Combines air temperature, relative humidity and wind speed into a single
index between 0 and 1 describing how favourable the weather is for adult
mosquito activity. The index is the product of the three response functions
mwi_temperature(), mwi_humidity() and mwi_wind().
Usage
mwi(temperature, humidity, wind_speed, units = c("km/h", "m/s"))Value
A numeric vector of index values in [0, 1], recycled to the length
of the longest input. NA in any input gives NA in the output.
Details
Because the three responses are multiplied, any one of them falling outside its favourable range sets the whole index to zero. The index reaches 1 only when temperature is between 20 and 25 degrees Celsius, relative humidity is exactly 95%, and wind speed is at or below the cut-off.
The index must be computed before it is averaged, not after. mwi() is a
non-linear function of its inputs, so evaluating it on daily mean or daily
maximum weather gives a different – and empirically much less useful –
answer than evaluating it hourly and then summarising the result. Daily
maxima of humidity and of temperature typically occur many hours apart, so
an index built from them describes an hour that never happened. Use
mwi_summarise() to aggregate in the correct order.
See also
mwi_category() to map the index onto its five activity classes,
mwi_summarise() to aggregate hourly values over time, and mwi_fhft()
for the temperature-and-humidity-only variant.
Examples
mwi(temperature = 22, humidity = 70, wind_speed = 10)
#> [1] 0.5454545
# Vectorised, with recycling
mwi(temperature = c(18, 22, 28), humidity = 70, wind_speed = 5)
#> [1] 0.3272727 0.5454545 0.2181818
# Any factor out of range zeroes the index
mwi(temperature = 22, humidity = 30, wind_speed = 5)
#> [1] 0
mwi(temperature = 22, humidity = 70, wind_speed = 30)
#> [1] 0