Using the SPIChanges R package at the heart of the Amazon rainforest

Authors

In brief

The Standardized Precipitation Index assumes a stationary climate, which is exactly the assumption a changing climate breaks. SPIChanges compares the cumulative probability of an observed rainfall amount under stationary and non-stationary versions of the same gamma distribution, and so quantifies how drought frequency itself has shifted. The authors apply it to 25 years of daily rainfall at Manaus.

“The package enhanced drought assessment in a location situated at the heart of the Amazon rainforest.”

What the article covers

• Up to sixteen increasingly complex gamma-based models, selected by the second-order Akaike criterion.
• A quasi-weekly time scale that divides each month into four periods.
• In Manaus, expected precipitation falls and the frequency of moderate and severe droughts rises by roughly 17 per cent.
• The shift concentrates at the end of austral winter and the start of spring.

How to cite

Gabriel Constantino Blain, Adam H. Sparks, Graciela da Rocha Sobierajski and Letícia Lopes Martins. “Using the SPIChanges R package at the heart of the Amazon rainforest.” vISIon: The ISI Magazine Vol. 1 No. 1, October 2025, pp. 21–22.