Assuming you have adequate minerals etc. ... here is some events that seem to influence sweetness.
Drought: How the Heat Intensifies Fruit and Vegetable Flavors | TIME ...
http://healthland.time.com/2012/07/27/are-your-fruits-and-veggies-bursting-with-flavor-thank-the-drought/Here is a drought reported in 2012 that was interesting as it received large attention for the sweetness of their various crops. They were guessing various factors including: 1. plant stress “When melons are under stress, there can be an increase in sugars and an accumulation of sucrose,” (for them stress was primarily reduction in water & increase heat) 2, Hotter temperatures (increase stress but probably internal ripening also facilitated)3. Increased sun exposure more photosynthesis vs. cloudy & rainy days.
For them in 2012:::“but the heat in the early part of the season has made the fruit special.”
Google search pulled up::: How to Sweeten Citrus Fruit 1.AVOID
growing citrus fruit in an area with COOL summers. (other factors normal growing advice & tree selection)
Expanding search lead to a study::: The optimum temperature range for photosynthesis
is 35-40ºC in sweet orange leaf discs... ABSTRACT:::
http://www.scielo.br/pdf/cagro/v30n4/v30n4a12(35C = 95F) They considered 35C optimum as plant damage to leaf discs above 35C
Thus my bet is that warmer temperatures & sunlight might be more important in increasing sweetness than water (rain) decreasing it... But with rain comes lower temperatures & less sunlight... so definitely related to each other and hard to tell the chicken vs. egg coming first........ Also, I do not seem to notice the lack of sweetness with the rains in July & August & I speculate it to be due to the higher temperatures later in year vs. now...
https://www.maximumyield.com/the-science-of-sweet-how-fruit-ripens/2/1300 = standard description of ethylene gas minerals etc.
Topic: High rainfall == Low brix? (Read 3857 times)