spi
Create a time series of the Standardised Precipitation Index
Description
The program calculates a time series of the Standardised Precipitation Index (SPEI) at a
given time interval from an input data file containing a monthly time series of
precipitation.
Usage
spi [timeInterval] [inputFile] [outputFile]
Arguments
timeInterval A time interval, in months.
inputFile The name of an input file, with extension.
outputFile The name of the output file to be produced, with extension.
Details
The SPI index is a standardised monthly value indicating the departure of a given month's
cummulative precipitation from the average value for that month. Details on the index
calculation and applications can be found in the references below.
The SPI can be calculated at the monthly scale with timeInterval = 1, or accumulated
at more than one month with timeInterval > 1. Typical values are 1, 3, 6, 12 and 24
months. If the accumulated index is calculated, the starting date of the resulting SPI series
will be lagged a number of months equal to timeInterval – 1.
The input file (inputFile) can have any extension, but must be a plain text file (ASCII).
The file structure is as follows:
sao paulo
1900;01
12
197.10
...
The first line contains the name of the observatory, and is only used for identification