Drought Analysis – U.S. Drought Monitor
This past week I have taken a closer look at several aspects of drought across the region: soil moisture, stream flow, and reservoir levels. Today, I’d like to pull it all together by a review of the U.S. Drought Monitor. The Drought Monitor has only been around since 2000, however it has quickly caught on as an effective tool to monitor the extent and intensity of drought across the nation. For each update of the Drought Monitor, subject-matter-experts, e.g., agriculture, rivers, water supply, provide input to assign a classification from D0 (Abnormally Dry) to D4 (Exceptional Drought).
I put together some statistics to put the current situation in perspective. First, keep in mind that these records are fairly short-term, going back not much more than a dozen years. This is an extremely short record when discussing potential climate trends. Also, it is a subjective classification, so variance in classification is likely.
Taking a look back at the Drought Monitor, one can easily see alternating periods of drought followed by periods of reprieve. Drought is a natural occurrence over the Southeast U.S. It is the intensity, extent, and duration that define ordinary from extraordinary. Let’s look a bit closer at the current situation.
Is the extent of overall drought for this time of year unusual? I thought it was until I looked at the statistics. Currently, 77% of the Southeast U.S. is in some degree of drought. I found that there tends to be a lot of variability this time of year, and it is not unusual for a majority of the region to be in some degree of drought. The average percent of the region in drought around April 1st is 55% (compared to 77% this year). However, it is important to note that this average comes about by averaging 8 years around or above 70% with 3 years at zero percent. Thus, it is not all that unusual to have significant areas of the Southeast U.S. in some degree of drought heading out of the recharge season. On the other hand, it is not unusual to have none of the region in drought. Again, there is a high degree of variability.
D0 – D4: Percent of Southeast U.S. in Drought around April 1st.
Last Year: 69%
There is another way to look at these statistics which look more ominous. Winter and spring season rainfall typically “knocks down” the intensity of drought. Since the start of Drought Monitor statistics, this has happened every single year. Winter and spring recharge does tend to temper drought, but not necessarily end it. The percent of the region currently in D3 or D4 drought is around 27%. It has never before (keep in mind the short-term nature of these records) been anywhere close to this high. In fact, the average this time of year is only 6%, and a majority of the years have been zero.
D3 – D4 Percent of Southeast U.S. in Drought around April 1st.
Last Year: 4.4%
Thus, as we enter out of peak recharge season and into summer, we see that winter/spring season rainfall did not “knock down” the core of D3-D4 drought centered over southeast Georgia and surrounding states. This has never occurred before since statistics began in 2000. The extent of overall drought remains persistently high as well, 77%, but this is not as unusual.
Finally, my experience as a forecaster, plus Drought Monitor statistics, show that both the extent and intensity of drought can change fairly quickly if the weather pattern would change.
Have a great weekend.