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PDSI Index (Palmer Drought Severity Index)

PDSI Index - Current situation - May 2025

According to the PDSI index, at the end of May the whole of mainland Portugal was still not in a meteorological drought, although there was a decrease in the intensity of the rainfall classes. There was a significant decrease in the severe rainfall class in the Central and Southern regions

In terms of the percentage distribution by class of the meteorological drought index, PDSI, in mainland Portugal, at the end of May there were:

  • 2.8% in the severe rainfall class,
  • 64.5% in the moderate rainfall class,
  • 25.9% in the light rain class,
  • 6.8% in the normal class.

Drought monitoring

  • Summary and about

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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

Last 12 month evolution