In 2012, I worked on a groundwater sustainability study of Thompson Creek, in Poway, California. The field work involved interviewing the residents of the community of Old Coach Estates, to gather grass-root information on the issues at hand. The properties are typically somewhat large and many of them have sizable fruit groves.

On one of the visits, I interviewed a resident who had an avocado grove. He mentioned to me, in passing, that that year (2012) they have had a bumper crop. I inquired whether there had been a lot of rain that year.1 He said: "No, not this year, but last year we did." 2

I immediately realized that his observation made sense. Crop productivity depended not so much on the availability of water that year (2012) but on the leaching of the salts accumulated in the soil profile in the previous five years (2006-2010), where leaching of the salts had been limited due to lack of rainfall (see figure below).

1 The total amount of rain in the year 2012 (Oct. 2011 - Sept. 2012) was 10.88 in.
2 The total amount of rain in the year 2011 (Oct. 2010 - Sept. 2011) was 23.22 in.