dynatopmodel (version 1.2.1)

approx.pe.ts: Create sinsuiodal time series of potential evapotranspiration input

Description

Create sinsuiodal time series of potential evapotranspiration input

Usage

approx.pe.ts(start, end, dt = 1, emin = 0, emax = 5/1000)

Arguments

start

Start time of returned series in a format that can be coerced into a POSIXct instance. Defaults to start of rainfall data

end

End time for returned series in a format that can be coerced into a POSIXct instance. Defaults to end of rainfall data.

dt

Time interval in hours

emin

Minimum daily PE total (m or mm)

emax

Maximum daily PE total (m or mm)

Value

Time series (xts) of potential evapotranspiration ([L]/[T]) covering the given time range and at the desired interval in m or mm/hr

Details

Dynamic TOPMODEL requires a time series of potential evapotranspiration in order to calculate and remove actual evapotranspiration from the root zone during a run. Many sophisticated physical models have been developed for estimating PE and AE, including the Priestly-Taylor (Priestley and Taylor, 1972) and Penman-Monteith (Montieth, 1965) methods. These, however, require detailed meteorological data such as radiation input and relative humidities that are, in general, difficult to obtain. Calder (1983) demonstrated that a simple approximation using a sinusoidal variation in potential evapotranspiration to be a good approximation to more complex schemes.

If the insolation is also taken to vary sinusoidally through the daylight hours then, ignoring diurnal meteorological variations, the potential evapotranspiration during daylight hours for each year day number can be calculated (for the catchment's latitude). Integration over the daylight hours allows the daily maximum to be calculated and thus a sub-daily series generated.

References

Beven, K. J. (2012). Rainfall-runoff modelling : the primer. Chichester, UK, Wiley-Blackwell.

Calder, I. R. (1986). A stochastic model of rainfall interception. Journal of Hydrology, 89(1), 65-71.

Examples

# NOT RUN {
# Create PE data for 2012 for use in the Brompton test case

require(dynatopmodel)

data("brompton")

# Generate time series at hourly and 15 minute intervals
pe.60 <- approx.pe.ts("2012-01-01", "2012-12-31", dt=1)
pe.15 <- approx.pe.ts("2012-01-01", "2012-12-31", dt=0.25)

# Check annual totals - should be around 900mm
sum(pe.60)*1000
sum(pe.15*0.25)*1000

# Check maximum daily total on the 1st of July
sum(pe.60["2012-07-01"])*1000
sum(pe.15["2012-07-01"]*0.25)*1000
# }