Seasonal trend analysis of minimum air temperature in La Plata river basin

Abstract

Regional economies that depend predominantly on agriculture and livestock are heavily affected by changes in air temperature, one such case are the activities in La Plata river basin (LPB). Some studies suggest that variations in the seasonal cycle and season onset would affect efficiency in the use of radiation by vegetation. This paper evaluates the distribution of minimum temperature seasonality trends over LPB, describes the trends in the seasonal cycle, and detects changes of minimum temperature extremes characterized by the number of frost days and the frequency of warm and cold nights. The analysis includes absolute minimum temperature 0(TnMin) and minimum average temperature (TnMean) from ERA5 reanalysis for the 1980–2015 period. Significant positive trends in the amplitude of annual average TnMin and TnMean are observed over more than half the area (53.5% and 69.9% of the basin, respectively). Amplitude and phase parameters suggest that average minimum temperature underwent greater variation than absolute minimum temperature over LPB. The shifts in phase indicate that minimum temperatures occurred earlier than usual in the year considering the 35-year series. In general terms, there is a shift toward warmer conditions. This warming is evident in seasonal trends of minimum temperature as well as in the significant increase in the number of warm nights, a significant decrease of cold days and a significant decrease in the number of frost days in the highest Andes mountains in the west of the LPB.