Second century megadrought in the Rio Grande headwaters, Colorado: How unusual was medieval drought?

Routson, C. C., Woodhouse, C. A., & Overpeck, J. T. (2011). Second century megadrought in the Rio Grande headwaters, Colorado: How unusual was medieval drought?. Geophysical Research Letters, 38(22). https://doi.org/10.1029/2011GL050015