Chilling Accumulation Models:
Their Calculation, Explanation, & Comparison

Using Various Models

Calculations or Current and Historic Chilling Accumulation at California CIMIS Sites

Cumulative Chilling Hours:
Cumulative Chill Hours and
Modified Chill Hours
Hours below 45° F
Hours between 32 F and 45° F
November 1 through February 28/29

Cumulative Chilling Portions:
Dynamic Model
September 1 through August 31

Chilling Hour & Unit Accumulations:
Historic Accumulation of
Chill Hours, Modified Chill Hours,
& Chill Units (Utah Model)
Hours below 45° F
Hours between 32° F and 45° F
September 1 through August 31

Dynamic Model & Chill Portions Accumulation Guide

A how-to guide (pdf) by Kitren Glozer, Project Scientist, Dept. of Plant Sciences, for calculating chill portions, using weather data from a data logger in your orchard, and the Dynamic Model (Excel file). Both available for download.

Chilling Accumulation Models: Their Explanation and Comparison

Chill Hour, Chill Unit & Chill Portion: Model Comparisons
Fruit & Nut Crop Chill Portion Requirements: Chill Requirements in Chill Portions, calculated using the Dynamic Model. Because the Dynamic Model is still unfamiliar to many, to provide a frame of reference, a list of chilling requirements for many temperate tree crops has been compiled from the literature. (compiled by Katherine Jarvis-Shean, Dept. of Plant Sciences, UC Davis)

Chilling Accumulation Models: Their Calculation, Explanation, & Comparison

Chilling Accumulation Models:
Their Calculation, Explanation, & Comparison