Calculates prewhitened nonlinear trends on annual streamflow data. Uses the zyp package to calculate trends. Review zyp for more information Calculates statistics from all values, unless specified. Returns a list of tibbles and plots. All annual statistics calculated using the calc_all_annual_stats() function which uses the following fasstr functions:

compute_annual_trends(
  data,
  dates = Date,
  values = Value,
  groups = STATION_NUMBER,
  station_number,
  zyp_method,
  basin_area,
  water_year_start = 1,
  start_year,
  end_year,
  exclude_years,
  annual_percentiles = c(10, 90),
  monthly_percentiles = c(10, 20),
  stats_days = 1,
  stats_align = "right",
  lowflow_days = c(1, 3, 7, 30),
  lowflow_align = "right",
  timing_percent = c(25, 33, 50, 75),
  normal_percentiles = c(25, 75),
  ignore_missing = FALSE,
  include_plots = TRUE,
  zyp_alpha
)

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.

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 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.

zyp_method

Character string identifying the prewhitened trend method to use from zyp, either 'zhang' or 'yuepilon'. Required.

basin_area

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.

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 to use the first year of the source data.

end_year

Numeric value of the last year to consider for analysis. Leave blank to use the last year of the source data.

exclude_years

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

annual_percentiles

Numeric vector of percentiles to calculate annually. Set to NA if none required. Used for calc_annual_stats() function. Default c(10,90).

monthly_percentiles

Numeric vector of percentiles to calculate monthly for each year. Set to NA if none required. Used for calc_monthly_stats() function. Default c(10,20).

stats_days

Numeric vector of the number of days to apply a rolling mean on basic stats. Default c(1). Used for calc_annual_stats() and calc_monthly_stats() functions.

stats_align

Character string identifying the direction of the rolling mean on basic stats 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'. Used for calc_annual_stats(), calc_monthly_stats(), and calc_annual_outside_normal() functions.

lowflow_days

Numeric vector of the number of days to apply a rolling mean on low flow stats. Default c(1,3,7,30). Used for calc_lowflow_stats() function.

lowflow_align

Character string identifying the direction of the rolling mean on low flow stats 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'. Used for calc_lowflow_stats() function.

timing_percent

Numeric vector of percents of annual total flows to determine dates. Used for calc_annual_flow_timing() function. Default c(25,33.3,50,75).

normal_percentiles

Numeric vector of two values, lower and upper percentiles, respectively indicating the limits of the normal range. Default c(25,75).

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.

include_plots

Logical value indicating if annual trending plots should be included. Default TRUE.

zyp_alpha

Numeric value of the significance level (ex. 0.05) of when to plot a trend line. Leave blank for no line.

Value

A list of tibbles and optional plots from the trending analysis including:

Annual_Trends_Data

a tibble of the annual statistics used for trending

Annual_Trends_Results

a tibble of the results of the zyp trending analysis

Annual_*

each ggplot2 object for each annual trended statistic

References

References from zyp package:

  • Wang, X.L. and Swail, V.R., 2001. Changes in extreme wave heights in northern hemisphere oceans and related atmospheric circulation regimes. Journal of Climate, 14: 2204-2221.

  • Yue, S., P. Pilon, B. Phinney and G. Cavadias, 2002. The influence of autocorrelation on the ability to detect trend in hydrological series. Hydrological Processes, 16: 1807-1829.

  • Zhang, X., Vincent, L.A., Hogg, W.D. and Niitsoo, A., 2000. Temperature and Precipitation Trends in Canada during the 20th Century. Atmosphere-Ocean 38(3): 395-429.

  • Sen, P.K., 1968. Estimates of the Regression Coefficient Based on Kendall's Tau. Journal of the American Statistical Association Vol. 63, No. 324: 1379-1389.

See also

Examples

if (FALSE) { # Working examples: # Compute trends statistics using a data frame and data argument with defaults flow_data <- tidyhydat::hy_daily_flows(station_number = "08NM116") trends <- compute_annual_trends(data = flow_data, zyp_method = "yuepilon") # Compute trends statistics using station_number with defaults trends <- compute_annual_trends(station_number = "08NM116", zyp_method = "yuepilon") # Compute trends statistics and plot a trend line if the significance is less than 0.05 trends <- compute_annual_trends(station_number = "08NM116", zyp_method = "yuepilon", zyp_alpha = 0.05) # Compute trends statistics and do not plot the results trends <- compute_annual_trends(station_number = "08NM116", zyp_method = "yuepilon", include_plots = FALSE) }