Climatologists often compare recent rainfall with long-term averages to quantify drought conditions. A large deficit signals that soil moisture is declining and vegetation is stressed. This simplified calculator computes the percentage difference between your actual precipitation and the historical normal for the same period. While not a full Palmer Drought Severity Index, it offers a quick snapshot of dryness.
The rainfall deficit percentage is expressed as:
where is the actual rainfall and is the normal rainfall. We interpret the result using general guidelines: less than 25% deficit is mild, 25–50% moderate, 50–75% severe, and more than 75% extreme drought.
Enter your measured rainfall and the typical amount expected in your region for the same timeframe—often averaged over 30 years. The calculator returns the deficit percentage and a severity label so you can gauge water scarcity and plan irrigation or conservation efforts accordingly.
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