Identifying Opportunities for Improving Water Use Efficiency in CA Rice Systems, 2019


Bruce Linquist, UCCE rice specialist, Dept. of Plant Sciences, UC Davis

This project previously focused on quantifying water use in California rice systems and identifying opportunities for conserving water. This work has been completed. Three areas of accomplishment include a model predicting crop development, quantifying salinity, and understanding the hydrology of rice systems—seepage and percolation rates, in particular.

The focus has now shifted to examining land-use changes in the Sacramento Valley. From 2000 to 2013, California rice averaged 543,000 acres per year. Since 2013, rice acreage has decreased and is now less than 500,000 acres. Some rice acreage is being converted to permanent crops, some is rotated with other annual crops, and still other land is being fallowed. What is driving these changes can be linked to water. For instance, water sales during times of drought have left significant acreage fallow.

Understanding the nature of these changes is important to the future of the rice industry. Project scientists will be looking at and talking to growers about a broad range of issues, such as where annual crops have been grown successfully in rotation with rice. Objectives for 2019 research included:

  • Collect Landsat satellite data from 2000 to present for the Central Valley.
  • Identify other crops in the region with a focus on annual field crops, orchards, and fallow land.
  • Develop methods for detecting land-use change.
  • Rather than downloading and collecting Landsat satellite data, researchers utilized Google Earth Engine, a cloud-based computing platform to efficiently analyze and interpret Landsat satellite imagery.

    Planted acres from 1912 to 2018 in California (Source: USDA)
    Preliminary crop estimates within the 15 major water districts of the Sacramento Valley 10 years apart. Further research and farmer input is planned for 2020 to fine-tune the data.
    Additional research focused on analyzing the USDA Cropland Data Layer (CDL) dataset. This consists of annual crop maps from 2008 to 2018 for the entire United States. Also, Landsat data for rice in the Sacramento Valley is not available for 2000 through 2008.

    By working with CDL, researchers were able to identify the major crops in California’s Central Valley. Preliminary analysis shows, not surprisingly, six major players in land-use change dynamics in the Sacramento Valley: rice, walnuts, almonds, alfalfa, annual crops, and fallow.

    However, some problems were noted with the CDL data, such as low detection accuracy for fallow and some orchard crops and low accuracy for field boundaries. By assessing the CDL dataset and conducting preliminary analysis of land-use change patterns in the Sacramento Valley, researchers developed a road map for building their own improved crop map dataset. This is a primary objective for 2020 research and will improve field-crop detection accuracy and better acreage estimates. Farmer input will be incorporated into the validation process to further increase accuracy.

    While researchers improve the dataset, early tests confirm that rotation with annual crops is most common in the southern part of the Sacramento Valley, fallowed rice fields are most common in Butte County, and fields in rice production every year are most common in Colusa and Glenn Counties. Once dataset improvements are made, precise figures about land use in the Sacramento Valley can be made with greater confidence.