Physicist and weather scientist Joe Wheatley used R to design and create a useful visual representation of how drought affects a region over long time-scales. Instead of charting absolute rainfall (or lack thereof), he instead charts the Standardized Precipitation Index (SPI), where extreme values (above 2 or below -2) indicate extreme wetness or dryness compared to the usual precipitation in that region. He then charts the SPI over time using colors to indicate extreme SPI values: red means dry, blue means wet. Here’s the chart for the Murray Darling basin, an important agricultural zone in Australia (click to enlarge):
That region suffered a drought from 2002-2007, and the chart makes plain that it was the most severe drought event in 60 years. The R code used to normalize the data (by transforming to a shifted Gamma distribution) and create the chart can be found here.