Weekly mean values of solar radiation, rainfall, evapotranspiration and air temperature were used for establishing the lower climatic risk to the cotton crop. For irrigated fields, the potential crop yield was evaluated by the cumulative growth index (CGI), while for rain-fed conditions the climatic risk was determined by the water potential deficit (WPD). Under irrigated and rain-fed conditions, the lower climatic risk occurs when cotton crop is sowing from 6 to 19 August and from the 44th (West region of Bahia state) to the 19th week of the year. From the 1st week of the year, the most suitable date for cotton sowing start in the Central region of Piauí state, reaching maximum covering area of Piauí, Rio Grande do Norte, Paraíba, Pernambuco states and North of Bahia state in the period between the 4th and the 8th week. In the South and West regions of Bahia state, the lower climatic risk is reached by cotton crop when sowing in the 10th and 46th weeks. In the northeast Coast, otherwise the cotton crop sowing is more suitable in the period from the 14th to 17th week, covering most of the coastal shore table lands from Rio Grande do Norte to Bahia states and almost the total areas of the Alagoas and Sergipe states.
Rain-fed and irrigated cropping; cumulative growth index; water potential deficit
