Estimation of crop production from area and yield estimates based on sample surveys and crop-cutting experiments, an approach currently being followed in India, can give final estimates only after the crops are actually harvested. However, various policy decisions related to pricing, marketing, export/import, distribution, etc., necessitate the use of advance estimates. A simple model based on weather indices can be used to obtain accurate estimates of annual rice production even before the crop is harvested.
Crop production in India largely depends on the summer monsoon (June to September), which provides about 80–90% of annual rainfall in most parts of the country. The summer monsoon rainfall is the main source of water for the kharif crop. Rainwater stored as soil moisture and other water resources (lakes, reservoirs, and rivers) are also important for the–rabi–and other irrigated crops. Parthasarathy et al (1988) have estimated the annual food-grain production in the country using the all-India summer monsoon rainfall data. The rainfall data, however, showed significant variations in time and space. To obtain more accurate production estimates, the temporal and spatial variations of monsoon rainfall were also included in the model through suitable weather indices.