Figure 28

Running averages of annual rainfall for the Dempsey Divide study area since the instrumental record began in 1893. Running averages smooth out the interannual variability in rainfall to detect long-term trends. The upper graph is a five year running average, in which each year is averaged with the two before it and the two after. This detects decade-scale patterns, and a roughly 11-13 year cycle is apparent, possibly driven by the 11 year solar cycle and in synch with a strong 12-13 year cycle in Atlantic ocean-atmosphere dynamics (Black et al. 1999). In the lower graph, each year is averaged with the seven before and seven after to detect century-scale trends. Note the upward progression of the record, interrupted by the severe climatic correction of the Dust Bowl and the decades which followed. The steady increase in average rainfall since 1970 has recapitulated the record of 1895-1925. See also Table 3 on this website.

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