In der neuen Studie Drought duration and frequency in the U.S. Corn Belt during the last millennium (AD 992-2004) (Pdf-Format, ca. 890 KB), stellen sich die Autoren der nicht ganz unwichtigen Aufgabe, (to) "characterize the historic occurrence, duration, and frequency of drought events" (Stambaugh et al., 155).
Aus dem Abstract:
We used a new long tree-ring chronology developed from the central U.S. to reconstruct annual drought and characterize past drought duration, frequency, and cycles in the U.S. Corn Belt region during the last millennium. This is the first paleoclimate reconstruction achieved with subfossil oak wood in the U.S. and increases the current dendroclimatic record in the central U.S. agricultural region by over 500 years. A tree ring-width drought response function was calibrated and verified against monthly instrumental Palmer Hydrologic Drought Index (PHDI) during the summer season (JJA).
Für uns von Interesse, das Mittelalter. Wir finden dazu in der Studie folgende Aussagen:
In the thirteenth-century the most severe multidecadal drought in the entire record occurred during the 20-yr period 1229-1248 (Table 4). This drought pre-dates by several decades the end-of-century "Great Drought" of the Pueblo area in the southwest (Douglas, 1935). A drought almost twice as long occurred in the late 11th century (Table 4), but the approximately 61-yr drought in the late 12th century (ca. AD 1148-1208) appears to be the most significant drought of the entire reconstruction. This period corresponds to the single greatest megadrought in North America during the last 2000 years (Cook et al., 2007) and unmatched persistent low flows in western U.S. river basins (Meko et al., 2007). The region affected by this drought appears to have also included portions of the central U.S. (Laird et al., 1996). This drought marks the middle of the Medieval Warm Period - an interval of warmer temperatures between approximately AD 800-1300 characterized by greater drought duration and frequency in the Northern Great Plains compared to more modern times.
Stambaugh, et al., 160f.
 Douglass, A.E., 1935. Dating Pueblo Bonito and other ruins of the Southwest. Nat. Geog. Soc. Contrib. Tech. Papers.
 Cook, E.R., Seager, R., Cane, M.A., Stahler, D.W., 2007. North American drought: reconstructions, causes, and consequences. Earth Science Reviews 81, 93-134.
 Meko, D.M., Woodhouse, C.A., Baisan, C.A., Knight, T., Lukas, J.J., Hughes, M.K., Salzer, M.W., 2007. Medieval drought in the upper Colorado River Basin. Geophysical Research Letters 34, L10705.
 Laird, K.R., Fritz, S.C., Maasch, K.A., Cumming, B.F., 1996. Greater drought intensity and frequency before AD 1200 in the Northern Great Plains, USA. Nature 384, 552-554.