Description

The Standardized Precipitation Index (SPI) is widely regarded as one of the most accessible tools for quantifying and reporting meteorological drought. At shorter timescales, SPI values are highly correlated with soil moisture, while at extended timescales, they reflect variations in groundwater and reservoir storage. The SPI model derives probability distributions from historical precipitation records, which are then normalized using an incomplete gamma function across multiple timescales. SPI values indicate the number of standard deviations the observed anomaly departs from the long-term period of record, with positive values corresponding to wetter-than-average conditions. Time periods calculated for monthly precipitation percentiles are 1, 2, 3, 6, 9, 12, 18, 24 months. Each ISO week is numbered from 1 to 52 (sometimes 53) within a year. An ISO week starts on Monday and ends on Sunday. Historical record goes back to 1980 Indices values were calculated using the xclim python package The National Agroclimate Series of Derived Indicators (NASDI) products provide a collection of comprehensive and regularly updated datasets on key agroclimatic variables, including accumulated precipitation, standardized precipitation index, and difference from normal temperature, among others. These datasets incorporate both real-time and historical climate information, offering enhanced insight into conditions and trends across Canada’s diverse agricultural regions.

Resources

Name	Format	Description	Link
Pre-packaged GeoTIF files (monthly)	Unknown		https://agriculture.canada.ca/atlas/data_donnees/nasdi/data_donnees/monthly/standardized_precipitation_index/
Pre-packaged GeoTIF files (weekly)	Unknown		https://agriculture.canada.ca/atlas/data_donnees/nasdi/data_donnees/weekly/standardized_precipitation_index/
Data Product Specification (English)	PDF		https://agriculture.canada.ca/atlas/data_donnees/nasdi/supportdocument_documentdesupport/en/ISO_19131_NASDI_-_Data_Product_Specification.pdf
Data Product Specification (French)	PDF		https://agriculture.canada.ca/atlas/data_donnees/nasdi/supportdocument_documentdesupport/fr/Série_nationale_indicateurs_agroclimatiques_dérivés_-_SPC_19131.pdf
Standardized precipitation index (SPI)	Ersi REST		https://agriculture.canada.ca/imagery-images/rest/services/nasdi/standardized_precipitation_index/ImageServer
Standardized precipitation index (SPI)	Ersi REST		https://agriculture.canada.ca/imagery-images/rest/services/sniad/indice_normalise_des_precipitations/ImageServer

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