> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/introduction-1/climate/weather-wgn.cli/pcp_sd.md).

# pcp\_sd

This parameter quantifies the variability in precipitation for each month. The standard deviation is calculated as

$$
σ\_{mon}=\sqrt{(\frac{∑*{d=1}^N\*(R*{day,mon}-R\_{mon} )^2 }{N-1}})
$$

where $$σ\_{mon}$$ is the standard deviation for daily precipitation in month $$mon$$ (mm H2O), $$R\_{day,mon}$$ is the amount of precipitation for day $$d$$ in month $$mon$$ (mm H2O), $$R\_{mon}$$ is the average precipitation for the month (mm H2O), and $$N$$ is the total number of daily precipitation records for month $$mon$$. Daily precipitation values of 0 mm are included in the standard deviation calculation.