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1.
Sci Total Environ ; 848: 157759, 2022 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-35931167

RESUMO

The eastern Mediterranean is a hotspot in terms of geomorphic hazards, but the activity of gravitational processes in mountainous areas is largely unexplored. We carried out dendrogeomorphic research in the Helmos Mountains (Northern Peloponnese, Greece) to determine the timing, spatial extent, and hydrometeorological triggers of debris flows and snow avalanches. Specifically, we sampled increment cores from 123 injured Greek firs (Abies cephalonica L.) growing on a debris flow cone and growing along a snow avalanche track. Tree rings were counted and cross-dated with the reference chronology using CooRecorder and CDendro software and the event years were determined on the basis of the location of scars and traumatic resin ducts. We compiled an 118-year chronology (1904-2021) with seven debris flow event years and only one severe debris flow occurring in the 1970/1971 dormant period (WIt = 148.0), followed by spatially limited records for 1986/1987 (WIt = 3.8) and 1993/1994 (WIt = 2.5). Similarly, seven snow avalanche event years were identified in the period 1854-2021, with one major event in 1997/1998 (WIt = 304.5) followed by the 1998/1999 event (WIt = 6.3). Extremely wet conditions in February-March 1971 followed by rain-on-snow precipitation were considered as the most likely trigger of the analysed debris flow event using data from nearby meteorological stations and the ERA5 reanalysis. The snow avalanche event was deciphered in the spring of 1998, when heavy snowfall over three days (62 cm) was followed by rapid snowmelt due to high average temperatures (6-11 °C). We conclude that the abundance of snow is a crucial factor in the geomorphic activity in the study region and that the temperature fluctuations and rain-to-snow transitions are the leading factors for the debris flows or snow avalanches to occur. Furthermore, the dendrogeomorphic approach used can be useful to clearly identify large-scale geomorphic events and excludes potential geomorphic noise caused by other ecological stresses.


Assuntos
Avalanche , Neve , Grécia , Chuva , Estações do Ano
2.
Sci Total Environ ; 763: 142953, 2021 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-33498116

RESUMO

Unlike large rivers, floods in headwaters have been poorly documented despite the fact that greater discharges are expected in such areas due to ongoing rainfall intensification. The purpose of this study is to carry out intra-annual dating of past floods combined with analysis of their climate linkages which may point on distribution and origin of floods. To this end, we applied dendrogeomorphic dating of impact scars on riparian vegetation to provide flood chronologies in twelve headwaters of eastern Czechia and determined their seasonal occurrences. Furthermore, we analyzed the precipitation indices and evaluated the flood events using reanalysis of pressure fields and the climate oscillation indices, particularly those representing the North Atlantic, Scandinavian, and East Atlantic/Western Russian patterns. Based on 434 dated trees, we identified 22-31 flood event years in each region over the last 70 years. The most frequent floods occurred from May to July. In addition, in ten event years it was possible to identify multiple flood events: for example May and July-August floods in 2010, 2014, and 2016. The monthly precipitation showed the strongest, but still weak, correlation with indices of Scandinavian climate oscillation during summer months (Rs = 0.23-0.42; p < 0.00), suggesting the influence of a blocking anticyclone over Scandinavia and wet air propagation to central Europe. This finding was also confirmed by the most frequent positions of low-pressure centers located east of the study sites except for the region with western orographic enhancement. In addition, timing shift of extreme precipitation to earlier period was identified at two out of three regions. We conclude that intra-annual dating of floods supported by analyses of climate extremes provides new data from sparsely gauged headwaters, thereby supplementing the information on possible changes in flood occurrences during ongoing climate change.

3.
Sci Rep ; 9(1): 14560, 2019 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-31601991

RESUMO

Landslides are frequently triggered by extreme meteorological events which has led to concern and debate about their activity in a future greenhouse climate. It is also hypothesized that dry spells preceding triggering rainfall may increase slope predisposition to sliding, especially in the case of clay-rich soils. Here we combined dendrogeomorphic time series of landslides and climatic records to test the possible role of dry spells and extreme downpours on process activity in the Outer Western Carpathians (Central Europe). To this end, we tested time series of past frequencies and return periods of landslide reactivations at the regional scale with a Generalized Linear Mixed (GLM) model to explore linkages between landslide occurrences and triggering climate variables. Results show that landslide reactivations are concentrated during years in which spring and summer precipitation sums were significantly higher than usual, and that triggering mechanisms vary between different types of landslides (i.e. complex, shallow or flow-like). The GLM model also points to the susceptibility of landslide bodies to the combined occurrence of long, dry spells followed by large precipitation. Such situations are likely to increase in frequency in the future as climate models predict an enhancement of heatwaves and dry spells in future summers, that would be interrupted by less frequent, yet more intense storms, especially also in mountain regions.

4.
Sci Total Environ ; 665: 1083-1094, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-30893740

RESUMO

Dendrogeomorphic methods are frequently used for the analysis of past landslide behaviour and have become the standard approach used to date landslide activity. Unfortunately, many questions related to the application of tree-rings to landslide analysis remain unsolved. This study points to the significance of dividing a large complex slope deformation area into homogenous zones to obtain as much relevant chronological data as possible and to help with a more precise landslide hazard assessment. The multidisciplinary approach included geophysical measurement and geomorphic mapping. The clay mineral content in weathered slope sediments was analysed to verify the presence of expanding minerals contributing to slope instability. Furthermore, 713 samples from 271 trees and 18 tree roots were analysed to create event chronologies for each zone. The results provided evidence about the different behaviours of each zone. The intensity of tree responses to slope movement significantly changed even within one isolated zone. Chronological data were used to identify landslide triggers using rainfall characteristics and indices for climate variability and extremes. The results suggested a significant contribution of spring rainfall to landslide activity. In addition, shallow landslides movement was dependent on above-average rainfall characteristics compared to the movement of deep-seated blocks. Tree-ring-based chronologies of individual zones were used to characterise the general concept of complex slope deformation development.


Assuntos
Monitoramento Ambiental/métodos , Deslizamentos de Terra , Árvores/crescimento & desenvolvimento , República Tcheca , Hidrologia , Conceitos Meteorológicos
5.
Sci Total Environ ; 579: 1904-1917, 2017 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-27998654

RESUMO

Hydro-geomorphic processes have significantly influenced the recent development of valley floors, river banks and depositional forms in mountain environments, have caused considerable damage to manmade developments and have disrupted forest management. Trees growing along streams are affected by the transported debris mass and provide valuable records of debris flow/flood histories in their tree-ring series. Dendrogeomorphic approaches are currently the most accurate methods for creating a chronology of the debris flow/flood events in forested catchments without any field-monitoring or a stream-gauging station. Comprehensive studies focusing on the detailed chronology of hydro-geomorphic events and analysis of meteorological triggers and weather circulation patterns are still lacking for the studied area. We provide a spatio-temporal reconstruction of hydro-geomorphic events in four catchments of the Hrubý Jeseník Mountains, Czech Republic, with an analysis of their triggering factors using meteorological data from four nearby rain gauges. Increment cores from 794 coniferous trees (Picea abies [L.] Karst.) allowed the identification of 40 hydro-geomorphic events during the period of 1889-2013. Most of the events can be explained by extreme daily rainfalls (≥50mm) occurring in at least one rain gauge. However, in several cases, there was no record of extreme precipitation at rain gauges during the debris flow/flood event year, suggesting extremely localised rainstorms at the mountain summits. We concluded that the localisation, intensity and duration of rainstorms; antecedent moisture conditions; and amount of available sediments all influenced the initiation, spatial distribution and characteristics of hydro-geomorphic events. The most frequent synoptic situations responsible for the extreme rainfalls (1946-2015) were related to the meridional atmospheric circulation pattern. Our results enhance current knowledge of the occurrences and triggers of debris flows/floods in the Central European mountains in transition between temperate oceanic and continental climatic conditions and may prompt further research of these phenomena in the Eastern Sudetes in general.

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