Seasonal Small Integral Deviation (SSID) and Standardized Precipitation Index (SPI).
an index that is intended to provide timely warnings about meteorological
drought, vegetation stress conditions and agricultural drought.
aim and methodology in brief:
the best SSID-correlated SPI cumulating interval (1 or 3 months) is
selected for each pixel. A meteorological drought warning is provided
for those pixels presenting negative SPI and for which no vegetative
growing season is yet detected (for these pixels, a blue palette are used in the map).
Once the vegetative growing season begins, the interested pixels will be assigned to
a different warning value if the calculated SSID, SPI, or both, are negative
(amber to brown palette is used in the map). Where the vegetative growing season
is ongoing and the SSID is negative, a negative SPI value entails an agricultural
drought warning, while a positive SPI implies a vegetation stress warning.
A negative SPI value during the vegetation season, with no detectable vegetation
stress effects (i.e. positive SSID), produces a meteorological drought warning.
Drought aggregated index based on vegetation and precipitation anomalies