Future Changes in the Indian Ocean Walker Circulation and Links to Kenyan Rainfall

King, James; Washington, Richard

doi:10.1029/2021jd034585

Cited by 5 publications

(4 citation statements)

References 82 publications

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“…A negative IOD event often tends to be associated with La Niña via the Walker Circulation despite some exceptions (Behera et al., 2006, 2008; Luo et al., 2010). The modified Walker Circulation could influence East African climate via atmospheric convergence/divergence (King & Washington, 2021; Kohyama et al., 2021; Zhao & Cook, 2021). The combination of the 2021 negative IOD and the La Niña‐like state in the tropical Pacific was also successfully predicted by SINTEX‐F (Figure S2 in Supporting Information ).…”

Section: Resultsmentioning

confidence: 99%

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

Doi

Behera

Yamagata

2022

Geophysical Research Letters

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Many parts of East Africa experienced extremely dry conditions during the short rains season (October-December) of 2021 (Figure 1a.), and suffered severe food insecurity outcomes afterward (Famine Early Warning Systems Network at https://fews.net/east-africa/, (e.g., Funk, 2020)). Regarding the time series of East African rainfall anomalies within 10°S-10°N; 30°E−45°E (hereafter, East African rainfall (EAR) index, e.g., Lu et al., 2018) during October-December, the 2021 drought reached the level that is comparable to the extreme drought events in 1996, 1998, 2005, and 2016 in the past 40 years (Figure 2a). Such devastating droughts in East Africa always lead to unsafe drinking water, food insecurity, and possible resurgence of infectious diseases (e.g., Azage et al., 2017;Doi, Nonaka, & Behera, 2020). Thus, successful prediction of such an extreme drought at least a few months ahead may contribute to reducing the socio-economic losses by taking necessary mitigation measures. In general, climate models are better at predicting dry extremes than wet extremes (Slater et al., 2019). Therefore, predictions of the drought in East Africa may serve as an optimal test-bed for a study on managing risk with seasonal climate forecasts. Such a research stream is critically important because extreme impacts due to natural climate variability are becoming more serious under the ongoing global warming (e.g., Charles et al., 2012).It is known that major sources of seasonal climate predictability are generally rooted in the tropical sea surface temperature (SST) anomalies and their possible teleconnection patterns (Bjerknes, 1966(Bjerknes, , 1969. Some previous works showed two potential sources of seasonal predictability of East Africa drought; ENSO (Philander, 1989) and the Indian Ocean Dipole (IOD) (Saji et al., 1999). Hastenrath et al. (1993 considered that the short rains increase/decrease were related to El Niño/La Niña possibly via atmospheric teleconnections. However, after the discovery of the IOD (Saji et al., 1999), it is now known that the impacts of the IOD on rainfall variability in East Africa are overwhelming as compared to those of ENSO (

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Section: Resultsmentioning

confidence: 99%

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

Doi

Behera

Yamagata

2022

Geophysical Research Letters

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“…However, the reliability of such a projection has been questioned due to common model biases in the IO [47][48][49][50] . In comparison to observation, climate models exhibit stronger easterly winds over the equatorial IO, a larger west-east SST gradient, and a shallower thermocline in the EIO 47,48 .…”

Section: Introductionmentioning

confidence: 99%

Local meridional circulation changes contribute to a projected slowdown of the Indian Ocean Walker circulation

Sharma

Cai

et al. 2022

npj Clim Atmos Sci

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The weakening of zonal atmospheric circulation, a widely accepted projection of climate change in response to global warming, features a weakening of the Indian Ocean Walker circulation (IWC), with an anomalous ascending motion over the western and anomalous descending motion over the eastern Indian Ocean. The projected IWC weakening has previously been attributed to slower warming in the east than the west, that is, to a positive Indian Ocean Dipole (IOD)-like warming pattern. However, such a warming pattern can also be induced by IWC weakening. As a result, the cause-and-effect relationship cannot be easily determined, and the projected change is poorly constrained and highly uncertain. Here, using a suite of coupled climate model simulations under a high-emission scenario, we find that the IWC slowdown is accompanied by not only a positive IOD-like warming pattern but also anomalous meridional circulation that is associated with anomalous descending motion over the eastern Indian Ocean. We further show that the anomalous local meridional circulation is closely linked to enhanced land-sea thermal contrast and is unlikely to result from the positive IOD-like warming pattern, suggesting that the IWC weakening is in part driven by the anomalous local meridional circulation. Our findings underscore the important role of local meridional circulation changes in modulating future IWC changes.

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“…Because of man-made climate changes, it is most probable that the occurrence of anomalies in meridional monsoon and zonal Walker circulations in the tropical Indian Ocean increase in the future (Cai et al, 2013;Cai et al, 2020;King & Washington, 2021;Kripalani et al, 2003;Sharmila et al, 2015;Wang et al, 2015). However, their dynamics and how they impact precipitation are still under debate, causing uncertainties for regions that provide homes and livelihood for billions of people.…”

Section: Plain Language Summarymentioning

confidence: 99%

Summer and Autumn Insolation as the Pacemaker of Surface Wind and Precipitation Dynamics Over Tropical Indian Ocean During the Holocene: Insights From Paleoproductivity Records and Paleoclimate Simulations

Zhou,

Duchamp‐Alphonse,

Bassinot

et al. 2024

Paleoceanog and Paleoclimatol

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Insolation is the engine of monsoon and Walker circulations over the tropical Indian Ocean. Here, we present Holocene coccolith‐related net primary productivity (NPP) signals from two sediment cores retrieved in the wind‐driven coastal upwelling systems off southern India and southern Sumatra. Upwelling‐induced NPP is enhanced during summer and autumn and is a powerful tool to reconstruct atmospheric features at a seasonal scale. Our records indicate that during summer and autumn, westerly winds off southern India strengthened from the early‐Holocene (EH) to late‐Holocene (LH), while southeasterly winds off southern Sumatra strengthened from the EH to mid‐Holocene (MH) and weakened from the MH to LH. Comparisons with previous paleoclimate records and simulations, allow us to confirm such wind patterns at a regional scale and identify distinct atmospheric features associated to insolation before and after the MH. From the EH to MH, as the insolation in the Northern Hemisphere weakens during summer and strengthens during autumn, the equatorial Indian Ocean is characterized by more vigorous Walker and monsoon circulations in summer and autumn, respectively. From the MH to LH, as the insolation weakens in the Northern Hemisphere during summer and over the equator during autumn, the equatorial Indian Ocean is influenced by a general reinforcement of the Walker circulation during both seasons, a feature that we relate to a modern negative IOD‐like mode. The changes in wind result in increasing precipitation over Indonesia and India from EH to MH and over Indonesia from MH to LH as India is getting dryer.

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Future Changes in the Indian Ocean Walker Circulation and Links to Kenyan Rainfall

Cited by 5 publications

References 82 publications

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

Local meridional circulation changes contribute to a projected slowdown of the Indian Ocean Walker circulation

Summer and Autumn Insolation as the Pacemaker of Surface Wind and Precipitation Dynamics Over Tropical Indian Ocean During the Holocene: Insights From Paleoproductivity Records and Paleoclimate Simulations

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