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El Niño and La Niña

The impact of El Niño and La Niña on the climate of Hong Kong




El Niño

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In winter (Dec-Feb) and spring (Mar-May), El Niño affects the atmospheric circulation over the northern part of the South China Sea, bringing generally more rainfall to the coastal region compared to normal condition (Figure 1a and 1b).

 

Winter rainfall of Hong Kong

Figure 1a    Winter (Dec-Feb) rainfall of Hong Kong, 1950-2013.  
 

 

Spring rainfall of Hong Kong

Figure 1b    Spring (Mar-May) rainfall of Hong Kong, 1950-2013.

 Temperature and rainfall statistics during El Niño springs, summers, autumns & winters in recent decades



During El Niño, there are fewer tropical cyclones developed in April and May and the genesis positions are usually located further east over the western North Pacific compared to normal condition. Hence, tropical cyclones are unlikely to affect the territory before June (Figure 2).

 

Number of TC coming within 500 km of HK

 Figure 2    Number of tropical cyclones coming within 500 km of Hong Kong, 1961-2013.

 


 

La Niņa

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During La Niña, the northeast monsoon over southern China is generally stronger in autumn (Sep-Nov) and winter (Dec-Feb), bringing lower temperature in Hong Kong compared to normal condition (Figure 3a and 3b).

 

Autumn temperature of Hong Kong

Figure 3a    Autumn (Sep-Nov) temperature of Hong Kong, 1950-2013.

 

Winter temperature of Hong Kong

Figure 3b    Winter (Dec-Feb) temperature of Hong Kong, 1950-2013.


 Temperature and rainfall statistics during La Niña springs, summers, autumns & winters in recent decades


During La Niña, tropical cyclones in August-October are likely driven by an anomalous steering flow into the South China Sea and hence more tropical cyclones are likely to affect Hong Kong compared to normal condition (Figure 4).


Number of TC coming within 500 km of HK in Aug-Oct
Figure 4 Number of tropical cyclones coming within 500 km of Hong Kong in August-October, 1961-2013.

 


Note:
1.
Normal condition refers to the situation with neither an El Niño nor a La Niña in place.


Related links:
What are El Niņo, La Niña, ENSO?
Latest status of El Niño and La Niña
References on El Niño and La Niña

Seasonal forecastAnnual outlookClimate change | 



Last revision date: <19 Jun 2014>