How Does El Niño Cause Drought in One Place and Floods in Another?

The El Niño phenomenon can alter climate patterns worldwide, causing some regions to face rainfall shortages and drought while others experience heavy rain and flooding. But how can a single phenomenon produce opposite consequences?

According to Ambassador Arjan, the effect of El Nino is not limited to the Pacific Ocean. This phenomenon can change the patterns of atmospheric circulation and rainfall in remote areas through long-range atmospheric communication called "teleconnection". One of the important mechanisms in this process is the change in the latent heat released during the formation of clouds and precipitation. The displacement of the main areas of convection and precipitation in tropical regions can change the temperature of different parts of the troposphere and affect the circulation of the atmosphere in other regions. These changes in some seasons can increase the probability of low rainfall in the Sahel region of Africa, located south of the Great Sahara. However, the intensity and direction of this effect depends on the season, the type of El Niño event and other atmospheric conditions.

Another mechanism is changes in large-scale atmospheric waves that can alter the path of jet streams and storm systems in distant regions. El Nino may affect the climate in Europe, including the UK, but to attribute increased autumn rainfall or the occurrence of cold winter spells to this phenomenon, specific and seasonal evidence must be relied upon.

El Niño can also interact with the Indian Ocean Dipole. This phenomenon is related to the difference in water surface temperature in the western and eastern parts of the Indian Ocean and plays an important role in changing the rainfall patterns of East Africa. These two phenomena can influence each other, but El Nino does not necessarily cause the formation of the Indian Ocean Dipole.

Under normal conditions, the trade winds in the tropical Pacific Ocean blow from east to west and direct the warm surface waters to the west of the ocean. In the eastern Pacific Ocean, during a process called upwelling, colder water from the underlying layers rises to the surface and replaces the surface water pushed westward.

Hot water increases evaporation. The moist air above this water is also heated and moves upwards. As the air cools at altitude, water vapor condenses and forms clouds and rain. For this reason, parts of Indonesia usually have a lot of rain, while the coast of Peru in South America is drier.

But during El Nino, the prevailing winds weaken and warm surface waters spread eastward, and sea surface temperatures rise in the central and eastern Pacific. As a result, the main area of ​​evaporation, ascent of moist air and cloud formation is shifted to the east.

How does the effect of El Niño reach distant places?

El Niño's influence is not limited to the Pacific Ocean. This phenomenon can change the wind and rainfall patterns at a distance of thousands of kilometers through atmospheric communication called "teleconnection".

One of the important mechanisms is the change in heat released during the formation of clouds and precipitation. The displacement of the main regions of air ascent can change the temperature of the middle and upper layers of the atmosphere in the tropics. These changes may make it more difficult for moist air to ascend and form rain clouds in some areas, increasing the likelihood of drought.

Another mechanism is the creation of large atmospheric waves that can change the direction of winds and storm systems in distant areas. El Nino can also affect the phenomenon called "Indian Ocean Dipole" by changing the conditions of the Indian Ocean. This phenomenon is related to the difference in water temperature in the western and eastern parts of the Indian Ocean and is involved in changing the rainfall patterns of East Africa and parts of India.

Some areas of Thailand may still experience heavy rains and floods during the period when El Nino is associated with reduced rainfall in parts of Southeast Asia. In India, the reduction of rainfall in the overall monsoon scale can occur simultaneously with heavy rains and floods in some areas. To use these examples, the year and source of the data must be known.

These differences show that regional patterns of atmospheric circulation, the path of precipitation systems and storms, and other atmospheric factors can produce a different result from the general trend associated with El Niño.

Finally, El Nino is not the definitive cause of all droughts and floods. Knowing the interaction between the ocean and the atmosphere, together with the study of regional conditions, can help to better predict climate risks and better prepare communities.