The Newsom administration’s strategy for dealing with flood flows relies heavily on diversions to farmland for groundwater recharge. But flooding in the Tulare basin this year is showing how orchards are not resilient to floods. And orchards have also not been resilient to recent droughts.
— Tom Frantz (@airqualityguy) May 9, 2023
As farm advisor David Doll explains (Doll 2023):
The sensitivity of almond roots to saturation is dependent on the timing and duration of the flood event. During dormancy, trees are reasonably tolerant due to lower soil temperatures and low rates of respiration. Flood events that are shorter than 7 days will not have any affect on tree performance. Extending beyond this, however, some root loss will occur, and poor spring tree growth may occur. With extended periods – beyond 10 days – tree loss may occur.
After the trees have leafed out, the period of tolerance is much shorter. Standing water within an orchard for 5 days will kill mature trees.
David Doll also notes,
Post flooding, there are also problems… Phytophthora, a water borne disease, can affect roots that have been saturated as these roots are weaker. Additionally, if the orchard is under water, Phytophthora can affect the aerial parts of the tree, often leading to a quick death once temperatures increase.
UC Extension advisors have confirmed an outbreak of Phytophthora syringae in orchards this year. (Dooley 2023).
A large number of orchards in the San Joaquin Valley also had to be taken out during the recent drought. As one observer noted:
In more average years researchers have shown that you can recharge aquifers during peak flows and reduce irrigation during mild droughts — without permanently damaging trees and vines. But outside that managed Goldilocks zone there may be friction. pic.twitter.com/s8TbRoCzr6
— felinecannonball (@feline_cannon) March 23, 2023
(O’Geen et. al. 2015) also found that the majority of land in the Central Valley was classified as “Moderately Poor, Poor or Very Poor” in suitability for groundwater recharge, mostly because of limitations in deep percolation.
This year has shown that California desperately needs a realistic, scalable strategy to deal with flooding. Voluntary diversions of flood flows to orchards will help growers but seem very unlikely to work as a primary strategy.
This post was updated on May 15 to add more references on plant pathology.
Doll, D 2023 Jan 15. Flooding and Almond Tree Survival.The Almond Doctor. [Accessed 2023 May 15] .
Dooley, E 2023 May 15. Winter Atmospheric Rivers Gave Pathogens, Diseases Path to Infect Crops:Outbreaks Similar to El Niño-Influenced Issues of the 1990s. UC Davis. [Accessed 2023 May 15].
Gebremichael M, Krishnamurthy PK, Ghebremichael LT, Alam S. 2021. What Drives Crop Land Use Change during Multi-Year Droughts in California’s Central Valley? Prices or Concern for Water? Remote Sensing. 2021; 13(4):650.
Newsom, G., Office of. 2023 Mar 10. Governor Newsom Issues Executive Order to Use Floodwater to Recharge and Store Groundwater. [Accessed 2023 May 15].
O’Geen A, Saal M, Dahlke H, Doll D, Elkins R, Fulton A, Fogg G, Harter T, Hopmans J, Ingels C, Niederholzer F, Sandoval Solis S, Verdegaal P, Walkinshaw M. 2015. Soil suitability index identifies potential areas for groundwater banking on agricultural lands. Calif Agr 69(2):75-84.