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Teleconnections between Rainfall in Equatorial Africa and Tropical Sea Surface Temperatures: A Focus on Western Uganda

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  • 1 a Georgia State University, Atlanta, Georgia
  • | 2 b Colorado State University, Fort Collins, Colorado
  • | 3 c University of New Hampshire, Durham, New Hampshire
  • | 4 d University of Colorado Boulder, Boulder, Colorado
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Abstract

Substantial research on the teleconnections between rainfall and sea surface temperatures (SSTs) has been conducted across equatorial Africa as a whole, but currently no focused examination exists for western Uganda, a rainfall transition zone between eastern equatorial Africa (EEA) and central equatorial Africa (CEA). This study examines correlations between satellite-based rainfall totals in western Uganda and SSTs—and associated indices—across the tropics over 1983–2019. It is found that rainfall throughout western Uganda is teleconnected to SSTs in all tropical oceans but is connected much more strongly to SSTs in the Indian and Pacific Oceans than in the Atlantic Ocean. Increased Indian Ocean SSTs during boreal winter, spring, and autumn and a pattern similar to a positive Indian Ocean dipole during boreal summer are associated with increased rainfall in western Uganda. The most spatially complex teleconnections in western Uganda occur during September–December, with northwestern Uganda being similar to EEA during this period and southwestern Uganda being similar to CEA. During boreal autumn and winter, northwestern Uganda has increased rainfall associated with SST patterns resembling a positive Indian Ocean dipole or El Niño. Southwestern Uganda does not have those teleconnections; in fact, increased rainfall there tends to be more associated with La Niña–like SST patterns. Tropical Atlantic Ocean SSTs also appear to influence rainfall in southwestern Uganda in boreal winter as well as in boreal summer. Overall, western Uganda is a heterogeneous region with respect to rainfall–SST teleconnections; therefore, southwestern Uganda and northwestern Uganda require separate analyses and forecasts, especially during boreal autumn and winter.

SIGNIFICANCE STATEMENT

Seasonal rainfall greatly impacts the millions of rural households practicing rain-fed agriculture across equatorial Africa; therefore, understanding the relationship between rainfall and tropical sea surface temperatures (SSTs) can benefit smallholder farmers and other stakeholders. This study examines over the 1983–2019 period the relationships between SSTs and monthly and seasonal rainfall totals in western Uganda. During Northern Hemisphere (boreal) spring and summer, increased SSTs in the Indian Ocean along with La Niña–like SST patterns are generally associated with increased rainfall for the entire region. Rainfall–SST relationships have substantial spatial variability during boreal autumn and winter: only northwestern Uganda has increased rainfall strongly associated with the positive Indian Ocean dipole and El Niño–like SST patterns. These findings have implications for the region-specific forecasts provided to farmers.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Jeremy E. Diem, jdiem@gsu.edu

Abstract

Substantial research on the teleconnections between rainfall and sea surface temperatures (SSTs) has been conducted across equatorial Africa as a whole, but currently no focused examination exists for western Uganda, a rainfall transition zone between eastern equatorial Africa (EEA) and central equatorial Africa (CEA). This study examines correlations between satellite-based rainfall totals in western Uganda and SSTs—and associated indices—across the tropics over 1983–2019. It is found that rainfall throughout western Uganda is teleconnected to SSTs in all tropical oceans but is connected much more strongly to SSTs in the Indian and Pacific Oceans than in the Atlantic Ocean. Increased Indian Ocean SSTs during boreal winter, spring, and autumn and a pattern similar to a positive Indian Ocean dipole during boreal summer are associated with increased rainfall in western Uganda. The most spatially complex teleconnections in western Uganda occur during September–December, with northwestern Uganda being similar to EEA during this period and southwestern Uganda being similar to CEA. During boreal autumn and winter, northwestern Uganda has increased rainfall associated with SST patterns resembling a positive Indian Ocean dipole or El Niño. Southwestern Uganda does not have those teleconnections; in fact, increased rainfall there tends to be more associated with La Niña–like SST patterns. Tropical Atlantic Ocean SSTs also appear to influence rainfall in southwestern Uganda in boreal winter as well as in boreal summer. Overall, western Uganda is a heterogeneous region with respect to rainfall–SST teleconnections; therefore, southwestern Uganda and northwestern Uganda require separate analyses and forecasts, especially during boreal autumn and winter.

SIGNIFICANCE STATEMENT

Seasonal rainfall greatly impacts the millions of rural households practicing rain-fed agriculture across equatorial Africa; therefore, understanding the relationship between rainfall and tropical sea surface temperatures (SSTs) can benefit smallholder farmers and other stakeholders. This study examines over the 1983–2019 period the relationships between SSTs and monthly and seasonal rainfall totals in western Uganda. During Northern Hemisphere (boreal) spring and summer, increased SSTs in the Indian Ocean along with La Niña–like SST patterns are generally associated with increased rainfall for the entire region. Rainfall–SST relationships have substantial spatial variability during boreal autumn and winter: only northwestern Uganda has increased rainfall strongly associated with the positive Indian Ocean dipole and El Niño–like SST patterns. These findings have implications for the region-specific forecasts provided to farmers.

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Corresponding author: Jeremy E. Diem, jdiem@gsu.edu
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