Rainy-season duration estimated from OLR versus rain gauge data and the 2001 drought in southeast Brazil

Large precipitation deficits observed during the 2001 austral summer over the southeast region of Brazil contributed to the worsening of the energy crisis that was occurring in the country, with unprecedented social and economic consequences. Reliable information on the beginning of the rainy season was essential for the Brazilian government to manage the energy crisis. The purpose of this study is to determine the rainy season in this region and to point out the risk of using outgoing longwave radiation (OLR) data to estimate the beginning of it. The results show that when OLR data are used the beginning and the end dates of the rainy season are wrongly anticipated and delayed, respectively. The present study aims to provide useful information for the management of the impact of adverse climate conditions such as the one in 2001 by basing the analysis on rainfall data instead of on OLR.