- Author: Ben Faber
Spatial Overview - How it Works
The California Irrigation Management Information System (CIMIS) currently manages over 145 active weather stations throughout the state. Archived data is also available for 85 additional stations that have been disconnected from the network for various reasons. Most of the CIMIS stations produce estimates of reference evapotranspiration (ETo) for the station location and their immediate surroundings, often in agricultural areas. Because of California's diverse landmass and climate, many locations within the state lack a representative CIMIS station. Some counties, for example, do not have a CIMIS station and others have only one or two stations. As a result, there are significant spatial ETo data gaps, especially in urban areas. In an attempt to mitigate this problem, CIMIS initiated a study to investigate the possibility of coupling remotely sensed satellite data with point measurements from the CIMIS weather stations to generate spatially distributed ETo values (ETo maps).
A contract was awarded to the University of California Davis (UCD) remote sensing group, lead by Professor Susan Ustin, to conduct the study. The Department of Water Resources (DWR) formed an advisory committee comprised of individuals with expertise in remote sensing, GIS, modeling, and water management from DWR and UCD. The committee met, on an as needed basis to discuss new developments and plan future actions. After thorough research, the team decided to use combinations of data derived from satellites and interpolated from CIMIS station measurements to estimate ETo at a 2 kilometer (km) spatial resolution. The resulting product has been vigorously tested and has demonstrated a degree of accuracy that is acceptable for most irrigation applications. The CIMIS program will continue to evolve and expand to meet the future irrigation information needs of California. For a brief description of the methodology used to generate the ETo maps, see the Spatial Model discussion below.
Spatial Model
Daily reference evapotranspiration (ETo) at a 2 km spatial resolution are calculated statewide using the American Society of Civil Engineers version of the Penman-Monteith equation (ASCE-PM). Required input parameters for the ASCE-PM ETo equation are solar radiation, air temperature, relative humidity, and wind speed at two meters height. These parameters are estimated for each 2 km pixel using various methods.
Daily solar radiation is generated from the visible band of the National Oceanic and Atmospheric Administration's (NOAA) Geostationary Operational Environmental Satellite (GOES) using the Heliosat-II model. This model is designed to convert images acquired by the Meteosat satellite into maps of global (direct plus diffused) irradiation received at ground level. The model has also been used with other geostationary satellites such as the GOES. For details on the Heliosat-II model and its accuracy, please refer to the HelioClim web page.
Interpolation
Air temperature, relative humidity, and wind speed values at each pixel were obtained by interpolating point measurements from CIMIS stations. Originally two interpolation methods, Spline and DayMet, were selected based on accuracy of results, code availability, and computational efficiency. Spline – the method currently used – is an interpolation method that fits a surface through or near known points using a function with continuous derivatives. Two- or three-dimensional Spline is used based on which weather parameter is to be interpolated.
The accuracy of both methods has been tested using cross-validation analysis, but DayMet is no longer used. DayMet is an interpolation method that was developed at the University of Montana to generate daily surfaces of temperature, precipitation, humidity, and radiation over large regions of complex terrain. It determines the weights associated with a given weather station for each point where weather parameters are to be determined depending on the distance and density of the stations.
The accuracy of ETo values estimated from these methods depends on many factors. For example, solar radiation remotely sensed through GOES is significantly affected by such factors as cloudiness and snow cover. Therefore, mountainous areas with snow cover and coastal areas with cloud and fog are more susceptible to errors. Also, interpolation accuracy is affected by the density of the weather stations and geographic features of the region. CIMIS stations are purposely placed in irrigated, open, flat areas – usually valleys – to provide the best reference data for adjacent farmlands and other irrigated areas. As a result, interpolation in valleys between CIMIS stations may not provide accurate data for mountainous terrain. Despite these potential problems, however, we believe the ETo estimates provided will be superior to only using data from a distant weather station with a different microclimate. For CIMIS station Siting criteria click the “Siting” tab.
Further Details
For detailed descriptions of the methodology used to map daily ETo, refer to the RESOURCES navigation button https://cimis.water.ca.gov/Resources.aspx
If you would like to get ETo data created using the methods described here, you may do so by logging into your account, clicking on the SPATIAL navigation bar, then on the Spatial Report tab. If you do not have a CIMIS account, you can create one by registering with us. Please note that CIMIS data is provided free of charge and registration is required for statistical purposes only. https://cimis.water.ca.gov/Default.aspx
- Author: Susie Kocher
- Author: Kim Ingram
- Editor: Sophie Kolding
The 2004 Sierra Nevada Forest Plan Amendment that guides the management of the national forests in the Sierra has been ripe with controversy since its inception. Disagreements over harvesting plan details, the effectiveness of SPLAT fuels treatments and their effects on wildlife and water issues led to the formation of the Sierra Nevada Adaptive Management Project (SNAMP) as a way to address these controversies and learn from the best available science. The US Forest Service, US Fish & Wildlife Service and California Resource agencies contracted with the University of California to be an independent, neutral third party to research key management issues, develop a multi-party adaptive management program that builds on new research and to increase public participation in all aspects of the project. UC scientists are working in five areas: Fire & Forest Ecosystem Health, Water Quality & Quantity, Wildlife (CA Spotted Owl and Pacific Fisher), Spatial, and Public Participation. These teams are conducting scientific research in an open and transparent manner to measure physical and natural processes at relevant management scales, all the while integrating competing public interests, identifying conflicting outcomes and building public trust. The overall goal of this seven year project is to provide the Forest Service and resource agencies with quality information derived from deliberate experimentation that can be used to improve future management decisions and reduce conflict.
SNAMP has two study sites, Last Chance in the northern Sierra and Sugar Pine in the southern Sierra. These sites were selected because they represent the major bio-geographical features of the Sierra Nevada. They have mixed conifer forests with suitable control and treatment watersheds and old forest habitat for species at risk. They are also large enough to support fireshed scale research and active planning by local Forest Service districts for fuels management projects. Two to four years of pre-treatment data has been collected by the UC teams prior to the start of fuels reduction treatments (including thinning, mastication and prescribed fire) that began during summer 2011. Treatments are scheduled for completion by late 2012.
Logs being sorted at the Last Chance thinning project near Foresthill, CA, September 2012.
Photo by Shufei Lei
Analysis of pre-treatment data has led to some initial findings from the various UC science teams. The Forest Team collected data on tree size and species, as well as fuel loading in the study area, then modeled how fire behavior would be affected both before and after the treatment. They predict that both treatments will be effective at moderating wildfire behavior. They also analyzed hundreds of tree core samples and compared growth patterns between live and dead trees. Initial evidence suggests that thinning can improve tree growth even under adverse environmental conditions such as drought.
Dr. John Battles, UC Berkeley forest ecologists shows a SNAMP participant how to read a tree ring core.
Photo by Susie Kocher
The fisher team has used radio collars to track the movements and dispersal of over 66 Pacific fishers in the Sugar Pine area. By retrieving fisher carcasses, the team, in conjunction with UC Davis scientists, has identified the top four causes of fisher mortality in the study site: predation from bobcats, mountain lions and coyotes, disease, rodenticide and road kill. They are currently developing measures of the population dynamics for the species, including reproduction and survival as well as locations of fisher source and sink areas in the study area.
The CA Spotted Owl Team has identified 75 owls in 48 territories within the SNAMP study area. Using data from monitoring territory occupancy and reproductive success of the owls, initial findings suggest that the owl population is in an overall decline. The team is conducting a retrospective analysis on the history of land use and vegetation looking at all observable changes in owl habitat due to disturbance to identify potential causes of decline.
With meteorological and hydrological instruments, the Water Team records and collects data on a daily basis. This data is fed into computer models to produce potential trends in stream discharge and sediment loading or snow accumulation and snowmelt rates. Using different parameters, such as a reduction in leaf area index (LAI), the team is modeling effects of fuels treatments on stream flows and evapo-transpiration rates.
Remote sensing of both study areas was done using Lidar (light detecting and ranging). This data has allowed the Spatial Team to produce many two and three dimensional maps and other products for use by the science teams. Examples include bare earth, slope, aspect and elevation maps; canopy cover and LAI maps; as well as providing information incorporated into fire behavior models. The team has developed methods to detect individual trees from a lidar data point cloud and has used this data to characterize habitat structure for the wildlife teams.
Digital elevation model and vegetation layers Visualization of forest structure developed by the SNAMP
developed by the UC Spatial Team Spatial Team using Lidar data
The role of the Public Participation team is to promote SNAMP through strategic facilitation and outreach and to support the progress of adaptive management. The team reaches many diverse participants through meetings, field trips and workshops; presentations to community leaders and groups; submissions to blogs, industry publications and other media outlets; and the SNAMP website. Current work includes papers on perceptions of forest health, social network analysis and lessons learned through outreach. SNAMP participants in September 2011 on a field trip to see progress in implementation
of the Last Chance Project near Foresthill. Photo by Shufei Lei.
Funding difficulties affected the scope of the project in 2011. However, the majority of funding has been restored and the project will be completed with a few changes to the original scope of work.
Data collection by these teams will continue for a year after the fuels treatments are complete in order to characterize the effects of the treatments on forest health, fire, water, and wildlife. There will be a final report to agency partners and the public in 2014. For more information, please see the SNAMP website http://snamp.cnr.berkeley.edu/.