After IPL, watch El Nio vs La Nia

Written by Sandip Das | Updated: Apr 25 2013, 05:54am hrs
Though weather scientists have forecast a normal monsoon, Indias rainfall will depend on how temperature in eastern and western Pacific Ocean plays out

What is the impact of the monsoon on Indian agriculture

The south-western monsoon is crucial for Indian agriculture as only about 40% of the cultivable area has irrigation cover. The monsoon plays a critical role in determining the performance of many summer or kharif crops, which contributes 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. Due to deficient rainfall in many parts of the country last year, Indias foodgrain output is expected to be around 250-255 million tonnes in 2012-13, down from the previous years record output of 259 million tonnes. The rains also help improve the moisture level in the soil, and improved moisture content helps the winter or rabi crop. Note that the agricultural sector contributes about 15% to Indias GDP and engages more than 55% of the countrys workforce. The rains also help improve the water level in reservoirs. This has an impact on hydel power generation.

What is the progress path and duration of the monsoon

The south-western monsoon enters the country because of a low pressure area thats caused by the extreme heat of the Thar Desert and adjoining areas during the summers. 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 south-west, bringing heavy rainfall to most parts of undivided India. Usually, the south-western monsoon hits the Kerala coast around June 1, then it takes about a week to cover the coffee, tea and rubber-growing areas of south Indian states such as Kerala, Karnataka and Andhra Pradesh. 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. In fact, more than 60% of the total annual rains in India occur during the June-September period.

What is the long period average (LPA), used in the measurement of the monsoon

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.

IMD officials are cautious this year as last year (2012) it had initially predicted that the south-eastern monsoon would be mostly likely normal, with a rainfall of 99% of LPA. Then, in June last year, IMD downgraded the forecast by stating that rains would be 96% of LPA. However, the actual rainfall during the monsoon months of 2012 was 92% of its LPA as many parts of the country such as Maharashtra, Gujarat and Karnataka faced drought-like conditions.

The forecast for July rainfall over the country as a whole was an overestimate and that for rainfall during the second half of the monsoon season was an underestimate, IMD stated in its monsoon report 2012.

What are the models that IMD uses to forecast the monsoon

Under the earth sciences ministry, IMD gives forecasts for the monsoon and also monitors its progress across 36 meteorological sub-divisions in the country. For improving the accuracy of its forecast, IMD has started to use state-of-the-art dynamic models in place of statistical models. An experimental forecast for the 2012 south-western 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 Centres 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 El Nio and the La Nia phenomena impact the 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 the 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 South Asian Forum has also noted that this year there is uncertainty partly because of the spring time predictability limit and partly due to the likely absence of La Nia and El Nio conditions in the Pacific during the monsoon. While the presence of El Nio weakens the monsoon, La Nia strengthens it.

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

IMD makes its predictions on the basis of five parameters, including north Atlantic sea surface temperature, north-west 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 Centres for Environmental Prediction, the US International Research Institute for Climate and Society, the UK Meteorological Office, the Mto-France, the European Centre for Medium-Range Weather Forecasts, the Japan Meteorological Agency, the Japan Agency for Marine-Earth Science and Technology, 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.