Raster · dataset · 2025

Spatial CIMIS ETo maps — Daily Reference Evapotranspiration for California

Listed in California Open Data

🔔 Full-year 2025 data now available — Complete daily ETo for January–December 2025 has been published, replacing the partial-year v1 file.

Description

See the Change Log for details. 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.

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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 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. The dataset is provided in 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. Note that the current year’s dataset may have a lag of several months before all daily values are finalized and published. ###Access Via API For data via a web Application Programming Interface (API) please refer to data.cnra.ca.gov/dataset/cimis-weather-station-spatial-cimis-data-web-api ###Suggested

Citation

California Irrigation Management Information System. 2025, updated periodically. _Spatial CIMIS ETo maps—Daily reference evapotranspiration for California_. California Department of Water Resources. data.cnra.ca.gov/dataset/cimis-spatial-eto-maps. Accessed [Month Day, Year].

If citing a specific annual file in a publication, include the URL and filename of the file used from the Data and Resources section. ###Related dataset CIMIS Weather Station Data

Topics

Stated by source: Natural Resources · Water
From keywords: Earth & Environmental Science · Life Sciences
Inferred from text: Image 65% · Satellite remote sensing 65%

Provenance · 1 source records, 13 field assertions

Source	Key	Last seen	Raw
California Open Data	f2796747-a9c3-4880-993e-1dc507ad04ab	8 d ago	JSON v1

Field	Assertion	Extractor	Evidence
access_level	source · data ca gov	connector:data_ca_gov@1.0.0
concepts[field].local:field:earth-environmental	mapping · data ca gov	connector:data_ca_gov@1.0.0
concepts[field].local:field:life-sciences	mapping · data ca gov	connector:data_ca_gov@1.0.0
concepts[modality].local:modality:image	enrichment · data ca gov	keyword-concept-rules@1.0.0	title+description (65%)
concepts[modality].local:modality:remote-sensing	enrichment · data ca gov	keyword-concept-rules@1.0.0	title+description (65%)
concepts[topic].ckan_group:data_ca_gov:natural-resources	source · data ca gov	connector:data_ca_gov@1.0.0
concepts[topic].ckan_group:data_ca_gov:water	source · data ca gov	connector:data_ca_gov@1.0.0
created_date	source · data ca gov	connector:data_ca_gov@1.0.0
description	source · data ca gov	connector:data_ca_gov@1.0.0	/notes
license_text	source · data ca gov	connector:data_ca_gov@1.0.0
publication_date	source · data ca gov	connector:data_ca_gov@1.0.0
title	source · data ca gov	connector:data_ca_gov@1.0.0	/title
updated_date	source · data ca gov	connector:data_ca_gov@1.0.0

Spatial CIMIS ETo maps — Daily Reference Evapotranspiration for California

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