Thursday, July 21, 2016

2016 Drought Conditions vs 2012

The dry conditions in northern Ohio are getting worse as the daytime temperatures reach the lower 90s coupled with higher humidity levels--heat index between 100 and 105--this weekend.  Many people are comparing summer to 2012 both in temperature and in degree of dryness. Is it a valid comparison? How do our dry conditions compare to other years in mid July?  When was the last time we had conditions this dry in mid July in northern Ohio?

The index that's used in determining the degree of dryness or wetness historically is the Palmer Drought Severity Index. It gives us a good barometer in comparing drought events of the past.

According to the National Drought Mitigation Center:  "The PDSI is calculated based on precipitation and temperature data, as well as the local available water content (AWC) of the soil. (Link here) From the inputs, all the basic terms of the water balance equation can be determined, including evapotranspiration, soil recharge, runoff, and moisture loss from the surface layer." 

The more negative the number, the more severe the drought.  Whereas higher numbers indicate wetter conditions. Each week the Climate Prediction Center updates the drought conditions nationwide for each climate division. I circled Ohio for reference.

Based on the PDSI, this summer shows little similarities to the summer of 2012 nationally. The PDSI is falling to 2012 levels in some spots in northern Ohio but the overall degree of dryness in 2012 was far more severe. You could argue that the summer of 2007 is a closer match to 2016. I threw in the Super El Nino summer of 1998 at the end since we are at the end of the Super El Nino of 2015-16.