Ticker for February 25, 2004

                
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February 25, 2004  February 25, 2004  February 25, 2004  February 25, 2004


Rainfall & Soil Moisture Maps Show Different Scales of Drought

There's an interesting feature in today's OCS drought monitoring data.
Portions of southern Oklahoma received some beneficial precipitation
early this week, but it certainly wasn't enough to alleviate the
impact of long-term deficits over the area.

In the short term, precip has fallen in respectable amounts along
the Red River, as seen in this 30-day departure-from-normal map:



That surplus precip is reflected in near-surface Fractional Water
Index derived from Oklahoma Mesonet soil moisture observations:


(values near 1.0 are moist; values near 0.0 are dry)

However, a look at longer-term rainfall departures indicates
substantial deficits, especially in south-central Oklahoma:



Those deficits show up strongly in soil moisture conditions much
deeper in the soil (75 cm, or about two and a half feet):



So, what does all this mean?  It means that drought can have impacts
on several scales, depending on the population that is impacted.
This week's rain probably brought short-term relief in immediate
fire danger conditions and dustiness, but the underlying dryness
will continue to plague agriculture and water supplies until
extended periods of relief fall from the sky.

Moreover, the shallowness of the recovery can erode very quickly
without the "support" of a deeper soil moisture reserve.  This is
particularly true in the warm season.

This short-term/long-term duality is a major reason that many drought
decisions aren't changed in response to one or two weather events.
In the warm season, for example, heavy rains may seem to solve fire
danger problems, but the folks who make Red Flag decisions know
that subsurface dryness can continue to stress vegetation.