Precipitation anomalies in Eastern-Central Iowa from 1640 - Present

The Midwest has experienced several extreme hydrologic events over the last few decades, including severe drought events in 1988, 1989 and most recently in 2012. The economic impact of drought on the Midwest, specifically on the state of Iowa, is particularly substantial because of the region's reliance on agriculture. The Midwest drought in 2012 lead to decreased crop yield across most of Iowa and record high temperatures throughout the growing season (April-October). However, the severity of this and other recent extreme hydrologic events are better understood when placed in the context of multiple centuries of Midwest hydroclimatic variability. In this study we combine a 350. year tree ring reconstruction of annual precipitation from 17 archives in Eastern-Central Iowa to a shorter-term instrumental record from 43 COOP precipitation stations. We analyze precipitation anomalies between 1640 and 2013 and report the return rates of specific drought and pluvial events. The results show that the last 20. years in Iowa have been the wettest 20-year period on record, including the only three years which are 3 or more standard deviations wetter than the (1640-2013) mean. The 1990-2013 period coincides with previously reported increases in annual precipitation and extreme precipitation events, along with decreases in drought severity and spatial extent. The 2012 drought was the driest anomaly over the last 20. years. However, the event was not anomalous with respect to the entire 373. year record and had a return period of approximately 6. years.