This project maps the conversion from mid-20th century flood (and sprinkler irrigation) to sprinkler irrigation (center-pivot and other sprinkler), and other land types (fallow, crop, and flood remaining flood) in Montana, by 2019.
This file contains results of mapping the conversion from mid-20th century flood (and sprinkler irrigation) to sprinkler irrigation (center-pivot and other sprinkler), and other land types (to cropland—C, hayland--H, fallow –FA, and sprinkler remaining sprinkler) in Montana, by 2019.Over the past 50 years, many producers in Montana have made changes to their irrigation practice and infrastructure in an effort to increase irrigation efficiency, defined as the ratio of water consumed by crops to water diverted or pumped (consumed water ÷ diverted water). Changes in the method of irrigation, especially conversion from flood to sprinkler irrigation, may have significant on-farm benefits such as reduced labor and increased production. Conversion can have both beneficial and adverse impacts on streamflow and aquatic ecosystems depending on local site-specific hydrogeologic conditions and how irrigation water is managed. As part of the Montana Water Center’s effort to better understand the effects of increased irrigation efficiency in Montana (Lonsdale et al. 2020), historic conversion from flood to sprinkler irrigation was analyzed using available agricultural statistics, maps from state and federal sources, and an independent Geographic Information Systems (GIS) analysis. This project presents the GIS analysis and maps the amount and spatial distribution of conversion from flood to sprinkler irrigation, between the mid-20th century and 2019. Historic mid-20th century irrigation was mapped in detail from 1943-1965 by the State Engineer’s Office and from 1966-1971 by the Montana Water Resources Board—the predecessor of the Montana Department of Natural Resources and Conservation (DNRC). A scanned and georeferenced version of the Water Resources Surveys (WRS) was compared with maps of contemporary irrigated land (Montana Department of Revenue’s 2019 Final Land Unit Classification—DORFLU2019) to estimate the area of land converted from flood to sprinkler irrigation. Prior to GIS analysis, both datasets were edited to ensure valid comparison between irrigated field mapping conducted at the two points in time. To estimate the amount of conversion from flood to sprinkler irrigation, and other uses, the GIS layers (WRS flood and sprinkler 1946-1971 and DOR-FLU 2019) were overlain in ArcGIS; then the clipping erase functions were used to select the WRS flood and sprinkler parcels that were shown as sprinkler irrigated in 2019. Additional conversion classes were also mapped that represent the changes from WRS flood and sprinkler to cropland, hayland and fallow, and WRS sprinkler remaining sprinkler.

Please see the main project report: "Montana Conversion from Flood to Sprinkler Irrigation between Mid 20th Century and 2019.pdf" and Appendix C. "Methods and data for GIS mapping of conversion from flood to sprinkler irrigation.pdf" for details of the analysis and results. https://www.hydroshare.org/resource/15392cb3617b4519af6ae8972f603502/data/contents/Appendix_C._Methods_and_data_for_GIS_mapping_of_conversion_from_flood_to_sprinkler_irrigation.pdf