Long-term and recent changes in temperature-based agroclimatic indices in Argentina

Abstract

Changes in several temperature-based agroclimatic indices in the central-eastern of Argentina, most of them located within the Pampas region were analysed for 39 meteorological stations. Trends of first (FFD), last (LFD) and number (NFD) of frost days, frost period (FP), start (SGS), end (EGS) and length (LGS) of the growing season, growing degree days (GDD), diurnal temperature range (DTR), chilling hours and lowest annual minimum temperature were computed for two periods, 1940–2007 and 1975–2007. The largest changes were observed for the whole period 1940–2007 and were mostly indicative of a long-term minimum temperature warming throughout the region. During this period, generalized decreases in the NFD and in the FP (i.e., a delayed FFD and an earlier LFD) were found. Although the trends in the growing season indices were not as large as in the frost indices, they were consistent with the overall warming: an earlier SGS and a delayed in the EGS. The trends of the GDD showed a large variability between months with a generalized increased throughout the year. The DTR showed the largest number of stations with statistically significant negative trends from austral late spring (November) to austral early fall (April). For the period 1975–2007, the behaviour changes in all analysed indices: the short-term trends weakened and in some cases reversed sign. The LFD tended to occurred later in the year, particularly for the southern Pampas. The EGS shifted from mostly positive to negative trends, resulting in a shorter LGS. These trend changes were not spatially homogeneous. Although those short-term trends were predominantly non-statistically significant, they could potential affect management decisions and crop yields. In particular, frost is still an important hazard in agricultural activities and within the context of our results short- and long-term characterization of frost risk need to be considered at local and sub-regional scales.