RDI: Riou's drought index

Description

Calculation of Riou's drought index described in OIV bio-climatic indices for viticulture (see references)

Usage

RDI(series, clim_norm = NULL, first.yr = NULL, last.yr = NULL, TAW = 200, coeff_rad, coeff_Hargr = rep(0.75, 12), quant = c(0, 0.1, 0.5))

Arguments

series

series of mean monthly weather values

clim_norm

the reference climatic values for each month, used for gap filling. Default is NULL (no replacement of missing values)

first.yr

of the period over which water balance is calculated. Default is NULL (calculations start with the first year of the series)

last.yr

of the period over which water balance is calculated. Default is NULL (calculations start with the last year of the series)

TAW

total available water content of soil

coeff_rad

vector of solar radiation coefficients (12 values) for calculation of potential evapotranspiration

coeff_Hargr

(vector of monthly) correction coefficient(s) for Hargreaves' equation

quant

vector of quantiles for the statistical ranking of the year representative for balance (0..1)

Value

A two-column table reporting Riou's drought indices for each quantile chosen (one line each, minimum is 1). Both "harvest time" and minimum values are calculated (see details).

Details

For full description of algorithm see OIV standards at http://www.oiv.int/oiv/info/enresolution2012?lang=en and the references: Riou, 1994; Tonietto, 1999. Evapotranspiration is calculated by Hargreaves' equation (see arid).

series is a data frame of the monthly series (means) of: cumulated precipitation (mm), minimum temperature, maximum temperature, mean temperature (optional) - all in deg. C. Includes the following columns (and names): "year", "month", "P", "Tn", "Tx", "Tm" (optional), for precipitation, minimum, maximum and mean temperature, respectively. If Tm is missing it is calculated as (Tn + Tx)/2. Format is the same of lista_cli.

clim_norm is a monthly data frame of 12 climate normals, with the same column names of series, except "year". It can be the output of function climate. If clim_norm is not NULL, any missing value in the monthly series is substituted by the corresponding climatic value in clim_norm.

A default value of 200 mm for TAW is suggested by the authors of the index. It can be changed according to the known pedological features of soil.

coeff_rad corresponds to the mean monthly extra-atmospheric radiation (see function ExAtRa). It is required in Hargreaves' equation.

coeff_Hargr is either a single value or a vector of 12 coefficients to adjust Hargreaves' estimation of potential evapotranspiration. From calibration in 6 stations from the same network of Trent_climate, its average value is 0.75.

quant_vector a vector of minimum one element. 0 yields minimum absolute case, 0.5 the median. Values range from 0 to 1 (inappropropriate if > 0.5).

The algorithm described in OIV assesses water balance at the last month of the ripenining period, early autumn. However, in humid or sub-humid climates the driest period for soil generally falls in summer. For this reason, the output table reports both cases ("harvest" time value and monthly minimum over the season, "WB_harv" and "WB_min", respectfully). Harvest time is conventionally September (N emisphere) or March (S emisphere).

References

Riou, C. 1994. Le determinisme climatique de la maturation du raisin: application au zonage de la teneur en sucre dans la Communaute Europeenne (E. Commission, ed.). Office des Publications Officielles des Communautes Europeennes, Luxembourg, 322p.

Tonietto, J. 1999. Les Macroclimats Viticoles Mondiaux et l'Influence du Mesoclimat sur la Typicite de la Syrah et du Muscat de Hambourg dans le Sud de la France Methodologie de Caracterisation. These de doctorat, Ecole Nationale Superieure Agronomique de Montpellier, Montpellier (France), 216p.

Examples

Run this code

data(Trent_climate)
RDI(lista_cli[[1]], clim_norm=clima_81_10[[1]], first.yr=1981, last.yr=2010, coeff_rad=coeff_rad)

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