PDSI Index (Palmer Drought Severity Index)
PDSI Index - Current situation - December 2025
According to the PDSI index, the mild drought that still existed at the end of November in the districts of Évora, Beja and Faro has ended. There has been an increase in the area in the rainfall classes, with the north and centre coastline in the moderate to severe rainfall classes being particularly noteworthy.
The percentage distribution by PDSI index classes in mainland Portugal at the end of December is as follows:
- 4.4% in the severe rainfall class
- 23.5% in the moderate rainfall class
- 45.7% in the mild rainfall class
- 26.4% in the normal
Drought monitoring
- Summary and about
Legend
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
Color legend
PDSI Classes
Description
greater than or equal to 4,0
Extreme rain
Extreme rain
3,00 to 3,99
Severe rain
Severe rain
2,00 to 2,99
Moderate rain
Moderate rain
1,00 to 1,99
Weak rain
Weak rain
-0,99 to 0,99
Normal
Normal
-1,99 to -1,0
Weak drought
Weak drought
-2,99 to -2,0
Moderate drought
Moderate drought
-3,99 to -3,0
Severe drought
Severe drought
less than or equal to -4,00
Extreme drought
Extreme drought