DETAW (Delta Evapotranspiration of Applied Water)

General Description	A tool for estimating evapotranspiration of applied water (ETaw), which is a seasonal estimate of the water requirement for evapotranspiration of a crop minus any water supplied by effective rainfall. ETaw information is needed to determine the demand side of water requirements. The model accounts for ET losses and water contributions from rainfall, seepage, irrigation, and using datasets with a daily time step. Model website at: https://water.ca.gov/Library/Modeling-and-Analysis/Bay-Delta-models-and-tools/DETAW
Model Domain	Consumptive use and net channel depletion in the Delta
Developer	California Department of Water Resources
Hardware computing requirements	1. Windows system 2. Python (Anaconda) 3. HEC-DSSVue (for viewing .dss output files)
Code language	V1.0 C++ (no longer available) V2.0 (beta) python
Original application	Developed by DWR to replace the Delta Island Consumptive Use Model (DICU) and reconcile two water simulation models used by DWR (namely Calsim II and DSM2)
Public/proprietary and cost	Public, available for download. General Public License.
Physically or empirically based	Empirical
Mathematical methods used	Hargreaves Samani (HS) equation, the reference evapotranspiration (ETo) at the CIMIS Lodi station was calculated; and by using the Penman-Monteith (PM) equation from nine CIMIS stations, including Lodi, isolines of correction factors to estimate Delta subareas ETo from the Lodi HS ETo were developed. Crop coefficients developed using SEBAL-based approach.
Input data requirements	All input are already formatted csv files. Easily updated with public data described in the user manual. Land Use: historical survey/derived estimates (1922-2008), USDA NASS (2009) and LandIQ (2015). Needs to have the same land cover classes. Precipitation: UC IPM database (CIMIS/NCDC) Air temp: UC IPM (Lodi required to develop isolines)
Outputs	HEC .dss (Data Storage Systems) – 1 daily, 1 monthly 168 subareas in 15 land use categories
Pre-processing and post-processing tools	Several input calaculated using ArcGIS, but they can be used as-is in the model. HEC-DSSVue program required to view output files.
Representation of uncertainty	ET results calibrated against other successful empirical ET models (SEBAL) (<3% difference)
Prevalence	Internal to DWR but used for academic comparison and as a component of other models
Ease of use for public entities	Package downloadable on the internet, all software required is open access.
Ease of obtaining information and availability of technical support	User manual for V1.0 and V2.0 available with software download containing instruction for installation and model inputs/outputs. Email contact for DETAW available online.
Source code availability	Available and freely modifiable under the General Public License
Status of model development	Beta version 2.0 released June 2018. V 2.0 updates: updated seepage assumptions; calibrated crop coefficients based on satellite image-based estimates of consumptive use; estimated actual net channel depletion by estimating island diversions, seepages, and drainages; and assigned island diversions, seepages, and returns to model nodes
Challenges for integration	Spatially explicit model requires model of nodes and spatial impacts of channels within each subarea (Liang & Suits 2017 pg. 3-11). Outputs for predetermined subareas (Liang & Suits 2017, fig. 3-2).

References

Kadir, T., & Liang, L. (2018). A Comparative Study for Estimating Crop Evapotranspiration in the Sacramento-San Joaquin Delta - Appendix D. Delta Evapotranspiration of Applied Water (DETAW). Davis, CA.

Liang, L., & Suits, B. (2017). Implementing DETAW in Modeling Hydrodynamics and Water Quality in the Sacramento-San Joaquin Delta. In Methodology for Flow and Salinity Estimates in the Sacramento-San Joaquin Delta and Suisun Marsh: 38th Annual Progress Report (p. 26). Department of Water Resources.

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

Figure source: Liang & Suits (2017)

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