Online Drought Indicators and Indices

Weighted Anomaly Standardized Precipitation Index (WASP)


Index name: Weighted Anomaly Standardized Precipitation Index (WASP).

Ease of use: Green.

Origins: Developed by B. Lyon to monitor precipitation in the tropical regions within 30 degrees of the equator.

Characteristics: Uses gridded monthly precipitation data on a 0.5° by 0.5° resolution, and is based on 12-month overlapping sums of weighted, standardized monthly precipitation anomalies.

Input parameters: Monthly precipitation and annual precipitation values.

Applications: Used mainly in wet tropical regions to monitor developing drought, taking into account the defined wet and dry periods in the climate regime. Can be used to monitor droughts that affect agriculture and other sectors.

Strengths: Using precipitation as a single input allows for simpler computations.

Weaknesses: Does not work so well in desert regions. Gridded precipitation data may be a challenge to obtain in an operational capacity.

Resources: The methods and calculations are explained in the literature and on the International Research Institute for Climate and Society (IRI) website.

Reference: Lyon, B., 2004: The Strength of El Niño and the Spatial Extent of Tropical Drought. Geophysical Research Letters, 31: L21204. DOI: 10.1029/2004GL020901.

  1. Sivaraman K R
    February 19, 2021 Reply

    studying prioritization of micro watersheds under the category “very high” ‘high’ “medium” and ‘low’. How to follow the weightage to be fixed for enlightening the drought or non-drought conditions. Thank you, Sir

    1. Katrin Ehlert
      March 23, 2021 Reply

      Dear Sivaraman

      The WASP index gives an estimate of the relative deficit or surplus of precipitation for different time intervals ranging from 1 to 12 months and is mainly used in areas with defined wet and dry seasons. It is used for drought monitoring. Prioritization of micro watersheds is a method to classify soil erosion for effective managment. The link you have drawn between these concepts in your question is not clear. Could you please be more specific?

      Best regards
      IDMP TSU

  2. Badebye Joan
    April 19, 2017 Reply

    would like to access this index , learn more about it and use it for my drought research.

    1. Robert Stefanski
      April 25, 2017 Reply

      Please find more information from the following link:

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