PDSI Index (Palmer Drought Severity Index)
PDSI Index - Current situation - July 2025
According to the PDSI index at the end of July, there was a significant increase in the meteorological drought situation, from 9% (June) to 67%, which extended to 2/3 of the mainland, with a particular worsening in the north-west region.
The percentage distribution by PDSI index classes in mainland Portugal at the end of July is as follows:
- 33.3% in the normal class
- 62.1% in the mild drought class
- 4.6% in the moderate 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