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OBTA-CA | Orchard Bloom Time Analytics — California

Or Sperling (ARO-Volcani)  ·  Maciej Zwieniecki (UC Davis)

OBTA-CA — Welcome

Orchard Bloom Time Analytics — California

⚠ Research Tool — Use at Your Own Risk

OBTA-CA is a collaborative research project in active development at UC Davis and ARO-Volcani. It provides bloom timing estimates based on the Carbohydrate-Temperature (C–T) model, chill accumulation models, and satellite-derived temperature data. Results are not certified bloom predictions and may differ from conditions in your specific orchard.

By using this tool you accept full responsibility for any management decisions made. For questions, or to participate in the research project, contact:

In California: Prof. Maciej Zwieniecki · UC Davis Plant Sciences · mzwienie@ucdavis.edu
In Israel: Prof. Or Sperling · ARO-Volcani · orsp@volcani.agri.gov.il

How to use OBTA-CA

  1. Find and click your orchard on the map. A marker will appear at that location. October sugar and starch values will be auto-filled from the Carbohydrate Observatory database based on your latitude and species.
  2. Select your species (almond, walnut, or pistachio). Changing species will update the NSC defaults for your location.
  3. Review or override NSC values. If you have October measurements from your own orchard, enter them to replace the Carb Observatory averages.
  4. Click “Get Bloom Forecast.” The tool downloads daily temperature data from Google Earth Engine (GRIDMET) for the current season and 3 prior seasons, detects winter onset, and runs the C–T model.
  5. Read the main chart. The blue line shows your orchard’s soluble sugar trajectory through winter. Colored bands at the bottom mark bloom windows — bloom is predicted when the line drops into the colored zone. Past seasons are shown in gray for comparison.
  6. Check the chill charts. Three small charts below show cumulative chill accumulation using Chill Hours, Utah, and Dynamic models — all starting from Nov 1.
  7. Temperature chart. Daily Tmin/Tmax for the current season is shown at the bottom.

About the C–T Model

The Carbohydrate-Temperature model tracks starch↔sugar interconversion driven by temperature-dependent enzyme kinetics. During cold winter nights, starch degrades into soluble sugars, building up reserves. When spring warmth arrives, sugar is converted back to starch, causing a sharp drop. Bloom is triggered when this drop pushes soluble sugars below a critical threshold (~60 mg/g).

References:
Sperling et al. (2019) Agric. For. Meteorol. 276–277:107643
Sperling & Zwieniecki (2021) Tree Physiology

Data: Google Earth Engine · GRIDMET (temperature) · Carbohydrate Observatory (NSC) · C–T model (Sperling et al. 2019, 2021) · Chill models: Chill Hours, Utah (Richardson 1974), Dynamic (Erez 1990)