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Hydroclimatic Index
for drought monitoring in
the
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Implementing the Hydroclimatic
Index in Short and Long Term Drought Forecasting within the
Principal Investigators
Andrew Ellis & Robert Balling, School of Geographical Sciences, Arizona State University
Funding Agency
United States Department of
the Interior, Bureau of Reclamation
(07SF320003)
Agency Partner
Mitchell Haws, Phoenix Area Office
Project Objectives
The primary goal of the project is to take a recently
derived method for representing hydroclimatic
variability, the Hydroclimatic Index, and extend it to monitoring and
predicting drought occurrence across the CRB. The final products will be of a
higher spatial resolution than what is presently used in drought monitoring
within the CRB and they will be made available to regional stakeholders for
operational use. The secondary goal of the project is to use various
downscaled global climate model forecasts of changes in temperature and
precipitation across the CRB during the 21st century to assess the
likelihood of more intense, more pervasive, and lengthier droughts. Hydroclimatic Index
Soil moisture is the focus of many drought indices, but
the Hydroclimatic Index (HI) stops short of representing soil moisture in its
characterization of the hydroclimatic condition.
Only a few operational soil moisture sensors exist in the CRB, and the
alternative of simulating soil moisture through time is difficult, as climate
conditions, land surface characteristics (soil type, vegetation type, topography) and the amount of moisture relative to the
soil’s capacity combine to control soil moisture. The HI simply
represents the difference between precipitation (P) and potential evapotranspiration (PE) (P-PE) through time at a given
location. PE is the climatic demand for water, or that amount of evapotranspiration that would occur from a grass-covered
soil for which soil moisture is maintained at capacity. Negative P-PE values
indicate the amount by which the climatic demand for water can not be met by
precipitation and actual soil moisture would decline if not irrigated.
Positive values represent the amount of excess water from precipitation that
would recharge soil moisture, percolate to ground water, or run to streams
and reservoirs through overland flow or interflow. Aggregates of P-PE are constructed for periods that
represent short-term conditions (1-, 3-month), intermediate conditions (6-,
12-month), and long-term conditions (24-, 36-, 48-month). Aggregate values are
converted to percentiles to form the HI. Percentile values of the HI are then
stratified into drought categories that represent levels of drought
intensity. _______________________________________________________________________________________________________ Proposal &
Reports
Research
Proposal
Progress
Report: Year 1-Quarter 1
Progress
Report: Year 1-Quarter 2
Progress Report: Year 1-Quarter 3
Presentations
Ellis, AW (2007) Incorporating the Hydroclimatic Index in Drought
Monitoring, Forecasting, and Scenario Building for the
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