The timing of the first real “heatwave” of 2017 here this week on the farm coincided with another “first” for the year. We started irrigating crops a few in late April, but it wasn’t until Monday that we started watering the orchards: peaches, apricots, pistachios, etc.
You’d think that with the drought over, farmers would be using a lot more water, right? Until just a few days ago, the soil down 4 or 5 inches was still quite wet. And a foot, two, three feet down where most trees have their roots, it was still saturated. Watering trees when the soil profile is already full of moisture is dangerous: you can easily drown the roots and/or encourage root-destroying pathogens that like saturated soil.
As long as the trees and roots are dormant, they don’t need oxygen so flooding isn’t as much of a problem in the winter, although they can and do tip over if the soil turns to liquid and storm winds are strong.
Once the trees “wake up”, though, heavy rains can kill them. Throughout Yolo and Solano counties, thousands of almond trees died in February this year when they came out of dormancy and began to bloom while the orchards were still flooded.
May 22nd is not the latest date that we have ever started irrigating our orchards. That record goes all the way back to 1997, when the orchards stayed wet well into June. That year the rain did not stop in April but continued through May.
During the drought, orchard farmers took a lot of flack for using too much water. And it’s true that many farmers had to irrigate their trees during the winter in 2014 and 2015 — especially small, younger trees without developed root systems. But in a year like this one, trees make better use of the accumulated moisture in the soil than row crops, which can only access water a a foot or two down (at most). Many of the vegetables we grow have shallow roots and need water every week if it’s not raining, even in the winter.
Now we ahve the flip side of what happened during the drought. Back then, it was a negative feedback loop: the lack of rain increased the demand for water, which drew down both ground and surface water year over year. Even with voluntary and mandatory cutbacks, there wasn’t enough water to meet the state’s needs.
Now, we have a positive feedback loop: demand for water is down thanks to the wet winter. Aquifers and reservoirs have filled dramatically and there is still an enormous snowpack that will continue to melt as we go into summer. And farmers are using less water because the soil is still quite damp. It’s entirely possible that California will go into the fall with reservoirs still at historically high levels.
Maybe you’re thinking “That’s a great thing”. But that’s not what water managers are thinking. Their mandate is flood protection first, water storage second. And they are legally obligated to reduce levels in the state’s reservoirs to “safe” levels before next winter. That may be difficult to achieve this year.
No one knows what the weather next winter will bring. But with the reservoirs and soils so full, even a “normal” precipitation year could bring floods. An above average year would be almost certain to do so, and another record year could be disastrous.
During droughts, agriculture uses valuable water to produce valuable product. But when there is too much water, farmers also play a vital role in “disposing” of it in a safe and productive manner. Global warming may cause more extreme weather, and it will be important to keep farmers in business during the droughts so that they will be still be in business when the floods come.