ScientSDI {PowerSDI}R Documentation

Estimate parameters of Gamma, Generalized Extreme Value, or Generalized Logistic Distributions

Description

Verifies concepts expected from SDI. The first step of the SPI and SPEI algorithms is to calculate the cumulative probabilities of their input variables (Guttman 1999). Function estimates the parameters of the gamma, generalized extreme value (GEV), or generalized logistic distributions (GLO) through the L-moments method are provided. This function also allows users to remove suspicious values from the data sample.

Usage

ScientSDI(
  lon,
  lat,
  start.date,
  end.date,
  distr = "GEV",
  TS = 4L,
  Good = "No",
  sig.level = 0.95,
  RainUplim = NULL,
  RainLowlim = NULL,
  PEUplim = NULL,
  PELowlim = NULL
)

Arguments

lon

longitude in decimal degrees: (+) Eastern Hemisphere, (-) Western Hemisphere.

lat

latitude in decimal degrees: (+) Northern hemisphere, (-) Southern Hemisphere.

start.date

date at which the indices estimates should start. Format: “YYYY-MM-DD”.

end.date

date at which the indices estimates should end. Format: “YYYY-MM-DD”.

distr

A character variable (“GEV” or “GLO”) defining the distribution to calculate the SPEI. Default is GEV.

TS

Time scale on the quart.month basis (integer values between 1 and 96). Default is 4.

Good

A character variable ("Yes" or "No") to calculate or not the goodness-of-fit and normality tests. Default is "No".

sig.level

A numeric variable (between 0.90 and 0.95) defining the significance level for parameter Good. Default is "0.95".

RainUplim

Optional. Upper limit in millimetres from which rainfall values larger than it will be removed. Default is NULL.

RainLowlim

Optional. Lower limit in millimetres from which rainfall values smaller than it will be removed. Default is NULL.

PEUplim

Optional. Upper limit in millimetres from which evapotranspiration values larger than it will be removed. Valid for Hargreaves and Samani method Default is NULL.

PELowlim

Optional. Lower limit in millimetres from which evapotranspiration values smaller than it will be removed. Valid for Hargreaves and Samani method Default is NULL.

Value

A list object with data calculated at the time scale selected by the user. If Good = "Yes", this list object includes:

SDI

The “NASA-SPI”, “NASA-SPEI.HS” and “NASA-SPEI.PM.”

DistPar

The parameters of the distributions (gamma and GEV) used to calculate the indices.

GoodFit

The Lilliefors and Anderson-Darling tests goodness-of-fit tests.

Normality

The outcomes of the two normality checking procedures (Wu et al., 2006 and Stagge et al., 2015).

If Good = "No", this list object includes SDI and DistPar.

This function also presents other data (in millimiters) calculated from the NASA POWER project:

References

Guttman, N.B., 1999. Accepting the standardized precipitation index: a calculation algorithm 1. JAWRA Journal of the American Water Resources Association, 35(2), pp.311-322.

Stagge, J.H., Tallaksen, L.M., Gudmundsson, L., Van Loon, A.F. and Stahl, K., 2015. Candidate distributions for climatological drought indices (SPI and SPEI). International Journal of Climatology, 35(13), pp.4027-4040.

Wu, H., Svoboda, M.D., Hayes, M.J., Wilhite, D.A. and Wen, F., 2006. Appropriate application of the standardized precipitation index in arid locations and dry seasons. International Journal of Climatology: A Journal of the Royal Meteorological Society, 27(1), pp.65-79.

Examples



# This example requires an Internet connection to fetch data and takes >5s
#  to run, and so is only run in interactive sessions

ScientSDI(
  lon = -47.3,
  lat = -22.87,
  start.date = "1993-01-01",
  end.date = "2022-12-31",
  TS = 1,
  Good = "no"
)


[Package PowerSDI version 1.0.0 Index]