The results point to increasing trends in heavy rainfall over the northern part of the study domain. Examination of the surface temperature record suggests that these increasing trends occur over the area with the largest increasing trends in temperature and, consequently, with an increase in atmospheric water vapor.
Villarini, G., J.A. Smith, M.L. Baeck, R. Vitolo, B. Stephenson, and W.F. Krajewski. “On the Frequency of Heavy Rainfall for the Upper Midwest of the United States,” Journal of Hydrology, 400, 1-2, pp. 103–120, 2011.