Time for a bigger rain gauge!

Wait…. What?  We’re in the middle of a drought and you’re talking about getting a bigger rain gauge?  What’s going on here?


The map shows location of selected rain gauges,
with blue (red) triangles depicting sites with
significant increasing (decreasing) trends,
and white circles showing sites
 with little or no change.
(Credit: Adapted from Villarini et al. (2013))

Even with the current drought situation plaguing much of the Midwest, some of you may actually want to consider getting a bigger rain gauge if you enjoy weather-watching.  Why?  Well, heavy rain events are becoming more common!  A study by the University of Iowa recently published in the Journal of Climate suggests that heavy rains have become more frequent in the Upper Midwest over the past 60 years, holding true even with the current drought situation.  The study also found that temperatures over the center of the nation are rising too, which helps to explain the heavy rain issue.  Warmer air can hold more water vapor, and when more water is available in the atmosphere for precipitation, a greater chance for heavy rains exists.

Lead author Gabriele Villarini stated “We have found that there is a tendency toward increasing trends in heavy rainfall in the northern part of the study region, roughly the Upper Mississippi River basin.  We tried to explain these results in light of changes in temperatures.  We found that the northern part of the study region – including Minnesota, Wisconsin, Iowa, and Illinois – is also the area experiencing large increasing trends in temperature, resulting in an increase in atmospheric water vapor.”

However, the current drought that has affected the Midwest is not part of the study.  It has occurred too recently (over the past year or two) while the study focused on rainfall and temperature data from about 1950 to 2010.  Also, it should be noted that the study was not looking at average annual rainfall, but rather just heavy rainfall events.  So while the area may currently be experiencing a deficit in overall rainfall, the area may be in the normal range when it comes to the number of heavy rainfall events/days.

In addition to the rising temperatures adding to the water vapor in the atmosphere, other studies point to changes in irrigation over the Ogallala Aquifer (which runs from Nebraska to northern Texas) as a source of increased water vapor in the atmosphere.  This suggests that human changes in land use, land cover, and agricultural practice also contribute to the increased frequency of heavy rains.

So in our warming atmosphere, you can expect to see more heavy rainfall events across not only the Upper Midwest but possibly the globe as a whole.  This will also increase the frequency and risk of flash flooding in the area as heavy rains quickly flow into area streams, creeks, and rivers before the ground can absorb the moisture (for those of you in the Coulee Region, think back to August of 2007 when parts of the area received over a foot of rain in about 2 days).  Keep this in mind if you live in or plan to move to a flood prone area in the future so you are aware of the risk.  It also raises the importance of early warnings from the National Weather Service and local media.  I will be going over the meanings of the warnings, watches, advisories, etc. that the National Weather Service issues coming up in April during Wisconsin’s Severe Weather Awareness Week (April 15^th – 19^th), so watch for that.  It never gets old going over these important messages since they save lives!