A Comparison of PRZM 3 and PRZM 5 

Simulations

Lauren Padilla1, Michael Winchell1, 

Russell Jones2, Scott Jackson3

1. Stone Environmental, 2. Bayer CropScience, 

3. BASF Corporation

28 October 2014

1
Overview

Objective: To quantify differences in 

model results due to updates from PRZM 3 

to PRZM 5.

Approach:

 Comparison of PRZM 3 and PRZM 5 runs 

for 59 standard scenarios

 Varied Koc at 100, 10000, 1 million

 Varied CAM 1 and CAM 2

 All other input parameters held constant

2
Background

 PRZM 5 introduced in the Surface Water 

Concentration Calculator 

 PRZM 5 is an update of PRZM 3 to 

Fortran 2003

 Mainly internal code changes

 Modules easier to read and search

 Variables easier to understand

 Bug fixes, including to degradation, 

erosion, and application routines

 Non-functioning and unused routines 

eliminated

3
Input Parameters Assumed All Runs

4

Parameter Value

Application Method CAM 1 or 2

Application Rate 2 @ 1.25 kg/ha 

Application Interval 7 days

First Application Date 1 month after emergence

Foliar Half Life 50 days

Soil Half Life 50 days

Koc 100, 10,000 or 1 million
Regression Comparison of Daily Loads - R2

5

 Generally very good agreement

 Some scenarios where loadings do not occur on the same day

R2 = 0.995 R2 = 0.185

Koc = 10000
Slide 5

LP7 The formulas are the same, it's a difference of interpretation of what is considered the 'model' and what is 'observation'. 

Calling it NSE is like saying PRZ3 are the observations and PRZM5 is the model. Calling it R2 is like saying, PRZM3 is the 

observed dependent variable and we are testing the model PRZM3_estimated = PRZM5 (the y=x line) against it. I think 

more people have heard of R2. Both concepts imply that we are looking at how well the time series match with a 1:1 

relationship.

Lauren Padilla, 10/22/2014
Comparison of R2 Values for Daily Load 

Time Series

6

Koc

CAM 1

CAM 2
7

Koc

Comparison of R2 Values for Daily Load 

Time Series

CAM 1

CAM 2
Comparison of R2 Values for Daily Load 

Time Series

8

Koc

CAM 1

CAM 2
Comparison of R2 Values for Daily Load 

Time Series

9

Koc

CAM 1

CAM 2
Comparison of R2 Values for Daily Load 

Time Series

10

 Scenarios with lower R2 values have irrigation applied.

 Foliar applications at low Koc tend to have lower R2
Bulk Loading Time Series, MS Cotton 

Koc = 10000, CAM = 1

11

R2 = 0.99 Without irrigation
Bulk Loading Time Series, ID Potato 

Koc = 10000, CAM = 1

12

R2 = 0.19 With irrigation
Load Time Series, ID Potato, 

Koc = 10000, CAM = 1

13

• Shifted time-series primary reason for low R2

• No changes to scenario data

• Irrigation applied on slightly different days
Conclusions from R2 Comparison

 Generally good agreement between 

PRZM 3 and PRZM 5 in both timing and 

magnitude.

 Some scenarios with irrigation have low 

R2.

 R2 does not have a strong trend with 

Koc.

 CAM 2 runs have slightly lower R2 than 

CAM 1 in some cases and significantly 

lower R2 in a few cases.

14
Comparison of Bulk 30-yr Cumulative Load

15

Koc

CAM = 2
Comparison of Soluble 30-yr Cumulative Load

16

CAM = 2

Koc
Comparison of Sorbed 30-yr Cumulative Load

17

Koc

CAM = 2
Comparison of 30-yr Cumulative Eroded 

Sediment Losses and Runoff

18
Conclusions from Cumulative Comparison

 Cumulative runoff and erosion are very 

similar.

 Bulk, soluble, and sorbed loadings are 

very similar.

 Slightly greater variations in soluble 

loadings than sorbed loadings at low 

Koc. 

19
Comparison of 90th %-ile Annual Maximum 

Daily Loads

20

Koc

CAM 1 CAM 2
90th %-ile Annual Maximum, Koc = 100

21

CAM = 1
90th %-ile Annual Maximum, Koc = 100

22

CAM = 1
90th %-ile Annual Maximum, Koc = 1 million

23

CAM = 1
90th %-ile Annual Maximum, Koc = 1 million

24

CAM = 1
Annual Max Distributions, MS Cotton

25

Koc

CAM = 1
Annual Max Distributions, ID Potato

26

Koc

CAM = 1
Conclusions

 Generally good agreement between PRZM 3 and 

PRZM 5 in both timing and magnitude for bulk 

daily time series and cumulative load totals.

 CAM 2 time series slightly more sensitive than 

CAM 1 to model changes from PRZM 3 to 5. 

 Slight differences in timing do not result in major 

differences in annual maximums.

 Soluble and sorbed loadings are similar in PRZM 

3 and PRZM 5; models have similar partitioning.

 Good agreement in distributions and 90th

percentile annual maximum daily loads at all 

Kocs and CAMs.

27