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Southwest Monsoon-IMD Predicts Excessive Rainfall

Context:

September monsoon forecast by IMD, predicts excessive rainfall for south, west, central India

Relevance:

GS-I: Geography (Important Geophysical Phenomenon, Climatology)

Dimensions of the Article:

  1. Details
  2. What is Monsoon?
  3. Importance of Monsoon for India
  4. Issues with Prediction of monsoon in India
  5. La Niña

Details:

  • AS per the latest forecast issued by the India Meteorological Department (IMD), the Southwest Monsoon rainfall will be above-normal in most of India with reducedprecipitation over the North East, some parts of east and northwest India.
  • IMD predicted 75 per cent excess rainfall or more in many areas of Rajasthan, Gujarat, Maharashtra, Uttar Pradesh, Uttarakhand, Madhya Pradesh, Karnataka, Telangana, Andhra Pradesh and Mizoram.
  • All these states have received excess or normal rainfall between June 1 and September 1
  • It warns repeat of floods in the States of Gujarat and Karnataka as seen earlier.
  • The southern parts of Uttar Pradesh is projected to have more than 75 per cent excess rainfall, the northern parts would remain dry with rainfall deficit between 35 and 75 per cent. 
  • Rainfall may be 35-75 per cent deficient in parts of Ladakh, Bihar, Jharkhand, Odisha, Sikkim, Assam, Arunachal Pradesh, Nagaland and Meghalaya may also record 35-75 per cent rainfall deficit.
  • Manipur in North East India has the highest rainfall deficit in the country at 45 per cent, followed by Uttar Pradesh (44 per cent) and Bihar (38 per cent). Tripura and Jharkhand have 29 and 27 percent deficit in rainfall respectively.

Reasons:

  • The major climatic conditions that may affect the monsoon rainfall are the La Niña phenomenon in the equatorial Pacific Ocean and the Indian Ocean Dipole (IOD)
  • While the La Niña is in an active phase right now and generally enhances rainfall over the country, the Indian Ocean Dipole is evolving into its negative phase and may get established in the coming months.
  • A negative IOD generally dampens rainfall over many parts of the country.

What is Monsoon?

  • Monsoon connotes the climate associated with a seasonal reversal in the direction of winds. India has a hot monsoonal climate which is the prevalent climate in the south and southeast Asia.
  • The Indian summer monsoon typically lasts from June-September with large areas of western and central India receiving more than 90% of their total annual precipitation during the period, and southern and northwestern India receiving 50%-75% of their total annual rainfall.
  • Overall, monthly totals average 200-300 mm over the country as a whole, with the largest values observed during the heart of the monsoon season in July and August.

Causes of Monsoon

  • During the summer months, sunlight heats the surfaces of both lands and oceans, but land temperatures rise more quickly due to a lower heat capacity.
  • As the land’s surface becomes warmer, the air above it expands and an area of low pressure develops.
  • Meanwhile, the ocean remains at a lower temperature than the land and so the air above it retains a higher pressure.
  • Since winds flow from areas of the high-pressure area to low, this deficit in pressure over the continent causes winds to blow in an ocean-to-land circulation (a sea breeze).
  • As winds blow from the ocean to the land, moist air is brought inland. This is why summer monsoons cause so much rain.

Importance of Monsoon for India

The Monsoon is one of the most important single variables in the Indian economy as a good monsoon can reduce the burden on the government, while a bad one can make it spend more.

Positive effects of Monsoon

  • The agricultural prosperity of India depends very much on time and adequately distributed rainfall. If it fails, agriculture is adversely affected particularly in those regions where means of irrigation are not developed.
  • Regional variations in monsoon climate help in growing various types of crops.
  • Regional monsoon variation in India is reflected in the vast variety of food, clothes and house types.
  • Monsoon rain helps recharge dams and reservoirs, which is further used for the generation of hydroelectric power.
  • Winter rainfall by temperate cyclones in north India is highly beneficial for Rabi crops.

Negative effects of Monsoon

  • Variability of rainfall brings droughts or floods every year in some parts of the country.
  • Sudden monsoon burst creates a problem of soil erosion over large areas in India.
  • In hilly areas, sudden rainfall brings landslide which damages natural and physical infrastructure subsequently disrupting human life economically as well as socially.

Issues with Prediction of monsoon in India

Prediction of the exact behaviour of monsoon is very difficult and this makes it a problem for the Indian Metrological Department (IMD) as every year millions of Indians are dependent on its forecast.

  1. The topography of the Indian subcontinent makes the monsoon system very complex. Tropical weather is difficult to predict because weather systems in the tropics aren’t understood very well.
  2. The weather systems destabilise faster in the tropics than they do in the extra-tropics, where they persist for longer durations.
  3. Since it is difficult to predict the exact amount of rainfall, IMD relies just on a probabilistic forecast.
  4. A major problem has been to identify a small set of stable and independent parameters that influences the monsoon rainfall and the bulk of its variance. Many of the once strongly influencing parameters have declined in their correlations over the years – Hence, the search for a minimal set of stable and strongly enforcing parameters thus remains a constant one.
  5. Presently, the lack of enough and quality data (the IMD collects weather data like temperature, humidity, wind and precipitation through automatic weather stations, surface observatories, radiosonde or weather balloons, radars and three satellites) is one of the biggest challenges. There are also major data gaps, like those involving dust, aerosols, soil moisture and maritime conditions.
  6. Further, the automatic weather stations are of sub-standard quality. The upkeep of instruments is a major problem.
  7. Another issue is that dynamical models require a huge number of computations, for which supercomputers are required. As such, the need for an increased number of supercomputers remains a challenge for India.
  8. The correlation between El-Nino and Indian monsoon is still under research. And it is difficult to forecast exactly how much the El-Nino will affect.
  9. In addition to this, Global warming has also emerged as a factor that affects the monsoon forecast.

La Niña

  • La Niña is a coupled ocean-atmosphere phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation (ENSO) climate pattern.
  • During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3 to 5 °C (5.4 to 9 °F).
  • An appearance of La Niña persists for at least five months.
  • It has extensive effects on the weather across the globe, particularly in North America, even affecting the Atlantic and Pacific hurricane seasons, in which more tropical cyclones occur in the Atlantic basin due to low wind shear and warmer sea surface temperatures, while reducing tropical cyclogenesis in the Pacific Ocean.
  • La Niña is a complex weather pattern that occurs every few years, as a result of variations in ocean temperatures in the Equatorial Pacific.
  • It occurs as strong winds blow warm water at the ocean’s surface from South America across the Pacific Ocean towards Indonesia.
  • As this warm water moves west, cold water from the deep sea rises to the surface near South America.
  • As a result, it is considered to be the cold phase of the broader El Niño–Southern Oscillation weather pattern, as well as the opposite of El Niño weather pattern.
  • La Niña impacts the global climate and disrupts normal weather patterns, which as a result can lead to intense storms in some places and droughts in others.

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