THE DRAMATIC IMPACT OF WEATHER DURING BLOOM

Updated: Jan 22

For the sixth consecutive year, California almond growers are on track to produce a record crop this season. USDA’s mid-season report projected almond production to out-perform last year’s record crop, both in terms of total production and yield per acre.

Almond production 2014-2020

There are a wide variety of factors that contribute to producing a record crop, most of which have to do with growers being good at what they do. But today, I want to look at a factor that growers can't control: weather during pollination.


The formula for optimal pollination is simple: good bees + good weather = good pollination. To quantify weather, a metric called Bee flight hours is used to measure the duration of ideal bee activity conditions during pollination.

It's logical to expect a positive correlation between Bee flight hours and yield. But as it turns out, that's not always the case. In 2019, weather during pollination season was abysmal. Pollination expert Joe Traynor called it “the worst season, weather-wise, for bee activity during almond bloom in the past 50 years.”

This season was the complete opposite—the weather was outstanding. Since pollination is critical for almond production, it's safe to assume that 2020 yield drastically outperformed 2019. But that’s not what happened.


Bee flight hours 2019 v. 2020

Let’s look at the numbers. I made some generalizations since I didn’t have time to make this perfect:

  • Weather data drawn from Fresno (courtesy of wunderground.com)

  • Pollination season defined as February 7th - 28th

  • Bee flight hours = >55 degrees, <10mph wind, 0 rain, 7AM-5PM

  • Prime flight days (made up metric) are days with 7 or more Bee flight hours

These results are remarkable. I was there during pollination in both years. I remember the weather being bad in 2019, but I didn't think it was quite this bad. Here are a few things that stand out to me:

  • Bees only had FOUR hours of flight time going into the final week of February last season.

  • 14 of the first 16 days had ZERO Bee flight hours last season.

  • The worst day in 2020 (3 BFH on 2/9) was better than 77% of Bee flight days in 2019.

  • Growers spent a lot of money for 40 hours of work in 2019!

  • Incredibly, bees somehow got the job done in 2019.

Now that we've seen the weather, let's take a look at the nuts.


Nut set 2019 v. 2020

Since this year’s harvest is still in progress, we can’t compare final yield numbers just yet. Instead, we'll use Nuts per Tree, a metric collected mid-way through each season as part of the USDA Objective Measurement Report. Nuts per Tree (or Nut set) isn’t the best indicator of pollination effectiveness, but it’s good enough for our purposes.

Almond nuts per tree 2016-2020

I see a couple interesting things going on here. First, 2019 was clearly a rough year across the board. It appears that low Bee flight hours had a significant impact on Nuts per Tree in 2019, yet this impact didn't seem to affect yield.

What stands out most to me is the variation between regions in 2020. Orchards in Northern and Central regions absolutely crushed it this year. Both regions produced higher Nut set this season than any region in the past 5 years, and it's not even close. But state-wide, Nuts per tree this year was the 2nd lowest in the past 5 years.


It appears that pollination season weather has very little impact on nut production in the South valley. Even with historically bad weather, the South valley gets enough bee flight hours due to its warmer climate. But in regions where Bee flight hours come at a premium, Nut set benefits tremendously from good weather.


These results also show that Nuts per Tree isn't a good predictor of yield. A tree with low Nut set can dedicate more resources to each nut, leading to larger, heavier nuts, as was the case in 2019.

Final thoughts

Initially, my goal with this post was to illustrate why bees deserve a pat on the back for this season’s record crop. But the data led me to a few conclusions I wasn’t expecting.

First and foremost, the bees do deserve a pat on the back. Not because of this season, but for their improbable performance in 2019. To deliver adequate pollination resulting in a record crop in a year with historically dreadful weather, is a testament to how important it is for growers to rent 2 or more strong hives per acre. With this year's weather, you probably would've done just fine with 1 hive per acre. But that wouldn't have been enough in 2019.

The other takeaway that took me by surprise was how this year’s weather impacted regions that traditionally get fewer Bee flight hours. This result makes me wish I had run the numbers on Bee flight hours in the North. Perhaps that’ll be a project for another day.

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