Final answer:
La Niña generally decreases monsoon rainfall due to its cooler-than-average sea surface temperatures in the eastern Pacific, which can affect atmospheric pressure and disrupt the normal monsoon patterns.
Step-by-step explanation:
La Niña typically decreases monsoon rainfall in the regions affected by the monsoon climate system. La Niña is characterized by cooler-than-average sea surface temperatures (SST) in the eastern Pacific, which can lead to high air pressure in the eastern Pacific and low in the western Pacific. The ENSO cycle, which includes both La Niña and El Niño, is known to influence global weather patterns, including altering the intensity and distribution of rainfall during monsoon seasons. During La Niña events, regions that normally experience monsoon rains may see diminished rainfall, impacting agriculture and water supply.
The Monsoon
The summer monsoon is critical for providing the rainfall necessary for agriculture in South Asia. It's a complex system influenced by numerous factors, including sea surface temperatures and the differential heating of land and sea. Any change in these dynamics, such as those introduced during La Niña events, can significantly alter the monsoon’s behavior. Therefore, La Niña's cooling effect on ocean waters tends to weaken the monsoon system, reducing the amount of summer rainfall in affected regions.