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by eric (980 points)
While it seems sensible that costal bacteria counts would be connected to rainfall does when the rain falls matter? Maybe rain early in the rainy season matters more, because it’s the first to flush pollutants into the oceans.

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by eric_busboom (1.7k points)
selected by eric
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There does appear to be a seasonal pattern to the bacteria count, and it’s basically the pattern of rainfall. Here is the last 10 years of averaged rainfall, using the sandiegodata.org-beachwatch-4 dataset

And here is the plot of above-median bacteria counts, at all stations. The Y axis is the ratio of the number of readings, per month that had a result larger than the median for the station group to the number of measurements for the month, where the measurement is for Enterococcus.

These images are from a Jupyter Notebook exploring the seasonality of bacteria counts, which is part of the Data Library’s water quality project.
It does look like counts in November are higher than you’d expect, given the small amount of rain, so it is plausible that it results in more than expected bacteria because it’s early in the season.

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