In the hot seat: Insolation, ENSO, and vegetation in the African tropics

Ivory, Sarah J.; Russell, J. L.; Cohen, Andrew S.

doi:10.1002/jgrg.20115

Cited by 6 publications

(4 citation statements)

References 65 publications

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“…The savanna plains reveal such a clear phenological cycle since they are strongly linked with the bimodal annual rainfall distribution [51]. For the entire north-eastern quarter of the study area, for instance, Detsch et al [11] reported long-term seasonal amplitudes in the range of 0.2 between the long rains and the pronounced dry season.…”

Section: Seasonalitymentioning

confidence: 81%

A Comparative Study of Cross-Product NDVI Dynamics in the Kilimanjaro Region—A Matter of Sensor, Degradation Calibration, and Significance

et al. 2016

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While satellite-based monitoring of vegetation activity at the earth's surface is of vital importance for many eco-climatological applications, the degree of agreement among certain sensors and products providing estimates of the Normalized Difference Vegetation Index (NDVI) has been found to vary considerably. In order to assess the extent of such differences in highly heterogeneous terrain, we analyze and compare intra-annual seasonal fluctuations and long-term monotonic trends (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) in the Kilimanjaro region, Tanzania. The considered NDVI datasets include the Moderate Resolution Imaging Spectroradiometer (MODIS) products from Terra and Aqua, Collections 5 and 6, and the 3rd Generation Global Inventory Modeling and Mapping Studies (GIMMS) product. The degree of agreement in seasonal fluctuations is assessed by calculating a pairwise Index of Association (IOA s ), whereas long-term trends are derived from the trend-free pre-whitened Mann-Kendall test. On the seasonal scale, the two Terra-MODIS products (and, accordingly, the two Aqua-MODIS products) are best associated with each other, indicating that the seasonal signal remained largely unaffected by the new Collection 6 calibration approach. On the long-term scale, we find that the negative impacts of band ageing on Terra-MODIS NDVI have been accounted for in Collection 6, which now distinctly outweighs Aqua-MODIS in terms of greening trends. GIMMS NDVI, by contrast, fails to capture small-scale seasonal and trend patterns that are characteristic for the highly fragmented landscape which is likely owing to the coarse spatial resolution. As a short digression, we also demonstrate that the amount of false discoveries in the determined trend fraction is distinctly higher for p < 0.05 (52.6%) than for p < 0.001 (2.2%) which should point the way for any future studies focusing on the reliable deduction of long-term monotonic trends.

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Section: Seasonalitymentioning

confidence: 81%

A Comparative Study of Cross-Product NDVI Dynamics in the Kilimanjaro Region—A Matter of Sensor, Degradation Calibration, and Significance

et al. 2016

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“…Near‐real time monitoring of IOD and ENSO teleconnections is therefore essential in developing early warning systems for drought risk in East Africa [ Pozzi et al , ; Pulwarty and Sivakumar , ]. Ivory et al [] found that the impact of interannual climatic variability on vegetation is also expressed through fluctuations in atmospheric circulation resulting in alterations of the dry season length. SST‐derived indices such as ONI and DMI are thus not the sole indicators of imminent wet and dry episodes.…”

Section: Discussionmentioning

confidence: 99%

Vegetation response to precipitation variability in East Africa controlled by biogeographical factors

et al. 2016

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Ecosystem sensitivity to climate variability varies across East Africa, and identifying the determinant factors of this sensitivity is crucial to assessing region‐wide vulnerability to climate change and variability. Such assessment critically relies on spatiotemporal data sets with inherent uncertainty, on new processing techniques to extract interannual variability at a priori unknown time scales and on adequate statistical models to test for biogeographical effects on vegetation‐precipitation relationships. In this study, interannual variability in long‐term records of normalized difference vegetation index and satellite‐based precipitation estimates was detected using ensemble empirical mode decomposition and standardized precipitation index with varying accumulation periods. Environmental effect modeling using additive models with spatially correlated effects showed that ecosystem sensitivity is primarily predicted by biogeographical factors such as annual precipitation distribution (reaching maximum sensitivity at 500 mm yr−1), vegetation type and structure, ocean‐climate coupling, and elevation. The threat of increasing climate variability and extremes impacting productivity and stability of ecosystems is most imminent in semiarid grassland and mixed cropland ecosystems. The influence of oceanic phenomena such as El Niño–Southern Oscillation and Indian Ocean Dipole is foremost reflected in precipitation variability, but prolonged episodes also pose risks for long‐term degradation of tree‐rich ecosystems in the East African Great Lakes region.

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“…Important ocean‐atmosphere factors, such as the El Niño‐Southern Oscillation (ENSO), as the strongest signal of inter‐annual climate variability at low latitudes, can directly affect the local climate through atmospheric circulation. Previous studies have demonstrated that ENSO‐related atmospheric circulation can significantly affect the climate in low‐latitude regions such as the Amazon (Asner et al., 2000), Indonesia (Erasmi et al., 2009), Australia (Jones et al., 2001) and tropical Africa (Ivory et al., 2013) and cause evident anomalies in vegetation conditions. However, the Walker circulation plays an essential role.…”

Section: Introductionmentioning

confidence: 99%

Joint Impact of the AO and ENSO on Vegetation NPP Over Indo‐Myanmar in Boreal Winter

Lan,

Gong

2024

JGR Atmospheres

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In this paper, the authors quantitatively investigated the joint impact of the Arctic Oscillation (AO) and El Niño‐Southern Oscillation (ENSO) on vegetation net primary productivity (NPP) over Indo‐Myanmar in boreal winter from 1981 to 2018, and found that there is a significant in‐phase variation between them. When the warm ENSO co‐occurs with the positive AO, the NPP in more than 80% of the grids in the study region significantly increases by approximately 24 gC m−2. For the cold ENSO plus the negative AO, the regionally averaged NPP anomalies are approximately −10 gC m−2, and the local minimum is as low as −60 gC m−2. The combination of AO and ENSO can explain approximately 36% of the total variance of NPP in Indo‐Myanmar. The AO/ENSO linkages to the NPP are very likely due to regional precipitation anomalies through atmospheric circulation. In association with the positive (negative) AO, the Rossby wave, propagating eastward along the subtropical jet stream, brings an anomalous cyclone (anticyclone) over Indo‐Myanmar. This enhances (weakens) Indo‐Myanmar Trough, and resulting in more (less) regional precipitation. During the warm (cold) ENSO, through the Gill‐type response, an anomalous high (low)‐pressure appears in the lower and middle troposphere over Philippine‐South China Sea. The Walker circulation is also weaker (stronger) than normal. These are conducive to anomalous southerly (northerly) winds in Indochina. As a result, in the warm ENSO plus positive AO winters, the mean precipitation anomaly in Indo‐Myanmar increased by 27% as averaged for five data sets. In contrast, when the cold ENSO co‐occurs with negative AO, the precipitation is significantly reduced where the largest anomaly exceeds 100 mm in the ERA5. The precipitation changes are consistent with the local NPP anomalies, whereas the temperature does not seem to be a dominant limiting factor.

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In the hot seat: Insolation, ENSO, and vegetation in the African tropics

Cited by 6 publications

References 65 publications

A Comparative Study of Cross-Product NDVI Dynamics in the Kilimanjaro Region—A Matter of Sensor, Degradation Calibration, and Significance

A Comparative Study of Cross-Product NDVI Dynamics in the Kilimanjaro Region—A Matter of Sensor, Degradation Calibration, and Significance

Vegetation response to precipitation variability in East Africa controlled by biogeographical factors

Joint Impact of the AO and ENSO on Vegetation NPP Over Indo‐Myanmar in Boreal Winter

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