In late October 2024, the western Mediterranean (WMed) region experienced an extreme precipitation event (EPE) centred over Valencia, southeastern Spain, associated with a quasi-stationary cut-off low (COL), producing record rainfall, flash floods, and severe societal impacts. The COL generated an atmospheric-river-like moisture plume from northwestern Africa, while additional moisture originated from the warm Mediterranean Sea. Interaction with regional orography under a highly unstable environment, favoured deep convection and intense local rainfall. To assess the influence of anthropogenic climate change on the synoptic-scale thermodynamic evolution of the event, we analyse high-resolution (similar to 9 km) storyline simulations from the European Union's Destination Earth initiative, using the coupled IFS-FESOM model spectrally nudged with ERA5. Two climate scenarios are compared: Factual (present-day) and Counterfactual (similar to 1950), isolating thermodynamic responses while preserving the observed large-scale circulation. Long-term IFS-FESOM and ERA5 datasets provide a climatological reference for event extremeness using percentile-based thresholds of selected key variables. Results show that the synoptic configuration alone was sufficient to produce extreme rainfall, but human-induced warming substantially enhanced its magnitude. Moisture content and transport increased by 18 %-24 %, convective instability by similar to 25 %, and precipitation over Valencia increased by similar to 20 % in the Factual scenario. Sea surface temperatures in the Western Mediterranean were similar to 2 degrees C warmer, amplifying evaporation. Peak precipitation rates exhibited nonlinear amplification, on 29 October were about 36 % higher in the Factual scenario, exceeding the Clausius-Clapeyron scaling expected from the mean warming between scenarios. These findings indicate that anthropogenic warming can intensify EPEs in the WMed even when synoptic drivers alone would generate extreme rainfall, highlighting thermodynamic amplification as a key mechanism in Mediterranean flood events. High-resolution, physically consistent storyline simulations offer a robust framework for event-based attribution and improve understanding of future climate risks in vulnerable coastal regions.

We characterize trends in maximum seasonal daily precipitation (seasonal Rx1day), minimum (Tn), and maximum (Tx) daily temperatures during days with precipitation over continental Chile for the period 1979–2017, using surface stations and the AgERA5 gridded product derived from the ERA5 reanalysis dataset. We also examine seasonal trends of Sea Surface Temperature (SST), Precipitable Water (PW), Convective Available Potential Energy (CAPE), Eddy Kinetic Energy (EKE), Atmospheric Rivers (ARs) frequency, and upper air observations to seek possible mechanisms that explain precipitation trends. Our results show an increase in seasonal Rx1day during fall in the south part of Northern Chile (15–30°S) and during fall and winter in Austral Chile (45–57°S), and mostly negative trends in Central Chile (30–36°S), where a few locations with positive trends along the coast during summer. Temperature trends presented cooling patterns north of 33°S in almost all the seasons (< -2 °C/dec), while warming trends prevail south of 38°S (> 1 °C/dec). The highest values in Tn trends are obtained on the western slopes of the Andes around 30°S. We also explore temperature scaling in surface stations, finding strong positive super Clausius Clapeyron with Tn, especially between fall and spring in the 33–40°S region. Sounding observations in five stations across Chile suggest warming trends at 23.5°, 33°S, and 53°S, with a stabilization effect by enhanced warming in the upper troposphere, while presenting cooling trends in Puerto Montt (41.5°S). Seasonal trends in PW reveal moistening along southern Peru and northern Chile during spring and summer. Positive trends in CAPE are observed over 35–40°S (austral summer and fall) and the north Altiplano (autumn). SST analyses reveal strong cooling around 30°S in winter, which may explain the negative trends in seasonal Rx1day in central Chile. A warming spot on the northern Peruvian coast during fall may be responsible for humidification in front of Northern Chile, particularly during summer and fall. Positive EKE trends are detected south of 40°S, being stronger and reaching almost all of the coast during spring. ARs frequency unveils negative trends up to -5 days/dec during summer and positive trends of 1 day/dec in 40°- 50°S coastal regions during spring. More generally, the results presented here shed light on the main large-scale processes driving recent trends in precipitation extremes across continental Chile.

There is a growing need to understand why the Euro-Mediterranean region and, especially Catalonia, are hotspot regions for both warming as well as drying signals in climate simulations and projections, particularly in summer. Local decision makers call for specific climate information requirements, highlighting the difficulty in having a large range of data sources –observations, global and regional projections, sensitivity and attribution experiments– which lead to discrepancies and analogies regarding the conclusions extracted from different climate data sources. In this context, CLIMCAT is a joint project between the Barcelona Supercomputing Center and the Meteorological Service of Catalonia in which a variety of data-storing, evaluation and visualisation tools are employed to provide user-centred climate indices and filtered future projections. For the latter, a process-based evaluation framework based on atmospheric circulation patterns (CPs) is designed, focusing on capturing the synoptic configurations that dominate the Euro-Mediterranean region and their impacts in Catalonia. The hypothesis behind this research is that better-performing GCMs may present more plausible future simulations in a global warming scenario.CPs are defined using daily mean sea-level pressure (SLP) by means of an Empirical Orthogonal Function (EOF) data reduction combined with Ward's hierarchical clustering. The ECMWF ERA5 reanalysis is considered as reference during 1950-2022 to evaluate a set of 24 global climate models (GCMs) from the Coupled Model Intercomparison Project version 6 (CMIP6). The link between CPs and surface variables –precipitation, maximum and minimum temperatures– is analysed. Model performance is quantified through multiple spatial and temporal metrics, allowing the ranking of the best-performing GCMs. It is found that most of the GCMs are able to capture the annual cycle of the CPs frequency in their historical runs, with a dominant summer CP enhancing warm and dry conditions. However, the correct timing of this pattern and the transitional CPs (autumn and spring) are often misrepresented. The analysis of the surface patterns discriminated by CPs presents an overall good model performance, better for the temperatures than rainfall, particularly in the transition seasons, for which the GCMs spread in their skill score increases. Finally, when combining spatial and temporal skill metrics, we are able to identify the best-performing GCMs over the Euro-Mediterranean region, allowing a filtering of the large set of CMIP6 projections in different future scenarios. This is a flexible workflow that can be easily modified based on user needs, such as emphasising model capabilities in specific variables and/or atmospheric structures, depending on the regional and local needs to reduce model uncertainty. The approach is designed to support the provision of useful and robust climate information that can benefit policy making at a regional scale.

Interannual variability of precipitation in Central Chile has long been associated with changes in the dry atmospheric dynamics of the Southern Pacific. This is due to the interaction between the extratropical storm track and the polar anticyclonic circulations established by the Pacific South American (PSA) teleconnection mode, which results from changes in tropical convection. Here, we show that an enhanced subtropical moisture transport during the warm ENSO phase leads to an increase in the frequency of atmospheric rivers, larger values of precipitable water, and heightened zonal integrated water vapor transport. This occurs in a region of the Southern Pacific situated between the tropical high and the subtropical low of the PSA mode. These increases in zonal water vapor transport result in greater precipitation and moister, long‐lived atmospheric rivers making landfall in Central Chile.

Abstract The Antarctic Peninsula (AP) experienced a new extreme warm event and record high surface melt in February 2022, rivaling the recent temperature records from 2015 and 2020, and contributing to an alarming series of extreme warm events there. The northern/northwestern AP was directly impacted by an intense atmospheric river (AR) bringing anomalous heat and rainfall, while AR-enhanced foehn effect further warmed its northeastern side. The event was triggered by multiple large-scale atmospheric circulation patterns linking the AR formation to tropical convection anomalies and stationary Rossby waves, with anomalous Amundsen Sea low and record-breaking blocking high. The cascade of impacts culminated in widespread and intensive surface melt across the AP. The event was statistically attributed to global warming. Increasing frequency of such events can undermine the stability of the AP ice shelves, with multiple local to global impacts, including acceleration of the AP ice mass loss and changes in sensitive ecosystems.

The Antarctic Peninsula (AP) experienced a new extreme warm event and record-high surface melt in February 2022, rivaling the recent temperature records from 2015 and 2020, and contributing to the alarming series of extreme warm events over this region showing stronger warming compared to the rest of Antarctica. Here, the drivers and impacts of the event are analyzed in detail using a range of observational and modeling data. The northern/northwestern AP was directly impacted by an intense atmospheric river (AR) attaining category 3 on the AR scale, which brought anomalous heat and rainfall, while the AR-enhanced foehn effect further warmed its northeastern side. The event was triggered by multiple large-scale atmospheric circulation patterns linking the AR formation to tropical convection anomalies and stationary Rossby waves, with an anomalous Amundsen Sea Low and a record-breaking high-pressure system east of the AP. This multivariate and spatial compound event culminated in widespread and intense surface melt across the AP. Circulation analog analysis shows that global warming played a role in the amplification and increased probability of the event. Increasing frequency of such events can undermine the stability of the AP ice shelves, with multiple local to global impacts, including acceleration of the AP ice mass loss and changes in sensitive ecosystems.

A major storm impacted the subtropical Andes during 28–31 January 2021 producing 4-days accumulated precipitation up to 100 mm over central-south Chile. These are high accumulations even for winter events but the storm occurred in the middle of the summer when precipitation is virtually absent, conferring it an extraordinary character. Similar storms have occurred only 2–3 times in the past century. The January 2021 event included periods of high rainfall intensity, hail and lighting, causing dozens of landslides and flash floods with the concomitant social impacts and economical losses. Here we examine the meteorological drivers of this storm at multiples scales, its climatological context, the associated surface impacts, and some aspects of its predictability.About a week before the storm development over central Chile, a large-scale perturbation in the central South Pacific set the stage for the formation of a zonal jet aloft and zonal atmospheric river (ZAR) that extended eastward until reaching the west coast of South America. The ZAR landfalled at 39°S and its subsequent northward displacement resulted in copious orographic precipitation over the Andes and adjacent lowlands, concomitant with a relatively warm environment during the first phase of the storm (28–29 January). During the second phase (30–31 January) the ZAR decayed rapidly but left behind significant amount of water vapor and the formation of a cut-off low (COL) in its poleward flank. The COL facilitated both advection of cyclonic vorticity and cold air at mid-levels, setting the environment for deep convection, intense rain showers, significant lightning activity, and hail.An assessment of the quantitative precipitation forecast (QPF) from the operational Global Forecast System (GFS) indicates that the model captured well the 96-h precipitation accumulation (28–31 January) in terms of timing and spatial extent. However, specific zones with the largest accumulations varied as a function of lead time. The more stable precipitation during the ZAR phase was better predicted than the convective precipitation during the COL phase. Proper dissemination of these forecast and recently established infrastructure contributed to ease the impact of this extraordinary event on the general population.

In late May 2019, at least seven tornadoes were reported within a 24-h period in southern Chile (western South America, 36°–38°S), including EF1 and EF2 events causing substantial damage to infrastructure, dozens of injuries, and one fatality. Despite anecdotal evidence and chronicles of similar historical events, the threat from tornadoes in Chile was regarded with skepticism until the 2019 outbreak. Herein, we describe the synoptic-scale features instrumental in the development of these tornadic storms, including an extended southwest–northeast trough along the South Pacific, with a large postfrontal instability area. Tornadic storms appear to be embedded in a modestly unstable environment (positive convective available potential energy but less than 1,000 J kg −1 ) and strong low- and midlevel wind shear, with high near-surface storm-relative helicity values (close to −200 m 2 s −2 ), clearly differing from the Great Plains tornadoes in North America (with highly unstable environments) but resembling cold-season tornadoes previously observed in the midlatitudes of North America, Australia, and Europe. Reanalyzing rainfall and lightning data from the last 10 years, we found that tornadic storms in our region occur associated with locally extreme values of both CAPE and low-level wind shear, where a combination of the two in a low-level vorticity generation parameter appears as a simple first-order discriminant between tornadic and nontornadic environments. Future research should thoroughly examine historical events worldwide to assemble a database of high-shear, low-CAPE midlatitude storms and help improve our understanding of these storms’ underlying physics.

© 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).Corresponding author: Anna M. Wilson, amw061@ucsd.edu

From 18 to 27 March 2015, northern, central, and southern Chile experienced a series of extreme hydrometeorological events. First, the highest surface air temperature ever recorded in Santiago (with reliable records dating to 1877), 36.8 degrees C at Quinta Normal, was measured at 15:47 local time on 20 March 2015. Immediately following this high heat event, an extreme precipitation event, with damaging streamflows from precipitation totals greater than 45 mm, occurred in the semiarid and hyperarid Atacama regions. Finally, concurrent with the heavy precipitation event, extremely warm temperatures were recorded throughout southern Chile. These events were examined from a synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each analysis which provides operational context by which to identify and predict similar events in the future. Primary findings were as follows:(1) record warm temperatures in central Chile resulted from anomalous lower troposphere ridging and easterly downslope flow, both of which developed in response to an anomalous midtroposphere ridge-trough pattern; (2) a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25 degrees S by circulation around a very strong ridge (anomalies more than 3 standard deviations above normal) centered near 60 degrees S; (3) anomalously high precipitable water content (20 mm above climatological norms) over the Peruvian Bight region was advected southward and eastward ahead of the cutoff low by low-level northwesterly flow, greatly enhancing observed precipitation over northern Chile.

Four sets of downscaling simulations based on the Eta Regional Climate Model forced by two global climate models, the HadGEM2-ES and the MIROC5, and two RCP scenarios-8.5 and 4.5, have been carried out.The objective of this work is to assess the climate change over South America based on the Eta simulations.The future changes are shown in timeslices of 30 years: 2011-2040; 2041-2070 and 2071-2100.The climate change response of the Eta simulations nested in Had-GEM2-ES is larger than the Eta nested in MIROC5.Major warming area is located in the central part of Brazil.In austral summer, the reduction of precipitation in the central part and the increase in the southeastern part of the continent are common changes in these simulations, while the Eta-HadGEM2-ES intensifies the decrease of precipitation in central Brazil, the Eta-MIROC5 expands the area of increase of precipitation in southern Brazil toward the end of the century.In austral winter, precipitation decrease is found in the northern part of South America and in most of Central America, whereas the reduction in southeastern South America is limited to near coastal region.The time series of temperatures show that warming trends are larger in the Eta-HadGEM2-ES than in the Eta-MIROC5 simulations.Heavier precipitation rates are projected in the Central-South of Brazil toward the end of the century.Increase in the length of consecutive dry days (CDD) in Northeast of Brazil and the decrease of consecutive wet days (CWD) in the Amazon region are common features in these simulations.

To provide long-term simulations of climate change at higher resolution, Regional Climate Models (RCMs) are nested in global climate models (GCMs).The objective of this work is to evaluate the Eta RCM simulations driven by three global models, the HadGEM2-ES, BESM, and MIROC5, for the present period, 1961-1990.The RCM domain covers South America, Central America, and Caribbean.These simulations will be used for assessment of climate change projections in the region.Maximum temperatures are generally underestimated in the domain, in particular by MIROC5 driven simulations, in summer and winter seasons.Larger spread among the simulations was found in the minimum temperatures, which showed mixed signs of errors.The spatial correlations of temperature simulations against the CRU observations show better agreement for the MIROC5 driven simulations.The nested simulations underestimate precipitation in large areas over the continent in austral summer, whereas in winter overestimate occurs in southern Amazonia, and underestimate in southern Brazil and eastern coast of Northeast Brazil.The annual cycle of the near-surface temperature is underestimated in all model simulations, in all regions in Brazil, and in most of the year.The temperature and precipitation frequency distributions reveal that the RCM and GCM simulations contain more extreme values than the CRU observations.Evaluations of the climatic extreme indicators show that in general hot days, warm nights, and heat waves are increasing in the period, in agreement with observations.The Eta simulations driven by Had-GEM2-ES show wet trends in the period, whereas the Eta driven by BESM and by MIROC5 show trends for drier conditions.