Prediction of Monsoon Rainfall and River Discharge on 15–30-day Time Scales

In final form 11 May 2004 ©2004 American Meteorological Society uring the summer of 2002, drought conditions persisted over India from mid-June to mid-July following a later-than-average arrival of seasonal monsoon rain. By the end of that summer, the average summer Indian rainfall totaled 711 mm or 19% below normal. With the exception of the area near the foothills of the Himalayas in the very north of India, where above-average rainfall occurred, most of India was in deficit, with the state of Rajasthan 64% below normal. Figure 1 provides a geographical reference for the locations discussed in the text. The summer of 2002 was the sixth driest in 130 yr (Table 1). The failure of the 2002 monsoon rains was not anticipated. The official Indian Meteorological Department seasonal outlook issued in mid-April called for an essentially normal monsoon with seasonal rains about 1% lower than normal. Other forecasts suggested similar outcomes. For example, predictions by the International Research Institute for Climate (IRI) and the European Centre for Medium-Range Weather Forecasts (ECMWF) made in the spring for the 2002 June–August period suggested slightly below-average precipitation in the south of India but normal precipitation elsewhere (see http://iri.columbia.edu/climate/ forecast and www.ecmwf.int/products/forecasts). The effects of the midseasonal drought were disastrous to India’s agrarian economy, especially since the drought occurred early in the monsoon season when agriculture is at its most susceptible stage. The severe reduction in agricultural productivity resulted in hardship and suffering for millions of people and a significant economic loss to the country. Only stores of rice accumulated over a period of years by the government of India prevented an even greater disaster. Figures 2a and 2b show precipitation time series averaged over central India for the period 1986 through PREDICTION OF MONSOON RAINFALL AND RIVER DISCHARGE ON 15–30-DAY TIME SCALES