1. Spatial portability of empirical leaf wetness duration models
Kwang Soo Kim, Mark Gleason, Elwynn Taylor, Len Coop, Bill Pfender, et al.
(Submitted 9/09 to Agric. and Forest Meteorology)

2. Western Weather
Working Group
Midwest Weather
Working Group

3. Why model LWD? ALTERNATIVES ARE NEEDED.
Input to many disease-warning systems
Problems with measurements:
No calibration standard
LWD sensor performance is variable
Placement, coating, etc.
Not measured at most weather stations
Expense, logistics of monitoring
LWD is highly variable in crop canopies
Where to measure?
ALTERNATIVES ARE NEEDED.

4. Modeling LWD Physical to empirical
From contributing environmental factors
Aim: Avoid pitfalls of measuring LWD
Spectrum of models:
Physical to empirical

5. Physical models Energy balance at crop surface PRO: CON:
Highly accurate anywhere
CON:
Radiation inputs are not measured at most weather stations.

6. Empirical models Use statistical best-fit approaches PRO: CON:
Use widely measured inputs
RH, wind speed, air temperature
CON:
Portability may be limited

7. Portability

8. Portability

9. Portability

10. “Hybrid” LWD models
Physical principles AND empirical best-fit methods.
Most LWD models have both physical and empirical features.

11. Empirical LWD models Three models compared:
RH>90% (Sentelhas et al., 2008)
CART/SLD/Wind (Kim et al., 2004)
Fuzzy logic model (Kim et al., 2006)

12. 43 study sites
Pacific NW
Midwest
Brazil
Costa Rica
Italy

13. Approach Meta-analysis of existing data sets
RH, wind speed, air temperature
LWD:
Painted vs. non-painted sensors
How well did each model do in estimating measured (“true”) LWD?

14. LWD sensors
Non-painted sensor
Painted sensor

15. Results Painted LWD sensors Fuzzy logic model most accurate
Highest % correct estimates
Lowest coefficient of variation
Highest agreement across sites

16. Results Non-painted LWD sensors Less sensitive that painted sensors
Correction factor applied to fuzzy logic model
RH-dependent
Adjusted Fuzzy model: highest accuracy and agreement across sites.

17. MANUSCRIPT ON MWWG WEBSITE
Summary
Fuzzy logic model had greater spatial portability than RH or CART.
Reason:
Fuzzy model incorporates physical principles more explicitly than the other empirical models.
RH model may need a site-specific correction threshold.
MANUSCRIPT ON MWWG WEBSITE