‘Onset’ of the Monsoon| Class 11 Geography Notes

Class 11 Geography ‘Onset’ of the Monsoon Notes: These notes are helpful for Class 11 students learning about the onset of the monsoon. It covers important topics such as what causes the monsoon to begin, how pressure systems affect it, and what happens in different regions when the monsoon arrives.

By studying these notes, students can gain a better understanding of how the monsoon influences weather patterns, farming, and people’s lives in India. The explanations are clear and easy to follow, making it easier for students to grasp this important concept.

‘Onset’ of the Monsoon| Class 11 Geography Notes

What is the “Onset” of the Monsoon?

The onset of the monsoon marks the arrival of the southwest monsoon winds over the Indian subcontinent, occurring around late May or early June in Kerala and progressing northward over subsequent weeks.

During the Southwest Monsoon, India receives over 70% of its annual rainfall. However, the onset does not necessarily coincide with the first rainfall of the season, which may occur in certain areas even before the official onset is declared.

According to the Indian Meteorological Department (IMD), the onset of the monsoon is determined by significant transitions in the large-scale atmospheric and oceanic circulations in the Indo-Pacific region. The IMD announces the onset of the monsoon only after specific, precisely defined, and measurable parameters are met.

Conditions for the Onset of Monsoon

The necessary conditions for onset of monsoon are as follows:

Rainfall

The onset of the monsoon is declared if at least 60% of 14 designated meteorological stations in Kerala and Lakshadweep record at least 2.5 mm of rain for two consecutive days after May 10. The onset over Kerala is declared on the second day, provided specific wind and temperature criteria are also met.

Wind Field

According to the IMD, the depth of westerlies should extend up to 600 hectopascal (hPa) in the area bounded by the equator to 10ºN latitude, and from longitude 55ºE to 80ºE. The zonal wind speed over the region bound by 5-10ºN latitude (Maldives to Kochi) and 70-80ºE longitude (Arabian Sea to Chennai) should be around 15-20 knots (28-37 kph) at 925 hPa.

Heat

The INSAT-derived Outgoing Longwave Radiation (OLR) value should be below 200 watts per square meter (wm2) in the area between 5ºN and 10ºN latitudes, and 70ºE and 75ºE longitudes.

Is a delay in the onset of the monsoon unusual?

The normal date for the onset of the monsoon over the Kerala coast is June 1, and significant delays, like the one observed this year, are not uncommon. However, neither an early nor a late onset of the monsoon is unusual. For example, in recent years such as 2021, 2019, 2016, and others, the monsoon onset was declared after June.

The timing of the onset does not necessarily correlate with the quality or quantity of rainfall or its regional distribution across the country. In some instances, despite an early onset, the season may end with below-average rainfall, highlighting the unpredictable nature of the monsoon.

Does a delayed onset mean cascading delays across the country and for the rest of the season?

A delay in the onset over Kerala can potentially postpone the arrival of the monsoon in other parts of the country, particularly in the southern states, which typically begin receiving rain shortly after the monsoon reaches the Kerala coast. The northward progression of the monsoon after its arrival in Kerala is not consistent and is influenced by local factors such as the formation of low-pressure areas. Consequently, the monsoon may linger over certain regions in certain years or advance more rapidly than usual.

However, it has been observed that despite a delayed onset over Kerala, other regions of the country may still receive monsoon rainfall on schedule. This indicates that the timing of the monsoon’s onset in one area does not necessarily dictate the timing of its arrival in other regions, highlighting the complex and variable nature of monsoon dynamics.

Impact of Monsoons life in India

Agriculture: The monsoon is crucial for agriculture in India, as a significant portion of the population relies on rain-fed farming. The timely arrival and distribution of monsoon rains are essential for crop growth and yield.

Water Resources: The monsoon plays a vital role in replenishing water resources such as rivers, reservoirs, lakes, and groundwater. Adequate rainfall during the monsoon season ensures sufficient water availability for drinking, irrigation, and other needs.

Flooding: The intense rainfall associated with the monsoon can lead to flooding in many parts of India. Excessive rainfall can overwhelm drainage systems and cause rivers to overflow, resulting in inundation of low-lying areas, damage to crops, infrastructure, and loss of lives.

Public Health: During the monsoon season, stagnant water and increased humidity create favorable conditions for the breeding of mosquitoes. This, in turn, leads to the spread of diseases like malaria, dengue fever, and chikungunya, posing significant health risks to the population. Waterborne diseases may also become more prevalent due to contamination of water sources during heavy rainfall and flooding.

Impacts of Climate change on the Indian monsoon

Changes in Rainfall Patterns: Climate change may alter the spatial and temporal distribution of rainfall during the monsoon season. This could result in shifts in the intensity and frequency of rainfall, leading to changes in the patterns of precipitation across different regions. Areas that traditionally receive abundant rainfall may experience drier conditions, while regions with lesser rainfall may witness increased precipitation.

Monsoon Variability: Climate change may lead to increased variability in the monsoon, with fluctuations in the onset, duration, and withdrawal of the monsoon season. Variability in monsoon patterns can impact agricultural practices, water resource management, and overall socio-economic activities dependent on monsoon rains. Understanding and adapting to these changes are crucial for sustainable development and resilience to climate impacts.

Conclusion

The onset of the monsoon means the start of the rainy season in India. It’s when the Southwest Monsoon winds bring rain to the country. Rain is very important for farming, filling up rivers and lakes. The India Meteorological Department tells us when the monsoon starts based on certain rules, like how much rain falls in Kerala and the direction of the wind. Sometimes, the monsoon starts late, but that doesn’t mean the rain will be less or the season will be bad. It isimportant to pay attention to the monsoon because it affects many parts of our lives.

Related Links

1. CBSE Notes Class 10 Geography Chapter 4 – Agriculture
2. CBSE Notes Class 10 Geography Chapter 5: Minerals and Energy Resources
3. CBSE Notes Class 10 Geography Chapter 7- Lifelines of National Economy
4. Manufacturing Industries Class 10 Geography Notes Chapter 6

FAQs on Class 11 Geography ‘Onset’ of the Monsoon

What does “onset of the monsoon” mean?

The “onset of the monsoon” refers to the beginning of the rainy season in India when the Southwest Monsoon winds bring rain to the country.

How is the onset of the monsoon determined?

Onset of the monsoon is determined by the India Meteorological Department (IMD) based on specific criteria such as rainfall patterns in Kerala and the direction of the wind.

Why is the onset of the monsoon important?

Onset of the monsoon is important because it marks the beginning of the rainy season, which is important for agriculture, water resources, and overall public health in India.

Can the onset of the monsoon be delayed?

Yes, the onset of the monsoon can be delayed, but this doesn’t necessarily mean that the rainy season will be less productive or that there will be less rain overall.