Orographic Barrier Research Articles

Coastal and orographic effects on extreme precipitation revealed by weather radar observations

Abstract. The yearly exceedance probability of extreme precipitation of multiple durations is crucial for infrastructure design, risk management, and policymaking. Local extremes emerge from the interaction of weather systems with local terrain features such as coastlines and orography; however, multi-duration extremes do not follow exactly the patterns of cumulative precipitation and are still not well understood. High-resolution information from weather radars could help us quantify their patterns better, but traditional extreme value analyses based on radar records were found to be too inaccurate for quantifying the extreme intensities required for impact studies. Here, we propose a novel methodology for extreme precipitation frequency analysis based on relatively short weather radar records, and we use it to investigate the coastal and orographic effects on extreme precipitation of durations between 10 min and 24 h. Combining 11 years of radar data with 10 min rain gauge data in the southeastern Mediterranean, we obtain estimates of the once in 100 years precipitation intensities with ∼26 % standard error, which is lower than those obtained using traditional approaches on rain gauge data. We identify the following three distinct regimes which respond differently to coastal and orographic forcing: short durations (∼10 min), related to peak convective rain rates, hourly durations (∼1 h), related to the yield of individual convective cells, and long durations (∼6–24 h), related to the accumulation of multiple convective cells and to stratiform processes. At short and hourly durations, extreme return levels peak at the coastline, while at longer durations they peak corresponding to the orographic barriers. The distributions tail heaviness is rather uniform above the sea and rapidly changes in presence of orography, with opposing directions at short (decreasing tail heaviness, with a peak at hourly durations) and long (increasing) durations. These distinct effects suggest that short-scale hazards, such as urban pluvial floods, could be more of concern for the coastal regions, while longer-scale hazards, such as flash floods, could be more relevant in mountainous areas.

Geomorphic evaluation of landslides along the Teesta river valley, Sikkim Himalaya, India

Landslides are a common and widespread phenomena in tectonically active mountains, impacting on landscape development, and lanslides pose a serious threat to the lives and properties when these interfere with humans and their associated infrastructure. However, the spatial distribution of these landslides is controlled by various geological and geomorphological parameters, including the neotectonic activity and the climatic pattern of the area. In the present study, various geomorphic parameters such as longitudinal and topographic swath profile, valley floor width to valley height ratio, channel steepness index, and stream length gradient index, along with the rainfall pattern of the Teesta river valley, Sikkim Himalaya, were correlated with the spatial distribution of landslides in the area. It has been concluded that landslides in the Higher Himalaya, north of the Main Central Thrust behind the orographic barrier, owe their origin mainly to the higher tectonic activity, and adjacent to the Main Central Thrust in the front of the orographic barrier to both tectonic activity and the higher rainfall. The distribution of landslides in the Lesser Himalaya is dominantly controlled by lithology and is mainly triggered by the rainfall.

Resilience and adaptation to volcanoes in Late Middle Ages in Lipari island (Aeolian, Italy)

Volcanic activity resumed during early Middle Ages times at Lipari following at least 6000 years of quiescence. This phenomenon occurred in a social context that had continuously developed from prehistoric times to the Roman age and was burdened by a demographic crisis that involved the archipelago between the 6th and 11th century AD. The rare archaeological records relating to the 6th - 11th centuries suggest abrupt changes in the population of the islands. The medieval sources are rich in religious and fantastic references to volcanic events linked to Lipari and Vulcano, testifying the uneasy condition for the human communities. This work concerns the resilience and adaptation of the communities to volcanic activity during the Late Middle Ages in Lipari. Starting from 1083 the Aeolian archipelago was involved in a repopulation program, implemented in 1095 by the Constitutum and organized by the Benedictine Monastery with the annexed S. Bartolomeo Cathedral on the castle. From the 13th century the volcanic phenomena, strictly limited to the northern sector of the island, did not interfere as previously with the anthropic activities. The Monastery will be enlarged in the Norman phase during the first half of the 12th century with the construction of the cloister. New historical documents relating to the 1264, report news of fires and land movements on Lipari. Recent age determinations obtained for the obsidian flow of Rocche Rosse at 1220 ± 30 AD (archaeomagnetic dating) and for an obsidian block of the Lami pyroclastic cone at 1243 ± 190 (fission-track dating) allow to define the age of the last phase of activity of the Monte Pilato-Lami-Rocche Rosse complex, and to associate it the events reported on 1264’s historical documents. This work makes in comparison volcanological, archaeological and historical dates and described an updated summary of one of the lesser known phases of the history of the archipelago. The main consequence of the medieval volcanic activity at Lipari caused a clear division of the territory with the population confined in the southeast quadrant, protected to the north by Serra and Monte Rosa which represented a natural orographic barrier.

Determinants of zoogeographical boundaries differ between vertebrate groups

AbstractAimWorldwide distribution patterns of living animals are structured in multiple zoogeographical regions, characterized by faunas with homogeneous composition that are separated by sharp boundaries. These zoogeographical regions can differ depending on the considered animal group, probably because they have distinct characteristics such as dispersal, metabolism, or evolutionary history, and thus divergent responses to major biogeographical drivers, such as tectonic movements, abrupt climate transitions and orographic barriers. Here, we tested if the drivers of biogeographical boundaries are different between vertebrate classes with strongly divergent traits and evolutionary history.LocationGlobal.Time periodPresent.Major taxa studiedAmphibians, birds and mammals.MethodsWe focused on terrestrial biogeographical boundaries, considering multiple potential drivers: spatial heterogeneity of present‐day climate, altitudinal variation, long‐term tectonic movements and past climate change (temperature). We used spatially explicit regression models and geographically weighted regressions to select and quantify the factors explaining the position of the biogeographical boundaries between vertebrate classes.ResultsFor mammals, tectonic movements, abrupt climatic transitions and orographic barriers jointly determined extant biogeographical boundaries, with tectonic movements being the most important. For birds, abrupt climatic transitions played the strongest role, while the effect of orographic barriers was weak. For amphibians, biogeographical boundaries mostly corresponded to areas with abrupt climatic transitions. The strongest transitions of amphibian faunas occur in areas with abrupt shifts of temperature and precipitation regimes.Main conclusionsOur analyses confirmed that different drivers have jointly shaped the global vertebrate biogeographical regions, and highlight that taxa with different features show heterogeneous responses across the globe. Eco‐physiological constraints likely increase the importance of spatial heterogeneity of climate, while dispersal limitations magnify the relevance of physical barriers (mountain chains and long‐term tectonic instability). Integrating among‐taxa heterogeneity into analyses thus provides a more complete view of how different processes determine biodiversity variation across the globe.

Impact of the Southern Ecuadorian Andes on Oxygen and Hydrogen Isotopes in Precipitation

Determining how the elevation of the Northern Andes has evolved over time is of paramount importance for understanding the response of the Northern Andes to deformational and geodynamic processes and its role as an orographic barrier for atmospheric vapor transport over geologic time. However, a fundamental requirement when using stable isotope data for paleoaltimetry reconstructions is knowledge about the present-day changes of δ18O and δD with elevation (isotopic lapse rate). This study defines the present-day river isotopic lapse rate near the Equator (∼3°S) based on analysis of δ18O and δD of surface waters collected from streams across the Western Cordillera and the Inter-Andean depression in Southern Ecuador. The results for the two domains show a decrease of δ18O with elevation which fits a linear regression with a slope of −0.18‰/100 m (R2= 0.73,n= 83). However, we establish a present-day lapse rate of −0.15‰/100 m for δ18O (R2= 0.88,n= 19) and -1.4‰/100 m for δD (R2= 0.93,n= 19) from water samples collected along the west facing slopes of the Western Ecuadorian Cordillera which is mainly subject to moisture transport from the Pacific. We argue that this empirical relationship, consistent with those obtained in different tropical areas of the world, can inform stable isotope paleoaltimetry reconstructions in tropical latitudes.

On the characterization of mountain waves and the development of a warning method for aviation safety using WRF forecast

Mountain wave and icing episodes are adverse meteorological conditions that can affect aviation safety and air traffic management in the vicinity of airports. This study presents a mountain wave characterization performed for the winter months from 2001 to 2010 in the center of the Iberian Peninsula, close to an important orographic barrier and next to the busiest Spanish airport. Sixty-eight episodes were simulated using the Weather Research and Forecasting model (WRF). Five simulated atmospheric variables (wind direction, wind speed, atmospheric stability, liquid water content and temperature) were evaluated in several grid points at 2800 meters above sea level in leeward, windward and over the summit of the mountains. Based on the percentiles and thresholds obtained from the characterization, a decision tree was developed with the aim to forecast and warn the occurrence of mountain waves, wave clouds and icing events. The decision tree and the three warning methods were validated against satellite images. The results show satisfactory scores, with a percentage correct of detection above 70% for the three warnings.

Geostatistical Tools to Assess Existing Monitoring Network of Forest Soils in a Mountainous National Park

Environmental changes in national parks are generally subject to constant observation. A particular case is parks located in mountains, which are more vulnerable to climate change and the binding of pollutants in mountain ranges as orographic barriers. The effectiveness of forest soil monitoring networks based on a systematic grid with a predetermined density has not been analysed so far. This study’s analysis was conducted in the Stolowe Mountains National Park (SMNP), SW Poland, using total Pb concentration data obtained from an initial network of 403 circle plots with centroids arranged in a regular 400 × 400 m square grid. The number and distribution of monitoring plots were analysed using geostatistical tools in terms of the accuracy and correctness of soil parameters obtained from spatial distribution imaging. The analysis also aimed at reducing the number of monitoring plots taking into account the economic and logistic aspects of the monitoring investigations in order to improve sampling efficiency in subsequent studies in the SMNP. The concept of the evaluation and modification of the monitoring network presented in this paper is an original solution and included first the reduction and then the extension of plot numbers. Two variants of reduced monitoring networks, constructed using the proposed procedure, allowed us to develop the correct geostatistical models, which were characterised by a slightly worse mean standardised error (MSE) and root mean squared error (RMSE) compared to errors from the original, regular monitoring network. Based on the new geostatistical models, the prediction of Pb concentration in soils in the reduced grids changed the spatial proportions of areas in different pollution classes to a limited extent compared to the original network.

Geological evolution of a tectonic and climatic transition zone: the Beyşehir-Suğla basin, lake district of Turkey

Central-west Turkey is a transition zone both tectonically and climatically between the quite different central and western regions of Anatolia. Central Anatolia represents the seismically quiet part of the otherwise highly active Turkey. On the other hand, this region has some of the lowest precipitation and highest evaporation ratios of Turkey. Conversely, west Anatolia is one of the most rapidly extending regions of the world and seismically very active. The climate is very different from the central part of Turkey and more humid. The zone between these two regions is also known geologically as the Isparta Angle. This reverse-V-shaped fold and thrust belt has several lake basins today, which have archived the geological and geomorphological history of this tectonic and climatic transition zone. The Beysehir-Sugla basin is located on the eastern part of this zone. This NW–SE trending basin includes the largest natural freshwater lake of the Mediterranean region: Lake Beysehir. Lakes Beysehir and Sugla are located in this tectonic depression that discharge into an incised river gorge opening to the Konya closed basin. In order to shed light on the development of the Beysehir-Sugla basin, our study was mainly conducted within the Neogene and Quaternary units of the region. Our structural results indicate that the depression was probably formed by a transtensional regime in the middle Miocene, which is controlled by extensional tectonics since the early Quaternary. Also, the current depression has mainly embodied the structures that are the products of these tectonic phases. According to our sedimentary data and palaeoecological interpretation of available palaeontological data, the Beysehir-Sugla basin was developed initially under a humid and warm climate in the middle Miocene; then since the late Miocene-Pliocene it was controlled by a relatively more arid and, at times, humid climate more like the central Anatolian basins. Although the Beysehir-Sugla basin is hydrologically connected to the Konya closed basin in central Anatolia, it was protected from arid climatic conditions for over millions of years as evidenced by the lack of evaporites in the studied basin and surrounding basins located in the interior part of the Isparta Angle. While the regional climate seems to have changed consistently with the geomorphic response to large-scale tectonics (i.e. orographic barrier development), the Beysehir-Sugla basin seems to be protected from hydrological closure by the existence of karstic features in the surrounding carbonate basement rocks.

Orographic Effect on Extreme Precipitation Statistics Peaks at Hourly Time Scales

AbstractOrographic impact on extreme subdaily precipitation is critical for risk management but remains insufficiently understood due to complicated atmosphere‐orography interactions and large uncertainties. We investigate the problem adopting a framework able to reduce uncertainties and isolate the systematic interaction of Mediterranean cyclones with a regular orographic barrier. The average decrease with elevation reported for hourly extremes is found enhanced at subhourly durations. Tail heaviness of 10‐min intensities is negligibly affected by orography, suggesting self‐similarity of the distributions at the convective scale. Orography decreases the tail heaviness at longer durations, with a maximum impact around hourly scales. These observations are explained by an orographically induced redistribution of precipitation toward stratiform‐like processes, and by the succession of convective cores in multihour extremes. Our results imply a breaking of scale‐invariance at subhourly durations, with important implications for natural hazards management in mountainous areas.

Climate extreme variables generated using monthly time‐series data improve predicted distributions of plant species

Extreme weather can have significant impacts on plant species demography; however, most studies have focused on responses to a single or small number of extreme events. Long‐term patterns in climate extremes, and how they have shaped contemporary distributions, have rarely been considered or tested. BIOCLIM variables that are commonly used in correlative species distribution modelling studies cannot be used to quantify climate extremes, as they are generated using long‐term averages and therefore do not describe year‐to‐year, temporal variability. We evaluated the response of 37 plant species to base climate (long‐term means, equivalent to BIOCLIM variables), variability (standard deviations) and extremes of varying return intervals (defined using quantiles) based on historical observations. These variables were generated using fine‐grain (approx. 250 m), time‐series temperature and precipitation data for the hottest, coldest and driest months over 39 years. Extremes provided significant additive improvements in model performance compared to base climate alone and were more consistent than variability across all species. Models that included extremes frequently showed notably different mapped predictions relative to those using base climate alone, despite often small differences in statistical performance as measured as a summary across sites. These differences in spatial patterns were most pronounced at the predicted range margins, and reflect the influence of coastal proximity, continentality, topography and orographic barriers on climate extremes. Species occupying hotter and drier locations that are exposed to severe maximum temperature extremes were associated with better predictive performance when modelled using extremes. Understanding how plant species have historically responded to climate extremes may provide valuable insights into our understanding of contemporary distributions and help to make more accurate predictions under a changing climate.

High Space-Time Resolution Observation of Extreme Orographic Rain Gradients in a Pacific Island Catchment

In the vicinity of orographic barriers, interactions between mountains and prevailing winds can enhance rainfall and generate strong spatial gradients of precipitation. Orographic rainfall is still poorly quantified despite being an important driver of headwater catchment hydrology, in particular when considered at high space-time resolution. In this paper, we propose a complete framework for the observation and quantification of orographic rainfall gradients at the local scale. This framework, based on the stochastic interpolation of drop-counting rain gauge observations, provides reconstructions of local rain fields at high space-time resolution. It allows us to capture the life-cycle of individual rain cells, which typically occurs at a spatial scale of approximately 1–5 km and a temporal scale of approximately 5–15 min over our study area. In addition, the resulting rain estimates can be used to investigate how rainfall gradients develop during rain storms, and to provide better input data to drive hydrological models. The proposed framework is presented in the form of a proof-of-concept case study aimed at exploring orographic rain gradients in Mānoa Valley, on the leeward side of the Island of Oʻahu, Hawaiʻi, USA. Results show that our network of eight rain gauges captured rainfall variations over the 6 × 5 km2 study area, and that stochastic interpolation successfully leverages these in-situ data to produce rainfall maps at 200 m × 1 min resolution. Benchmarking against Kriging shows better performance of stochastic interpolation in reproducing key statistics of high-resolution rain fields, in particular rain intermittency and low intensities. This leads to an overall enhancement of rain prediction at ungauged locations.

Extreme precipitation events over northern Italy. Part II: Dynamical precursors

AbstractThe connection between weather extremes and Rossby wave packets (RWP) has been increasingly documented in recent years. RWP propagation and characteristics can modulate the midlatitude weather, setting the scene for temperature and precipitation extremes and controlling the geographical area affected. Several studies on extreme precipitation events (EPEs) in the Alpine area reported, as the main triggering factor, a meridionally elongated upper‐level trough as part of an incoming Rossby wave packet. In this work, we investigate a wide number of EPEs occurring between 1979 and 2015 in northern‐central Italy. The EPEs are subdivided into three categories (Cat1, Cat2, Cat3) according to thermodynamic conditions over the affected region. It is found that the three categories differ not only in terms of the local meteorological conditions, but also in terms of the evolution and properties of precursor RWPs. These differences cannot be solely explained by the apparent seasonality of the flow; therefore, the relevant physical processes in the RWP propagation of each case are further investigated. In particular, we show that RWPs associated with the strongest EPEs, namely the ones falling in Cat2, undergo a substantial amplification over the western North Atlantic due to anomalous ridge‐building 2 days before the event; arguably due to diabatic heating sources. This type of development induces a downstream trough which is highly effective in focusing water vapour transport toward the main orographic barriers of northern‐central Italy and favouring the occurrence of EPEs.

Global significance of oxygen and carbon isotope compositions of pedogenic carbonates since the Cretaceous

Few global syntheses of oxygen and carbon isotope composition of pedogenic carbonates have been attempted, unlike marine carbonates. Pedogenic carbonates represent in-situ indicators of the climate conditions prevailing on land. The δ18O and δ13C values of pedogenic carbonates are controlled by local and global factors, many of them not affecting the marine carbonates largely used to probe global climate changes. We compile pedogenic oxygen and carbon isotopic data (N= 12,167) from Cretaceous to Quaternary-aged paleosols to identify potential trends through time and tie them to possible controlling factors. While discrete events such as the Paleocene-Eocene Thermal Maximum are clearly evidenced, our analysis reveals an increasing complexity in the distribution of the δ18O vs δ13C values through the Cenozoic. As could be expected, the rise of C4 plants induces a shift towards higher δ13C values during the Neogene and Quaternary. We also show that the increase in global hypsometry during the Neogene plays a major role in controlling the δ18O and δ13C values of pedogenic carbonates by increasing aridity downwind of orographic barriers. Finally, during the Quaternary, an increase of 3‰ in δ18O values is recorded both by the pedogenic carbonates and the marine foraminifera suggesting that both indicators may be used to track global climate signal.

Karst geomorphology in the Oštarije–Tounj area and its significance in the geomorphological evolution of the broader area

The Oštarije–Tounj area lies in the contact zone of two large geomorphological units: the Ogulin-Plaški basin and the Una-Korana plateau, along the northern edge of Dinaric karst in Croatia. This is a highly karstified landscape, with numerous surface and subterranean karst forms. The objective of this study was to determine the significance of the karst relief and the processes of its formation, with the aim of examining the interaction of these two large units during their geomorphological evolution. General and specific digital geomorphometric analyses were used, with geomorphological mapping. Within the morphogenetic approach, the morphostructural conditions of karstification, spatial distribution and significance of karst, and fluviokarst relief forms were analysed. Several dry valleys were established, indicating that this area was the important corridor for surface runoff from the Ogulin-Plaški basin towards the Una-Korana plateau. Tectonic up-lifting of the narrow zone between these two units created an orographic barrier, which hindered any further surface runoff and created the conditions for the development of karst subterranean watercourses. This paper provides a proposal of the morphogenesis model of the Ogulin-Plaški basin, summarised with the description “flattening and closure”.

Exhumation and structural evolution of the high-elevation Malcante Range, Eastern Cordillera, NW Argentina

As an integral part of the Eastern Cordillera, the fault-bounded Malcante mountain range (up to 5100 m) in the NW Argentine Andes (ca. 25°S) is located in the transition between the arid Puna Plateau to the west and the humid broken foreland to the east. At this latitude, the topographic gradient of the eastern Andean margin forms an efficient orographic barrier that causes pronounced east–west rainfall and surface-process gradients. In this setting, the Malcante Range is an important, yet poorly studied structural high formed during the Cenozoic topographic growth of the Central Andes. In this study, we combine (a) detailed field observations, (b) a two-dimensional structural reconstruction, (c) apatite fission track and (U–Th-Sm)/He thermochronology of bedrock samples from a vertical transect across the western flank of the Malcante Range, and (d) inverse thermal modelling using QTQt software with the aim of deciphering the exhumation history of this mountain range. Field data indicate the presence of an angular unconformity between Cenozoic foreland deposits and older sedimentary strata, suggesting an initial episode of deformation during the middle-late Eocene, while our thermal model constrains the onset of exhumation at ~10 Ma. We suggest that exhumation was related to the unroofing of the easily erodible sedimentary cover, which prevented significant initial surface uplift. This may have changed as more resilient bedrock was exposed at ~5 Ma according to the thermal model, promoting rapid rock uplift. In combination with published data, our thermochronology allows us to speculate on the existence of a zone of deformation concentrated in the area of the present-day Pasha (24.5°S), Malcante (25°S), and Agua de Castilla (25.4°S) mountain ranges by ca. 10 Ma.

A Late Miocene to Late Pleistocene Reconstruction of Precipitation Isotopes and Climate From Hydrated Volcanic Glass Shards and Biomarkers in Central Alaska and Yukon

AbstractThe Pliocene (5.3–2.6 Ma), an epoch with periods of climatic warmth and possible analogue for the future, has been well‐characterized globally by marine geochemical proxies. However, far less is known about Pliocene warmth at continental high latitudes, where the greatest impacts of warming are expected. This study seeks to better characterize the Pliocene climate of central Alaska and Yukon based on a reconstruction of the stable hydrogen isotope composition of precipitation relative to modern (ΔδDprecip) preserved in volcanic glass shards, a proxy for mean air temperature. The studied tephras are from a regional suite of outcrops that, when assembled into a composite record of ΔδDprecip, can be used to resolve broad trends during the late Miocene (6.7–5.86 Ma, n = 5), Pliocene (5.08–2.81 Ma, n = 7), and late Pleistocene (0.74–0.03 Ma, n = 3). These trends indicate that Pliocene ΔδDprecip estimates were generally more enriched in heavy isotopes than the latest Miocene, Pleistocene, and modern intervals. ΔδDprecip is likely influenced by changes in regional boundary conditions including orographic barriers, depositional environments, and ocean‐atmospheric circulation, but ΔδDprecip trends are most consistent with reconstructed temperatures from Yukon‐Alaska and North Pacific marine records. As such, this record appears predominantly sensitive to regional climate. Furthermore, qualitative temperature inferences from branched‐chain glycerol dialkyl glycerol tetraethers (brGDGTs) from four of our sites dating between 2.91 and 6.17 Ma corroborate elevated temperatures during the early Pliocene. Overall, this study demonstrates the viability of volcanic glass δD as a proxy for ΔδDprecip and late Cenozoic climate change in this region.

Will global change modify the distribution of the Anadenanthera colubrina (Fabales: Fabaceae) plant, a key species in dry tropical forest?

Introduction: Seasonally dry tropical forests (SDTF) are one of the most threatened terrestrial ecosystems on the planet as a consequence of global change. They harbor high biodiversity and provide a wide range of ecosystem services; therefore, their conservation is a priority worldwide. Climate warming, as well as land use patterns, are leading to species distribution range shifts. Objective: The objective of this work was to study the current and future potential distribution of a SDTF representative tree species (Anadenanthera colubrina) in the Argentinian Sub Andean Piedmont nucleus and to assess the effects of land use and climate changes. Methods: Current and future potential distribution was modeled with Maxent, using 49 presence points and 20 variables. Climate change effects were estimated in four different temperature and carbon dioxide concentration scenarios. Land use changes were determined subtracting the deforested area until 2017 to the current and future potential distribution of the species. Results: A. colubrina current distribution represents 18 % of Northwestern Argentina. Land use changes decreased almost 25 % of it and climate change will probably cause a retraction in the East and a slight expansion towards the West and South of the current distribution. The synergistic effect of land use and climate change projected to the worst scenario would reduce 63 % of its current distribution. Conclusions: Our data demonstrate the central role of distribution range studies to assess the effects of anthropic activities. Climate change and land use change would have a negative and synergistic effect on the distribution of A. colubrina. Although a possible expansion of the Sub Andean Piedmont nucleus of SDTF would occur, this expansion may be limited by the Sub Andean mountain range that could act as an orographic barrier.

Barrier winds in the Italian region and effects of moist processes

Barrier winds form when a sufficiently high mountain range causes a stratified airflow directed towards the orographic barrier to slow down at the low levels, producing a pressure imbalance, which in turn generates a mountain-parallel wind. The present study analyses barrier wind occurrence in the Italian region and surrounding seas from both a climatological and dynamical perspective. The main goals are to assess the applicability of the linear theory of upstream blocking to real-world cases and to investigate the role of atmospheric moist processes in promoting the formation and influencing the evolution of barrier winds. A 2-year climatology of barrier winds reveals that they occur more frequently than the opposite regime of flow over the orography, especially in the cold season. Barrier wind events are found to be associated with an upstream flow having a significantly higher inverse Froude number (or non-dimensional mountain height) values than flow-over events on average, consistently with the theory. An Alpine case study is simulated using numerical models and sensitivity tests are performed to investigate the dependence of barrier wind development and properties on the non-dimensional mountain height. Simulations reveal the strong influence of precipitation-related diabatic processes on the development of an upstream cold pool, which in turn supports barrier wind maintenance and strengthens its intensity. Idealized numerical experiments with varying upstream flow moisture shed light on processes leading to significant strengthening of barrier wind intensity, in particular on the crucial role of latent heat exchanges associated with precipitation.

Late Cenozoic topographic evolution of the Eastern Cordillera and Puna Plateau margin in the southern Central Andes (NW Argentina)

The Andes constitute an important orographic barrier in the southern hemisphere, impacting atmospheric circulation, the amount and distribution of rainfall, and Earth-surface processes in a highly asymmetric manner. In the Central Andes of NW Argentina, the Andean Plateau (Puna) and the intermontane basins of the adjacent Eastern Cordillera constitute geological archives that furnish spatiotemporal information on surface uplift and associated paleo-environmental change. Today, rainfall in NW Argentina is focused along the windward flanks of the Eastern Cordillera, while its intermontane basins and the Puna constitute high-elevation regions with strongly reduced rainfall. The present-day influence of these topographic characteristics on precipitation patterns is reflected by systematic changes in the hydrogen stable isotope ratios of meteoric water. Proxy archives from basin strata record past environmental conditions and provide insight into the nature of topographic growth through time. We present 34 new hydrogen isotopic compositions of volcanic glass (δDg), extracted from tuffs interbedded with the sedimentary deposits of three different regions across the eastern Andean margin between ca. 24°S and 25°S latitude. Combined with new zircon U-Pb geochronology, our data show clear spatiotemporal variations in δDg correlating with topographic growth and ensuing orographic effects during the Miocene and Pleistocene. In particular, variations in δDg indicate that the Pastos Grandes (Puna) and the Toro (Eastern Cordillera) basins had attained modern elevations by ca. 8 and 6 Ma, respectively. A strong positive shift in the δDg record of the Toro Basin after 840 ka coincides with deposition of thick fluvial/alluvial conglomerates suggesting orographically induced aridification due to progressive range uplift to the east. Other δDg records from the Eastern Cordillera show similar, but diachronous events emphasizing the importance of regional tectonics for environmental change with implications for the formation of orogenic plateaus.

Influence of transboundary transport of trace elements on mountain peat geochemistry (Sudetes, Central Europe)

Mountain ombrotrophic peatlands in Central Europe are an important stock of transboundary contamination both of natural and anthropogenic origin. The Śnieżka Mountain (West Sudetes) forms a significant orographic barrier and receives aerosols from broadly-recognized anthropogenic sources (production and use of stainless steel, processing of uranium, coal combustion, nuclear weapon tests, and Chernobyl accident). The main objective of the study was to assess the pattern of distribution and origin of trace elements and to distinguish the long-range transport vs. local signals in two 210Pb and 14C – dated peat cores from the highest summit of the Karkonosze (West Sudetes) spanning the last 280 years.Maximum values and accumulations of almost all investigated elements (Pb, Zn, Cu, Ni, Cr, Ti, Al, U, Sc, and REE) were identified around the 1970s. The analysis of peat using scanning electron microscopy (SEM) confirmed the occurrence of spheroidal aluminosilicate fly ash particles (SAP) in the topmost 40 cm (from AD 1938) together with a maximum of mullite (3Al2O3·2SiO2), an anthropogenic marker originating from coal-based power plants. The overall 206Pb/207Pb signature ranges from 1.160 to 1.173, indicating a predominant contribution of anthropogenic Pb. Human activities promote the release of mobile 234U, due to the weaker bonds to mineral structure, and cause the radiogenic disequilibrium between 238U and its daughter 234U.