There are many different aridity indices attempting to express how anomalous precipitation and temperatures are. One such index formulation is the subject of today's IEM daily feature. This index is computed by taking the standardized departure of average high temperature and subtracting the standardized precipitation departure over trailing 180 day windows of time. The standardization is done by dividing the actual departure by the standard deviation value, which creates a unit-less value that be used to lump the temperature and precipitation values together. Of course, no index is perfect, but some are useful. Anyway, values that are more positive are indicative of periods of water availability stress (warmer air temperatures and low precipitation totals). The trick is to realize that the precipitation departure is being subtracted in the equation, so negative precipitation departures increase the index value. What is interesting about the plot showing data for Ames since 2012 is that current values are some of the most positive shown and starting to be comparable to those during the drought of 2012. The drought situation is not urgent yet as the growing season has yet to start, but increases in precipitation would certainly help to improve drought indices like the one shown here.

Voting:
Good = 9
Bad = 0

Tags:   aridity