Planting Progress and Flood Risks in the Corn Belt - UNL CropWatch, May 20, 2011
May 20, 2011
Wet, cool conditions from mid-April through the first five days of May contributed to significant planting delays across most of the Corn Belt. During the next 10 days, a return to above normal temperatures and below normal moisture led to a major increase in planted acreage across the western Corn Belt.
In Nebraska corn, soybean, and sorghum planting progress as of May 15 was similar to levels for last year and the five-year average (see story). This week planting progress slowed as a potent upper air low brought moderate to heavy rainfall May 17-20 across areas of the state. A return to normal temperatures and normal moisture forecasted for the last full week of May should allow producers to ramp up planting activity.
The most significant planting delays are across the northern Midwest and eastern Corn Belt. Most Ohio locations have had precipitation 20 of the last 30 days. This excessive moisture is one of the factors leading to the intense flooding on the Ohio-Mississippi River confluence south to the Gulf of Mexico.
Substantial acreage losses due to flooding are occurring within the lower Mississippi basin with little chance that producers will be able to replant during the next 30 days. Precipitation also continues to plague the Dakota’s and parts of Minnesota, Wisconsin, Michigan, and Indiana. Models indicate these areas will receive generous moisture over the next couple of weeks and planting delays would be expected. If and when these areas dry out enough to plant, crops will require an abundance of warmth to mature before the first fall freeze.
The greatest threat for widespread flooding in Nebraska continues to be in the Platte River watershed. With a second consecutive year of significant snow pack near the headwaters of the southern and northern branches of the Platte, reservoir water managers are scrambling to make room for the projected 2 million acre-feet of runoff expected during the next three months.
Reservoir storage data from Seminoe, Pathfinder, Glendo, and McConaughy as of May 17 indicate 832,000 acre-feet of space was available to reach full pool. An additional 250,000 acre-feet of storage is available in Glendo’s flood pool. In essence, just over one million acre-feet of storage is available, leaving water managers to manage an additional one million acre-feet of runoff through the Platte while minimizing flooding.
Interests along the northern Platte channel upstream of McConaughy can expect near record to record stream flow rates for the next 30 or more days. Runoff into Seminoe has been averaging close to 6000 cubic feet per second (cfs). If the rains fall on the snow pack, runoff could easily eclipse the 18,000 cfs rate observed last summer during peak runoff.
Heavy rainfall across the eastern Wyoming Plains and Nebraska Panhandle would also intensify stream flow rates on the Platte upstream from McConaughy. Although this region was exceptionally dry last fall, precipitation the past two months has been average to above average. Under these conditions, the runoff component from heavy rains will only aggravate the situation.
Downstream of McConaughy the most significant flood risk in in the North Platte area. A record flood stage of 7.2 feet is predicted at North Platte, eclipsing the previous record of 7.1 feet set in 1971. These levels could easily increase as contributions from the southern branch of the Platte increase over the next 30 days and/or additional heavy precipitation occurs within this section of the basin.
Above average flows are likely from North Platte to the Missouri River as the snow melt and reservoir releases increase. These stepped up releases will mean near bank full flows to Columbus for the next 30-60 days. Flood risk will certainly be high, but not necessarily guaranteed. The most significant threat for this region will be from a widespread high intensity rain or several consecutive rains with little surface drying between events.
Extension State Climatologist