California study tests pesticide records as a tool for mapping crops

What you need to know

• In a comparison with California Department of Water Resources (DWR) data for 2018, the study reported a log-transformed Lin’s concordance correlation coefficient of 0.77 for acreage estimates and a mean proportional bias of −15%. These figures describe agreement between datasets, not proof that either estimate is correct. 1
• For crop categories, overall agreement was 67%, with Cohen’s kappa of 0.56. The study also found that user’s accuracy exceeded 83% for each evaluated crop class when CalPUR-LUE identified agricultural activity, while grain underestimation contributed to disagreement. 1
• The two mapping approaches draw on different information. DWR’s statewide crop maps use remotely sensed imagery, analytical techniques and field visits; CalPUR-LUE derives estimates from pesticide records and the study’s processing methods. 12
• Pesticide records document applications, rather than crop plantings directly. CalPUR-LUE uses filtering and other processing assumptions to infer crop classes and acreage, so estimates may be affected by reporting patterns, repeated applications and methodological choices. 13
• The researchers compared CalPUR-LUE with both DWR crop mapping and county agricultural reports. The study suggests pesticide data may add to existing land-use estimates, rather than serve as a replacement for other sources. 1

Why this matters

Crop and land-use maps inform agricultural water planning and related management needs. A further data source could help practitioners assess land use, but the reported disagreements mean estimates should be interpreted with their limitations in view. 12

What happens next

The study identifies further questions about performance in other years, places and crop classes, and whether estimates can be checked against independent field observations. Its usefulness for conservation decisions also remains to be established. 1

What we know

• California agricultural pesticide use is reported to county agricultural commissioners, who report it to the state Department of Pesticide Regulation. 3
• The state’s pesticide-use portal can be searched by year, county, crop or site, and COMTRS location. 4
• DWR describes its statewide crop mapping as one source of information for agricultural water planning. 2

What we don't know

• The supplied study comparison does not establish how well CalPUR-LUE performs across years other than 2018 or across areas and crop classes with weaker agreement. 1
• The reporting does not identify an independent reference source, such as field-level observations, that could determine which estimates are more accurate in locations where datasets disagree. 1
• The study does not establish how useful these estimates would be for conservation decisions beyond agricultural land-use and water planning. 12

Read the reporting

This WildNews briefing synthesises and summarises reporting from the sources below. WildNews did not produce the original reporting. Learn more about how we use AI