The Vegetation Drought Response Index :

1
The Vegetation Drought Response Index A New
Drought Monitoring Tool Integrating Climate,
Satellite, and Biophysical Data
Semi-Operational Production of VegDRI
Brian Wardlow1, Tsegaye Tadesse1, Jesslyn
Brown2, Michael Hayes1, Don Wilhite1, and Mark
Svoboda1
1National Drought Mitigation Center, University
of Nebraska-Lincoln, Lincoln, NE
68583-0988 2SAIC, U.S. Geological Survey Center
for Earth Resources Observation and Science
(EROS), Sioux Falls, SD 57198
Monitoring drought using modern techniques can
help reduce the drought impacts that influence
many sectors of society. Traditionally, drought
monitoring has taken a climate-based approach
using meteorological observations as the primary
data source. Most climate-based maps depict
general spatial patterns of drought severity,
but lack the spatial detail to adequately
characterize local to regional-scale variations
in drought conditions. Satellite-based
vegetation index (VI) data, which has been widely
used to assess vegetation conditions, has the
synoptic, repeat coverage and higher spatial
resolution for characterizing more localized
drought patterns than the climate-based
approaches. However, the VI-based approaches do
not discriminate between drought-induced
vegetation stress and that driven by other
processes (e.g., flooding, fire, delayed greenup,
and land cover change). Climate information
enables the drought-related vegetation anomalies
expressed in the VI data to be discriminated from
those driven by other factors. The integration
of climate and satellite-derived VI information
holds considerable promise to identify and
monitor vegetation stress caused by drought with
finer spatial detail than current drought
indicators such as the U.S. Drought Monitor
(USDM) (http//www.drought.unl.edu/dm/). The
National Drought Mitigation Center (NDMC), the U.
S. Geological Surveys (USGS) National Center for
Earth Resources Observation and Science (EROS),
and the High Plains Regional Climate Center
(HPRCC) have teamed together to develop and
implement a new drought monitoring indicator, the
Vegetation Drought Response Index (VegDRI), that
integrates climate, satellite, and biophysical
variables. The VegDRI is calculated using a data
mining technique that incorporates complex
information from climate-based drought indices,
satellite-based VI data (1-km Advanced Very High
Resolution Radiometer (AVHRR) normalized
difference vegetation index (NDVI) data), and
environmental data sets that summarize land
use/land cover (LULC) and soil characteristics.
A 1-km VegDRI map is produced at 2-week intervals
to provide timely regional to sub-county-level
scale information of drought effects on
vegetation, which can be used by agricultural
producers and decision makers for a variety of
planning and mitigation activities. Currently, a
semi-operational, bi-weekly VegDRI product is
being generated for a 7-state region of the U.S.
Northern Great Plains (http//gisdata.usgs.gov/web
site/Drought_Monitoring) with future plans to
expand coverage to the conterminous U.S. An
overview of the VegDRI methodology, examples of
the regional-scale and sub-county level products
are presented and future work tasks are
highlighted. An initial evaluation of the VegDRI
and its products are currently underway by
climate experts and drought impact specialists.
The production of VegDRI at two-week intervals
has been semi-operational for a seven states in
the U.S. Northern Great Plains since the
beginning of the 2005 growing season. The VegDRI
is available at the USGS Drought Monitoring
website (above) and can be viewed in combination
with other geospatial data sets using the sites
dynamic map interface. VegDRI will be expanded
over the coming years with nationwide coverage
planned by 2009. Current VegDRI maps and
additional information can be found at
http//edc2.usgs.gov/phenological/drought/index.ht
ml.
Inter-Annual Variations of Drought Conditions
Characterized in VegDRI (VegDRI maps from the
late-July to early-August bi-weekly composite
period for selected years)
This series of maps demonstrates the capability
of the VegDRI to characterize the inter-annual
variability in the level of drought stress
experienced across the seven-state region of the
U.S. Northern Great Plains. In 1989, the VegDRI
depicts the moderate levels of drought stress
that occurred across the region with localized
areas of severe drought (e.g., northwest Nebraska
and southwest South Dakota). In 1993, wide
spread above average precipitation was received,
which was reflected in the large areas assigned
the moist VegDRI classes. In 1997, the VegDRI
reflects the near average precipitation was
received across most of the region. In 2002, the
VegDRI map shows the severe drought that the
entire region experienced with many localized
areas under extreme drought conditions.
Local-Scale Drought Information in VegDRI
Comparison of VegDRI and the U.S. Drought Monitor
VegDRI and Land Cover Maps Red Willow County,
Nebraska
U.S. Drought Monitor Map (July 23, 2002)
VegDRI Map (July 25, 2002)
The 1-km2 spatial resolution of the VegDRI allows
more detailed patterns and localized variability
of drought-related vegetation drought stress to
be characterized than commonly used drought
indicators such as the USDM. The USDM is
objectively produced from a synthesis of multiple
drought indices, outlooks, and news accounts and
represents a consensus of federal and academic
scientists of current drought conditions.
General, broad-scale patterns of drought are
represented in the USDM map, but it lacks the
spatial detail depicted in the 1-km VegDRI map.
For example, the USDM (above) classifies all of
eastern Colorado as D3-Drought Extreme, whereas
the VegDRI illustrates considerable variability
in drought conditions across this area. VegDRI
also highlights drought patterns that may differ
considerably from the USDM. For example, the
VegDRI identified the severe to extreme drought
conditions for western South Dakota and
north-central North Dakota in 2002, which was not
represented in the USDM. The higher resolution
VegDRI information can be used by a variety of
decision makers and stakeholders and also serve
as an additional indicator in the USDM process.
Acknowledgements
This work was funded by the United States
Geological Survey and the United States
Department of Agriculture Risk Management
Agencys Partnership Agreement 05-IE-0831-0254.
Global Vegetation Workshop 2006 Missoula, MT
August 8-10, 2006
For further information contact Dr. Brian
Wardlow Jesslyn Brown National
Drought Mitigation Center USGS Center
for Earth Resources Observation and
University of Nebraska-Lincoln
Science (EROS) Telephone [phone]
Telephone [phone] Email
bwardlow2_at_unl.edu Email
jfbrown_at_usgs.gov
The example for Red Willow County, NE illustrates
the sub-county level drought patterns that are
characterized in the 1-km VegDRI map and the
specific drought impact information that can be
summarized at a local scale using this tool.