Jacksonville, Fla - Dry Spell vs. the Drought Indexes
My yard looks dried up and it hasn't rained in weeks. Basically what many of us are experiencing right now. Yes, we are in a dry spell. The good news is that it's spring and this dryness typically happens every spring. Sure there are those nice wet Springs, but they tend to be very wet and they only happen about once every 5-6 years.
This year, 2017, our spring has been different than some springs, we started off dry. Going back to our last big rainfall (Hurricane Matthew) many locations across north Florida are now running between 5-8" below normal. And, we haven't seen widespread rainfall since April 6th (two weeks ago).
Still, not super dry, but the signs are building that we could get into a deeper situation if the rains don't return. The concerns will build for fire danger first and if the summer rains don't return in June, possible water restrictions.
Keetch-Byrum vs. Palmer Drought Indexes
When we discuss fire danger the best drought index to follow is the Keetch-Byrum Drought Index. This measures recent rainfall amounts and soil conditions to determine an overall look at the current possibilities of a larger scale fire condition. Sure, day to day weather conditions will directly influence fire conditions, but the KBDI gives us a look at overall dryness. If you go 6-8 months well below normal for rainfall, especially in the hotter months, this index will rapidly swing from wet (blue) to dry (red). Jacksonville is basically experiencing wet (blue) conditions.
Palmer Drought Index - Longer term (past 5 years, or more) based upon lake/river/stream/well levels. Helps determine local regions decide about water restrictions.
KBDI - Keetch-Byram Drought Index looks back at rainfall and ground soil. Mainly used for fire danger. Blue is wet, yellow is normal, orange to red is extremely dry.
The best longer term drought indicator is the Palmer Drought Index. When all of the water restrictions were put into place in California where they went nearly a decade without above normal rainfall, this index showed burgundy red, for extreme drought. The Palmer Index measures various longer term conditions including: Lake levels, river levels, stream levels, well water levels along with longer term rainfall amounts. The Palmer index around Jacksonville is just now showing longer term drought hints, just hints.
So, where do we stand here in Jacksonville?
It's complicated. Isn't it always?
Right now we are definitely in a dry spell. But, soil conditions (KBDI) are moist so we are not in a terrible fire condition. Yet, longer term, if the summer rains were to fail to show up, we could be looking at water restrictions in 2018. Yes, 2018. The Palmer Index is a slowly changing index. It takes years to get to a point of water restrictions (except for local issues). Typically, it also takes a while to get out of a longer term drought, unless you have what the Western United States had this winter, literally their wettest winter on record!
Palmer Index for California on January 1st, 2017 - Burgundy red is for extreme drought and extreme water restrictions.
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