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. Copyright © 2012 Royal Meteorological Society

Soil water surplus and deficit occur frequently in Buenos Aires province in Argentina. This paper analyses the soil water surplus in a sub-area, the Salado River basin, in the period 1968–2008. This basin is divided in seven drainage areas, delimitated according to the National Water Resources. The series of soil water surplus data were adjusted by means of the theoretical normal cubic-root probability distribution, and the mean areal soil water surplus value of 300 mm was considered as a threshold above which floods can cause severe damage. An increase in the frequency of extreme events and in their tendency exists during the recent years, coherent with the increase of precipitation recorded in the region. The statistical significance of the results was assessed using the Mann Kendall and MAKESENS tests. The results showed a relevant temporal variability, but did not show significant tendencies.

This paper presents the soil water deficit and soil water surplus obtained from soil water balance in three drainage areas of Buenos Aires province for the period from 1971 to 2010. The soil water balance had been performed using the evapotranspiration formula of Penman-Monteith and considering the soil water constants: field capacity, soil water moisture, and soil wilting point for all the different types of soils of the region. The obtained soil water deficit and surplus are considered as triggers of extreme hydrologic events. Annual threshold values of 200 mm of soil water deficit and 300 mm of soil water surplus were considered for drought and flood, respectively. It was found that almost the 25% of the floods are severe and extreme while the 50% of droughts were of these intensities. Mann-Kendall statistical test was performed, and significance trends at level 0.1 were found for drought and for two periods, one of twenty years (1991–2010) and the other of ten years (2001–2010). As a sample of the temporal evolution of both events and their trends, the results of one locality (Junin) were deeply analyzed.

Las inundaciones y sequías son una constante en la Región Pampeana (Argentina). Casi todos los años uno de estos eventos hidrológicos extremos tiene lugar y, a veces, ambos. La evolución temporal del exceso de agua en el suelo, durante sesenta años se analiza en nueve estaciones meteorológicas localizadas en importantes áreas cuyos usos del suelo tienen impacto económico y social. Ellas se ubican en las provincias de Córdoba, Santa Fe, Entre Ríos, La Pampa y Buenos Aires. Los datos meteorológicos diarios fueron provistos por Servicio Meteorológico Nacional para el período 1951- 2010. El modelo de balance de agua en el suelo fue el utilizado por Forte Lay et al. que está basado en el de Thornthwaite-Mather y la evapotranspiración diaria de referencia normal media fue estimada con la fórmula de Penman-Monteith. En el presente trabajo al parámetro exceso de agua en el suelo se lo utiliza como indicador del riesgo de inundación. La metodología Makesens se usó para el análisis estadístico, el mismo se basa en el test no paramétrico de Mann-Kendall para el estudio de la tendencia y el método no paramétrico Sen para su magnitud. Todas las estaciones analizadas mostraron diferente evolución del exceso de agua en el suelo y experimentaron riesgo de inundación en algún momento del período estudiado.

For environmental and economic conditions, precipitation can be considered as the most important climatic element. its drought and wet periods are known to change the natural water suply, river discharges and crops yields, as well as natural vegetation. Argentine agriculture was and surely will drive the national economy and the most important agriculture region is the Pampa or pampean flatlands, mainly because it allows the rain - fed crops production. The grain production increased from 23 to 90 million tones during the period 1970 - 2010 by means of the best available technology application and this growth had two components: a) the soybean which has now a ratio of 6 to 1 with respect to corn and b) the increase of precipitation amounts during the last decades of XX century. There is a need to maintain agricultural sustainability and for that changes in production patterns would be considered. On the other hand, the pampean flatlands experienced a succession of extreme hydrological events related to precipitation. Droughts and floods were a constant, according ancient documents during the Spanish domain, the argentine goverment and the installation of meteorological stations near 1870. Documented droughts occurred during 1604, 1614, 1620 and 1824 and floods in 1636, 1770, 1817, 1857 and 1900 can be mentioned as examples. The climate of the studied region according Thornthwaite classification is Perhumid, Humid and Subhumid from East to West, with fluctuations in their limits answering climate variability. And so, the agriculture was influenced. The surface of croplands is greater in the Perhumid and Humid climates regions then in the last one, where livestock is important. Subhumid region has suffered important changes in its land uses and surely, it will be vulnerable in the future. In this paper the three zones are studied using meteorological data, soil water balance and crops data. More recently there were important floods in 1980, 1985, 1993, 2001 and 2002 and severe droughts in 1978, 1983, 1989, 1995 and 2008. Extreme hydrological events acted in short periods but the losses reached high importance because precipitation variability acts over the soil water balance influencing its parameters and the water table depth.