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)

Questions? Comments?

Contact Information:

Heather Dinon

hadinon@ncsu.edu

919-515-3056