Iowa 340 Year Drought and Precipitation Reconstructions Cleaveland, M.K.; Duvick, D.N. Cleaveland, M.K. Duvick, D.N. Palmer Drought Index Reconstruction Precipitation Reconstruction drought earth science/paleoclimate/climate reconstructions|tree ring (age,null,null,year Common Era,null,climate reconstructions|tree ring,null,null,N,null) earth science/paleoclimate/climate reconstructions|tree ring (Palmer Drought Severity Index,null,null,dimensionless,Jul,climate reconstructions|tree ring,null,null,N,null) earth science/paleoclimate/climate reconstructions|tree ring (precipitation,null,null,inch,Aug-Jul,climate reconstructions|tree ring,null,null,N,state of iowa) earth science/paleoclimate/climate reconstructions|tree ring (Palmer Hydrologic Drought Index,null,null,dimensionless,Jun,climate reconstructions|tree ring,null,null,N,null) earth science/paleoclimate/climate reconstructions|tree ring (precipitation,null,null,inch,Aug-Jul,climate reconstructions|tree ring,null,null,N,Farmersburg) earth science/paleoclimate/climate reconstructions|tree ring (Palmer Hydrologic Drought Index,null,null,dimensionless,Jul,climate reconstructions|tree ring,null,null,N,null) earth science/paleoclimate/climate reconstructions|tree ring (Palmer Drought Severity Index,null,null,dimensionless,Jun,climate reconstructions|tree ring,null,null,N,null) earth science/paleoclimate/reconstructions earth science/paleoclimate/reconstructions (Iowa>LATITUDE >LONGITUDE ) Tree ring indices from an expanded network of 17 white oak (Quercus alba) sites in eastern and central Iowa were used to reconstruct state average July Palmer hydrological drought index (PHDI), annual precipitation (previous August to current July), and other climate variables for 1640-1982. We removed nonclimatic variance trends caused by changing sample size and senescent growth. July PHDI correlated better with tree growth than annual precipitation. Occurrence of prolonged droughts throughout the reconstruction suggests that decades like the 1930s occur about twice per century in Iowa. Iowa climate is correlated with the Southern Oscillation Index (SOI) from June in the year of El Nino onset (Yr0) through the next February (Yr+1), with negative SOI (El Nino) associated with wetter conditions. When the June (Yr0) to February (Yr+1) average SOI reaches extremes >= + 1.0 or <=-1.0, it correlates significantly with observed and reconstructed July PHDI (r = -0.37 and -0.56, respectively). Climate during solar cycles centered on sunspot minima alternates between wet and dry regimes that differ by an average of 1.21 units of observed July PHDI and 46.7 mm of annual precipitation for 1877-1982. The solar relationship has been stable since 1640. Combining solar and SOI influences in forecasts may improve prediction of Iowa climate. STUDY NOTES: Reconstructed drought indices (PDSI, PHDI) and precipitation for the state of Iowa for the past 340 years, derived from tree-ring data. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Cleaveland, M.K. Investigator : Duvick, D.N. 1994-07-01 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/16456 https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southusa/iowa.recon https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southusa/iowa.recon English https://www.ncdc.noaa.gov/paleo/study/16456 https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southusa/iowa.recon M.K. Cleaveland and D.N. Duvick1992Iowa climate reconstructed from tree rings, 1640-1982Water Resources Research28102607-261510.1029/92WR01562http://onlinelibrary.wiley.com/doi/10.1029/92WR01562/abstract START YEAR: 1640 AD * END YEAR: 1982 AD -97 41 -90.5 43.5