Update 2012: Modeling Orchard ET

Regional Estimates of Crop Evapotranspiration ETc with the Coupled WRF-ACASA Modeling System for Almonds

The goals of this project within the SCRI framework include:

• 

  Fig. 1. ACASA
  to incorporate detailed canopy structure and leaf area (LAI) in the land surface scheme (ACASA) of a 3-D research model (WRF)
• to provide accurate crop evapotranspiration (ETc) estimates over irrigated orchards on relevant scales for growers and policy makers
• to produce spatial maps of actual ETc
• to demonstrate the capability to run reanalysis and forecasts

The regional scale model system used for this study is the community WRF model coupled with the UC Davis ACASA multi-layer surface model. ACASA includes 10 layers within the canopy, 10 layers above, and 4 soil layers (Fig. 2). WRF-ACASA provides regional scale estimates of ETc, temperature, humidity, wind speed, and other micrometeorological parameters at a horizontal grid scale of approximately 0.5 to 1 km around the experimental orchard sites. Sample outputs for Etc and sensible heat flux (H) are shown in Fig. 3.

The ALBEDO map shows how ACASA modifies the albedo to account for presence of vegetation and leaf area amount. The total ALBEDO shown here is the aggregate total of all canopy and ground surface values, which includes soil, stem and, if present in the domain, snowpack influences both within and beneath the canopy. ACASA uses a 2-stream approximation that includes reflection and transmission of beam and diffuse visible and near infrared radiation.

For more information see the presentations and publications under Outreach