Flood/Flash Flood
Flooding is a concern
for most people around the world. Whether it is a tropical
system or thunderstorm, there are not many places
that escape this event. Even in Arizona and Nevada, flooding
occurs. The continued development of urban areas has the
potential to increase flooding in a given area. Research in
this area now involves the impact humans have on this event.
In June 2001, the remnants of Tropical Storm Allison produced
upwards of 30 inches of rainfall in 24 hours. Significant
flooding occurred in southwest through northeast Houston, with
others areas in the eastern part flooding. Parts of the
eastern sections received a 500 year flood. In southwest
Houston, some areas had a 100 year flood. Many people in the
500 year flood area did not have flood insurance and had to rely on
government and family assistance.
Research today isn't
focused on if it will flood, but how we can limit flood damage.
Contributing factors to flooding: soil type, soil moisture,
duration of rainfall, intensity of rainfall, geography, and urban
development. The U.S. Government has produced maps that would
equate a 10, 50, 100, and 500 year rainfall event.
Corresponding maps show the locations of flood prone areas as a
function of typically the 100 year flood plain. Many state and
local jurisdictions are limiting development in the 100 year flood
plain.
Meteorologists study
weather patterns that favor prolonged rainfall over a given area.
These events are typically called excessive rainfall events.
The Hydrometeorological Prediction Center (HPC) forecasts rainfall
amounts for the lower 48 out to five days. Coordination among
NWS offices, HPC, and when needed the Tropical Prediction Center (TPC)
help forecast and warn for these events.
Many homes and
businesses still remain within designated 100 year flood plains.
Programs are in place, typically by FEMA, that will buy out these
structures and return the land to pre-construction condition.
In areas where the land is too valuable, structures are typically
elevated above the 100 year flood plain. This is noted in
Houston where homes destroyed are being rebuilt 3-4 feet above the
previous foundation.
Advisories, Watches,
and Warnings -
A flash flood watch is
issued by a local National Weather Service Forecast Office (WSFO),
lasting 12 to 24 hours.
A flash flood warning
is also issued by a local WSFO, lasting 2 to 4 hours.
A river flood warning
is also issued by a local WSFO, lasting a few hours to days.
An urban stream
advisories is also issued by a local WSFO, lasting a few hours.
Know what to do when a
watch or warning is issued for your area. More importantly,
know the quickest path to safe ground.
References -
HPC - http://www.hpc.ncep.noaa.gov/
FEMA - http://www.fema.gov
NFIP - http://www.fema.gov/nfip/
