Weather and tart cherry yields in Michigan
At the beginning of the Pileus Project, researchers sat down with farmers who have been part of the industry since the early 1940s. As the farmers recalled years of both exceptionally high and low yield, they discussed how weather events might influence crop yield. "What was the cause of the low yield in 1991?” or “what were the weather conditions of 1995, which was a really good year?” Roll over the yellow circles in “Weather and Tart Cherry Yields in Michigan (1944-2004)” graph in the tools to view some of the growers’ comments related to yield for that year.
Tart cherry growers clearly stated that the most important, climate-related factor impacting tart cherry production has been freeze events in the spring. Early spring freeze events, preceded by warm temperatures that bring over-wintering crops out of dormancy was identified as the number one issue (See Agriculture User Case 1 for an example of the spring freeze event for 2002).
Developing a model
A credible model should be able to reproduce when and if these yield events occurred, and at least some of the associated weather events. The researchers began developing the phenological or growth and development model. Using phenological growth curves, observed minimum temperatures and cold injury observations, Pileus researchers developed a set of regressions to estimate winter injury in terms of surviving viable buds. Based on this research, the frequency and magnitude of spring freeze events appear to have not changed significantly over time, but the period of vulnerability is longer compared to 10 or 20 years ago due to warmer temperatures earlier in the spring season.
Model simulation conditions
Results from the model showed that three major weather/climate-related factors associated with year to year yield variability were identified during the research process: 1) bud cold damage, 2) pollination conditions, and 3) total precipitation during the end of the previous growing season.
Generally, in terms of yield*:
- The greater the bud damage due to cold injury » the lesser the yield
- The warmer and drier the pollination period » the greater the yield
- The greater the precipitation total at the end of the previous growing season » the greater the yield.
Click on a year of the x- axis in the graph and see the "Critical drivers for tart cherry yield" simulation conditions below.
*Note that these associations may not always hold true due to other factors not considered in yield estimation (e.g. wind whip, poor fruit quality)