According to the PDSI index, at the end of December the meteorological drought situation remains in almost the entire territory, with a slight decrease in the percentage of the territory in the severe drought class and an increase in the moderate drought class.
The percentage distribution by classes of the PDSI index in the territory is as follows:
PDSI Index (Palmer Drought Severity Index) was developed by Palmer (1965) and implemented and calibrated for mainland Portugal (Pires, 2003).
> This index is based on the concept of the water balance taking into account data on the amount of precipitation, air temperature and available water capacity in the soil and allows the detection of periods of drought by classifying them in terms of intensity (weak, moderate, severe and extreme).
Table - Classification of the PDSI index for dry and rainy periods
greater than or equal to 4,0
3,00 to 3,99
2,00 to 2,99
1,00 to 1,99
-0,99 to 0,99
-1,99 to -1,0
-2,99 to -2,0
-3,99 to -3,0
less than or equal to -4,00