scholarly journals Characteristics of Lake Chad Level Variability and Links to ENSO, Precipitation, and River Discharge

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Churchill Okonkwo ◽  
Belay Demoz ◽  
Sium Gebremariam
Keyword(s):  
Wavelet Analysis ◽  
El Niño ◽  
River Discharge ◽  
El Nino ◽  
Southern Oscillation ◽  
Resource Planning ◽  
Precipitation Trend ◽  
Lake Chad ◽  
Precipitation Regimes ◽  
Increasing Precipitation

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.

scholarly journals Combined effect of El Niño southern oscillation and Atlantic multidecadal oscillation on Lake Chad level variability

2015 ◽  
Vol 1 (1) ◽  
pp. 1117829 ◽  
Author(s):  
Churchill Okonkwo ◽  
Belay Demoz ◽  
Ricardo Sakai ◽  
Charles Ichoku ◽  
Chigozie Anarado ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Atlantic Multidecadal Oscillation ◽  
Combined Effect ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Lake Chad

scholarly journals Influence of three phases of El Niño–Southern Oscillation on daily precipitation regimes in China

2019 ◽  
Vol 23 (2) ◽  
pp. 883-896 ◽  
Author(s):  
Aifeng Lv ◽  
Bo Qu ◽  
Shaofeng Jia ◽  
Wenbin Zhu
Keyword(s):  
El Niño ◽  
Daily Precipitation ◽  
El Nino ◽  
Southern Oscillation ◽  
Annual Precipitation ◽  
Rainfall Events ◽  
Enso Events ◽  
Precipitation Regimes ◽  
Precipitation Anomalies ◽  
Three Phases

Abstract. In this study, the impacts of the El Niño–Southern Oscillation (ENSO) on daily precipitation regimes in China are examined using data from 713 meteorological stations from 1960 to 2013. We discuss the annual precipitation, frequency and intensity of rainfall events, and precipitation extremes for three phases (eastern Pacific El Niño – EP, Central Pacific El Niño – CP, and La Niña – LN) of ENSO events in both ENSO developing and ENSO decaying years. A Mann–Whitney U test was applied to assess the significance of precipitation anomalies due to ENSO. Results indicated that the three phases each had a different impact on daily precipitation in China and that the impacts in ENSO developing and decaying years were significantly different. EP phases caused less precipitation in developing years but more precipitation in decaying years; LN phases caused a reverse pattern. The precipitation anomalies during CP phases were significantly different than those during EP phases, and a clear pattern was found in decaying years across China, with positive anomalies over northern China and negative anomalies over southern China. Further analysis revealed that anomalies in frequency and intensity of rainfall accounted for these anomalies in annual precipitation; in EP developing years, negative anomalies in both frequency and intensity of rainfall events resulted in less annual precipitation, while in CP decaying years, negative anomalies in either frequency or intensity typically resulted in reduced annual precipitation. ENSO events tended to trigger extreme precipitation events. In EP and CP decaying years and in LN developing years, the number of very wet day precipitation (R95 p), the maximum rainfall in 1 day (Rx1d), and the number of consecutive wet days (CWD) all increased, suggesting an increased risk of flooding. On the other hand, more dry spells (DSs) occurred in EP developing years, suggesting an increased likelihood of droughts during this phase. Possible mechanisms responsible for these rainfall anomalies are speculated to be the summer monsoon and tropical cyclone anomalies in ENSO developing and decaying years.

scholarly journals A Regime-Based Evaluation of TRMM Oceanic Precipitation Biases

2017 ◽  
Vol 34 (12) ◽  
pp. 2613-2635 ◽  
Author(s):  
David S. Henderson ◽  
Christian D. Kummerow ◽  
David A. Marks ◽  
Wesley Berg
Keyword(s):  
El Niño ◽  
Rain Rate ◽  
El Nino ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Convective Systems ◽  
Enso Events ◽  
Precipitation Regimes ◽  
Rain Rates ◽  
Stratiform Rainfall

AbstractOver the tropical oceans, large discrepancies in TRMM passive and active microwave rainfall retrievals become apparent during El Niño–Southern Oscillation (ENSO) events. This manuscript describes the application of defined precipitation regimes to aid the validation of instantaneous rain rates from TRMM using the S-band radar located on the Kwajalein Atoll. Through the evaluation of multiple case studies, biases in rain-rate estimates from the TRMM radar (PR) and radiometer (TMI) are best explained when derived as a function of precipitation organization (e.g., isolated vs organized) and precipitation type (convective vs stratiform). When examining biases at a 1° × 1° scale, large underestimates in both TMI and PR rain rates are associated with predominately convective events in deep isolated regimes, where TMI and PR retrievals are underestimated by 37.8% and 23.4%, respectively. Further, a positive bias of 33.4% is observed in TMI rain rates within organized convective systems containing large stratiform regions. These findings were found to be consistent using additional analysis from the DYNAMO field campaign. When validating at the TMI footprint scale, TMI–PR differences are driven by stratiform rainfall variability in organized regimes; TMI overestimates this stratiform precipitation by 92.3%. Discrepancies between TMI and PR during El Niño events are related to a shift toward more organized convective systems and derived TRMM rain-rate bias estimates are able to explain 70% of TMI–PR differences during El Niño periods. An extension of the results to passive microwave retrievals reveals issues in discriminating convective and stratiform rainfall within the TMI field of view (FOV), and significant reductions in bias are found when convective fraction is constrained within the Bayesian retrieval.

scholarly journals Influence of three phases of El Niño-Southern Oscillation on daily precipitation regimes in China

2018 ◽  
Author(s):  
Aifeng Lv ◽  
Bo Qu ◽  
Shaofeng Jia ◽  
Wenbin Zhu
Keyword(s):  
El Niño ◽  
Daily Precipitation ◽  
El Nino ◽  
Southern Oscillation ◽  
Annual Precipitation ◽  
Rainfall Events ◽  
Enso Events ◽  
Precipitation Regimes ◽  
Precipitation Anomalies ◽  
Three Phases

Abstract. In this study, the impacts of the El Niño-Southern Oscillation (ENSO) on daily precipitation regimes in China are examined using data from 713 meteorological stations from 1960 to 2013. We discuss the annual precipitation, frequency and intensity of rainfall events, and precipitation extremes for three phases (Eastern Pacific El Niño (EP), Central Pacific El Niño (CP), and La Niña (LN)) of ENSO events in both ENSO developing and ENSO decaying years. A Mann–Whitney U test was applied to assess the significance of precipitation anomalies due to ENSO. Results indicated that the three phases each had a different impact on daily precipitation in China and that the impacts in ENSO developing and decaying years were significantly different. EP phases caused less precipitation in developing years but more precipitation in decaying years; LN phases caused a reverse pattern. The precipitation anomalies during CP phases were significantly different than those during EP phases and a clear pattern was found in decaying years across China, with positive anomalies over northern China and negative anomalies over southern China. ENSO events which altered the frequency and intensity of rainfall roughly paralleled anomalies in annual precipitation; in EP developing years, negative anomalies in both frequency and intensity of rainfall events resulted in less annual precipitation while in CP decaying years, negative anomalies in either frequency or intensity typically resulted in reduced annual precipitation. ENSO events triggered more extreme precipitation events. In EP and CP decaying years and in LN developing years, the number of very wet days (R95p), the maximum rainfall in one day (Rx1d), and the number of consecutive wet days (CWD) all increased, suggesting an increased risk of flooding. In addition, more dry spells (DS) occurred in EP developing years, suggesting an increased likelihood of droughts during this phase.

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