Key climate data added to enhance grower decision-support tool

With advance notice from CalAgroClimate, farmers may be able to use heaters, wind machines, irrigation and other tactics to lessen some of the impacts of cold weather, such as damaging almond blooms. Photo by Will Suckow

Free CalAgroClimate tool helps growers protect crops from frost and extreme heat

California farmers can see how climatic conditions that may affect agriculture are changing in their regions by using CalAgroClimate so they can make strategic changes. Nine new agriculturally important climate indicatorshave been added to the decision-support tool created by UC Cooperative Extension and U.S. Department of Agriculture scientists.

These new tools use a high-resolution climate dataset called PRISM to provide location-specific or county-aggregated long-term trends in agroclimatic indicators from 1980 to last year. These new agroclimate indicators include Frost Days, Last Spring Freeze, First Fall Freeze, Freeze-Free Season, Tropical Nights, Hot Days, Extreme Heat Days, Heatwaves and Diurnal Temperature Range (see definitions below). These indicators were derived from a study published in the journal Agronomy.

All of the new tools are free and available on CalAgroClimate for anyone to access.

Growers may be able to protect grapes from extreme heat. Photo by George Zhuang

“Frost-related tools such as Frost Days, Last Spring Freeze, First Fall Freeze, and Freeze-Free Season can help farmers and agricultural clientele make informed long-term choices,” said Tapan B. Pathak, UC Cooperative Extension specialist in climate adaptation in agriculture based at UC Merced, who is leading the CalAgroClimate project.

“For instance, if you are planning to invest in a frost sensitive crop in your region, these indicators can provide valuable information on whether frost risk has changed over time and whether it is less risky to make such an investment,” he said. “Wine grapes, for instance, are very sensitive to frost. Although not all frost events are damaging, understanding long-term trends in frost can help in making long-term strategic decisions such as whether to invest in frost protections.”

Another set of new agroclimatic indicators, on CalAgroClimate – Tropical Nights, Hot Days, Extreme Heat Days, Heatwaves and Diurnal Temperature Range – are based on higher maximum and minimum temperatures. Tropical Nights, for instance, calculates total number of nights when overnight temperatures exceed 68 F. More frequent tropical nights can increase crop respiration rates and can be detrimental for fruit quality and quantity, increase the risk of damage from pathogens, and potentially impact fruit set and yield.

Knowing how trends are evolving over time can assist growers in managing their crops to reduce risks. Similarly, growers can easily look at trends related to heat – hot days, extreme heat and heatwaves – on CalAgroClimate to assess their options on what they need to do to be adaptive. In the short term, growers may put up shade or for longer term, choose varieties that are more heat-tolerant.

Pistachios need a certain number of chill hours, but heat units for bloom.

“In recently published work, one of the farmers in the Central Valley told us, ‘When you really see so much difference in a short amount of time in your immediate area…we would have to look at that and say, well, we're going to have to adapt varieties because this is a 20- or 25-year planting and we're going to have to find crops or varieties that will adapt to that,'” Pathak said.

Another farmer told us, “Knowing what's going to happen or at least having a good idea, if you know something's going to be become or won't be viable, then obviously you're going to try to phase that out, and phase in something that's better suited.”

Pathak added, “The new agroclimatic indicators on CalAgroClimate provide a reality check on how conditions are changing in short and long-term, what it means for farmers and to assist them on deciding what they need to do to be adaptive. These tools will greatly benefit farmers and agricultural clientele in assessing risks and making informed decisions.”

Other collaborators include StevenOstoja and Lauren Parker of theUSDA California Climate Hub,PrakashKumarJha of UC Agriculture and Natural Resources and Robert Johnson and ShaneFeirer of UC Agriculture and Natural Resources' Informatics and Geographic Information Systems.

If citrus growers anticipate frost, they may irrigate because moist soil retains heat better than dry soil.

Definitions of AgroClimatic Indicators:

Frost Days are days in a year with minimum temperature below or equal to 32F.

Last Spring Freeze is the latest day in spring when minimum temperature is below or equal to 32F.

First Fall Freeze is the earliest day in fall when minimum temperature falls to 32F or below.

Freeze-Free Season is the time between the last spring and first fall freeze, represented by the number of consecutive days in a year without freezing temperatures.

Tropical Nights are number of nights when temperatures exceed 68F.

Hot Days are the days per year with maximum temperature exceeding 100 °F.

Extreme Heat Days are the number of days per year with maximum temperatures warmer than the 98^th percentile of historical summer maximum temperature for the selected location.

Heatwaves are events that occur when extreme heat lasts for at least three consecutive days.

Diurnal Temperature Range is the difference between daily maximum and minimum temperatures.

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