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Cal-SIMETAW (California Simulation of Evapotranspiration of Applied Water)

General Description

Estimates daily soil-water balance to determine potential crop ET and applied water ET for 132 individual crops, 20 crop categories, and four land-use categories by DAU/county for use in California Water Plan.
 Model website at:  https://water.ca.gov/Programs/Water-Use-And-Efficiency/Land-And-Water-Use/Agricultural-Water-Use-Models

Model Domain

Water use by crops in California

Developer

California Department of Water Resources

Hardware computing requirements

NA. Computer power is dependent on area of analysis.

Code language

C# & Oracle Spatial Database 

Original application

Developed from SIMETAW, constrained to CA scenario for 20 crops, 4 land uses and historical data. Designed to estimate daily soil-water balance to determine ETc (crop) and ETaw (applied water) for California Water Plan updates.

Public/proprietary and cost

Public by request through DWR

Physically or empirically based

Empirical

Mathematical methods used

  • ETo is estimated by using a Hargreaves-Samani equation calibrated to estimate regional Penman-Monteith equation-derived ETo to account for spatial climate differences
  • Crop coefficients: most fo 120 Kc developed in California using empirical data for ETc/ETo (potential ET measured for the crop/reference ET for the region)

Input data requirements

  • Weather/climate data: PRISM (monthly) and NCDC (daily)
  • ETo: Spatial CIMIS correction for PRISM data
  • Land cover (e.g. LandIQ)
  • Crop coefficients (Kc)
  • Soil characteristics (e.g. SSURGO) – water holding capacity, soil depth
  • Irrigation schedules – can be developed assuming minimal water stress and 100% application efficiency
  • Geographic DAU/County boundaries

Outputs

Format: Oracle database files.

  • Climate and calculated ETo data by PRISM grid (latitude and longitude) and DAU/county over the entire state.
  • Daily soil water balance output by unit for individual crops and 20 crop categories by DAU/county.
  • Monthly total ETo, ETc, Ep, ETaw, and AW by unit for individual crops and 20 crop categories by DAU/county.
  • Seasonal and annual ETc, Ep, ETaw, and AW by unit for 20 crop categories by DAU/county within DAUs, counties, planning areas (PAs), hydrologic regions (HR), and region offices (ROs).
  • Seasonal ETc, Ep, ETaw, and AW by volume for 20 crop categories by DAU/county, DAU, County, PA, HR, and RO.
  • Volume values of seasonal and annual ETc, Ep, ETaw, and AW for 20 crop categories by DAU/county, DAU, County, PA, HR, and RO for a specific water year and calendar year.

Pre-processing and post-processing tools

NA

Representation of uncertainty

Model verification vs. CIMIS (R = 0.98), no measure of error and several major assumptions required to run the data.

No correction for runoff and runon the sites. Assumption that rainfall cannot exceed soil water depletion. Uncertain results for longer timescales (currently run on a daily scale).

Prevalence

Primarily used for California Water Plan updates every 5 years

Ease of use for public entities

Requires access to additional data sources (land cover) which can add additional costs to running the model.
Requires GIS and coding capabilities to synthesize datasets and run model

Ease of obtaining information and availability of technical support

Direct contacts for developers available through DWR, technical manuals and model schematics not available online.

No help desk or active working group advertised.

Source code availability

Not immediately downloadable, but accessible through program in C# 

Status of model development

Completed and used for Water Updates every 5 years (DWR). No announcements on new directions/upgrades.

Challenges for integration

Requires some detailed information of irrigation for crop types. Constrained number of crop types. Output can only be generated for DAUs and county level, not spatially explicit.


References:
Medellín-Azuara, J., & Howitt, R. E. (2013). Comparing Consumptive Agricultural Water Use in the Sacramento - San Joaquin Delta. Davis, CA.

Orang, M. N., Snyder, R. L., Hart, Q., Sarreshteh, S., & Eching, S. (2018). A Comparative Study for Estimating Crop Evapotranspiration in the Sacramento-San Joaquin Delta - Appendix C. CalSIMETAW (California Simulation of Evapotranspiration of Applied Water). Davis, CA.

Orang, M. N., Snyder, R. L., Shu, G., Hart, Q. J., Sarreshteh, S., Falk, M., … Eching, S. (2013). California Simulation of Evapotranspiration of Applied Water and Agricultural Energy Use in California. Journal of Integrative Agriculture, 12(8), 1371–1388. https://doi.org/10.1016/S2095-3119(13)60742-X

Rayej, M., Snyder, R. L., Orang, M. N., Geng, S., & Sarreshteh, S. (2011). CalSIMETAW and WEAP Models for Water Demand Planning. ICID 21st International Congress on Irrigation and Drainag ICID Transactions No.30-A, 111–128.