What is the Benefit of Reporting Precipitation as a Percentile rather than Percent of Average?
Defining drought is complicated because the timing, intensity and spatial characteristics vary from year to year and location to location. For example, the mixed grass Prairie region experiences less precipitation than the Parkland region and tends to be more variable about the mean than many locations in the Parkland. Case in point, if you look at the historical distribution of the annual precipitation at Edmonton the driest ten years occur at and below 80 percent of average while at Swift Current the driest ten years on record occur at and below 76 percent of average. The driest year at Swift Current was 62 percent of average whereas the driest year at Edmonton was 68 percent of average. This indicates that there is less variability at Edmonton compared to Swift Current. As a result, farming systems tend to be more intense and less drought tolerant in the more moist and less variable precipitation zones. To account for this, precipitation percentile values provide a method to define
