While it is widely accepted that the global mean atmospheric temperature has increased in recent decades, the spatial distribution of global warming has been complex. In this study we comprehensively characterize the spatial pattern, including vertical structure, of temperature trends along the subtropical west coast of South America (continental Chile) for the period 1979–2006 and examine their consistency with expectations based on the CMIP‐3 ensemble of coupled ocean‐atmosphere simulations for the late 20th century. In central and northern Chile (17°–37°S) the most notable feature is a strong contrast between surface cooling at coastal stations (−0.2°C/decade) and warming in the Andes (+0.25°C/decade), only 100–200 km further inland. Coastal radiosonde data imply that the coast‐Andes variation is largely due to strong vertical stratification of temperature trends in the atmosphere west of the Andes. The coastal cooling appears to form part of a larger‐scale, La Niña‐like pattern and may extend below the ocean mixed layer to depths of at least 500 m. Over continental Chile the CMIP‐3 GCM ensemble predicts temperature trends similar to those observed in the Andes. The cooling along the Chilean coast is not reproduced by the models, but the mean SST warming is weaker there than any other part of the world except the Southern Ocean. It is proposed that the intensification of the South Pacific Anticyclone during recent decades, which is also a simulated consequence of global warming, is likely to play a major role in maintaining cooler temperatures off the coast of Chile.

Central Chile (32°-35°S) is a mountainous and densely populated strip of land between the South American Pacific coast and the main divide of the Andes, 5000 m in height. In this study, wintertime precipitation episodes in central Chile are characterized using precipitation gauge, river discharge, radiosonde, and Special Sensor Microwave Imager (SSM/I) passive microwave radiometer observations over a 10-yr period (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002). Precipitation episodes that typically occur as cold frontal rainstorms move over the region from west to east, within which the cross-mountain flow is blocked at lower levels. The influence of the Andes on the climatological precipitation pattern extends several hundred kilometers upstream of the coast. Over the mainland, the wintertime precipitation is most strongly related to the height of the mean topography surrounding the rain gauge sites, rather than the actual altitudes of the instruments, although higher-elevation locations are not well sampled by available rainfall observations. Between the coast and foothills of the Andes, the precipitation pattern is relatively uniform despite the complex coastal topography. On the western face of the Andes climatological enhancement factors of between 1 and 3 are inferred.Regression analysis against radiosonde data at a coastal site reveals that the precipitation is strongly related to the zonal (cross mountain) moisture flux. The strongest relationship is found when the moisture flux is multiplied by the relative humidity. This variable explains 50% of the variance in daily area average precipitation in central Chile and up to 60% of the variance in the daily precipitation recorded at individual stations. The factors contributing to events of heavy precipitation enhancement in the Andes were examined. Events of heavy, but isolated, precipitation in the Andes tend to occur in the warmer, prefrontal sector of approaching storms and are associated with unusually high moisture fluxes near to and above the crest of the mountain range. Strongly frontal episodes, characterized by widespread rainfall throughout central Chile, lead to variable, but on average rather weak, enhancement in the Andes.

[1] The water resources of high-altitude areas of Chile's semiarid Norte Chico region (26-32°S) are studied using surface hydrological observations (from 59 rain gauges and 38 hydrological stations), remotely sensed data, and output from atmospheric prediction models. At high elevations, the observed discharge is very high in comparison with precipitation. Runoff coefficients exceed 100% in many of the highest watersheds. A glacier inventory performed with aerial photographs and ASTER images was combined with information from past studies, suggesting that glacier retreat could contribute between 5% and 10% of the discharge at 3000 m in the most glacierized catchment of the region. Snow extent was studied using MOD10A2 data. Results show that snow is present during 4 months at above 3000 m, suggesting that snow processes are crucial. The mean annual sublimation ($80 mm a À1 at 4000 m) was estimated from the regional circulation model (WRF) and data from past studies. Finally, spatial distribution of precipitation was derived from available surface data and the global forecast system (GFS) atmospheric prediction model. Results suggest that annual precipitation is three to five times higher near the peak of the Andes than in the lowlands to the west. The GFS model suggests that daily precipitation rates in the mountains are similar to those in the coastal region, but precipitation events are more frequent and tend to last longer. Underestimation of summer precipitation may also explain part of the excess in discharge. Simple calculations show that consideration of GFS precipitation distributions, sublimation, and glacier melt leads to a better hydrological balance.

Glaciers are strongly retreating and thinning in Patagonia. We present new inferences about the climatic situation and the surface mass balance on the Northern Patagonia Icefield in the past and the future using a combined modeling approach. The simulations are driven by NCAR/NCEP Reanalysis and ECHAM5 data, which were physically downscaled using the Weather Research and Forecasting regional climate model and simple sub‐grid parameterizations. The surface mass balance model was calibrated with geodetic mass balance data of three large non‐calving glaciers and with point mass balance measurements. An increase of accumulation on the Northern Patagonia Icefield was detected from 1990–2011 as compared to 1975–1990. Using geodetic mass balance data, calving losses from the Northern Patagonia Icefield could be inferred, which doubled in 2000–2009 as compared to 1975–2000. The 21st century projection of future mass balance of the Northern Patagonia Icefield shows a strong increase in ablation from 2050 and a reduction of solid precipitation from 2080, both due to higher temperatures. The total mass loss in the 21st century is estimated to be 592±50 Gt with strongly increasing rates towards the end of the century. The prediction of the future mass balance of the Northern Patagonia Icefield includes several additional sources of errors due to uncertainties in the prediction of future climate and due to possible variations in ice dynamics, which might modify the geometry of the icefield and change the rate of mass losses due to calving.

ABSTRACT:The west coast of subtropical South America is characterized by a semi-arid climate and very persistent southerly winds that often exhibit a low-level jet structure. The nearly alongshore flow forces coastal and offshore upwelling of cold, nutrient-rich waters, thus supporting one of the most productive marine ecosystems in the world and a wealth of fishery resources. Therefore, the evaluation of the changes in the coastal winds in future climate is a key step to predict the regional environmental impacts of global climate change linked to anthropogenic greenhouse gas (GHG) increases.In this work we document the wind changes between present-day conditions and those projected for the end of the 21st century under two Intergovernmental Panel on Climate Change (IPCC) scenarios (A2 and B2). We first estimate and interpret the changes of the wind field over the southeast Pacific from 15 coupled atmosphere-ocean Global Circulation Models (GCMs). Very consistent among the GCMs is the strengthening of the southerlies along the subtropical coast as a result of a marked increase in surface pressure farther south. We then examine the coastal wind changes in more detail using the Providing REgional Climate for Impact Studies (PRECIS) regional climate model (RCM) with 25 km horizontal resolution nested in the Hadley Centre Atmospheric global Model (HadAM3). PRECIS results indicate that the largest southerly wind increase occurs between 37-41°S during spring and summer, expanding the upwelling-favourable regime in that region, at the same time that coastal jets at subtropical latitudes will become more frequent and last longer than current events. During fall and winter, the strengthening of the southerlies occurs at subtropical latitudes maintaining a mean jet year-round. Finally, we discuss the possibility that strengthening of the coastal southerlies might actually lead to a relative regional cooling even as the world as a whole continues to warm up.