One of the head scratchers that climate change brings is that despite overall temperatures rising, some daily low temperatures in the winter are actually getting colder in California. That is especially true in drought years: clouds and precipitation (both rain and snow) actually keep the air warmer than it might be otherwise at night. Water falling from the sky can’t get much colder than 32 degrees. And the wind that normally accompanies storms stirs up the air, which also warms it.
Even if rain is not actually falling from the sky at a certain moment, air is warmer when it contains more water in the form of humidity. So after a good rainstorm or long wet period, it’s less likely to get very cold than if it’s been dry. Snowstorms are different, and not really relevant to the farm so I’ll skip that explanation.
Since New Years’, 2022 has been a great example of this phenomena in real time. The year started out incredibly damp with all the leftover moisture in the air and ground from the storms in October and December. It was foggy and chilly, but not freezing cold. But as we got further into the year without any more rain, the air and ground got drier and drier after weeks of warm, sunny days and wind. Yet the days were still very short and the cloudless nights got colder and colder. In late January, we had our first big freeze when temperatures went down to 28 degrees. Ever since, we’ve had frost most nights — unless it’s been windy. The air has continued to get drier and drier, making it easier for it to quickly cool down after sunset. Mornings have been 33-38 degrees.
On the other hand, the warm, sunny days have tricked most plants into thinking it’s spring. On our farm, peaches, nectarines, and apricots are in full bloom and some varieties have already pushed out their leaves. Strawberries are starting to flower. And all around us, thousands of acres of almonds are blooming as well. All of these are sensitive to freezing temperatures.
TFF Peach Trees in full bloom
Now, a cold air mass has moved in from Canada and there is a Freeze Warning in effect for Wednesday and Thursday nights. If the wind stops completely, temperatures look to plummet into the mid- to high-20s. That’s too cold, and will likely set records. A short duration of temperatures below 32 is manageable, but the longer it stays below freezing, the more likely there is to be extensive damage to blossoms, fruit or nuts, and even the trees themselves. Frozen blossoms dry up and fall off without pollinating. Tiny fruits that freeze fall off the trees. And young leaves and even green twigs turn black and die.
Most fruit and nut trees only flower once each year. If the bloom or the fruit is destroyed, there’s no second chance. For us at Terra Firma, that would mean no peaches, nectarines, or apricots in your boxes. Unthinkable! Strawberries are different. The freeze will ruin any green fruit out there and kill any flowers, but the plants will rally and continue making more.
There are several ways to protect crops from freezing temperatures. In orchards, wind machines can be used to stir up the air or sprinklers can be used to raise the humidity, but both those methods work best when the temperature is at or just below freezing. We have just finished a project to hang our microsprinklers up in the trees in our stone fruit orchard, which could help make them more effective at preventing damage to the crop. We’ll be turning the pump on during the night when temperatures fall below 35 degrees.
Luckily for us, we only have 8 acres of fruit trees. Our pump is big enough to irrigate that entire area. But if we had planted fruit trees on the entire 80 acres where the orchard is located, we would only be able to protect a fraction of the trees. That is the situation that most growers face this week. For them, purchasing crop insurance is the best option to protect themselves from a catastrophic loss.
At Terra Firma, we have never lost our entire summer crop of fruit to a freeze. That is partially because the trees normally wait longer before flowering — freezing weather this time of year is not unheard of. It’s also partially because we always irrigate the orchards on very cold nights. But the sprinklers do not save every fruit and flower, and we have lost a certain amount of fruit in past years. We could see a big loss this year.
Freezing weather this time of year is a big deal for farmers, and the National Weather Service knows it. They began mentioning this event late last week — enough time to give farmers plenty of time to prepare. If the forecast ends up wrong, no one will complain. It will be a huge relief. In the meantime, we’ll have a few sleepless nights checking the weather station and turning on pumps at 2 a.m. Then, we’ll have a period of uncertainty where we wait to see how much fruit remains on the trees.
People like to ask me “How cold is too cold?”. There’s no exact number that you can cite. Even within the tree canopy, temperatures can vary widely. But every time one of these cold events happens, the University of California collects data and tries to correlate it with reports of crop damage. As continue into the unknown territory that climate change brings to agriculture, these studies will become more and more important.