Chasing Indias monsoon

Written by Sandip Das | Updated: Jun 26 2012, 06:34am hrs
What is the usual progress path and duration of the Indian monsoon

The southwest summer monsoon enters the country because of a low-pressure area thats caused by the extreme heat of the Thar Desert and adjoining areas, during summer. The term was first used by the British, to refer to the big seasonal winds blowing from the Bay of Bengal and Arabian Sea in the southwest, bringing heavy rainfall to most parts of undivided India.

Usually, the southwestern monsoon hits the Kerala coast around June 1, then takes about a week to cover the coffee, tea and rubber growing areas of southern India. The rains progress to paddy-growing areas of eastern India during the first fortnight of June, entering the oilseed-producing areas of central India in the third week of June. Cotton areas in the western region get rains by the first week of July.

So, June-September is the period during which monsoon rains occur. More than 60% of the total rains received in India occur during these four months.

What is the Long Period Average, used in the measurement of monsoon rains

LPA is calculated on the basis of the average annual rainfall received during 1951-2000, at 89 cm. IMD declares a normal monsoon year if rainfall during a year is between 95% to 105% of LPA. If the rainfall during June-September falls below 85% of LPA, IMD declares it a deficient monsoon year.

This year, with the June rainfall showing a deficiency of 24%, IMD has marginally downgraded the southwestern monsoon forecast, but predicted widespread rains during July and August. Releasing the second long-term forecast for the year, IMD now says monsoon season rainfall for the country as a whole is likely to be 96% of LPA. In its first forecast in April, it had stated that rains during the June-September season were likely to be 99% of LPA.

Whats the monsoons impact on Indian agriculture

The monsoon is crucial for Indian agriculture as only about 40% of the cultivable area has irrigation cover. So, the southwestern monsoon plays a critical role in determining the performance of many summer or kharif crops, which contribute more than half of the countrys food production and include the likes of pulses, oilseeds, sugarcane and paddyagricultural commodities that play a critical role in determining the food inflation graph. These rains also help improve the moisture levels in the soil; improved moisture content helps the winter or rabi crop as well. Note that the agriculture sector contributes about 15% to Indias GDP and engages more than 55% of the countrys workforce. Monsoon rains also help improve the water level in reservoirs.

What kind of models does the India Meteorological Department use to forecast monsoon rains

Under the earth sciences ministry, IMD gives forecasts for the monsoon and also monitors its progress across 36 meteorological sub-divisions in India. For improving the accuracy of its forecasts, IMD has started to use state-of-art dynamic models in place of statistical models. An experimental forecast for the 2012 southwest monsoon was generated using the research version of a high resolution, coupled dynamical model being implemented at the Indian Institute of Tropical Meteorology, Pune. The model was developed by the US National Centers for Environmental Prediction. IMD officials say that within a few years, weather forecasts would be shifted entirely to the more reliable dynamic model.

How do the La Nia and El Nio phenomena impact the Indian monsoon

El Nio means little boy in Spanish and refers to an abnormal warming of the eastern Pacific ocean, which wreaks havoc on weather patterns across Asia-Pacific. A strong El Nio can lead to monsoon failure in Asia and droughts in Australia, as well as wetter-than-normal weather in parts of South America. The name La Nia also originates from Spanish, meaning the girl. La Nia usually enhances the Asian monsoon, and it can be a factor in shaping the Indian monsoon. Ocean temperatures in the western Pacific have been warmer than normal.

The latest long-term forecast by IMD says its most likely that La Nia neutral conditions will prevail during this monsoon season. There is also a substantial probability for weak El Nio conditions emerging during the later part of the season.

What are other forecasts or reports that IMD consults before giving its monsoon forecasts

IMD makes its predictions on the basis of five parameters, including north Atlantic sea surface temperature, northwest Europe land surface air temperature, and East Asia mean sea level pressure. Besides, it takes into account the experimental forecasts prepared by national institutes like the Space Applications Centre (Ahmedabad), the Centre for Mathematical Modeling and Computer Simulation (Bangalore), the Centre for Development of Advanced Computing (Pune) and the Indian Institute of Tropical Meteorology (Pune). Besides these, operational or experimental forecasts prepared by global institutes like the US National Centers for Environmental Prediction, the US International Research Institute for Climate and Society, the UK Meteorological Office, Meteo France, the European Centre for Medium-Range Weather Forecasts, the Japan Meteorological Agency, the Japan Agency for Marine-Earth Science and Technology and the Asian-Pacific Economic Cooperation Climate Centre, etc, are also consulted by IMD.

How are various sectors of the economy impacted by the monsoon or weather in general

According to a December 2010 report of the National Council of Applied Economic Research on the economic benefits of weather and marine services, an estimated 30 sectors such as aviation, agriculture, tourism, fishery, forestry, insurance, port and harbour management, commerce and retail trade depend directly on weather conditions. In most countries, weather and climate are forecast by National Meteorological Services, who also provide weather forecasts tailored to support agriculture, municipal services, disaster management, water resource planning and management, transport, environmental protection, public health and other sectors, the report noted.

sandip.das@expressindia.com