[en] Predicting extreme temperature events can be very useful for different sectors that are strongly affected by their variability. The goal of this study is to analyze the influence of the main atmospheric, oceanic, and soil moisture forcing on the occurrence of summer warm days and to predict extreme temperatures in Argentina northern of 40°S by fitting a statistical model. In a preliminary analysis, we studied trends and periodicities. Significant positive trends, fundamentally in western Argentina, and two main periodicities of summer warm days were detected: 2–4 years and approximately 8 years. Lagged correlations allowed us to identify the key predictors: El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Standardized Precipitation Indices (SPI). We also noticed that the frequency of warm days in spring acts as a good predictor of summer warm days. Due to the collinearity among many predictors, principal component regression was used to simulate summer warm days. We obtained negative biases (i.e., the model tends to underestimate the frequency of summer warm days), but the observed and simulated values of summer warm days were significantly correlated, except in northwest Argentina. Finally, we analyzed the predictability of the summer warm days under ENSO neutral conditions, and we found new predictors: the geopotential height gradient in 850 hPa (between the Atlantic Anticyclone and the Chaco Low) and the Atlantic Multidecadal Oscillation (AMO), while the PDO and SPI lost some relevance.

[en] In Part I of our study (Zazulie et al. Clim Dyn, 2017, hereafter Z17) we analyzed the ability of a subset of fifteen high-resolution global climate models (GCMs) from the Coupled Model Intercomparison Project phase 5 to reproduce the past climate of the Subtropical Central Andes (SCA) of Argentina and Chile. A subset of only five GCMs was shown to reproduce well the past climate (1980–2005), for austral summer and winter. In this study we analyze future climate projections for the twenty-first century over this complex orography region using those five GCMs. We evaluate the projections under two of the representative concentration pathways considered as future scenarios: RCP4.5 and RCP8.5. Future projections indicate warming during the twenty-first century over the SCA region, especially pronounced over the mountains. Projections of warming at high elevations in the SCA depend on altitude, and are larger than the projected global mean warming. This phenomenon is expected to strengthen by the end of the century under the high-emission scenario. Increases in winter temperatures of up to 2.5 °C, relative to 1980–2005, are projected by 2040–2065, while a 5 °C warming is expected at the highest elevations by 2075–2100. Such a large monthly-mean warming during winter would most likely result in snowpack melting by late winter-early spring, with serious implication for water availability during summer, when precipitation is a minimum over the mountains. We also explore changes in the albedo, as a contributing factor affecting the net flux of energy at the surface and found a reduction in albedo of 20–60% at high elevations, related to the elevation dependent warming. Furthermore, a decrease in winter precipitation is projected in central Chile by the end of the century, independent of the scenario considered.

[en] The presence of large water masses influences the thermal regime of nearby land shaping the local climate of coastal areas by the ocean or large continental lakes. Large surface water bodies have an ephemeral nature in the vast sedimentary plains of the Pampas (Argentina) where non-flooded periods alternate with flooding cycles covering up to one third of the landscape for several months. Based on temperature records from 17 sites located 1 to 700 km away from the Atlantic coast and MODIS land surface temperature data, we explore the effects of floods on diurnal and seasonal thermal ranges as well as temperature extremes. In non-flooded periods, there is a linear increase of mean diurnal thermal range (DTR) from the coast towards the interior of the region (DTR increasing from 10 to 16 K, 0.79 K/100 km, r² = 0.81). This relationship weakens during flood episodes when the DTR of flood-prone inland locations shows a decline of 2 to 4 K, depending on surface water coverage in the surrounding area. DTR even approaches typical coastal values 500 km away from the ocean in the most flooded location that we studied during the three flooding cycles recorded in the study period. Frosts-free periods, a key driver of the phenology of both natural and cultivated ecosystems, are extended by up to 55 days during floods, most likely as a result of enhanced ground heat storage across the landscape (~2.7 fold change in day-night heat transfer) combined with other effects on the surface energy balance such as greater night evaporation rates. The reduced thermal range and longer frost-free periods affect plant growth development and may offer an opportunity for longer crop growing periods, which may not only contribute to partially compensating for regional production losses caused by floods, but also open avenues for flood mitigation through higher plant evapotranspirative water losses.

[en] The Working Group I contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) provides a comprehensive assessment of the physical science basis of climate change. It builds upon the Working Group I contribution to the IPCC's Fourth Assessment Report in 2007 and incorporates subsequent new findings from the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, as well as from research published in the extensive scientific and technical literature. The assessment considers new evidence of past, present and projected future climate change based on many independent scientific analyses from observations of the climate system, paleo-climate archives, theoretical studies of climate processes and simulations using climate models. During the process of scoping and approving the outline of its Fifth Assessment Report, the IPCC focussed on those aspects of the current understanding of the science of climate change that were judged to be most relevant to policy-makers. In this report, Working Group I has extended coverage of future climate change compared to earlier reports by assessing near-term projections and predictability as well as long-term projections and irreversibility in two separate chapters. Following the decisions made by the Panel during the scoping and outline approval, a set of new scenarios, the Representative Concentration Pathways, are used across all three Working Groups for projections of climate change over the 21. century. The coverage of regional information in the Working Group I report is expanded by specifically assessing climate phenomena such as monsoon systems and their relevance to future climate change in the regions. The Working Group I Report is an assessment, not a review or a text book of climate science, and is based on the published scientific and technical literature available up to 15 March 2013. Underlying all aspects of the report is a strong commitment to assessing the science comprehensively, without bias and in a way that is relevant to policy but not policy prescriptive. This report consists of a short Summary in French for Policy-makers followed by the full version of the report in English comprising a longer Technical Summary and fourteen thematic chapters plus annexes. An innovation in this Working Group I assessment is the Atlas of Global and Regional Climate Projections (Annex I) containing time series and maps of temperature and precipitation projections for 35 regions of the world, which enhances accessibility for stakeholders and users. The Summary for Policy-makers and Technical Summary of this report follow a parallel structure and each includes cross-references to the chapter and section where the material being summarised can be found in the underlying report. In this way, these summary components of the report provide a road-map to the contents of the entire report and a traceable account of every major finding