Variation of Rainfall and Drought Occurrence in the SW Uruguayan Dairy Basin in the Period 1939 - 2011

Abstract

Dairy grazing production is one of the most sensitive activities to climate variability that affect production costs and volumes exported from the country. The aim of this work was to characterize and analyze the occurrence and frequency of agronomic droughts over a period of 72 years (1939 - 2011), for the Departments of Florida and Colonia, Uruguay. Rainfall variability was analyzed using historical records of the meteorological stations of Colonia and Florida. According to the geographical location of the majority of the dairy farms, the San Gabriel and Ecilda Paullier ground units were used. The existence of water deficit trends was verified statistically, in spring and summer, using the Mann-Kendall test. Agronomic droughts were characterized using the Water Wellbeing Index (IBH). The occurrence of drought was considered when IBH values were found below 0.5 for at least three consecutive months. The frequency and recurrence of agronomic droughts were calculated. The results indicate that there is a statistically significant trend of decreasing water deficiencies for summer for both the Department of Florida and the Department of Colonia and for the spring in the Department of Florida. The high inter-annual variability in both sites is remarkable. Frequency and recurrence of droughts varied according to the region and unit of soil.