Developing a Reference Crop Evapotranspiration Climatology for the
Southeastern U.S. using the FAO Penman-Monteith Estimation
Heather Dinon*, Ryan Boyles, Gail Wilkerson
Carolinas and Virginia Climate Conference October 21, 2009
Wilmington, NC
Motivation
• NC Agriculture: – Annual $71B economy– 19% of state income– Over 16% of work force
(NCDA&CS 2008) • Agriculture is largest
consumer of water in US (NOAA 2002)
Photo courtesy of Bridget Lassiter, of NCSU Crop Science Department
• Weather/Climate Agriculture/Irrigation
What is this? Why do we need?
Robust ET estimate:
Efficient water use
Maximize yields
http://science.howstuffworks.com/trees-affect-weather.htm/printable
Introduction
• ET provides guidance for crop management• Limited ET observations• Solution: UN FAO Penman-Monteith method
to estimate daily reference crop ET– Theoretical grass reference crop
• Height of 0.12m• Albedo of 0.23• Surface resistance of 70s/m• Weekly irrigation schedule
– Min/Max Temp, Min/Max RH, Avg SR, Avg WS– Dependent on time of year & location (elev, lat)
http://www.nc-climate.ncsu.edu/et
Daily estimation
• Calculates RefET for stations on selected date of interest (YY-MM-DD)– Date range: 01 Jan 2002 - yesterday– ASOS, AWOS, ECONET, RAWS, USCRN– Virginia, Carolinas, Georgia, Florida, Alabama
Climatology product
• Years: 2002-2008• Daily average: 7-day moving average
– Annual time series for each station
• Average monthly totals– Annual bar chart for each station
Both products require >80% of data, and data must pass QC checks
*Note: Upper and lower boundaries capture ~50% of the distribution.
Only shown if 5 or more years of data.
Sensitivity analysis
• Sensitivity of inputs: – min/max temp, min/max RH, avg SR, avg WS
• Case study:– Lake Wheeler Field Lab, Raleigh, NC
• Elevation: 382 feet above sea level• Station type: ECONET
– Average each parameter during July (2002-2008)
Min Temp 20.5°CMax RH 94.8%Min RH 46.6%Avg WS 2.01m/s
Avg SR 245.3 W/m2
Max Temp 31.7°CMax RH 94.8%Min RH 46.6%Avg WS 2.01m/s
Avg SR 245.3 W/m2
Max Temp 31.7°CMin Temp 20.5°C
Min RH 46.6%Avg WS 2.01m/s
Avg SR 245.3 W/m2
Max Temp 31.7°CMin Temp 20.5°CMax RH 94.8%Avg WS 2.01m/s
Avg SR 245.3 W/m2
Max Temp 31.7°CMin Temp 20.5°CMax RH 94.8%Min RH 46.6%
Avg SR 245.3 W/m2
Max Temp 31.7°CMin Temp 20.5°CMax RH 94.8%Min RH 46.6%Avg WS 2.01m/s
Summary - Tool
• Dataset of ET for assistance with crop management across Southeast US
• Daily estimate (2002 up to yesterday)• Climatology product (daily/monthly)• Spatial (maps) & temporal (graphs)
Summary - Analysis
• Direct relationship: SR, temp, WS• Indirect relationship: RH• SR main energy source for ET
Future Work
• Analyze trends across the Southeast– Sensitivity analysis of inputs– Spatial variation (regional trends)– Temporal variation (seasonal trends)
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