Just three years ago, the thought that western North Dakota would be experiencing historic floods in the near future would have been seen as unrealistic considering how dry that area was as seen with the Palmer Indexes in June 2008.
Back in the summers from 2005 through 2008, moisture was in short supply, the rivers were barely running, Lake Sakakawea in 2005 was running at historic lows and rain was desperately needed. Much of this past decade the western one-third of North Dakota experienced frequent dry spells, whereas, the eastern part of North Dakota and western Minnesota was generally experiencing very moist conditions.
By the summer of 2009, enough rain had fallen in western North Dakota that the drought was over and the transition to over saturation was starting to become more evident in some parts of central North Dakota. This excessive moisture was from a combination of winter snow and abundant rainfall that occurred during the spring of 2009.
Unknown at that time, but the Minot flood had its roots in 2009. But the main branches of the flood came in 2010 when the word drought seemed like a distant memory as the rains came turning the semi-arid high plains into a vast wetland. The rivers went from dry to flowing fast, the low areas were once again filled with water and the dry days were a memory. Instead, seeping basements, sump pumps running frequently became the norm in areas that were missed by the wetness that plagued eastern North Dakota and western Minnesota since the early 1990s.
The wet summer of 2010 was followed by a wet autumn, that was followed by a snowy winter. Then another season of saturation occurred in the spring of 2011. The spring of 2011 was the 7th consecutive season with above average precipitation for the state of North Dakota. In eastern Montana it was the wettest spring on record.
The extremely wet winter in combination with one of the wettest springs since 1893 lead to a massive surge of moisture down the Missouri River. The Missouri River flooding, although certainly made worse by spring rains, was mostly caused by the tremendous snow that fell during the winter of 2010-2011. The abundant moisture in recent years has cause Lake Sakakawea to rise 49 feet since 2005. That 49 foot rise would be enough water to cover the state of North Dakota to a depth of 4″. That is just one small example as to how much water this area has received in recent years.
The excessive snow from the winter was not only an Rocky Mountain event, but it was also very snowy over much of the northern Great Plains. I’m sure few of us have forgotten that Fargo Moorhead recorded the 3rd snowiest winter on record. The prairie provinces of Canada also observed abundant snow fall this pass winter, that was followed with continuous spring rains. Some parts of Saskatchewan likely had their wettest first six months of a year since at least 1900.
Below is a graphic for the precipitation anomalies from average (rain and melted snow) that has fallen over the northern part of the United States. That area in eastern Montana with nearly 20″ of rain above normal does extend, from reports, into Saskatchewan, the source region of the Souris River that flows through Minot. That part of the United States and Canada only averages between 12″ and 18″ of rain per year and many areas received that much in just the past two months.
Therefore, it should surprised no one that the entire northern tier of the high plains of the United States was completely saturated by the end of May 2011. Although this Palmer Index chart below is only for the United States, the prairie provinces of Canada would be listed as extremely moist as well.
The excessive moisture found its way into all the river systems. In Minot, the Souris has been flowing high since early April, with the river at or above flood stage for most of the last three months.
Although the Souris was running very high, it was manageable for the city of Minot until mid June. In fact, after a mandatory evacuation of parts of the city, the residents were allowed back in and many thought the flood fight of 2011 was over, yet, only days later, parts of the city were evacuated again and then the battle was quickly lost as the river surged to record levels.
What changed? More rain. With all the up stream reservoirs near or at capacity, a major rain event hit Saskatchewan with another 4-7″ of rain. Doppler estimates of that event can be seen below:
Because of the distance from the dopplers in the United States, the estimates above do not fully describe the areal extent of the heavy rain in Canada. This was the last straw that finally broke the proverbial “camel’s back”. With so much water flowing into the reservoirs that were already at capacity, the dam operators had no choice but to have outputs equal inputs. This cause the flows into the Souris River to increase from around 11,000 cubic feet per second to near 30,000 cubic feet per second rushing toward the city of Minot. This in turn raised the Souris to record breaking levels flooding hundreds of homes and businesses.
Some floods happen in a day, but wide scaled flooding as what occurred along a huge stretch of the Missouri, the Souris and other river systems, usually have their roots in a long slow process. Hints to the devastation in Minot came nearly two years ago with the rapid saturation of the soils and the corresponding high river flows for the past two years.
The Red River Valley has been wet for two decades now, our hints are already evident. A major precipitation event could bring devastation to any part of the Red River drainage system. We have seen this in the Devils Lake Basin and in Grand Forks in 1997. Will we see it somewhere else? Hopefully not, but if it does happen, we sadly shouldn’t be surprised.