Minimum temperature over short grass in Santa Maria, RS: climatology, interannual variability, and historical trend

The objective of this study was to calculate the descriptive statistics to characterize the climatology of minimum air temperature at 5 cm over short grass (Tmr) in Santa Maria, RS. A further objective was to associate the interannual variability of Tmr with the ENSO phenomenon and also to verify if there is a trend in the historical series for this meteorological variable. Data used in this study were daily minimum air temperature over short grass measured at the Meteorological Station in Santa Maria, RS, Brazil (29 degrees 43'S, 53 degrees 43'W and altitude of 95 m) from 1(st) May 1970 to 31 December 2009. Years were grouped in El Nino, La Nina, and Neutral years, from 1(st) July to 30 June. Mean monthly minimum air temperature varied from 6.9 degrees C in July to 17.3 degrees C in January, with the lowest value of -8.4 degrees C in June and the highest value of 28.6 degrees C in October. There is an ENSO signal on the minimum air temperature over short grass during the months of Fall, Winter and Spring. Minimum air temperature is greater during El Nino, lower during La Nina and intermediate in Neutral years. There was increase in grass minimum temperature during the 1970-2009 period in April, June, October, November and December, with increased trends starting mainly in the 80's. Non-significant climatic trends were detected in the other months.