PDSI Index (Palmer Drought Severity Index)
PDSI Index - Current situation - September 2025
According to the PDSI index, at the end of November there was an easing of the meteorological drought throughout the country, with the drought ending in the northern and central regions that were still affected at the end of October. In the southern region, despite the easing of the area and intensity of the meteorological drought, some municipalities in the districts of Évora (inland area), Beja, and Faro still remain in the mild drought category.
The percentage distribution by PDSI index class in mainland Portugal at the end of October is as follows:
- 2.0% in the moderate drought class
- 37.7% in the light rain class
- 29.7% in the normal class
- 20.6% in the weak drought class.
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