Analysis of Agronomic Drought of two Livestock Production Regions in Uruguay

Abstract

Agronomic droughts are a historical problem of increasing concern for grazing livestock production in Uruguay and the region. However, the historical evolution of this phenomenon and its impacts are not characterized for Uruguay. The agrohydropotential value (AHP) is the ratio between real evapotranspiration of a pasture and the potential evapotranspiration, and it is used to characterize its hydric condition. The objective of this study was to characterize the frequency, intensity, and duration of agronomic droughts in two locations of importance for livestock production in Uruguay: Salto (31°40’S; 57°97’W) and Treinta y Tres (33°22’S; 54°39’W). Monthly rainfall (1948-2010) and climate potential evapotranspiration (1961-1990) data were used to calculate water balances for two soils. The AHP was calculated and annual and seasonal water deficits were charac-terized. A Mann-Kendall test was conducted to determine the existence of trends. In summer, water deficits were more frequent for all soils and locations. In spring differences were found between soils, and in the fall there was a more restrictive situation in Treinta y Tres. The probability of drought occurrence was less than 15 % for all seasons and locations. Most drought periods affected both locations, with 4 to 5 months duration. The Mann-Kendall test showed no significant trends in drought frequency or intensity in the last 62 years.