Spatial CIMIS ETo maps — Daily Reference Evapotranspiration for California
🔔 **Data now available in Cloud-Optimized GeoTIFF format for faster access!** ### Summary This dataset contains daily grass-reference evapotranspiration (ETo) maps for California at 2 km spatial resolution. The ETo values are expressed in millimeters (mm) per day. Spatial data are provided in EPSG:3310 (NAD83 / California Albers) with units in meters. ETo values are calculated statewide using the ASCE-Penman-Monteith equation (ASCE-PM), with required input parameters including solar radiation, air temperature, relative humidity, and wind speed at two meters height. Daily solar radiation is derived from NOAA GOES satellite imagery using the Heliosat-II model, which converts visible-band satellite images into global horizontal irradiation at ground level. Air temperature, relative humidity, and wind speed are interpolated across the 2 km grid from CIMIS weather station measurements using Spline interpolation. This hybrid method allows spatially distributed ETo maps statewide, filling gaps where station coverage is sparse. Refer to https://cimis.water.ca.gov/SpatialData.aspx and the “Daily reference evapotranspiration for California using satellite imagery and weather station measurement interpolation” (Civil Engineering and Environmental Systems, October 2007) for detailed methodology. ###Update (Dec 2025) Dataset name updated to “Spatial CIMIS ETo maps — Daily Reference Evapotranspiration for California. Added Cloud-Optimized GeoTIFF (COG) format for annual datasets (2004–present) to improve accessibility and enable efficient streaming. Original links to ASCII files remain available. ###Formats Available The dataset is provided in two formats to allows users to choose the format best suited for their analysis and workflows. 1. Original ASCII files — organized in a year/month/day folder structure. 2. Cloud-Optimized GeoTIFF (COG) files — one per year, enabling efficient streaming and subset access without downloading entire files. Each COG contains daily ETo values in a 2×2 km grid, covering 2004 through the most recently available year. ###Temporal Coverage Data are available annually from 2004 through the most recent year in both ASCII and Cloud-Optimized GeoTIFF (COG) formats. Note that the current year’s dataset may have a lag of several months before all daily values are finalized and published. Prior to 2004, data are available only in ASCII format for 2003 (February through December) and for October 2000. ###Access Via API For data via a web Application Programming Interface (API) please refer to https://data.cnra.ca.gov/dataset/cimis-weather-station-spatial-cimis-data-web-api ###Suggested Citation California Irrigation Management Information System. (n.d.). CIMIS spatial ETo maps: Daily reference evapotranspiration for California. California Department of Water Resources. Retrieved from https://data.cnra.ca.gov/dataset/cimis-spatial-eto-maps ###Related dataset [CIMIS Weather Station Data](https://data.cnra.ca.gov/dataset/cimis-weather-station-data) ###Change Log Dec 2025: Added COG format and updated dataset name. Updated metadata and clarified description.
Data files
Supporting files
| Data title and description | Access data | File details | Last updated |
|---|---|---|---|
Spatial CIMIS ETo maps The ETo maps are presented as compressed ASCII files (ETo.asc.gz). The ETo maps are contained in folders defined by Year, Month, and Day. ETo data is expressed in millimeters.The ASCIII files can be converted to conventional raster formats (TIF, img) using commercial and open source software. The spatial reference of the maps are defined as EPSG Projection 3310 - NAD83 / California Albers (http://spatialreference.org/ref/epsg/3310/). . | Download | ASCII | 07/18/25 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2004 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2004. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2005 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2005. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2006 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2006. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2007 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2007. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2008 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2008. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2009 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2009. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2010 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2010. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2011 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2011. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2012 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2012. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2013 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2013. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2014 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2014. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2015 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2015. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2016 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2016. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2017 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2017. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2018 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2018. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2019 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2019. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2020 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2020. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2021 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2021. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2022 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2022. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2023 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2023. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2024 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2024. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |
Spatial CIMIS ETo Map — Daily Reference ETo for California, 2025 (v1) This resource provides annual Reference Evapotranspiration (ETo) data for California for the year 2025. The dataset is referenced in EPSG:3310 — NAD83 / California Albers. Data type: Daily composite values. | Download | GEOTIFF | 01/01/26 |