spatialBehaviour

In StormR: Analyzing the Behaviour of Wind Generated by Tropical Storms and Cyclones

``` {r setup, include = FALSE} library(StormR)

The `spatialBehaviour()` function allows computing wind speed and direction for
each cell of a regular grid (i.e., a raster) for a given tropical cyclone or set
of tropical cyclones. The `product="Profiles"` argument allows producing 2D wind
fields during the lifespan of the cyclone at a temporal resolution of up to 15
minutes. The `spatialBehaviour()` function also allows to compute three
associated summary statistics: the maximum sustained wind speed
(`product="MSW"`), the power dissipation index (`product="PDI"`) and the
duration of exposure to winds reaching defined speed thresholds along the life
span of the cyclones (`product="Exposure"`). Then the `plotBehaviour()` and the
`writeRast()` functions can be used to visualise and export the output.
In the following example we use the `test_dataset` provided with the package to
illustrate how cyclone track data can be used to compute, plot, and export 2D
wind field profiles or summary statistics.

### Computing and plotting spatialBehaviour products

We can compute the behaviour of winds generated by the topical cyclone Pam
(2015) near Vanuatu. First, track data are extracted as follows:

```r
sds <- defStormsDataset()
st <- defStormsList(sds = sds, loi = "Vanuatu", names = "PAM", verbose = 0)
plotStorms(st)

Wind profiles

Using track data and the spatialBehaviour() function with the product="Profiles argument we can generate 2D wind fields at any time as follows:

pf <- spatialBehaviour(st, product = "Profiles", verbose = 0)
pf

The function returns a SpatRaster object with two rasters, one for the wind speed and one for the wind direction, for each observation or interpolated observation. Rasters' names follow the following terminology, the name of the storm in capital letters, "Speed" or "Direction", and the index of the observation, separated by underscores. Note that actual observations have entire indices (e.g., 41, 42, ...) while interpolated observation have decimals (e.g., 41.1, 41.2, ...). Most tropical cyclone track data sets are based on observations gathered every 3 or 6 hours. Therefore, to be able to compute wind fields every 1 hour, the observations are interpolated.

Wind speed and direction profiles at the 41^th^ observation can be plotted as follows:

plotBehaviour(st, pf$PAM_Speed_41)
plotBehaviour(st, pf$PAM_Direction_41)

Summary statisics

The spatialBehaviour() function can compute the different products (i.e., "Profiles", "MSW", "PDI", "Exposure") either separately or together. Here, we compute all three summary statistics together as follows:

ss <- spatialBehaviour(st, product = c("MSW", "PDI", "Exposure"), verbose = 0)
ss

The spatialBehaviour() function returns a SpatRaster object with eight rasters: one for the maximum sustained wind speed ("MSW"), one for the power dissipation index ("PDI"), and one for each of the six defaults wind thresholds values set for the duration of exposure ("Exposure").

names(ss)

By default, the function returns the duration of exposure (in hours) to wind speeds above the thresholds used by the Saffir-Simpson hurricane wind scale (i.e., 18, 33, 42, 49, 58, and 70 $m.s^{-1}$). This can be change using the wind_threshold argument.

The maximum sustained wind speed can be plotted as follows:

plotBehaviour(st, ss$PAM_MSW)

The power dissipation index can be plotted as follows:

plotBehaviour(st, ss$PAM_PDI)

The duration of exposure to wind stronger than 58 $m.s^{-1}$ (i.e., Saffir-Simpson's categories 4 and 5) can be plotted as follows:

plotBehaviour(st, ss$PAM_Exposure_58)

Spatio-temporal resolution

As in the WorldClim database (https://worldclim.org/data/worldclim21.html) four spatial resolutions are available. By default the spatial resolution is set to 2.5 min (~4.5 km at the equator), but a finer spatial resolution of 30 s (~1 km at the equator) and coarser spatial resolutions of 5 min (~9 km at the equator) or 10 min (~18.6 km at the equator) can be set using the spaceRes argument. The temporal resolution is set to 1 hour by default but finer spatial resolution of 0.75, 0.50, or 0.25 hour can be set using the tempRes argument. Maximum sustained wind speed can be computed at a 10 min spatial resolution and a 30 min temporal resolution as follows:

ss <- spatialBehaviour(st, product = c("MSW"), verbose = 0, spaceRes = "10min", tempRes = 30)
plotBehaviour(st, ss$PAM_MSW)

Dynamic plot

plotBehaviour function also provide (See ExtractStorms vignette) a dynamic plot. Here is an example based on the same parameters as above.

plotBehaviour(st, ss$PAM_MSW, dynamicPlot = TRUE)

Exporting spatialBehaviour products

The spatialBehaviour() function returns rasters stored in a SpatRaster object than can be exported either in ".tiff" or ".nc" (NetCDF) formats using the writeRast() function. Here, we export the maximum sustained wind speed in the working directory as follows:

writeRast(ss$PAM_MSW)

StormR documentation built on Sept. 12, 2024, 6:52 a.m.