Dry Weather Could Impact the Severity of Summer Heat Waves

The Coastal Empire and Low Country has been dry over the past few months.
We are currently 5.20 inches of rain below normal so far in 2009 and the
drought monitor indicates a moderate drought has taken hold of the region.

This brings up the topic of my blog today… the connection between soil
moisture and potential impact and length of summer heat waves.

Let’s look back at the devestating heat waves of Europe in 2003. It was
incredibly sad… with an estimated 70,000 heat related deaths that summer.
France was particularly hard hit… being the center of the worst heat.

The combined high temperatures led to not only the fatalities, but also
drought, forest fires and crop losses that year in Europe. A new report in
this month’s Journal of Geophysical Research - Atmospheres
shows if soil moisture in Europe had been normal and not parched moving
into the summer heat wave, the temperatures which reached as high as 5
degrees celcius above normal, could have been reduced by 40%.

Why you may ask? A lack of soil moisture (water) to soak up summer heat
by evaporation can allow air temperatures to soar. Evaporation cools the
surface moist soil and the surrounding surface air. This takes a bit of a bite
out of the high temperatures and can make a heat wave less prolonged and
severe.

But if drought has made soil very dry… then heat waves can be made
worse and longer because of this variable.

Future satellite observations of soil moisture combined with numerical weather
guidance can help to better define a potential incoming heat wave.

It’s important to look at a satellite picture of soil moisture… because they
see better what ground soil moisture instruments miss. Soil moisture
can vary considerably from instrument to instrument… and these changes
can be missed while the satellite look shows the fine detail.

The European Space Agency plans to launch a new satellite this fall that will
look at planet-wide soil moisture and ocean salinity. This information… if it
is input into numerical weather models… will increase our acuracy of heat
wave prediction.

Currently… large scale ground soil moisture data is not
included in computer model forecasts of the weather.