Amazing Rainfall Amounts

We heard some petty amazing stories during the first weekend of the Minnesota State Fair regarding the large rainfall amounts that hit southeast Minnesota on August 18 and 19, with the highest amounts being 15-17 in. or more, in portions of Winona, Fillmore and Houston counties. This series of rainfall events caused one of the most serious flash flood incidences ever for southeast Minnesota. There was loss of life, 4,000 homes damaged or destroyed, roads and bridges destroyed, damage to farm buildings and equipment and loss of crops and livestock. The final total loss figure will be a very large number. For homeowners and farm operators without flood insurance on buildings and property, there may be very limited insurance protection.

The highest official total rainfall amount recorded by the National Weather Service (NWS) on August 18 was 15.10 in. at Hokah, Houston County, MN. The NWS data does not account for any additional rainfall that fell after midnight on Sunday, August 19. The rainfall event in Houston County was a new record-setting 24-hour rainfall amount for Minnesota, and was 39% higher than the previous state record of 10.84 in. recorded at Fort Ripley in central Minnesota, in 1972. A soil and water conservation weather station in Houston County reported 17.in. of rainfall on August 18 and 19.

Just like a rainbow after a big storm, it is great to see the outpouring of community support to assist families that were impacted by the severe storms. Hundreds of volunteers have assisted with clean-up efforts in the days since the storms. Emergency response efforts by local and state officials have also been very timely and well coordinated.

Soil Moisture
A large portion of the southern third of Minnesota received 5-8 in. of rain on August 17, 18 and 19, and interestingly there was very little flooding, with the exception of Houston, Winona, and Fillmore counties and some low-lying areas near small rivers and creeks in other areas. Most of southwest and south-central Minnesota had received less than 50% of normal rainfall from mid-June to mid-August, and were very dry heading into the big rainfall event on August 17-19. The continued dry weather period and extra corn acres caused a much larger draw-down on stored soil moisture reserves than during a normal growing season.

The recent rainfall, especially those areas getting 3 in. or higher, probably saw some pretty good recharge to the supply of stored soil moisture in most fields. At the University of Minnesota Research location at Waseca, MN, the amount of stored soil moisture on August 1 was just over 5 in. in the top 5 ft. of topsoil, which is less than 50% of capacity, and there were no tile lines flowing. Following the recent rainfall event, all the measuring sites are at the maximum of 11 in. of stored soil moisture in the top 5 ft. of soil, and title lines removing excess water are flowing. The results of the July and early August drought in southern Minnesota in 2007 would have been much more severe without the extra amounts of stored soil moisture that were available for the 2007 crop. The recent rainfalls should provide for very similar stored soil moisture conditions for the 2008 crops in southern Minnesota. Unfortunately, farmers and others in many portions of central and northern Minnesota are not as fortunate regarding recent beneficial rainfall. Drought-like conditions continue to plague many portions of this region affecting crop and livestock producers, state parks and forests, the tourism industry and many other businesses that rely on strong summer sales for their livelihood.

Editor’s note: Kent Thiesse is a former University of Minnesota Extension educator and now is Vice President of MinnStar Bank, Lake Crystal, MN. You can contact him at 507-726-2137 or via e-mail at kent.thiesse@minnstarbank.com.