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Characteristics of Lake Chad level variability and links to ENSO, precipitation, and river discharge.

Okonkwo C, Demoz B, Gebremariam S - ScientificWorldJournal (2014)

Bottom Line: The wavelet transform coherency (WTC) between LC level of the southern pool at Kalom and ENSO is statistically significant at the 95% confidence level and phase-locked, implying a cause-and-effect association.These strong coherencies coincide with the La Niña years with the exception of 1997-1998 El Niño events.Implications for water resource planning and management are discussed.

View Article: PubMed Central - PubMed

Affiliation: Beltsville Center for Climate System Observation (BCCSO), Atmospheric Science Program, Howard University, Washington, DC 20059, USA.

ABSTRACT
This study used trend, correlation, and wavelet analysis to characterize Lake Chad (LC) level fluctuations, river discharge, El Niño Southern Oscillation (ENSO), and precipitation regimes and their interrelationships. Linear correlation results indicate a negative association between ENSO and LC level, river discharge and precipitation. Trend analysis shows increasing precipitation in the Lake Chad Basin (LCB) but decreasing LC level. The mode of interannual variability in LC level, rainfall, and ENSO analyzed using wavelet analysis is dominated by 3-4-year periods. Results show that variability in ENSO could explain only 31% and 13% of variations in LC level at Kindjeria and precipitation in the northern LCB, respectively. The wavelet transform coherency (WTC) between LC level of the southern pool at Kalom and ENSO is statistically significant at the 95% confidence level and phase-locked, implying a cause-and-effect association. These strong coherencies coincide with the La Niña years with the exception of 1997-1998 El Niño events. The WTC shows strong covariance between increasing precipitation and LC level in the northern pool at a 2- to 4-year band and 3- to 4-year band localized from 1996 to 2010. Implications for water resource planning and management are discussed.

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Related in: MedlinePlus

ENSO and lake level cross-wavelet spectra: (a) northern LCB; (b) southern LCB and wavelet coherence; (c) northern LCB; and (d) southern LCB. The thick contour enclosed regions are greater than 95% confidence for a red-noise process. The thin solid line indicates the “cone of influence,” where edge effects become important.
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fig6: ENSO and lake level cross-wavelet spectra: (a) northern LCB; (b) southern LCB and wavelet coherence; (c) northern LCB; and (d) southern LCB. The thick contour enclosed regions are greater than 95% confidence for a red-noise process. The thin solid line indicates the “cone of influence,” where edge effects become important.

Mentions: Cross-wavelet transform of ENSO and LC level in the North Basin shows high common power (good correlation) at two bands: a 3- to 4-year band localized from 1985 to 1987 and a 3- to 4-year band localized between 1995 and 1997 (Figure 6(a)). The XWT between LC level in the Southern Basin and ENSO (Figure 6(b)) shows three common powers that are statistically significant: a 2- to 4-year band localized between 1983 and 1987, a 3-year band localized around 1997, and a 6-year band localized between 1987 and 1997. The 6-year periodicity of LC level in the northern pool (Figure 6(a)) has less significant power but the phase is locked. As a result, a strong link between ENSO and LC level at Kindjeria is speculated. Also, ENSO spectral coherence is very strong in the 3- to 8-year band around 1990–2000 (Figure 6(c)). The region that is statistically significant in the WTC at the periodicity of 3 to 8 years (Figure 6(b)), however, suggests that the association is not by chance. The 2- to 4-year band and the 3-year band correspond to the last two strongest ENSO events, namely, 1983-1984 and 1997-1998.


Characteristics of Lake Chad level variability and links to ENSO, precipitation, and river discharge.

Okonkwo C, Demoz B, Gebremariam S - ScientificWorldJournal (2014)

ENSO and lake level cross-wavelet spectra: (a) northern LCB; (b) southern LCB and wavelet coherence; (c) northern LCB; and (d) southern LCB. The thick contour enclosed regions are greater than 95% confidence for a red-noise process. The thin solid line indicates the “cone of influence,” where edge effects become important.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4265694&req=5

fig6: ENSO and lake level cross-wavelet spectra: (a) northern LCB; (b) southern LCB and wavelet coherence; (c) northern LCB; and (d) southern LCB. The thick contour enclosed regions are greater than 95% confidence for a red-noise process. The thin solid line indicates the “cone of influence,” where edge effects become important.
Mentions: Cross-wavelet transform of ENSO and LC level in the North Basin shows high common power (good correlation) at two bands: a 3- to 4-year band localized from 1985 to 1987 and a 3- to 4-year band localized between 1995 and 1997 (Figure 6(a)). The XWT between LC level in the Southern Basin and ENSO (Figure 6(b)) shows three common powers that are statistically significant: a 2- to 4-year band localized between 1983 and 1987, a 3-year band localized around 1997, and a 6-year band localized between 1987 and 1997. The 6-year periodicity of LC level in the northern pool (Figure 6(a)) has less significant power but the phase is locked. As a result, a strong link between ENSO and LC level at Kindjeria is speculated. Also, ENSO spectral coherence is very strong in the 3- to 8-year band around 1990–2000 (Figure 6(c)). The region that is statistically significant in the WTC at the periodicity of 3 to 8 years (Figure 6(b)), however, suggests that the association is not by chance. The 2- to 4-year band and the 3-year band correspond to the last two strongest ENSO events, namely, 1983-1984 and 1997-1998.

Bottom Line: The wavelet transform coherency (WTC) between LC level of the southern pool at Kalom and ENSO is statistically significant at the 95% confidence level and phase-locked, implying a cause-and-effect association.These strong coherencies coincide with the La Niña years with the exception of 1997-1998 El Niño events.Implications for water resource planning and management are discussed.

View Article: PubMed Central - PubMed

Affiliation: Beltsville Center for Climate System Observation (BCCSO), Atmospheric Science Program, Howard University, Washington, DC 20059, USA.

ABSTRACT
This study used trend, correlation, and wavelet analysis to characterize Lake Chad (LC) level fluctuations, river discharge, El Niño Southern Oscillation (ENSO), and precipitation regimes and their interrelationships. Linear correlation results indicate a negative association between ENSO and LC level, river discharge and precipitation. Trend analysis shows increasing precipitation in the Lake Chad Basin (LCB) but decreasing LC level. The mode of interannual variability in LC level, rainfall, and ENSO analyzed using wavelet analysis is dominated by 3-4-year periods. Results show that variability in ENSO could explain only 31% and 13% of variations in LC level at Kindjeria and precipitation in the northern LCB, respectively. The wavelet transform coherency (WTC) between LC level of the southern pool at Kalom and ENSO is statistically significant at the 95% confidence level and phase-locked, implying a cause-and-effect association. These strong coherencies coincide with the La Niña years with the exception of 1997-1998 El Niño events. The WTC shows strong covariance between increasing precipitation and LC level in the northern pool at a 2- to 4-year band and 3- to 4-year band localized from 1996 to 2010. Implications for water resource planning and management are discussed.

Show MeSH
Related in: MedlinePlus