West Pacific Gradient

Changes in Sea surface temperature (SST) over the Western Pacific, combined with El Niño and La Niña events, have far-ranging consequences across the globe. Simultaneous changes in the Western Pacific and El Niño-Southern Oscillation (ENSO) events are measured by an index called the West Pacific Gradient (WPG). The WPG (Figure 1) is measured as the difference in SST between the Niño4 region and the Western Pacific.

Western Pacific and Niño4 regions


Fig. 1. Western Pacific and Niño regions.
Source: NOAA/ESRL/PSD

WPG index, 1950–2010


Fig. 2. Temporal variations of the WPG.
Source: NOAA/ESRL/PSD

When the Western Pacific is warm during La Niña events (a negative WPG), the impacts on rainfall across the globe can be extreme. The table below lists the typical impacts when a warm Western Pacific and a La Niña event occur at the same time during specific seasons in specific regions.

Impacts of a Warm Western Pacific and a La Niña Event
Region Season Impact on Rainfall
East Africa Oct-Dec Drier than average
(strong)
East Africa Mar-May Drier than average
(strong)
Southern Africa Nov-Mar Wetter than average
(strong)
West Africa July-Sept Wetter than average
(strong)
Central America
and the Caribbean
Jun-Aug Wetter than average
(strong)
Central Asia Oct-May Drier than average
(strong)
Central Asia Jul-Aug Wetter than average
(strong)

Source: NOAA/ESRL/PSD

About FEWS NET

The Famine Early Warning Systems Network is a leading provider of early warning and analysis on food insecurity. Created by USAID in 1985 to help decision-makers plan for humanitarian crises, FEWS NET provides evidence-based analysis on approximately 30 countries. Implementing team members include NASA, NOAA, USDA, USGS, and CHC-UCSB, along with Chemonics International Inc. and Kimetrica.
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