data-raw/wy-index.R

In FlowWest/CDECRetrieve: Retrieve Data from the California Data Exchange Center

# Year Type Classification:     Index based on flow in million acre-feet:
#   Wet                      Equal to or greater than 9.2
# Above Normal             Greater than 7.8, and less than 9.2
# Below Normal             Greater than 6.5, and equal to or less than 7.8
# Dry                      Greater than 5.4, and equal to or less than 6.5
# Critical                 Equal to or less than 5.4

cdec_sac_wy_table <- function() {
      wy_index_url <- cdec_urls$wy_index

      html_page <- xml2::read_html(wy_index_url)
      html_pre_section <- rvest::html_text(rvest::html_nodes(html_page, css = "pre"))

      raw <- unlist(strsplit(html_pre_section, "\n"))

      start_of_index_table <-
        which(stringr::str_detect(raw, "SACRAMENTO VALLEY WATER YEAR TYPE INDEX  40-30-30   \\(SVI\\)"))

      raw_table <- raw[start_of_index_table:(start_of_index_table + 8)]


      this_sep <- "       "

      cdec_table <- strsplit(raw_table[5:9], split = this_sep) %>%
        purrr::map_df(function(line) {
          line <- trimws(line)
          tibble::tibble(
            date_string = line[1],
            `99` = line[2],
            `90` = line[3],
            `75` = line[4],
            `50` = line[5],
            `25` = line[6],
            `10` = line[7]
          )
        }) %>%
        tidyr::gather(probability, index, `99`:`10`) %>%
        transmute(
          date = lubridate::mdy(date_string),
          probability = as.numeric(probability),
          index = as.numeric(index))

      cdec_table %>%
        mutate(classification = case_when(
          index >= 9.2 ~ "wet",
          index > 7.8 ~ "above normal",
          index > 6.5 ~ "below normal",
          index > 5.4 ~ "dry",
          index <= 5.4 ~ "critical",
          TRUE ~ as.character(NA)
        ))


}


current_wy_index <- cdec_sac_wy_table()

readr::write_rds(current_wy_index, "~/Projects/sho-wr/misc/data/2018-04-17-water-year-index.rds")
readr::write_rds(CDECRetrieve::sac_valley_wy_types, "~/Projects/sho-wr/misc/data/historical-water-year-index.rds")



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