Calculate cumulative monthly flow statistics for each month of the year of daily flow values from a daily streamflow data set. Calculates statistics from all values from complete years, unless specified. Defaults to volumetric cumulative flows, can use use_yield and basin_area to convert to area-based water yield. Returns a tibble with statistics.

calc_monthly_cumulative_stats(
data,
dates = Date,
values = Value,
groups = STATION_NUMBER,
station_number,
percentiles = c(5, 25, 75, 95),
use_yield = FALSE,
basin_area,
water_year_start = 1,
start_year,
end_year,
exclude_years,
transpose = FALSE
)

## Arguments

data Data frame of daily data that contains columns of dates, flow values, and (optional) groups (e.g. station numbers). Leave blank if using station_number argument. Name of column in data that contains dates formatted YYYY-MM-DD. Only required if dates column name is not 'Date' (default). Leave blank if using station_number argument. 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. 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. 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. Numeric vector of percentiles to calculate. Set to NA if none required. Default c(5,25,75,95). Logical value indicating whether to calculate area-based water yield, in mm, instead of volumetric discharge. Default FALSE. Upstream drainage basin area, in square kilometres, to apply to observations. Three options: (1) Leave blank if groups is STATION_NUMBER with HYDAT station numbers to extract basin areas from HYDAT. (2) A single numeric value to apply to all observations. (3) List each basin area for each group/station in groups (can override HYDAT value if listed) as such c("08NM116" = 795, "08NM242" = 10). If group is not listed the HYDAT area will be applied if it exists, otherwise it will be NA. Numeric value indicating the month (1 through 12) of the start of water year for analysis. Default 1. Numeric value of the first year to consider for analysis. Leave blank to use the first year of the source data. Numeric value of the last year to consider for analysis. Leave blank to use the last year of the source data. Numeric vector of years to exclude from analysis. Leave blank to include all years. Logical value indicating whether to transpose rows and columns of results. Default FALSE.

## Value

A tibble data frame with the following columns, default units in cubic metres, or millimetres if use_yield and basin_area provided:

Month

month (MMM-DD) of cumulative statistics

Mean

monthly mean of all cumulative flows for a given month of the year

Median

monthly mean of all cumulative flows for a given month of the year

Maximum

monthly mean of all cumulative flows for a given month of the year

Minimum

monthly mean of all cumulative flows for a given month of the year

P'n'

each monthly n-th percentile selected of all cumulative flows for a given month of the year

Default percentile columns:
P5

monthly 5th percentile of all cumulative flows for a given month of the year

P25

monthly 25th percentile of all cumulative flows for a given month of the year

P75

monthly 75th percentile of all cumulative flows for a given month of the year

P95

monthly 95th percentile of all cumulative flows for a given month of the year

Transposing data creates a column of "Statistics" and subsequent columns for each year selected.

## Examples

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

# Calculate annual monthly cumulative volume statistics
calc_monthly_cumulative_stats(station_number = "08NM116")

# Calculate annual monthly cumulative volume statistics with default HYDAT basin area
calc_monthly_cumulative_stats(station_number = "08NM116",
use_yield = TRUE)

# Calculate annual monthly cumulative volume statistics with custom basin area
calc_monthly_cumulative_stats(station_number = "08NM116",
use_yield = TRUE,
basin_area = 800)

}
#> Warning: One or more years contained partial data and were excluded. Only years with complete data were used for calculations.#> Warning: One or more years contained partial data and were excluded. Only years with complete data were used for calculations.#> Warning: One or more years contained partial data and were excluded. Only years with complete data were used for calculations.#> # A tibble: 12 x 10
#>    STATION_NUMBER Month   Mean Median Maximum Minimum     P5    P25    P75
#>    <chr>          <fct>  <dbl>  <dbl>   <dbl>   <dbl>  <dbl>  <dbl>  <dbl>
#>  1 08NM116        Jan     3.65   2.99    20.5    1.06   1.53   2.44   4.26
#>  2 08NM116        Feb     7.03   5.95    30.7    2.16   3.25   4.53   7.65
#>  3 08NM116        Mar    12.8   10.8     47.8    3.86   6.09   8.15  14.7
#>  4 08NM116        Apr    37.3   33.9     92.6    9.86  13.2   22.5   45.3
#>  5 08NM116        May   120.   112.     208.    52.3   65.8   94.4  139.
#>  6 08NM116        Jun   193.   198.     319.    95.3  102.   150.   231.
#>  7 08NM116        Jul   213.   222.     377.   102.   111.   159.   254.
#>  8 08NM116        Aug   220.   226.     390.   104.   114.   162.   269.
#>  9 08NM116        Sep   227.   232.     405.   106.   118.   165.   280.
#> 10 08NM116        Oct   234.   240.     422.   108.   122.   170.   287.
#> 11 08NM116        Nov   241.   243.     433.   110.   127.   176.   292.
#> 12 08NM116        Dec   245.   246.     439.   112.   130.   181.   296.
#> # ... with 1 more variable: P95 <dbl>