Jose A Rutllant
Universidad de Chile, Departamento de Geofísica, Faculty Member
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Research Interests: Geography and Climatology
Abstract The impact of future climate change on the native vegetation of subtropical Andes is relatively unknown. The semiarid region of north-central Chile (30–34°S) has experienced a mega-drought over the last decade, with a partial... more
Abstract The impact of future climate change on the native vegetation of subtropical Andes is relatively unknown. The semiarid region of north-central Chile (30–34°S) has experienced a mega-drought over the last decade, with a partial recovery during the 2015 El Nino year. To characterize the vegetation response to climate variability, we analyzed the seasonal precipitation, potential evapotranspiration, temperature extremes, and high-resolution normalized difference vegetation index (NDVI) data at five altitudinal floors above 2500 m. We considered the bi-monthly maximum NDVI in austral summer (NDVIx) and the difference between NDVIx and that of two months prior (NDVId) to reflect the primary productivity throughout the growing season. We observed positive linear correlations between NDVIx and winter precipitation and negative ones with autumn/winter maximum temperatures at lower altitudes (the latter likely led to the negative correlation between NDVIx and potential evapotranspiration). The NDVIx showed clear latitudinal and altitudinal variability, with the southern region exhibiting an opposite NDVIx climate correlation pattern at altitudes greater than 3500 m. The NDVId correlations were more spatially uniform and showed similar patterns to those of NDVIx at lower altitudes. Precipitation declined at a rate of −45%/decade, which contributed to the −1.5%/decade and −5%/decade decline in NDVIx and NDVId, respectively. The positive NDVIx trends (1.5%/decade) above 3500 m in the southern region led to an early snowpack retreat, which was consistent with the temporal increase in autumn maximum temperature of 1.23 °C/decade. Our results suggest that ongoing climate change will have a negative impact on the high-altitude ecosystems of the semiarid Andes.
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In Eastern Boundary Upwelling Systems (EBUS), the upwelling favorable wind speeds decrease toward the coast in the so‐called wind drop‐off coastal strip, which has been shown to be influential on the coastal upwelling dynamics,... more
In Eastern Boundary Upwelling Systems (EBUS), the upwelling favorable wind speeds decrease toward the coast in the so‐called wind drop‐off coastal strip, which has been shown to be influential on the coastal upwelling dynamics, particularly in terms of the relative contributions of Ekman drift and Ekman suction to coastal upwelling. Currently, the wind drop‐off length scale is not properly resolved by the atmospheric forcing of regional ocean models in EBUS, featuring a smoother cross‐shore wind profile that results in stronger near‐shore speeds that could partly explain the coastal cold bias often found in those model simulations. Here, as a case study for the upwelling system off Central Chile, the sensitivity of upwelling dynamics to the coastal wind reduction is investigated using a Regional Ocean Modeling System (ROMS). Coastal wind profiles at different resolutions are first generated using a regional atmospheric model, validated from altimeter data, and then used to correct t...
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The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°–23.4°S) are documented based upon up to 45 years of hourly observations of cloud type, coverage, and heights. Consistent... more
The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°–23.4°S) are documented based upon up to 45 years of hourly observations of cloud type, coverage, and heights. Consistent with the subtropical location, cloud types are dominated by stratocumuli having greatest coverage (>7 oktas) and smaller heights (600–750 m) during the nighttime of austral winter and spring. Meridionally, nighttime cloud fraction and cloud-base heights increase from south to north. Long-term trends in mean cloud cover are observed at all sites albeit with a seasonal modulation, with increasing (decreasing) coverage in the spring (fall). Consistent trend patterns are also observed in independent sunshine hour measurements at the same sites. Cloud heights show negative trends of about 100 m decade−1 (1995–2010), although the onset time of this tendency differs between sites. The positive cloud fraction trends during the cloudy season reported here...
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RESUMEN. La tierra enfrenta un cambio climático derivado de la actividad del hombre. Este cambio excede en magnitud y rapidez a las variaciones ocurridas en los últimos 10.000 años y plantea problemas importantes de adaptación y... more
RESUMEN. La tierra enfrenta un cambio climático derivado de la actividad del hombre. Este cambio excede en magnitud y rapidez a las variaciones ocurridas en los últimos 10.000 años y plantea problemas importantes de adaptación y planificación. Con la escasa ...
Research Interests: Geography and Humanities
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Theterral de Vicuñais a warm and dry wind that flows down the Elqui Valley in north-central Chile typically at dawn and early morning. Given that most terral episodes occur in austral winter when chill accumulation by deciduous fruit... more
Theterral de Vicuñais a warm and dry wind that flows down the Elqui Valley in north-central Chile typically at dawn and early morning. Given that most terral episodes occur in austral winter when chill accumulation by deciduous fruit trees proceeds, negative effects on agriculture may be expected. During 11 (2004–14) winters a meteorological characterization of terral winds and the assessment of their impact on chill accumulation, by the modified Utah Model and the Dynamic Model, were performed. Within this period, 67 terral days (TD) were identified as those in which nighttime to early morning wind direction and speed, air temperature, and relative humidity reached defined thresholds on an hourly basis (terral hours). Most frequent TD featured 6–9 consecutive terral hours; duration is considered here as a proxy for their intensity. Synoptic-scale meteorological analysis shows that 65% of moderate and strong terral events develop as a cold, migratory anticyclone drifts poleward of t...
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Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, which could lead to stress on water... more
Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, which could lead to stress on water supply in addition to climate feedback. A proposed pathway for this transport is the channelling through the network of canyons that connect the urban basin to the elevated summits, as suggested by modelling studies, although no observations have validated this hypothesis so far. In this work, atmospheric measurements from a dedicated field campaign conducted in winter 2015, under severe urban pollution conditions, in Santiago and the Maipo canyon, southeast of Santiago, are analysed. Wind (speed and direction) and particulate matter concentrations measured at the surface and along vertical profiles, demonstrate intrusions of thick layers (up to 600 m above ground) of urban black carbon deep into the canyon on several occasions. Transport of PM down-valley occurs mostly through shallow layers at the surface except in connection with deep valley intrusions, when a secondary layer in altitude with return flow (down-valley) at night is observed. The transported particulate matter is mostly from the vicinity of the entrance to the canyon and uncorrelated to concentrations observed in downtown Santiago. Reanalyses data show that for 10% of the wintertime days, deep intrusions into the Maipo canyon are prevented by easterly winds advecting air pollutants away from the Andes. Also, in 23% of the cases, intrusions proceed towards a secondary north-eastward branch of the Maipo canyon, leaving 67% of the cases with favourable conditions for deep penetrations into the main Maipo canyon. Reanalyses show that the wind directions associated to the 33% anomalous cases are related to thick cloud cover and/or the development of coastal lows.
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Raco is the local name given to a strong (gusts up to 17 m s−1), warm, and dry down-valley wind observed at the exit of the Maipo River Canyon in central Chile. Its climatology is documented based on eight years of surface measurements... more
Raco is the local name given to a strong (gusts up to 17 m s−1), warm, and dry down-valley wind observed at the exit of the Maipo River Canyon in central Chile. Its climatology is documented based on eight years of surface measurements near the canyon exit together with a more complete characterization of its structure during an intensive observational period (IOP) carried out in July 2018. Raco winds occur in the cold season under well-defined synoptic conditions, beginning abruptly at any time during the night, reaching maximum hourly averages around 10 m s−1, and terminating around noon with the onset of afternoon westerly up-valley winds. About 25% of the days in May–August have more than six raco hours between 0100 and 1200 LT, and raco episodes last typically 1–2 days. The sudden appearance of raco winds at the surface can be accompanied by conspicuous warming (up to 10°C) and drying (up to 3 g kg−1). Raco winds are associated with a strong along-canyon pressure gradient, a re...
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Water availability in the semiarid western coast of Chile (30–32°S) is conditioned by high interannual precipitation variability, reflecting the transition between arid subtropical and moist mid-latitude climates in the Southeastern... more
Water availability in the semiarid western coast of Chile (30–32°S) is conditioned by high interannual precipitation variability, reflecting the transition between arid subtropical and moist mid-latitude climates in the Southeastern Pacific Ocean. A paleoclimate reconstruction based on the latest Pleistocene–Holocene geological record from the Quebrada Santa Julia archeological site in Chile (31°50′S) and on modern meteorological mechanisms producing alluvial episodes in this region indicates a major change in the rainfall regime shortly after 8600 cal yr BP. This, together with other paleoclimate proxies along the west coast of South America (34°–14°S), suggests La Niña-like conditions 13,000–8600 cal yr BP. Based on sedimentological and geomorphologic evidence, we hypothesized that the absence of heavy rainfall events in northern Chile and the new hydrological regime that prevailed ca. 8600–5700 cal yr BP in north-central Chile resulted from an increase in the large-scale westerly...
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Nocturnal flows down the narrow Andean valleys within the western slope of the subtropical Andes (central Chile) are episodically enhanced by easterly downslope winds that flow into the Santiago basin over the radiatively cooled air above... more
Nocturnal flows down the narrow Andean valleys within the western slope of the subtropical Andes (central Chile) are episodically enhanced by easterly downslope winds that flow into the Santiago basin over the radiatively cooled air above the surface. Local, regional, and large-scale data have been used here to characterize the mean features of these episodes. About 80 % of easterly downslope flow episodes in austral winter are forced by a reversal in the sea level pressure gradient along the coast of south-central Chile, when a midlatitude cold high migrates from southern Chile eastward across the Andes under midtroposphere SW winds associated with a warm ridge aloft. Under these circumstances low-level, easterly (offshore) flow sets in, producing a compensating downslope flow that subsides over central Chile. The remaining cases are associated with prefrontal conditions under a midlatitude trough with NW winds aloft. Since in most of these cases the easterly low-level flow occurs ...
The main objective of this study was to assess the structure and the time-space variability of the marine boundary layer (MBL) in the subtropical southeast ...
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The relationship between modern debris flows in the Antofagasta region of northern Chile (23oS) and El Nino events was studied through the revision of local newspapers, rainfall data and the characterization of geologic sections [Vargas... more
The relationship between modern debris flows in the Antofagasta region of northern Chile (23oS) and El Nino events was studied through the revision of local newspapers, rainfall data and the characterization of geologic sections [Vargas et al., 2000]. During the twentieth century, all the debris flow episodes were associated to heavy rainfall (20-40 mm/3 hr) in austral winter during the development phase of strong to moderate El Nino events: August 1930, June 1940, May 1982, July 1987 and June 1991 (Figure 1). Meteorological conditions for the development of heavy rains in June18, 1991 have been described in Garreaud and Rutllant [1996], but further verification and search for additional meteorological mechanisms in different phases of the ENSO cycle should lead to improved ENSO reconstructions from Holocene alluvial sequences in this region.
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Surface winds along the subtropical west coast of South America are characterized by the quasi-weekly occurrences of low-level jet events. These short lived but intense wind events impact the coastal ocean environment. Hence, identifying... more
Surface winds along the subtropical west coast of South America are characterized by the quasi-weekly occurrences of low-level jet events. These short lived but intense wind events impact the coastal ocean environment. Hence, identifying long-term trends in the coastal low-level jet (CLLJ) is essential for understanding changes in marine ecosystems. Here we use ERA5 reanalysis (1979–2019) and an objective algorithm to track anticyclones to investigate recent changes in CLLJ events off central Chile (25–43 °S). Results present evidence that the number of days with intense wind (≥10 ms−1), and the number and duration of CLLJ events have significantly changed off central Chile in recent decades. There is an increase in the number of CLLJ events in the whole study area during winter (June-July-August; JJA), while during summer (December–January–February; DJF) a decrease is observed at lower latitudes (29–34 °S), and an increase is found at the southern boundary of the Humboldt system. W...
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Research Interests: Geology and Oceanography
To better forecast streamflow and water resource availability, it is important to have an understanding of the meteorological drivers of the orographic precipitation gradient (OPG), especially critical in semiarid mountainous areas.... more
To better forecast streamflow and water resource availability, it is important to have an understanding of the meteorological drivers of the orographic precipitation gradient (OPG), especially critical in semiarid mountainous areas. Although forced ascent over topography typically results in precipitation increasing with altitude (positive OPGs), mean annual OPGs and especially OPGs associated with individual storms can change widely in magnitude and even sign. Precipitation measurements from the Elqui Valley in the semiarid Andes of Chile (30°S) reveal a mean annual OPG of 6.3 mm km−1 (millimeters of precipitation over kilometers in elevation) ranging from −42 to 52 mm km−1 for individual storms over the last 35 years (1979–2013). Reanalysis data and precipitation measurements are used to characterize the observed OPG in this region in relation with their synoptic-scale flow. It is found that the Froude number correlates positively with the OPG, reflecting stronger zonal winds and ...
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... active upwelling. There, besides the Ekman-drift-associated coastal upwelling, cyclonic windstress curl (Ekman pumping) can be extremely important in the maintenance and offshore extension of the upwelling conditions. This ...
Research Interests: Earth Sciences, Sea Level, Low Frequency, Sea surface temperature, Biological Sciences, and 11 moreHigh Frequency, Cross Correlation, South America, Singular Spectrum Analysis, Continental shelf, Coastal upwelling, Band Pass, Large Scale, Singular-spectrum Analysis, Madden Julian Oscillation, and Sea Level Pressure
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Biological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly alongshore flow is driven by the southeast Pacific... more
Biological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly alongshore flow is driven by the southeast Pacific (SEP) anticyclone, and its intensity and position vary on a range of time scales. Variability of the SEP anticyclone has been linked to large-scale circulations such as El Niño–Southern Oscillation and the Madden–Julian oscillation. The actual timing, duration, and nature of the seasonal meridional drift of the SEP anticyclone are associated with the onset, demise, and strength of the local upwelling season. Seasonal variation is especially marked at the Punta Lavapié (37°S) upwelling focus, where there is a clear upwelling season associated with a change of the cumulative upwelling index (CUI) slope between positive and negative. The Punta Lengua de Vaca (30°S) focus typically exhibits upwelling year-round and has less distinct transitions, making ...
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ABSTRACT Upwelling areas play a major role in ocean biocheogemical cycles and ultimately in global climate, especially in higly productive regions as the South Eastern Pacific. This work is based on the analysis of the aeolian lithic... more
ABSTRACT Upwelling areas play a major role in ocean biocheogemical cycles and ultimately in global climate, especially in higly productive regions as the South Eastern Pacific. This work is based on the analysis of the aeolian lithic particles accumulated in laminated sediments off Mejillones (23°S) in the eastern boundary Humboldt Current System. It proposes a high-resolution quantitative reconstruction of the upwelling-favorable southerly wind strength in the past ∼250 years, comparing its variability with changes in organic carbon export/preserved changes to the sea bottom. The increase of the intensity and variability in fluxes of particles larger than 35 μm and 100 μm since the second half of the 19th century and during the 20th century confirms a general strengthening of southerly winds in the region. Spectral analysis on the complete time-series of yearly depositional fluxes indicates that sedimentary variability can be explained by a combination of interannual (ENSO) to decadal (PDO) oscillations similar to the ones yielded by the analysis of the Interdecadal Pacific Oscillation index. However, when applied separately to the lithic fluxes of the first and last centuries of the time-series, the method shows that relative to the one of the internanual mode of variability, the influence of the decadal mode has increased in the recent period.