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Generate a climate-adjusted design flood event

Source: R/flood_scenario.R
flood_scenario.Rd

Turns the design return levels from flood_extremes into a scenario for a chosen future, so that a flood can be modelled under present-day or changed-climate conditions. Three methods are offered, from zero-dependency to full-fidelity:

Usage

flood_scenario(
  x,
  method = c("delta", "trend", "cmip6"),
  change_factor = 1.15,
  horizon_year = NULL,
  scenario_label = NULL
)

Arguments

x

A flood_project whose extremes slot has been populated by flood_extremes, or a flood_extremes object directly.

method

One of "delta" (default), "trend" or "cmip6".

change_factor

Numeric multiplier for method = "delta". A value of 1 leaves rainfall unchanged; 1.15 raises it by 15%. Ignored by other methods.

horizon_year

Target year for method = "trend". The location trend is projected from the end of the record to this year. Ignored by other methods.

scenario_label

Optional character label for the scenario (for example "SSP5-8.5 2050"), stored with the result and used in maps.

Value

If x is a flood_project, the same object with its scenario slot populated. Otherwise a list of class flood_scenario with elements method, label, baseline (the present-day return-level data frame), adjusted (a data frame of period and level_mm under the scenario), and change (the ratio of adjusted to baseline at each period).

Details

"trend"

Extrapolate the fitted non-stationary location trend forward to a target year. Uses only the record already analysed.

"delta"

Scale the stationary return levels by a change factor (for example 1.15 for a 15% increase). The default and recommended route for data-scarce settings; change factors can come from published CMIP6 summaries per Shared Socioeconomic Pathway.

"cmip6"

Placeholder for ingesting downscaled CMIP6 projections directly; not yet implemented, and currently returns an informative error. Use "delta" with a CMIP6-derived change factor in the meantime.

References

IPCC (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

See also

flood_extremes for the design levels this adjusts.

Examples

set.seed(1)
rain <- data.frame(
  date = seq(as.Date("1985-01-01"), as.Date("2024-12-31"), by = "day"),
  precip_mm = round(rgamma(14610, 0.7, scale = 6) *
                    rbinom(14610, 1, 0.3), 1)
)
ext <- flood_extremes(rain)

# 15% wetter design storm
sc <- flood_scenario(ext, method = "delta", change_factor = 1.15,
                     scenario_label = "SSP2-4.5 2050")
sc$adjusted
#>   period level_mm
#> 1      2    28.69
#> 2     10    39.70
#> 3     25    45.48
#> 4     50    49.88
#> 5    100    54.35