Observed and simulated changes in precipitation seasonality in Argentina

Abstract

Seasonality in Argentina is examined using precipitation observations from 56 weather stations north of 42°S and CRU gridded precipitation. The Walsh and Lawler Seasonality Index (SI) and Precipitation Concentration Index (PCI) are calculated to determine the different seasonality regimes. The main characteristic is an eastwest gradient, where precipitation tends to be more evenly distributed throughout the different months of the year in the east while rainfall in the west is concentrated in 3 months or less. High replicability values indicate that the wettest month generally occurs during a same period of months in central and northern Argentina. Several stations in eastern humid Argentina have significant positive changes in the mean of seasonality indices between 1961 and 1985 and 1986 and 2010, and increasing trend. In most cases this leads to a change in the regime from rather seasonal with a short dry season to a seasonal regime. Through a PAM Clustering technique a new regionalization of precipitation seasonality is obtained. The mean series in each cluster show a tendency towards more seasonal and highly seasonal regimes in all regions. The SI and PCI indices were calculated using the precipitation outputs of 18 global climate models (GCMs) from the Coupled Model Inter‐comparison Project Phase 5 (CMIP5) to examine the ability of these models to represent seasonality spatial distribution and changes in Argentina. To some extent the spatial distribution of seasonality is captured by models; however, there are considerable discrepancies in the location and extension of the eastwest gradient. The sign and location of trends and changes in the mean SI and PCI are adequately reproduced in only a few models. The low ability of GCMs to represent seasonality and its changes is a consequence of the difficulties GCMs have simulating precipitation characteristics in Argentina reported by different authors.

Evaluation of ECMWF-SEAS5 Seasonal Temperature and Precipitation Predictions over South America

“…The Seasonality Index (SI) measures the monthly rainfall variability throughout the year, assessing seasonal contrasts in rainfall quantities rather than dryness or wetness of a month in an absolute sense [49]. Although the method uses rainfall distribution for all months, a seasonal pattern is detected when the SI value is above 0.6 [72].…”

Water Resources Change in Central-Western Argentina Under the Paris Agreement Warming Targets

“…The precipitation over this mountainous region has a Mediterranean regime (Viale and Nuñez, 2011), with precipitation concentrated mostly during the cold season (April to September) and a dry warm season (October to March) in response to the seasonal displacement of the Southeastern Pacific High (Rivera et al, 2017). On the other hand, the Lowlands region is characterized by a monsoonal precipitation regime, with a more marked seasonality near the Andean foothills (Doyle, 2020). Due to the marked rain shadow effect, the climate in the Lowlands is arid to semi-arid in the west and sub-humid in the east, with convective warm-season rainfalls favored by moist air masses from the Amazon and Atlantic basins (Garbarini et al, 2019;Viale et al, 2019;Camisay et al, 2020).…”

“…It must be noted that the Lowlands region was divided into two sub-domains: its Eastern and Western portions. This decision was made considering the spatial gradient of the expected changes in precipitation (Cabré and Nuñez, 2020), the observed trends over the last Century (Díaz et al, 2020;Rivera and Arnould, 2020), and the differences in the precipitation seasonality, which is more marked in the Eastern Lowlands than in the Western Lowlands (Doyle, 2020). The projected changes in annual total precipitation exhibit an east-west gradient, with increases in the Eastern Lowlands and decreases over the Andes region; although the uncertainties in the results are high due to the dispersion in the model simulations (Figure 4).…”

Observed and Projected Changes in Temperature and Precipitation in the Core Crop Region of the Humid Pampa, Argentina

“…The annual cycle of precipitation displays significant intra-annual variability. According to Doyle [44], Rosario has a precipitation regime with a short period of low precipitation in winter and fairly uniform precipitation in the rainiest months. Figure 3 shows that the rainy season runs from October to April, when it rains 78% of the annual average.…”

“…Winter months (JJA) registered monthly values of 30 mm and an average RX1day of nearly 19 mm. Low winter precipitation is a common feature throughout the region [13,44]. In this season, the northward displacement of the South Atlantic anticyclone restricts water vapor inflow over the south-central region of the continent, which, added to lower solar radiation, results in the weakening of convective processes and heavy rains [49,50].…”