Ticker for October 3, 2000

                
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October 3, 2000    October 3, 2000    October 3, 2000    October 3, 2000

An Assessment of the Severe Oklahoma Drought of 2000

As of very early October, severe drought and fire danger conditions
persist throughout the vast majority of Oklahoma, with significant
economic, agricultural and public safety impacts.  As with most summer
dry periods, unusually warm temperatures join this year's drought.
These conditions continue into early October, and are underscored by
well-above-normal temperatures in Oklahoma on October 3, 2000,
including a maximum of 106 F at Hollis, the warmest reading ever in
Oklahoma in October.

The immediate cause of these drought conditions is a virtual (and in
several locations, complete) lack of significant rainfall during the
months of August and September.  However, some locations in Oklahoma
may be feeling the effects of long-term drought, which intensify the
impact of the current situation.

The purpose of this document is to provide more detailed information
about the impact of drought in Oklahoma on both the short term and
the long term.  The descriptions are organized by Oklahoma's Climate
Divisions to facilitate its understanding and use on the local level.

Definitions of KBDI, normal, period of record and soil moisture
category follow these descriptions.


CD1: Panhandle
Since Aug 1: 0.66" rainfall, 4.09" below normal, 14% of normal
Driest Aug-Sep period on record

This is normally Oklahoma's driest climate division, and typically
receives rainfall in brief heavy events during the warm season.
CD1's expected rainfall is skewed more toward the warm months than
any of Oklahoma's climate divisions: two-thirds of the expected annual
total falls in the five months bookended by May and September.  During
the last four years, fifteen of the twenty months that compose this
period saw below normal rainfall.  In the short-term, the Aug-Sep 2000
period was the driest, and August 2000 was the warmest, on record for
this climate division. The western panhandle stations of Kenton, Boise
City and Goodwell are the only stations to collect more than one-half
inch of rainfall since July ended.  Every single Mesonet soil moisture
sensor at every depth (32 total) reports that soil moisture is in the
driest category.  KBDI values range from 448 at Kenton to 700 at
Buffalo.  Conditions worsen as one moves eastward in the climate
division.


CD2: North Central
Since Aug 1: 0.38" rainfall, 6.16" below normal, 6% of normal
Driest Aug-Sep period on record

Although long-term drought is not a problem in CD2, the last two
months have been severely dry and very warm throughout this entire
division, as the winter-wheat planting season draws near.  With the
exception of thundershowers in Woodward County on August 7th and 10th,
the vast majority of the climate division has received less than
1/2-inch of rainfall since July ended.  Taken individually, both
August and September were warmer than 90% of previous Augusts and
Septembers recorded in CD2.  The two-month period was easily the
driest Aug-Sep on record for the division.  Of the 52 Mesonet soil
moisture sensors (4 depths by 13 stations) deployed in the climate
division, all but one observe the soil moisture conditions in the
driest category (the remaining sensor reports very limited moisture).
KBDI values range from 536 at Woodward to 714 at Lahoma.  Twelve of
the thirteen stations report KBDI values exceeding 600.


CD3: Northeast
Since Aug 1: 1.24" rainfall, 7.26" below normal, 15% of normal
Driest Aug-Sep period on record

Like CD2, the summer drought of 1998 was not as severe in the
northeast as elsewhere in the state, but the short-term drought is a
major problem.  Since August 1st, just over two months ago, the
division stands at 7.26" below normal rainfall.  All but one of the
30 Mesonet soil moisture sensors installed at 60 cm and 75 cm in CD3
show soil moisture conditions in the driest category.  Eleven of the
fifteen installed at 25 cm, and eight of the fifteen installed at
5 cm, show soil moisture conditions in the driest category.  KBDI
values range from 449 at Jay to 711 at Burbank.  Eleven of CD3's
fifteen stations report KBDI values exceeding 600, primarily in
northern and western sections of the climate division.


CD4: West Central
Since Aug 1: 0.04" rainfall, 6.08" below normal, 1% of normal
Driest Aug-Sep period on record

According to precipitation data and Mesonet soil moisture
observations, it appears that CD4 never fully recovered from the
drought of 1998, and it is currently experiencing the most extreme
lack of rainfall of any region in Oklahoma this season.  Since July
ended, CD4 has observed less than one-tenth of an inch of rainfall,
the driest Aug-Sep period on record for any of Oklahoma's climate
divisions.  August 2000 was the 5th warmest August on record for CD4,
and September was warmer than 90% of Septembers on record for CD4.
During and since the severe drought of summer 1998, CD4 has received
little warm season precipitation.  More than 60% of the division's
precipitation normally falls in the five months bookended by May and
September.  During these periods of the last three years, only
June 1999 and June 2000 yielded above normal rainfall.  Ten of the
thirteen below-normal months were more than one inch short of normal.
Every single Mesonet soil moisture sensor at every depth indicates
conditions in the driest category.  All Mesonet-derived KBDI values
in the region exceed 600, and range from 644 at Cheyenne to 699 at
Bessie. Only a prolonged period of above normal rainfall will fully
mitigate the effects of the last 30 months in this climate division.


CD5: Central
Since Aug 1: 1.15" rainfall, 5.95" below normal, 16% of normal
Second driest Aug-Sep period on record: driest since 1956

Since the end of July, CD5 has observed just over an inch of rainfall.
Almost every drop of that came during a 24-hour period on September
23-24.  This year, August was warmer than 90% of those on record
for CD5, and  September was also well above normal. As winter wheat
planting season draws near, all but one of the 40 Mesonet soil
moisture sensors installed at 60 cm and 75 cm in CD5 show soil
moisture conditions in the driest category.  Seventeen of the twenty
installed at 25 cm and twelve of the twenty installed at 5 cm,
indicate soil moisture conditions in the driest category.  The worst
conditions are found primarily in western sections of the division,
in Oklahoma's "Wheat Belt".  KBDI values range from 484 at Norman
to 729 at Kingfisher.  Just over half of the 20 stations in the
division report values exceeding 600.


CD6: East Central
Since Aug 1: 2.43" rainfall, 5.44" below normal, 31% of normal
Fourth driest Aug-Sep period on record: driest since 1956

East Central Oklahoma experienced hot August and a warmer than normal
September in CD6, combined with below normal rainfall for the period.
While conditions are quite dry in late summer 2000, and short-term
conditions are poor, they are not as extreme as the rest of Oklahoma,
and this climate division was able to recover from the drought
conditions of summer 1998.   Mesonet soil moisture sensors show
conditions in the driest category throughout the division at 60 cm
and 75 cm, and across about half of the division at 25 cm.  Sensors
at 5 cm depict mostly adequate soil moisture conditions.  KBDI values
range from 473 at Tahlequah to 735 at Calvin.  Three of the CD6's
thirteen stations report KBDI values exceeding 600.


CD7: Southwest
Since Aug 1: 0.84" rainfall, 5.36" below normal, 14% of normal
Second driest Aug-Sep period on record: driest since 1952

Southwest Oklahoma is in a position of long-term drought, dating
from the onset of the drought of summer 1998, exacerbated by severe
conditions in August and September 2000.  No rainfall was observed in
the division in August and less than one inch in September (almost
every drop coming on the night of September 23-34), making this the
second-driest such period on record (next to 1958) for the region.
Perhaps the hardest-hit of Oklahoma's climate divisions during the
1998 drought, the region has received only slightly above normal
rainfall since, and much of this came during the cold season.
Mesonet soil moisture data indicates that CD7 never recovered from
the drought of 1998 at depths greater than one-foot.  Currently, soil
moisture is in the driest category throughout the region at depths
greater than 25 cm, and six of the division's eleven sensors at 5 cm
indicate dry conditions.  KBDI values at eight of the division's
eleven stations exceed 600, ranging from 509 at Apache to 756 at
Grandfield.  The worst conditions are found in the southern and
western portions of the division.  Only a prolonged period of above
normal rainfall will fully mitigate the effects of the last 30 months
in this climate division.


CD8: South Central
Since Aug 1: 0.90" rainfall, 6.46" below normal, 12% of normal
Third driest Aug-Sep period on record: driest since 1948

In addition to extreme short-term conditions, CD8 is in a period of
long-term drought, dating from the onset of the widespread drought
of summer 1998, and possibly to the winter drought of 1995-96.  Less
than one inch of rainfall has fallen on the division, on average,
since the end of July, and three of the state's four most extreme
KBDI values (Ringling, Waurika and Burneyville) are located in CD8.
Mesonet soil moisture observations indicate conditions are in the
driest category at and below 25 cm throughout the region and
predominantly dry at 5 cm as well.  All but two of the division's
15 stations report KBDI values exceeding 600, and range from 561 at
Durant to 777 at Ringling.  The value of 777 at Ringling is the most
extreme KBDI value indicated since the commissioning of the Oklahoma
Mesonet in 1994.   Mesonet soil moisture sensors indicate that most
of CD8 did not recover from the drought of 1998, and the division
has received below normal rainfall in eleven of the fifteen months
since July 1999. In CD8, half of the annual rainfall normally comes
in the five month period bookended by May and September, and in the
last four years, only four of the twenty months in this category have
seen above normal rainfall.  Only a prolonged period of above normal
rainfall will fully mitigate the effects of the last 30-60 months in
this climate division.


CD9: Southeast
Since Aug 1: 2.66" rainfall, 5.43" below normal, 33% of normal
Third driest Aug-Sep period on record: driest since 1963

While short-term conditions aren't quite as extreme as much of
southern and western Oklahoma, CD9 is in a period of substantial
long-term drought, dating to the onset of the widespread drought
of summer 1998.  CD9 has received below-normal rainfall for 20 of
the 30 months since April 1998.  Seventeen of those months had a
deficit of one inch or more.  Thirteen of the last 15 months have
yielded below-normal rainfall.  Soil moisture sensors indicate
mostly adequate moisture at shallow depths and predominantly dry
conditions at 60 cm and 75 cm.  KBDI values at five of the division's
nine stations exceed 600.  Values range from 501 at Wister to 709
at Antlers.  Only a prolonged period of above normal rainfall will
fully mitigate the effects of the last 30 months in this climate
division.


Terms and Definitions

KBDI:  Keetch-Byram Drought Index.  The KBDI is an indicator of the
amount of moisture available in the upper eight inches of soil at a
given location.  It has value both as a drought indicator and as a
fire danger index.  Values range from 0-800, with 0 indicating no
moisture deficit, and 800 indicating the maximum drought possible.
Values over 400 are considered significant to drought and fire danger.
Values over 600 indicate "Severe Drought" and the incorporation of
organic material in the soil itself as fuel for wildfire.

Normal Rainfall/Temperature: Normal values are derived from a 30-year
period, from 1961-1990.

Driest/Hottest on Record: Oklahoma's climate records per climate
division date to 1895.

Mesonet Soil Moisture Sensors: The Oklahoma Mesonet operates an array
of up to four soil moisture sensors at 102 stations across the state.
The sensors are placed at depths of 5 cm, 25 cm, 60 cm and 75 cm below
the surface.  Data from a sensor is used to determine a matric potential
category of one to four.  Matric potential can be considered as a
measure of how difficult it is for a plant to extract water from the
soil.  Values in the driest category suggest a complete lack of
available water to roots at that depth.