AUTHOR: Richard Cicone, Principal, ISCIENCES, L.L.C.
WHEN IT RAINS...
A few days ago on my way to Traverse City, along Hill Road near Rapid City I spied stacks and stacks of timber recently extracted from the local forest. These are the remains of mature trees mowed down by a derecho storm  that hit Michigan on August 2, 2015. The US Weather Service issued 17 warnings that day and recorded a 4.25 inch ball of hail near West Branch, the largest since records began in 1950 .
One hundred mile per hour winds accompanied by over two inches of precipitation extensively damaged forests and private properties, with estimates at $29.7 million in Leelanau and $15.4 million in Grand Traverse counties . Many large trees were uprooted in scenic Glen Arbor near Sleeping Bear Sand Dunes on Lake Michigan, and local farmers suffered a heavy toll. The devastation was so extensive that our Governor declared a “state of disaster” in the region . Glen Arbor is now back to normal but many fallen trees are still strewn on the landscape, and memories are etched with images of that dramatic storm.
More recently, on 8 July 2016, the sky darkened rapidly around midday. Strong winds, a torrential three inch rain, and ping pong ball size hail destroyed apple crops and other agricultural crops in the local area . Then as rapidly as the storm appeared, it gave way to clear blue skies.
Is this normal?
I grew up in Michigan and there are plenty of stories to tell about severe weather events, driving rains, tornadoes, and deep snowfalls. But it is different now.
In fact, precipitation events in the U.S. are often more intense than in the past. Scientists have examined changes in precipitation patterns in the U.S. documenting both increased levels of total precipitation and storms that deliver much more water than normal , . The 2014 U.S. National Climate Assessment addresses this issue stating, “Heavy downpours are increasing nationally, especially over the last three to five decades. Largest increases are in the Midwest and Northeast. Increases in the frequency and intensity of extreme precipitation events are projected for all U.S. regions” .
The National Climate Data Center at NOAA provides a useful online tool to explore regional variations - the U.S. Climate Extremes Index . Using the Index, Figure 1 (below) shows that in the Upper Midwest a much greater than normal proportion of precipitation is derived from extreme one day events (defined as the highest 10% of occurrences of cumulative daily precipitation) .
Typically about 10% of the land area in the Upper Midwest would experience more than an average amount of its total daily precipitation from extreme precipitation events. However, over the last three decades you see two, three, even as much as 4.5 times more land area receiving most of its precipitation from extreme events over historical norms. This is true throughout the continental U.S. You may wish to graph your region of interest using the U.S. Climate Extremes Index, which you can find at https://www.ncdc.noaa.gov/extremes/cei/graph.
There were hard rains that I recall as a youth, but these data reveal that we are in fact experiencing more intense storms in my senior years. And evidence points to this phenomenon occurring worldwide.
What is going on?
Since 1884 the average global temperature has increased 0.87 °C (1.56 °F) . What affect does this have on precipitation?
In physics, the Clausius-Clapeyron Relationship describes the rate of change in the vapor pressure of a liquid as a function of temperature . Precipitation starts as atmospheric water vapor that condenses into liquid as temperature falls. Using this relationship, scientists have determined that the water vapor holding capacity of the atmosphere will increase at a rate of 7% for every degree Celsius increase in temperature. Hence a warmer atmosphere can hold more water vapor. This does not necessarily mean that it will, since many other factors determine the evaporation of surface water to form water vapor. Nor is the temperature change everywhere uniform. Precipitation is subject to many dynamic factors that determine local weather conditions.
What has changed is the overall temperature constraint in the system. When the globe is warmer, there is more energy to work with. In 2002 Allen and Ingram  considered these various factors and estimated global average precipitation should be expected to increase about 2-3% per °C of warming.
If the atmosphere can hold more water, there is more water to release, suggesting that precipitation events will intensify. Since the rate of evaporation has not changed, the dry period between events will lengthen, providing time to refill the “water bucket” in the sky. Under warming conditions we can expect intense rain storms and droughts more often. And the warmer it gets, the more likely extreme events will become even more extreme.
Is this just theory?
In a recent paper, Markus Donat and colleagues (2016) compared observational data worldwide to the prediction of global circulation models . They tested a tenant of climate science that “the dry will get dryer, and the wet will get wetter” . That is, we can expect greater average worldwide precipitation, but more of it will fall in temperate and tropical climates, less in dryer subtropical climates. Donat did not find evidence strong enough to support this claim yet.
However, they did find that more intense precipitation events are occurring worldwide in both dry and wet climates, and in a manner consistent with estimates made using global climate models. Their examination of climate model ensembles showed that with increased warming of the globe, precipitation would intensify over the coming decades.
It is a big world, what patterns do we see?
McElroy and Baker (2012) examined the influence of warming on climate extremes. Their concern was the broader array of weather events that could be affected by global warming, but saw changes in the hydrological cycle as a proximate effect of the warming Earth.
This could impact human security in the near term, much more rapidly than more slowly developing concerns such as sea level rise. McElroy writes, “What we may expect is weather whose patterns are more variable and generally more extreme – increased incidences of floods in some regions with droughts in others. This is precisely the pattern observed over the past several years … the trend is likely to persist, indeed to become even more extreme, in the years ahead” .
During the climate extremes study, the authors reached out to ISciences to investigate current trends in temperature and precipitation to understand potential impacts on critical regional surface water supply. A previous version of ISciences' Water Security Indicator Model (WSIM) was applied . Consistent with Donat et al, their analysis found hints, but little convincing evidence, that the total surface water supply was altered. However, the analysis revealed that “strong regional differences in trends” were apparent in the prevalence of extreme freshwater surpluses and deficits.
Figure 2 below shows results for the Eastern Mediterranean region using a composite index of water security indicators. While one would statistically expect less than 10% of the surface area of the region to be impacted by “thirty year” events, in the recent two decades extreme dry conditions depart from the long term pattern in the Eastern Mediterranean region. Is this an indication that perhaps the “dry will become dryer”? That is not yet clear, as wet regions, like the Amazon, exhibited the same trend, as did other humid regions like the Mekong and Niger River environs. But decadal shifts like the ones observed in the ISciences analysis certainly support the claim that conditions will be more variable and more extreme.
What can we expect?
Some confuse global warming and climate change. Quite simply, it is a cause and effect relationship. By resetting Earth’s energetic conditions, the warming Earth affects climate and many other natural systems - the atmosphere, the hydrosphere, the cryosphere, the biosphere, the Oceans, the geosphere, humans and societies.
More heat (that is, more energy) begets more intense precipitation, and the possibility of more floods and more droughts. The most immediate threats of warming result from the changing risks of extreme weather. Unlike sea level rise which is real but less perceptible, this influence is already upon us and apparent.
In a recent report the U.S. National Academy of Sciences states unequivocally, “As climate has warmed over recent years, a new pattern of more frequent and more intense weather events has unfolded across the globe. Climate models simulate such changes in extreme events, and some of the reasons for the changes are well understood. Warming increases the likelihood of extremely hot days and nights, favors increased atmospheric moisture that may result in more frequent heavy rainfall and snowfall, and leads to evaporation that can exacerbate droughts” , .
Current trends in the consumption of fossil energy and depletion of forests point to more warming, and climate modelers point to further potential disruption of the “normal” regional hydrological cycle, among other impacts. Such models are, well, models.
Our commitment at ISciences will be to monitor and post observations of anomalous water surplus and deficit conditions that are based on actual experience and near term NOAA weather forecasts. In this way we can keep an eye on what we are actually experiencing. We welcome you to join us at http://www.isciences.com and watch as the water world evolves and changes.
[ABOUT THE AUTHOR: Ric Cicone is co-founder and former president of ISciences. He is an expert in the application of imaging and information technologies to address social, environmental and national security issues. Throughout his 42-year career he has conducted R&D using remote sensing and geospatial analysis methods to address social security, sustainability, and environmental intelligence questions.]
 “A widespread, long-lived wind storm associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems” http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm
 The day's events are summarized at http://www.weather.gov/apx/2015Aug2recap
 Lane, Amy. May 8, 2016 8:00 am, updated May 13, 2016. "Glen Arbor, recovered from 100-mph storms, ready for tourists." Crain's Business Detroit. [Online at http://www.crainsdetroit.com/article/20160508/NEWS/160509881/glen-arbor-recovered-from-100-mph-storms-ready-for-tourists
 Before and after pictures of the event damage can be seen at http://www.record-eagle.com/news/local_news/aug-storm-snapshots-then-and-now/article_22effe66-55af-11e6-a031-3b640cd3d3d0.html
 Barrett, Malachi. July 09, 2016 11:35 am, updated July 11, 2016 10:55 am. "Hailstorm damages Northern Michigan's specialty crops." MLive.com. [Online at: http://www.mlive.com/news/muskegon/index.ssf/2016/07/friday_hailstorm_devastates_no.html]
 Peterson, T. C., R. R. Heim, R. Hirsch, D. P. Kaiser, H. Brooks, N. S. Diffenbaugh, R. M. Dole, J. P. Giovannettone, K. Guirguis, T. R. Karl, R. W. Katz, K. Kunkel, D. Lettenmaier, G. J. McCabe, C. J. Paciorek, K. R. Ryberg, S. Schubert, V. B. S. Silva, B. C. Stewart, A. V. Vecchia, G. Villarini, R. S. Vose, J. Walsh, M. Wehner, D. Wolock, K. Wolter, C. A. Woodhouse, and D. Wuebbles, 2013: Monitoring and understanding changes in heat waves, cold waves, floods and droughts in the United States: State of knowledge. Bulletin of the American Meteorological Society, 94, 821-834, doi:10.1175/ BAMS-D-12-00066.1. [Online at http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-12-00066.1]
 Saunders S., D. Findlay, T. Easley (2012) Double Trouble: More Midwestern Extreme Storms, The Rocky Mountain Climate Organization and National Resource Defense Council [online at: http://www.rockymountainclimate.org/images/DoubledTroubleHigh.pdf] “Based on a new analysis of a half century of precipitation records in the Midwest, this report documents how much heavy precipitation has increased in the region, shedding new light on the major flooding of recent years in the Midwest.”
 Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, S. Doney, R. Feely, P. Hennon, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville(2014) Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 19-67. doi:10.7930/J0KW5CXT. [Online at http://s3.amazonaws.com/nca2014/high/NCA3_Full_Report_02_Our_Changing_Climate_HighRes.pdf?download=1]
 NOAA, National Centers for Environmental Information, U.S. Climate Extremes Index (CEI). Accessed 5 August 2016. [Online at https://www.ncdc.noaa.gov/extremes/cei/graph]
 Gleason, K.L., J.H. Lawrimore, D.H. Levinson, T.R. Karl, and D.J. Karoly 2008: A Revised U.S. Climate Extremes Index. J. Climate, 21, 2124-2137. [Online at http://iri.columbia.edu/~blyon/REFERENCES/P41.pdf]
 For the mathematically inclined see http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch14/clausius.php
 Allen, M.R., W.J. Ingram (2002), Constraints on future changes in climate and hydrologic cycle, Nature, 419, 224-232. [Online at http://www.nature.com/nature/journal/v419/n6903/pdf/nature01092.pdf]
 Donat, M. G., A.L. Lowry, L.V. Alexander, P.A. O’Gorman, N. Maher (2016), More Extreme Precipitation in the World’s Dry and Wet Regions,” Nature Climate Change, Volume 6, 508-513. doi:10.1038/nclimate2941 [Online at http://www.nature.com/nclimate/journal/v6/n5/full/nclimate2941.html]
 An explanation of this is beyond our scope here, but a good summary explanation and video can be found at http://thinkprogress.org/climate/2012/09/05/799721/climate-change-how-the-wet-will-get-wetter-and-the-dry-will-get-drier/
 M. McElroy, D.J. Baker (2012) "Climate Extremes: Recent Trends with Implications for National Security,” Harvard University. [Online at http://environment.harvard.edu/climate-extremes]
 ISciences L.L.C. now issues reports monthly using WSIM about anomalous conditions and trends in the fresh water supply worldwide. The reports can be found at http://www.isciences.com/blog/
 Attribution of Extreme Weather Events in the Context of Climate Change (2016) National Academy of Sciences, [Online at: http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-in-the-context-of-climate-change]
 The Academy report is nicely summarized by Heidi Cullen, “What Weather Is the Fault of Climate Change?”, New York Times, March 11, 2016. [Online at: http://www.nytimes.com/2016/03/11/opinion/what-weather-is-the-fault-of-climate-change.html]
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