Calculate annual high and low flows

Source: R/calc_annual_extremes.R

Calculates annual n-day minimum and maximum values, and the day of year and date of occurrence of daily flow values from a daily streamflow data set. Calculates statistics from all values, unless specified. Returns a tibble with statistics.

calc_annual_extremes(
  data,
  dates = Date,
  values = Value,
  groups = STATION_NUMBER,
  station_number,
  roll_days = 1,
  roll_days_min = NA,
  roll_days_max = NA,
  roll_align = "right",
  water_year_start = 1,
  start_year,
  end_year,
  exclude_years,
  months = 1:12,
  months_min = NA,
  months_max = NA,
  transpose = FALSE,
  complete_years = FALSE,
  ignore_missing = FALSE,
  allowed_missing = ifelse(ignore_missing, 100, 0)
)

Arguments

data

Data frame of daily data that contains columns of dates, flow values, and (optional) groups (e.g. station numbers). Leave blank or set to NULL if using station_number argument.

dates

Name of column in data that contains dates formatted YYYY-MM-DD. Only required if dates column name is not 'Date' (default). Leave blank or set to NULL if using station_number argument.

values

Name of column in data that contains numeric flow values, in units of cubic metres per second. Only required if values column name is not 'Value' (default). Leave blank if using station_number argument.

groups

Name of column in data that contains unique identifiers for different data sets, if applicable. Only required if groups column name is not 'STATION_NUMBER'. Function will automatically group by a column named 'STATION_NUMBER' if present. Remove the 'STATION_NUMBER' column beforehand to remove this grouping. Leave blank if using station_number argument.

station_number

Character string vector of seven digit Water Survey of Canada station numbers (e.g. "08NM116") of which to extract daily streamflow data from a HYDAT database. Requires tidyhydat package and a HYDAT database. Leave blank if using data argument.

roll_days

Numeric value of the number of days to apply a rolling mean. Default 1.

roll_days_min

Numeric value of the number of days to apply a rolling mean for low flows. Will override 'roll_days' argument for low flows. Default NA.

roll_days_max

Numeric value of the number of days to apply a rolling mean for high flows. Will override 'roll_days' argument for high flows. Default NA.

roll_align

Character string identifying the direction of the rolling mean from the specified date, either by the first ('left'), last ('right'), or middle ('center') day of the rolling n-day group of observations. Default 'right'.

water_year_start

Numeric value indicating the month (1 through 12) of the start of water year for analysis. Default 1.

start_year

Numeric value of the first year to consider for analysis. Leave blank or set well before start date (i.e. 1800) to use from the first year of the source data.

end_year

Numeric value of the last year to consider for analysis. Leave blank or set well after end date (i.e. 2100) to use up to the last year of the source data.

exclude_years

Numeric vector of years to exclude from analysis. Leave blank or set to NULL to include all years.

months

Numeric vector of months to include in analysis. For example, 3 for March, 6:8 for Jun-Aug or c(10:12,1) for first four months (Oct-Jan) when water_year_start = 10 (Oct). Default summarizes all months (1:12).

months_min

Numeric vector of specified months for window of low flows (3 for March, 6:8 for Jun-Aug). Will override 'months' argument for low flows. Default NA.

months_max

Numeric vector of specified months for window of high flows (3 for March, 6:8 for Jun-Aug). Will override 'months' argument for high flows. Default NA.

transpose

Logical value indicating whether to transpose rows and columns of results. Default FALSE.

complete_years

Logical values indicating whether to include only years with complete data in analysis. Default FALSE.

ignore_missing

Logical value indicating whether dates with missing values should be included in the calculation. If TRUE then a statistic will be calculated regardless of missing dates. If FALSE then only those statistics from time periods with no missing dates will be returned. Default FALSE.

allowed_missing

Numeric value between 0 and 100 indicating the percentage of missing dates allowed to be included to calculate a statistic (0 to 100 percent). If 'ignore_missing = FALSE' then it defaults to 0 (zero missing dates allowed), if 'ignore_missing = TRUE' then it defaults to 100 (any missing dates allowed); consistent with ignore_missing usage. Supersedes ignore_missing when used.

Value

A tibble data frame with the following columns:

Year

calendar or water year selected

Min_'n'_Day

annual minimum for selected n-day rolling mean, direction of mean specified by roll_align

Min_'n'_Day_DoY

day of year for selected annual minimum of n-day rolling mean

Min_'n'_Day_Date

date (YYYY-MM-DD) for selected annual minimum of n-day rolling mean

Max_'n'_Day

annual maximum for selected n-day rolling mean, direction of mean specified by roll_align

Max_'n'_Day_DoY

day of year for selected annual maximum of n-day rolling mean

Max_'n'_Day_Date

date (YYYY-MM-DD) for selected annual maximum of n-day rolling mean

Default columns:

Min_1_Day

annual 1-day mean minimum (roll_align = right)

Min_1_Day_DoY

day of year of annual 1-day mean minimum

Min_1_Day_Date

date (YYYY-MM-DD) of annual 1-day mean minimum

Max_1_Day

annual 1-day mean maximum (roll_align = right)

Max_1_Day_DoY

day of year of annual 1-day mean maximum

Max_1_Day_Date

date (YYYY-MM-DD) of annual 1-day mean maximum

Transposing data creates a column of 'Statistics' and subsequent columns for each year selected. 'Date' statistics not transposed.

Examples

# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())
if (file.exists(tidyhydat::hy_downloaded_db())) {

# Calculate annual 1-day (default) max/min flow data with 
# default alignment ('right')
calc_annual_extremes(station_number = "08NM116") 

# Calculate custom 3-day max/min flow data with 'center' alignment
calc_annual_extremes(station_number = "08NM116",
                     roll_days = 3,
                     roll_align = "center",
                     start_year = 1980)
                     
}
#> Warning: One or more calculations included missing values and NA's were produced. If desired, filter data for complete years or months, or use the 'ignore_missing' or 'allowed_missing' arguments (if applicable) to ignore or allow some missing values.
#> Warning: One or more calculations included missing values and NA's were produced. If desired, filter data for complete years or months, or use the 'ignore_missing' or 'allowed_missing' arguments (if applicable) to ignore or allow some missing values.
#> # A tibble: 41 × 8
#>    STATION_NUMBER  Year Min_3_Day Min_3_…¹ Min_3_Da…² Max_3…³ Max_3…⁴ Max_3_Da…⁵
#>    <chr>          <dbl>     <dbl>    <dbl> <date>       <dbl>   <dbl> <date>    
#>  1 08NM116         1980     0.632        9 1980-01-09    34.8     127 1980-05-06
#>  2 08NM116         1981     0.468      260 1981-09-17    54.6     142 1981-05-22
#>  3 08NM116         1982     0.883        6 1982-01-06    50.7     186 1982-07-05
#>  4 08NM116         1983     0.562      357 1983-12-23    57.7     149 1983-05-29
#>  5 08NM116         1984     0.742      365 1984-12-30    50.4     166 1984-06-14
#>  6 08NM116         1985     0.429      190 1985-07-09    49.2     144 1985-05-24
#>  7 08NM116         1986     0.663       50 1986-02-19    70.8     150 1986-05-30
#>  8 08NM116         1987     0.339      333 1987-11-29    31.9     122 1987-05-02
#>  9 08NM116         1988     0.150       32 1988-02-01    32.4     135 1988-05-14
#> 10 08NM116         1989     0.524      271 1989-09-28    34.2     153 1989-06-02
#> # … with 31 more rows, and abbreviated variable names ¹​Min_3_Day_DoY,
#> #   ²​Min_3_Day_Date, ³​Max_3_Day, ⁴​Max_3_Day_DoY, ⁵​Max_3_Day_Date