (more water surface, less land) is not following.
      I do not now find that article. Sorry.
      Another of my comments follows.

      1. AndyG55

        “as the Arctic area is warming faster than any other place”

        Is it ?

        Apart from the El Nino spike last year, UAH shows this…

        1. AndyG55

          And before the El Nino, the largest “anomalies” in UAH NoPol were in 1980 and 1981.

        2. John F. Hultquist

          You will have to find that article and comment there.
          I’ve read there are numerous places that are:
          a – warming faster than any others;
          b – drowning faster;
          c – producing climate refugees faster;
          e – experiencing animal extinctions faster;

          I seldom finish reading these things, and do not keep track of them.

          1. AndyG55

            “I seldom finish reading these things,”

            I give a quick look at actual data..

            so in basically all cases where the “climate change meme” is involved…

            …. they end up in the bin after the first sentence 🙂

    2. Bitter&twisted

      Climate “scientists” want more money.

  3. tom0mason


    “I thought the basic theory was that a warmer world would mean a smaller temperature gradient which would result in fewer extremes.”

    Maybe for some but the AGW alarmist/advocate have been touting the ‘extreme’ weather baloney for decades!

    Just a few…
    “Intense hurricanes, like Katrina, have steadily increased over the last 35 years. Warmer oceans could be the cause.”


    “…The recent increases in activity are linked, in part, to higher sea surface temperatures in the region that Atlantic hurricanes form in and move through. Numerous factors have been shown to influence these local sea surface temperatures, including natural variability, human-induced emissions of heat-trapping gases, and particulate pollution. Quantifying the relative contributions of natural and human-caused factors is an active focus of research…
    …The models are in better agreement when projecting changes in hurricane precipitation – almost all existing studies project greater rainfall rates in hurricanes in a warmer climate, with projected increases of about 20% averaged near the center of hurricanes. “


    “…said Diffenbaugh, who also is an assistant professor of earth and atmospheric sciences at Purdue. “The result was a general increase in days more favorable to storm creation. It appears that the increase in warm, humid air near the surface outweighs the reduction in strong winds higher in the atmosphere.”

    In addition, the study showed a strong seasonal and regional variation in the effects of climate change.

    “Some areas were only affected slightly, while others more than doubled the chance for severe thunderstorms,” Diffenbaugh said. “Also, the storm-favorable conditions appear to occur during the same seasons as they do today, with an extension of the season in some areas. This increases the seasonal extremes, as opposed to more storms spread throughout the year. It is essentially a longer, more intense storm season – sort of a feast or famine.”

    The team, which also included Michael Baldwin, a Purdue assistant professor of earth and atmospheric sciences, and Purdue research assistant Eric Robinson, looked at weather conditions over the U.S. landmass from the middle to latter part of 21st century, using the regional climate model and three global climate models.

    Diffenbaugh said the team used multiple climate models to achieve thorough research results and to reduce the impact of an idiosyncrasy of an individual model.”


    “…Numerous studies in recent years have found no evidence that the number of hurricanes and their northwest Pacific Ocean cousins, typhoons, is increasing because of the rise in global temperatures.

    But a new study in the journal Nature found that hurricanes and typhoons have become stronger and longer-lasting over the past 30 years. These upswings correlate with a rise in sea surface temperatures.

    The duration and strength of hurricanes have increased by about 50 percent over the last three decades, according to study author Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology in Cambridge. “

    And there are so many more.

  4. John F. Hultquist

    My view is that Dynamic Earth ‘bucks commonly held climate change theories’. The theory, hypothesis, WAG or whatever of AGW is based on bad white guys and their SUVs. No proof of this.
    Earth has warmed from the LIA. Why is a mystery, as is whatever is going on in the USA’s southwest.

    1. tom0mason

      Indeed. The science is not settled, climate science has turn into fantastic babble.

      1. AndyG55

        …. Or a FANTASY BUBBLE.

    2. SebastianH

      Not really a mystery …

      That’s what you have been told to believe or came to believe all by yourselves.

      1. AndyG55

        As I said.. A FANTASY BUBBLE.

        There is NO EMPIRICAL PROOF that CO2 causes any warming in a convective atmosphere.

        So funny that you still just “BELIEVE !!!!!!”

        Actual science seems to be irrelevant to you, seb.

  5. Martin

    “Since trends in convective rainfall are not easily detected in daily rainfall records, or well-simulated by global or regional climate models, the researchers created a new tool to assess the effects of climate change on rainfall patterns and trends in dryland areas. Their new model, STORM, simulates individual rainstorms and their expression over a river basin, and it can represent different classes of climate change over many decades”

    In my view climate models are crap, even if the results run contrary to the “consensus”.

    1. John F. Hultquist

      simulates individual rainstorms and their expression over a river basin

      Thus not a climate model. I don’t know squat about their model.

      Two other models that have proved useful that may be of this sort are:
      – BUFfalo’s forecasting toolKIT (BUFKIT): a model that attempts to forecast “lake effect snow” across the North American Great Lakes.

      – a wildfire progress model, now being used in the southern California area

      1. AndyG55

        “I don’t know squat about their model.”

        Almost certainly a standard flood routing model. Many exist. Some have actually been reasonably well validated against real life. We see them in use when we get flood peak estimates etc. Expectations of high accuracy? Nope.

        This is probably inked with a stochastic or similar rainfall/runoff model.

        Again, there are many such models, but generally the hydrologists using them know that they only give a rough possible estimate.

        Predicting the future is impossible, but predicting the run-off from a given storm at least has some chance of getting somewhere close to reality if you have enough prior data.

        1. AndyG55

          Correction.. inked -> linked

          “This is probably linked with a stochastic or similar rainfall/runoff model.”

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