Prof. Ramesh Shrestha 

Monsoon season is the major rainy time of year in Nepal, which falls in between mid–June and September. This is also summer time with wet period as well. During the Monsoon, it rains almost every day with occasional thunderstorms in the evenings also. Practically, Monsoon in Nepal is a great season as it brings heavy and long rainfalls, which is a boon for Nepalese agriculture and biodiversity.
The word monsoon is derived from Arabic word ‘Mausam’ meaning ‘season’. Mausam means a season in Nepali language also. This term was first used in English in British India and neighbouring countries to refer to the big seasonal winds bringing heavy rainfall to the region. Monsoon Meteorology, defines it as a seasonal reversing wind accompanied by corresponding changes in precipitation patterns.
Monsoons are large–scale sea breezes that take place when the temperature on land is significantly warmer (in summer) or cooler (in winter) than the temperature of the ocean. Monsoons are found throughout the world. The summer monsoon brings a humid climate and torrential rainfall to these areas.

Monsoon In South Asia
The summer and monsoons determine the climate for most of India and Southeast Asia. The summer monsoon is associated with heavy rainfall. Monsoon (in South Asia) is a system of winds, which is characterised by a seasonal reversal of wind direction, first applied to the winds blowing over the Arabian Sea and Bay of Bengal from the southwest for six months (April to September) and from the northeast for remaining six months (October to March).
It is a great southwest monsoon sea breeze that carries a large mass of water molecules blowing from a large body of water towards the hot dry land created due to differences in the air pressure. The summer monsoons roar onto the subcontinent from the southwest with the winds carrying moisture from the Indian Ocean and bringing heavy rains from June to September.
The monsoon of South Asia is among several geographically distributed global monsoons. The monsoon affects the Indian subcontinent, where it is one of the oldest and most anticipated weather phenomena and an economically important pattern every year from June through September. However, it is partly understood and infamously complicated to envisage even today. There are several theories that have tried to explain its origin, process, strength, variability, distribution and general notions, but still truly understanding and predicting are still in question. The exclusive geographical features of the Indian subcontinent with associated atmospheric, oceanic, and geophysical factors influence the behaviour of the monsoon.

Monsoon in Nepal
As Nepal lies within the Indian sub–continent geographical location on the southern slopes of great Himalayas, this country has significant summer monsoon season. Normally, Nepal receives an average of 105 days with around 80% of rains in the monsoon from mid–June to September. The monsoon in Nepal originates from the Bay of Bengal and moves along the southern flanks of the Himalayas. In Nepal, the eastern part of the country receives more rainfall from monsoon precipitation as it is nearer to Bay of Bengal. There is occasional rainfall during other seasons too, which does not belong to the part of summer monsoon.
Seasons in Nepal: Nepal lies in the temperate zone, but its climate varies dramatically due to the huge range in altitude across the country. Our country is probably most famous for its altitude as it contains the highest mountain in the world, Mount Everest (height 8,850). The most common dominant type of climate for Nepal is temperate with dry winter and hot summer (Cwa) or mild temperate climate under Köppen climate classification. In western world there are 4 seasons but, Nepal has 6 seasons. Two additional seasons in Nepal are Rainy season and Pre–winter season beside the normal summer, autumn, winter and spring. The average annual rainfall of Nepal is 1,600 mm, but it varies by eco–climatic zones with extremes, such as 3,345 mm in Pokhara and below 300 mm in Mustang. In an average 1,300 mm of rain falls in Kathmandu valley every year. Winter rains are more pronounced in the western hills.

Himalayas A Climatic Barrier
The Himalayas act as a barrier to the cold winds blowing from Central Asia in winter, and forms the northern boundary of the monsoon wind patterns. Winter rains are more pronounced in the western hills. Actually, the high mountains of the Himalayan Region are the successive growth of the hills in this region; climate and land is both moderate. Because of gentle hill slopes, river basins, wide valleys they receive enough rain and are most arable making Nepal an agricultural country.
Because of monsoon effects on agriculture, on flora and fauna and on the climates of our country as well as other nearby countries like Bangladesh, Bhutan, India, Pakistan and Sri Lanka it is one of the most anticipated, tracked, and studied weather phenomena in Nepal also. It has a significant consequence on the overall well being with economic, social, and environmental positive effects for more than one billion population of the region. During this time paddy is planted on arable fields everywhere, thus rice is the staple food of Nepali people. Increase in temperature and vents of erratic rainfall directly affect the agriculture and food supply through their effects on crops. The monsoon rains spread attractiveness with lush green vegetation far and wide everywhere.

(Prof. Shrestha writes about environment)