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 |
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 |
RainLowlim |
Optional. Lower limit in millimetres from which rainfall values smaller than
it will be removed. Default is |
PEUplim |
Optional. Upper limit in millimetres from which evapotranspiration values
larger than it will be removed. Valid for Hargreaves and Samani method
Default is |
PELowlim |
Optional. Lower limit in millimetres from which evapotranspiration values
smaller than it will be removed. Valid for Hargreaves and Samani method
Default is |
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:
Rainfall amounts (Rain),
potential evapotranspiration values estimated through the Hargreaves and Samani method (PEHS),
potential evapotranspiration values estimated through the FAO-56 Penman-Monteith method (PEPM), and
the difference between rainfall and potential evapotranspiration (PPEHS and PPEPM).
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"
)