Brief History

India is predominantly an agricultural country. Success or failure of crops in any year is always crucial for the development of Indian economy, which in turn controls the economy of the country. In 1950s and 1960s, Indian budget was regarded as a gamble on the monsoon rains. This holds good even now.

After the serious countrywide drought and famine in 1877, the Government of India’s anxiety for the earliest possible information about the progress of the monsoon grew and Sir H.F. Blanford, the first Chief Reporter of India Meteorological Department (IMD), was called upon to make attempts for estimating the prospective rains. Blanford issued tentative forecasts from 1882 to 1885 utilizing the indications provided by the snowfall in Himalayas. The success achieved infused greater confidence and in 1885, it was decided that a monsoon forecast should thence forward be issued annually as a matter of routine. The first of the regular series of forecasts was given on the 4th June 1886. This is continuing practically till date but for changes in its format and content.

In 1892, long range forecast (LRF) for the rainfall for the second half of the monsoon season (August-September) was also started.  In December 1893, the first forecast for winter precipitation over the Northern and central India was issued. Sir John Eliot who succeeded Blandford as the Head of India Meteorological Department (IMD) in 1895 applied subjective methods such as analogue and curve parallels for the LRF of ISMR. The efforts for better forecasts continued during the period (1904-1924) of Sir Gilbert T. Walker who took over as the Director General of IMD.

Sir Gilbert Walker started the forecasts based on objective techniques. He introduced correlation and regression techniques for preparing long range forecasts. Walker was well aware that seasonal prediction can be put on a scientific footing only on the basis of an accepted theory of general circulation. In his quest for identifying potential predictors for the long range forecasting of monsoon rainfall over India, Walker discovered three important large scale see saw variations in global pressure patterns. These are Southern Oscillation, North Atlantic Oscillation and North Pacific Oscillation.

From 1886, the monsoon forecasts were issued for the entire India and Burma. Walker realized that India being more or less continent cannot be considered as one homogenous area as regards the distribution of rainfall. In 1922, Walker divided India into three main homogenous areas, namely, i) Peninsula ii) N.E. India and iii)  North west India. In 1935, forecast for NE India was discontinued for wants of suitable predictors and skill of model. The practice of issuing forecasts for two homogenous regions of India (NW India and Peninsula) was continued till 1987.

In 1988, India Meteorological Department introduced the 16 parameter power regression and parametric models and started issuing forecasts for the southwest monsoon rainfall over the country as a whole. Using the power regression model, quantitative forecasts were prepared and using the parametric model, qualitative forecasts (whether normal/excess or deficient) were issued. After the failure of forecast in 2002, IMD introduced a new two stage forecast strategy in 2003, according to which the first stage forecast for the seasonal (June to September) rainfall over the country as a whole is issued in April and the update for the April forecasts is issued in June. Along with the update forecast, forecast for seasonal rainfall over broad homogeneous rainfall regions of India and July rainfall over country as a whole are also issued.  During the period 2003-2006, the first stage quantitative and 5 category probabilistic forecast for the season rainfall over the country as a whole were issued using 8-parameter power regression (PR) model and Linear Discriminant Analysis (LDA) model  respectively. Update for the first stage forecasts were issued using 10 –Parameter PR and LDA models. In 2007, IMD introduced new statistical forecasting system based on ensemble technique for the south-west monsoon season (June – September) rainfall over the country as a whole.