Arizona Center for Investigative Reporting explains their analysis of water usage in the Cochise County Douglas Basin
Our methods: Groundwater regulation weakness exploited by large farms
To understand the growth of active farmland and groundwater declines in the Douglas basin, AZCIR analyzed data from local and state agencies, including the Arizona Department of Water Resources, as well as satellite data compiled by federal agencies such as the U.S. Geological Survey (USGS) and the U.S. Department of Agriculture (USDA)
The analysis used satellite raster data, or data with an assigned value for each pixel in a given image, from the USGS and USDA, with the earliest available data in 2001 and 2008, respectively.
The USGS data categorizes general land use and denotes general farmland, while the USDA data categorizes farmland by the crop type grown on a given field.
AZCIR used shapefiles, or data files that show objects on maps, including boundaries, to identify the Douglas basin area, including the Irrigation Non-expansion Area designation within it. These files were acquired from ADWR’s mapping repository, and were used to isolate and count the pixels within these boundaries to determine the amount of farmland in each given year for which data was available.
USDA data was overlaid with ADWR’s Irrigation Grandfathered Right (IGFR) shapefiles, which maps the fields with irrigation rights, to verify that every irrigated field had an IGFR associated with it, and thus was legally allowed to be watered under the basin’s INA designation since 1980.
Interviews with Douglas basin residents pointed to fields appearing that, many said, were never previously irrigated. AZCIR used satellite imagery with false-color bands emphasizing green, which is specialized to spot vegetation and shows irrigated agriculture, to verify the claims.
Two of these images make up the comparison slider and maps used in the main story. Satellite images from 1983 were the earliest available, but images for the slider were selected based on clarity, cloud cover and season to match with the most recent clear image in 2024.
Several new fields did appear from these images, so AZCIR reporters then checked this information against the IGFR data, which shows grandfathered rights tied to specific fields.
The IGFR data also showed that some fields had corners of what was formerly a rectangular field retired from irrigation. Documentation tied to these specific parcels mentioned consolidation of irrigation rights from retired corners, which then led to new rights that matched the suspected new fields observed by AZCIR’s analysis.
This confirmed the creation of new fields through legal substitutions of retired land, as outlined within this story.
Separately, parcel shapefiles from the Cochise County Assessor’s Office were layered over the satellite imagery to confirm the identity of irrigated farmland owners. This allowed AZCIR to determine who owned the most intensely farmed area of the basin. However, because of inconsistencies in how the forms were filled out, some grouping was required: Some entries, for example, cite “Riverview LLP d.b.a. Coronado Farms LLP” and others cite variations of those same names. For the purposes of this analysis, these were all standardized.
USDA data helped AZCIR determine the type of crops grown in the basin. Although specific crops fluctuated from year to year, double-cropped fields were separately denoted in the data. This let AZCIR determine that double-cropped fields grew from an estimated 1,408 acres in 2008 to over 10,196 acres in 2024.
Finally, data from ADWR active index sites, or groundwater monitoring sites used to standardize measurements in specific areas within the basin, were used as another layer on AZCIR’s mapping analysis. Latitude and Longitude were imported onto the satellite images so AZCIR could place these wells on the maps. This is how AZCIR was able to determine the local impact from nearby pumping, in large part by reviewing each well’s hydrograph, or year-over-year water level measurements.
AZCIR also used ADWR data to determine basin-wide groundwater withdrawal, which was gathered by monitoring wells created by the INA regulation.
This article first appeared on Arizona Center for Investigative Reporting and is republished here under a Creative Commons license.