Author: Koen Hufkens
Date: 2024-05-23

# snotelr functionality

#### Koen Hufkens

#### 2024-05-23

## Introduction

The SNOTEL network is composed of over 800 automated data collection sites located in remote, high-elevation mountain watersheds in the western U.S. They are used to monitor snowpack, precipitation, temperature, and other climatic conditions. The data collected at SNOTEL sites are transmitted to a central database. This package queries this centralized database to provide easy access to these data and additional seasonal metrics of snow accumulation (snow phenology).

## Downloading site meta-data

The SNOTEL network consists of a vast number of observation sites, all of them listed together with their meta-data on the SNOTEL website. The `snotel_info()` function allows you to query this table and import it as a neat table into `R`. Some of the meta-data, in particular the site id (`site_id`), you will need of you want to download the data for a site. You can save this table to disk using the `path` variable to specify a location on your computer where to store the data as a csv. If this parameter is missing the data is returned as an `R` variable.

    # download and list site information
    site_meta_data <- snotel_info()
    head(site_meta_data)

## Downloading site data

If you downloaded the meta-data for all sites you can make a selection using either geographic coordinates, or `state` columns. For the sake of brevity I’ll only query data for one site using its `site_id` below. By default the data, reported in imperial values, are converted to metric measurements.

    # downloading data for a random site
    snow_data <- snotel_download(
      site_id = 670,
      internal = TRUE
      )

    # show the data
    head(snow_data)

    # A plot of snow accummulation through the years
    plot(as.Date(snow_data$date),
         snow_data$snow_water_equivalent,
         type = "l",
         xlab = "Date",
         ylab = "SWE (mm)"
        )

## Calculating snow phenology from downloaded data or data frames

Although the main function of the package is to provide easy access to the SNOTEL data a function `snotel_phenology()` is provided to calculate seasonal metrics of snow deposition.

    # calculate snow phenology
    phenology <- snotel_phenology(snow_data)

    # subset data to the first decade of the century
    snow_data_subset <- subset(snow_data, as.Date(date) > as.Date("2000-01-01") &
                                 as.Date(date) < as.Date("2010-01-01"))

    # plot the snow water equivalent time series
    plot(as.Date(snow_data_subset$date),
         snow_data_subset$snow_water_equivalent,
         type = "l",
         xlab = "Date",
         ylab = "SWE (mm)"
      )

    # plot the dates of first snow accumulation as a red dot
    points(phenology$first_snow_acc,
           rep(1,nrow(phenology)),
           col = "red",
           pch = 19,
           cex = 0.5
          )

A list of all provided snow phenology statistics is provided below.

Value | Description
--- | ---
year | The year in which the an event happened
first_snow_melt | day of first full snow melt (in DOY)
cont_snow_acc | start of continuous snow accumulation / retention (in DOY)
last_snow_melt | day on which all snow melts for the remaining year (in DOY)
first_snow_acc | day on which the first snow accumulates (in DOY)
max_swe | maximum snow water equivalent value during a given year (in mm)
max_swe_doy | day on which the maximum snow water equivalent value is reached (in DOY)

## Reference

Please use the proper Zenodo DOI when using this software for research purposes.