CLIMATIC SCENARIOS AND THE WATER REQUIREMENT FOR BEAN IN RIO GRANDE DO SUL

Abstract

This study aimed to analyze the irrigation water requirement (IWR) of bean in Rio Grande do Sul (RS), Brazil, based on current climate and future climate scenarios. The future projections for the years 2030 and 2060 were performed for the following scenarios: C1- considering monthly increase of air temperature of 1°C (2030) and 2°C (2060), and C2 - considering monthly increase of temperature air 1°C and 2°C and rainfall of 10 mm and 20 mm, respectively, for 2030 and 2060. To calculate the IWR during the cycle (difference between crop evapotranspiration (ETc) and effective rainfall (Reff)) and total net irrigation of bean, Cropwat 8.0 software was used. We considered three sowing dates for the 1st season (20 September, 20 October and 20 November) and a date for the 2nd season (January 10) of bean. In the current climate, the IWR (ETc-Reff) increases gradually from northeast to south-central of RS, being lower depths, for sowing in early January and the highest, for sowing in late October and/or November. For net irrigation, for the later sowing of the 1st season, higher is the water requirement. For each 1°C increase in temperature (C1) IWR (ETc-Reff) tends to increase 4-10 mm for sowing of the 1st season. The simultaneous increase of air temperature and rainfall (C2) results in lower IWR (ETc-Reff), despite differences in relation to that observed in the current climate are small.