R/leafwet.R

In weather: Weather data manipulation

# Author: Robert J. Hijmans, r.hijmans@gmail.com
# License GPL3

eLW <- function(rhmin, rhmax, tmin) {
# emperical leaf wetness estimation according to Hijmans, Forbes and Walker, 2001
    ewhr <- exp(-8.093137318+0.11636662*rhmax-0.03715678*rhmin+0.000358713*rhmin*rhmin)
    if (rhmin < 52) {
      ewhr52 <- exp(-8.093137318+0.11636662*rhmax-0.03715678*52+0.000358713*52*52);
      ewhr <- ewhr52 - (ewhr - ewhr52);
	}
    ewhr <- max(0, min(ewhr, 24))
    if (tmin < 0) {
		ewhr <- 0
	}
	return(ewhr)
}


leafWet <- function(w, simple=TRUE) {
	if (is.null(w@values$rhmin)) {
		w <- rhMinMax(w)
	} else if (is.null(w$rh)) {
		w@values$rh <- (w@values$rhmin + w@values$rhmax) / 2
	}
	
	# for each station ...
	rh <- diurnalRH(w)
	if (simple) {
		lw <- length(rh[rh>=90])
	} else {
		w <- rh
		x <- (rh - 80) / (95 - 80)
		w[rh > 95] <- 1
		w[rh < 95] <- x[rh < 95]
		w[rh < 80] <- 0
		lw <- sum(w)
	}
	return(lw)
}


leafWetWithRain <- function(w, simple=TRUE) {
	lw <- leafWet(w, simple=simple)
	prec[is.na(w$prec)] <- 0 
	prhrs <- pmin(12, w@w$prec / 5)
	return(lw + (1 - lw/24) * prhrs)
}