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Siting Information

Picture of a station siting The placement of a weather station and the local environment near weather station sites will affect the accuracy and reliability of the ETo calculation for that surrounding area. Buildings or trees too close to a weather station affect wind speed data, which in turn affects the calculated ETo. The absence of healthy green grass under a weather station can affect net radiation and humidity, which will adversely affect ETo. Bare soil instead of cropped land around the weather station will increase temperatures and decrease humidities, which would increase the ETo value.

Consistent CIMIS Station siting insures that any differences in data between stations are caused by the weather, not by different sites. A CIMIS station should be located within the area that the station is meant to represent. The station location should be typical of the largest possible surrounding area. This will insure the most effective and efficient use of the weather station network for supplying accurate and applicable ETo information. The ideal site for a CIMIS weather station is a 20-acre or larger cool-season perennial grass pasture that is well maintained. The station itself will be located in the center of the pasture, inside a 10-yard to by 10-yard fenced enclosure. Inside the enclosure, the grass would also be well maintained (properly irrigated and fertilized) and mowed frequently to maintain a height between three to six inches.

It can be difficult to find a site for a new weather station. In many areas, there are few pastures. If a pasture is found, the landowner must agree to allow a weather station to be sited there. DWR has prepared, with the help of UC Davis, the following criteria or guidelines to be used to find and judge sites for CIMIS weather stations.

Regional and Local Criteria
  • A station should be sited within the region it is meant to represent.
  • Avoid locating a station in a transition area between two regions of distinct climates unless you are attempting to characterize that transitional area.
  • Topographic depressions should be avoided, as the temperature is frequently higher during the day and lower at night. High points should also be avoided in most cases.
  • There should be a long-term commitment to maintain the same land use in and around the site, to avoid moving the station in the future.
Surrounding Environment Criteria
  • Avoid wind obstructions within 100 yards of the site. Avoid linear obstructions (windbreaks, buildings) within 150 yards perpendicular to the direction of the prevailing wind.
  • Avoid placing a station in a field where there are frequent rotations of crops, because between crops the field will have bare soils.
  • Avoid abrupt crop/vegetation changes (i.e. pasture to row crops) within 50 yards of site, or 100 yards upwind of site.
  • Avoid roads within 50 yards of the site. Unpaved roads should be no closer than 100 yards upwind of the site.
  • Small rivers should be no closer than 100 yards of the site and larger rivers should be no closer than 200 yards of the site. Lakes should be no closer than 1,000 yards of the site.
  • Avoid areas exposed to extensive or frequent applications of agricultural chemicals (can cause increasing degradation of sensors).
Other General/Desirable Criteria
  • Site might be somewhat in the vicinity of nearby dwellings (no closer than several hundred yards) to reduce risk of vandalism.
  • The station enclosure might be a 10-yard by 10-yard by five-foot high fence, livestock-tight where necessary. Enclosure material should not affect wind nor shade any instruments.
  • Site should have unrestricted access, seven days a week. There should be vehicle access to the site (except when wet).
  • The station enclosure should be close to existing telephone lines (within 150 yards) or have cellular telephone coverage.
  • There should be local personnel (private or public) to help maintain the site to meet DWR's requirements.

Some CIMIS stations are not located in the ideal large pasture situation and do not meet all the above siting criteria. These sites will be upgraded if possible or relocated to a better quality site in the future. Specific information on each CIMIS site can be obtained by clicking on the "Station List" tab and then the station number.