According to the PDSI index, at the end of December, there was a significant decrease in the situation of meteorological drought, ending in practically the entire territory; only a few places in the interior South region are still in mild drought (the least severe drought class of the PDSI index).
In the North and Center regions there was an increase in the intensity of rainfall classes, especially in the districts north of Mondego.
Thus, 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