Fig. 11. Annual minimum of weekly discharge rates from two gaged rivers draining the Colfax lobe of the Central Plains in Wisconsin (see maps in Figs. 4 and 6). Unlike the Anoka Plains, river discharge rates near Colfax rarely drop below a putative drought threshold of 30% of the long term average. This is consistent with tree mortality from drought being common in Anoka and rare near Colfax. The lowest recorded discharge rates in the Colfax area were in 1934 during the Dust Bowl. Low precipitation during 1988-89 (Fig. 7) produced a noticeable dip in discharge rates, but did not approach the 30% threshold, and did not produce significant mortality in red pines. Based on these data, we hypothesize that low soil water in 1959 and 1964 had notable impacts on agricultural yields in the area.