Just published: our recent studies
Tumajer J, Kašpar J, Kuželová H, Shishov VV, Tychkov II, Popkova MI, Vaganov EA and Treml V (2021): Forward Modeling Reveals Multidecadal Trends in Cambial Kinetics and Phenology at Treeline. Front. Plant Sci. 12:613643.
Woody plants experience prominent variability in their annual growth rates due to climate change. Increasing temperature stimulates formation of wider tree-rings mainly in cold environments but associated higher drought stress can reduce the tree-ring formation at dry locations. However, it is not known whether this alteration of growth is due to shifting phenology (changing growing season duration) or trends in growth kinetics (the production of cells is faster/slower). We seek the answer for this question at the treeline of the Krkonoše Mts. We employed the Vaganov-Shashkin process-based model of tree-ring formation to ‘slice’ the tree-ring width into daily growth segments. By the analysing specific model outputs, we were able to identify two main drivers of increased tree-ring widths of treeline trees since 1960 – (i) higher summer rate of cell production due to temperature increase and (ii) earlier spring onset of cambial activity. By contrast, autumn growth rates and phenology do not show significant trends. Surprisingly, we observed a clear pattern of drought stress on trees during warm and dry summer days controlling the formation of around 22 % of tree ring. The increasing drought stress might slow-down the future positive response of a cold treeline ecosystems to increasing temperature.
Lendzioch T, Langhammer J, Vlček L, Minařík R., 2021. Mapping the Groundwater Level and Soil Moisture of a Montane Peat Bog Using UAV Monitoring and Machine Learning. Remote Sensing. 13(5):907.
This paper presents a novel approach for using UAV thermal and multispectral imagery to enhance the spatio-temporal predictions of groundwater level and top-layer soil moisture of montane peat bogs using a machine learning model. Our research aimed to obtain information and predict the dynamic properties of groundwater level (GWL) and top-layer soil moisture (SM) in 2 dimensions and time based on data from digital surface models (DSMs), RGB, multispectral, and thermal data from drone imagery. We used a CAST spatiotemporal Machine Learning (ML) prediction model using the Random Forest algorithm. For two seasons, we have launched recurrent UAV monitoring campaigns and field sampling of GWL and SM ground truth data at the Rokytka Peat bog within the Sumava Mountains, Czechia. We used 34 predictors, derived from UAV imaging datasets to feed the random forest model. Results showed that the ML model, using the UAV-derived datasets, delivers accurate predictions of GWL and SM spatial distribution. The method is well suited and unique for planning and decision-making about the best sampling strategy, most notably with limited data.
Engel, Z., Braucher, R., Aster Team (2020): Origin and 10Be surface exposure dating of a coarse debris accumulation in the Hrubý Jeseník Mountains, Central Europe. Geomorphology, 365, 1˗12.
The paper deals with age and development oo block-field and tor in the Hrubý Jeseník Mts. and presents the first chronological evidence for planation surfaces and slopes in the East Sudetes Mts., on which mountain patterned ground formed. In addition, the paper provides broader paleoenvironmental interpretations and provides the first chronological evidence for the occurrence of permafrost and periglacial conditions in the High Sudetes during the penultimate (Saalian) cold period.
Engel, Z., Křížek, M., Braucher, R., Uxa, T., Krause, D., Aster Team (2021): 10Be exposure age for sorted polygons in the Sudetes Mountains. Permafrost and Periglacial Processes, 32, 1, 154-158.
This paper presents the first chronological evidence for sorted patterned ground using terrestrial in situ-produced cosmogenic nuclides (10Be) in the world. It provides age thresholds for relict sorted polygons sampled at four sites in the High Sudetes. (Mt. Luční hora and Mt. Vysoké Kolo in the Krkonoše Mts. and Mt. Břidličná and Větrná louka site in the Hrubý Jeseník, the highest part the central European uplands. The results indicate that these landforms started to form at the end of Marine Isotope Stage 3, and the main phase of their formation occurred between 30 and 20 ka. This research confirms the hypothesis of sorted-polygons formation within the last (Weichselian) glacial stage (110.6–11.7 ka) and suggests that earlier-sorted features are not preserved in the Sudetes. The recognized period of enhanced periglacial activity coincides with a prominent cold interval identified earlier in both regional and northern-hemispheric proxy records.
Kalovoda, J. (2020): The Dynamics of Geomorphic Evolution in the Makalu Barun Area of the Nepal Himalaya. P3K, 387 p. ISBN 978-80-7667-011-2.
Research into the dynamics of landform evolution in the East Nepal Himalaya is intended to provide knowledge of the long-term integrity of climate-driven morphogenetic and tectonic processes as an essential phenomenon of active collisional orogeny. Landform patterns of the Makalu – Barun region in the Himalaya are the result of orogenetic processes, as well as the denudation and erosional efficiency under very variable palaeoclimatic conditions during the late Cenozoic. Geomorphic processes and landforms in the region between the Chomolongma and Makalu Massifs and the Sapt Kosi lowland with an elevational gradient of over 8,000 m are explored in relation to morphostructural patterns and in the framework of extreme glacial, glacial and periglacial zones and the seasonally cold/warm humid zone. The observed landform changes in the Nepal Himalaya on a decadal scale indicate the high intensity of climate-driven morphogenetic processes, especially very effective erosion and transport of weathered material by a combination of diverse exogenic factors, integrated with active orogenetic processes. The dynamic evolution of landforms in the Himalaya is also essential evidence of the present-day severe natural hazards.
Vlach, V., Ledvinka, O., Matoušková, M. (2020): Changing Low Flow and Streamflow Drought Seasonality in Central European Headwaters. Water, 12 (12), 3575.
In the context of the ongoing climate warming in Central Europe, the seasonality and magnitudes summer streamflow droughts are expected to worsen in the future.nThis study analyzed the long-term variability and seasonality of low flows and streamflow droughts in 15 headwater catchments of 3 border regions within Central Europe during the 1968–2019 period. Our results showed a substantial increase in the proportion of summer streamflow droughts during the last 52 years, accompanied with an apparent shift in the average date of drought occurrence towards the start of the year. The most pronounced seasonality shifts were found mostly in catchments with the mean altitude 800–1000 metres above sea level. In contrast, the regime of low flows in catchments with terrain above 1000 metres remained nearly stable throughout the 1968–2019 period.
Hotovy, O., Jenicek, M. (2020): The impact of changing subcanopy radiation on snowmelt in a disturbed coniferous forest. Hydrological Processes, 34 (26), 5298-5314.
Understanding the role of forest on snowmelt processes enables better estimates of snow storages at a catchment scale and contributes to a higher accuracy of spring flood forecasting. Forests modify the snowpack energy balance by reducing solar shortwave radiation and enhancing the role of longwave radiation. Measurements of radiation fluxes were performed at three sites with different canopy structure, including one site affected by the bark beetle. The results showed that the forest decay causes significant changes in individual energy balance components, mainly shortwave radiation increase and longwave radiation decrease. These changes further lead to increase in snowmelt rates by 50% after forest disturbance. Our findings have important implications for runoff from areas affected by land cover changes due to either human activity or climate change.
Minařík, R.; Langhammer, J.; Lendzioch, T. (2020): Automatic Tree Crown Extraction from UAS Multispectral Imagery for the Detection of Bark Beetle Disturbance in Mixed Forests. Remote Sensing, 12, 4081.
Multispectral imaging using unmanned aerial systems (UAS) enables rapid and accurate detection of pest insect infestations, which are an increasing threat to midlatitude natural forests. Pest detection at the level of an individual tree is of particular importance in mixed forests, where it enables a sensible forest management approach. In this study, we propose a method for individual tree crown delineation and feature extraction to detect a bark beetle disturbance in a mixed urban forest using a photogrammetric point cloud and a multispectral orthomosaic. An excess green index threshold mask was applied to separate targeted coniferous trees from deciduous trees and backgrounds and different algorithms for automated delineation of tree crowns were tested and statistically compared. We found that for the accuracy of delineation, the density of the photogrammetric point cloud is more significant than the algorithm used. We conclude that the proposed automatic delineation workflow can substitute the time-consuming manual tree crown delineation, used for the detection and sanitation of individual infested trees in forests undergoing bark-beetle disturbance.
Vilímek, V., Klimeš, J., Ttito Mamani, R.V. et al. (2020): Contribution of the collaborative effort of the Czech WCoE to landslide risk reduction at the Machupicchu, Peru. Landslides 17, 2683–2688.
The paper presents results from monitoring of potentially dangerous slope movements at the archaeological site in the Machupicchu, Peru. This was achieved with the installation of an environmentally friendly network of dilatometric instruments. The 17-year-long monitoring identified no major hazard to the archaeological site which used to support decision of site managers to limit the entrance of tourists to the Intiwatana hill since 2019. Historical photographs of Czech travellers (from 1949, 1950, 1954, and 1961) were shared with Peruvian experts, who compared them with the oldest photos from the explorer Hiram Bingham and the most recent situation. The photographs were used to document the historical development of selected structures inside Machupicchu as well as landslide occurrences on the surrounding slopes.
Girons Lopez M., Vis, M.J.P., Jenicek, M., Griessinger, N., Seibert, J. (2020). Assessing the degree of detail of temperature-based snow routines for runoff modelling in mountainous areas in central Europe. Hydrology and Earth System Sciences, 24, 4441–4461.
Snow processes are a key component of the water cycle in mountainous areas. The complexity of these processes, coupled with the limited data available on them, has led to the development of different modelling approaches aimed at improving our understanding of these processes and supporting management practices. We assessed the suitability of a number of formulations of different components of the simple temperature-index method for rainfall-runoff modelling using the HBV model. We analysed a total of 64 alternative snow routine structures over 54 catchments. Overall, the most valuable modifications were (a) using an exponential snowmelt function coupled with no refreezing and (b) computing melt rates with a seasonally variable degree-day factor. Our results also demonstrated that increasing the degree of detail of the temperature-based snow routines in rainfall-runoff models did not necessarily lead to an improved model performance per se.
Huang et al. incl. Treml, V., Kašpar J. (2020): Photoperiod and temperature as dominant environmental drivers triggering secondary growth resumption in Northern Hemisphere conifers. Proceedings of the National Academy of Sciences, 117 (34), 20645-20652.
Forest trees fix approximately 15% of anthropogenic CO2 emissions annually by wood formation. In this study, we were interested in the environmental factors triggering wood formation onset in springtime and the cellular mechanisms underlying this onset. We report that the onset of wood formation in Northern Hemisphere conifers is driven primarily by photoperiod and mean annual temperature. Understanding the unique relationships between exogenous factors and wood formation could aid in predicting how forest ecosystems respond and adapt to climate warming, while improving the assessment of long-term and high-resolution observations of global biogeochemical cycles. This paper results from long-term collaboration of more than 10 research groups collecting data from various forest ecosystems in Northern Hemisphere.
Dalton AS, Margold M, Stokes CR et al. (2020): An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex. Quaternary Science Reviews, 234, article no. 106223, DOI: 10.1016/j.quascirev.2020.106223
We present an updated deglaciation of the North American Ice Sheet Complex (consisting of the Laurentide, Cordilleran and Innuitian ice sheets) using regional studies and recent radiocarbon data. The deglaciation sequence spans 20,000 years ago until 1,000 years ago and is available as 36 maps in PDF and shapefile format. Understanding the retreat of this ice sheet is critical for many facets of Geography, including the formation of modern-day landscapes, sea level evolution, paleoclimate and animal migration.
Baťka J.; Vilímek V.; Štefanová E.; Cook S.J.; Emmer A. (2020): Glacial Lake Outburst Floods (GLOFs) in the Cordillera Huayhuash, Peru: Historic Events and Current Susceptibility. Water, 12, 2664.
Glacial lakes pose threat to the lower sections of their valleys due to the possibility of their sudden outbursts resulting in glacial lake outburst floods (GLOFs). These events are well-known to cause significant loss of both lives and property. We created a complete inventory of glacial lakes in the Peruvian Cordillera Huayhuash, mapped past GLOFs based on the geomorphologic imprints in the landscape and used the original inventory to assess the current susceptibility to GLOFs of all lakes larger than 20,000 m2 (n=46). Only two lakes are currently susceptible to generate a GLOF, which would most likely be due to a GLOF originating in smaller upstream lakes that are in direct contact with glaciers. The future perspectives of lake evolution and implications for GLOF hazard management are discussed in light of the post-Little Ice Age glacier ice loss as well as in the context of extensive related research undertaken in the nearby Cordillera Blanca.
Mozny, M., Trnka, M., Vlach, V., Vizina, A., Potopova, V., Zahradnicek, P., … Zalud, Z. (2020): Past (1971–2018) and future (2021–2100) pan evaporation rates in the Czech Republic. Journal of Hydrology, 590, 125390.
In the context of the recent multi-year period of drought in Central Europe, significant losses of surface water deposits were observed in countries within this region. Recorded observations from the Czech Republic show an increase in evaporation from open water surface, which is mainly associated with an increase in global radiation and vapor pressure deficit. Most of 11 meteorological stations in the Czech Republic examined in this study show a strong increase during April, June, July and August. During the 1971–2018 period, the annual evaporation has been increasing by an average of almost 3 mm per year. For the period 2001–2018, the annual mean was 18% higher (519 mm) than the 1971–2000 average (440 mm). Our simulations of future scenarios predicted a growth in evaporation of up to 27–54%. Such an increase in evaporation can lead to serious consequences for surface water availability and agricultural production during the periods of drought in the Czech Republic.
Langhammer, J. and Bernsteinová, J. (2020): Which Aspects of Hydrological Regime in Mid-Latitude Montane Basins Are Affected by Climate Change?. Water, 12(8), 2279
We tested the common hypotheses on climate change effects on surface runoff dynamics in Central Europe on 8 catchments in mountain ranges in Central Europe based on daily discharge observations since 1952. We used a mix of 33 indicators of hydrologic alteration, 34 indicators of environmental flow components, baseflow index, surplus and deficit volumes and variability of peak and low flows. Across the regions, we have detected the significant shifts in runoff seasonality, coinciding with the timing of the air temperature rise, marked by earlier snowmelt, followed by a decline in spring flows and a prolonged period of low flows. There was detected a rise of baseflow across the mountain ranges. Unlike the common hypotheses, the rising variability and frequency of peak flows was not proven. However, we have identified significantly rising inner dynamics of the flood events.
Jenicek, M., Ledvinka, O. (2020): Importance of snowmelt contribution to seasonal runoff and summer low flows in Czechia. Hydrology and Earth System Sciences, 24 (7), 3475–3491.
A shift from snowfall to rain is expected in the future. Consequently, a decrease in snow storage and earlier snowmelt is predicted, which will cause changes in seasonal runoff. We simulated the snow storage, groundwater recharge and streamflow for 59 mountain catchments in Czechia in the period from 1980 to 2014. The results showed that 17 %–42 % of the total runoff in the study catchments originates as snowmelt, despite the fact that only 12 %–37 % of the precipitation falls as snow. This means that snow is more effective in generating catchment runoff compared to rain. The annual runoff and groundwater recharge decreased in the case of a precipitation shift from snow to rain. For most of the catchments, the lowest summer baseflow was reached in years with both relatively low summer precipitation and snow storage. This showed that summer low flows are significantly affected by the previous winter snowpack. This effect might intensify drought periods in the future when generally less snow is expected.
Blahusiakova, A., Matouskova, M., Jenicek, M., Ledvinka, O., Kliment, Z., Podolinska, J., Snopkova, Z. (2020): Snow and climate trends and their impact on seasonal runoff and hydrological drought types in selected mountain catchments in Central Europe. Hydrological Sciences Journal, 65(1-2), 2083-2096.
This study investigates changes in seasonal runoff and low flows related to changes in snow and climate variables in mountainous catchments in Central Europe. The period 1966–2012 was used to assess trends in climate and streamflow characteristics using a modified Mann–Kendall test. Droughts were classified into nine classes according to key snow and climate drivers. The results showed an increase in air temperature, decrease in snowfall fraction and snow depth, and changes in precipitation. This resulted in increased winter runoff and decreased late spring runoff due to earlier snowmelt, especially at elevations from 1000 to 1500 m a.s.l. Most of the hydrological droughts were connected to either low air temperatures and precipitation during winter or high winter air temperatures which caused below-average snow storages. Our findings show that, besides precipitation and air temperature, snow plays an important role in summer streamflow and drought occurrence in selected mountainous catchments.
Storrar, R. D., Ewertowski, M., Tomczyk, A. M., Barr, I. D., Livingstone, S. J., Ruffell, A., Stoker, B. J. & Evans, D. J. A. (2020): Equifinality and preservation potential of complex eskers. Boreas, Vol. 49, 211–231.
The hydrological system of a glacier can have a modulating influence on ice flow. Eskers are sinuous ridges of sediment that form from the infilling of glacier meltwater channels. The size, shape, and planform of eskers can vary considerably. Eskers can provide an insight into the meltwater processes within glaciers and ice sheets. Eskers are common on the beds of former ice sheets, but, are rare at contemporary glacier margins. In this study, we investigate two separate eskers systems in Iceland and Svalbard. At both locations, the eskers displayed a similar complex, cross-cutting pattern. Our results highlight the importance of the ice structure in controlling esker shape, and the influence of topography on the drainage system. This provides an insight into the complex nature of glacier drainage and the implications for landform creation in a modern setting.