Search

Warming and hydrological changes have already affected and shifted environments in the Arctic. Arctic wetlands are complex systems of coupled hydrological, ecological, and permafrost‐related processes, vulnerable to such environmental changes. This review uses a systems perspective approach to synthesize and elucidate the various interlinked responses and feedbacks of Arctic wetlands to hydroclimatic changes. Starting from increased air temperatures, subsequent permafrost thaw and concurrent hydrological changes are identified as key factors for both shrinkage and expansion of wetland area. Other diverse factors further interact with warming, hydrological changes, and permafrost thaw in altering the Arctic wetland systems. Surface albedo shifts driven by land cover alterations are powerful in reinforcing Arctic warming, while vegetation‐related factors can balance and decelerate permafrost thaw, causing negative feedback loops. With the vast amounts of carbon stored in Arctic wetlands, their changes in turn affect the global carbon cycle. Overall, the systems perspectives outlined and highlighted in this review can be useful in structuring and elucidating the interactions of wetlands with climate, hydrological, and other environmental changes in the Arctic, including the essential permafrost‐carbon feedback. This article is categorized under:Water and Life > Nature of Freshwater EcosystemsWater and Life > Stresses and Pressures on EcosystemsScience of Water > Water and Environmental Change [ABSTRACT FROM AUTHOR]

Subsurface solute transport under surface warming and degrading permafrost conditions is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in the subsurface water and inert solute pathways and travel times are analyzed for different modeled geological configurations. For all simulated cases, the minimum and mean travel times increase nonlinearly with warming irrespective of geological configuration and heterogeneity structure. The timing of the start of increase in travel time depends on heterogeneity structure, combined with the rate of permafrost degradation that also depends on material thermal and hydrogeological properties. The travel time changes depend on combined warming effects of: i) increase in pathway length due to deepening of the active layer, ii) reduced transport velocities due to a shift from horizontal saturated groundwater flow near the surface to vertical water percolation deeper into the subsurface, and iii) pathway length increase and temporary immobilization caused by cryosuction-induced seasonal freeze cycles. [ABSTRACT FROM AUTHOR]

Arctic warming alters regional hydrological systems, as permafrost thaw increases active layer thickness and in turn alters the pathways of water flow through the landscape. Further, permafrost thaw may change the connectivity between deeper and shallower groundwater and surface water altering the terrestrial water balance and distribution. Thermokarst lakes and wetlands in the Arctic offer a window into such changes as these landscape elements depend on permafrost and are some of the most dynamic and widespread features in Arctic lowland regions. In this study we used Landsat remotely sensed imagery to investigate potential shifts in thermokarst lake size-distributions, which may be brought about by permafrost thaw, over three distinct time periods (1973, 1987-1988, and 2007-2009) in three hydrological basins in northwestern Siberia. Results revealed fluctuations in total area and number of lakes over time, with both appearing and disappearing lakes alongside stable lakes. On the whole basin scales, there is no indication of any sustained long-term change in thermokarst lake area or lake size abundance over time. This statistical temporal consistency indicates that spatially variable change effects on local permafrost conditions have driven the individual lake changes that have indeed occurred over time. The results highlight the importance of using multi-temporal remote sensing data that can reveal complex spatiotemporal variations distinguishing fluctuations from sustained change trends, for accurate interpretation of thermokarst lake changes and their possible drivers in periods of climate and permafrost change. [ABSTRACT FROM AUTHOR]

The article presents a study on the influence of permafrost to the hydrologic response of a catachment scale in Yukon River Basin (YRB) in Alaska. It mentions the good relationship between the relative increase in recession flow intercept and the relative annual increase in groundwater flow. The study shows that the use of utility of recession flow analysis reflects catachment-scale changes in permafrost conditions.

A key question for the evolution of thermokarst wetlands and lakes in Arctic and sub-Arctic permafrost regions is how large-scale warming interacts with local landscape conditions in driving permafrost thaw and its spatial variability. To answer this question, which also relates to risks for ecology, society, and health, we perform systematic model simulations of various soil-permafrost cases combined with different surface-warming trends. Results show that both the prevalence and the thaw of permafrost depended strongly on local soil conditions and varied greatly with these for the same temperature conditions at the surface. Greater ice contents and depth extents, but also greater subsurface volumes thawing at depth under warming, are found for peat soils than other studied soil/rock formations. As such, more thaw-driven regime shifts in wetland/lake ecosystems, and associated releases of previously frozen carbon and pathogens, may be expected under the same surface warming for peatlands than other soil conditions. Such risks may also increase in fast permafrost thaw in mineral soils, with only small thaw-protection effects indicated in the present simulations for possible desertification enhancement of mineral soil covers. [ABSTRACT FROM AUTHOR]

Summary This paper investigates patterns of lake-area and hydro-climatic change in Arctic river basins, and possible influence of permafrost change reflected in such patterns. A salient change pattern, emerging across all investigated basins in both permafrost and non-permafrost areas, is an opposite change direction in runoff ( R ) from that in precipitation ( P ). To explain this change contrast, an increase (decrease) in relative water-balance constrained evapotranspiration ET wb / P is required where R decreases (increases). Increasing temporal variability of daily river discharge ( sdQ ) is found in all basins with spatially extensive lake decrease, which also exhibit decrease in ET wb / P . Clear indication of basin-wide permafrost thaw is found in only one basin, and is possible in two more, but unlikely in the largest of the total four investigated permafrost basins. [ABSTRACT FROM AUTHOR]

Change dynamics of permafrost thaw, and associated changes in subsurface flow and seepage into surface water, are analysed for different warming trends in soil temperature at the ground surface with a three-phase two-component flow system coupled to heat transport. Changes in annual, seasonal and extreme flows are analysed for three warming-temperature trends, representing simplified climate-change scenarios. The results support previous studies of reduced temporal variability of groundwater flow across all investigated trends. Decreased intra-annual flow variability may thus serve as an early indicator of permafrost degradation before longer-term changes in mean flows are notable. This is advantageous since hydrological data are considerably easier to obtain, may be available in longer time series, and generally reflect larger-scale conditions than direct permafrost observations. The results further show that permafrost degradation first leads to increasing water discharge, which then decreases as the permafrost degradation progresses further to total thaw. The most pronounced changes occur for minimum annual flows. The configuration considered represents subsurface discharge from a generic heterogeneous soil-type domain. [ABSTRACT FROM AUTHOR]

Summary: Permafrost, mainly of discontinuous type, that underlies the tundra and taiga landscapes of the Nadym and Pur river basins in northwestern Siberia has been warming during the recent decades. A mosaic of thermokarst lakes and wetlands dominates this area. In this study we tested the hypothesis chain that permafrost thawing changes thermokarst lake area and number, and is then also reflected in and detectable through other associated hydrological changes. Based on indications from previous studies, the other hydrological changes in a basin were expected to be decreasing intra-annual runoff variability (quantified by decreasing maximum and increasing minimum runoff) and systematically decreasing water storage. To test this hypothesis chain, we mapped thermokarst lake changes using remote sensing analysis and analyzed both climate (temperature and precipitation) and water flow and balance changes using available monthly data records. This was done for the whole Nadym and Pur river basins and a smaller sub-basin of the former (denoted 7129) with comparable data availability as the whole river basins. The results for the 7129 sub-basin show all the indicators (thermokarst lake and other hydrological) changing consistently, as could be expected in response to permafrost thawing that alters the connections between surface and subsurface waters, and leads to overall decreases in water (including ground ice) storage within a basin. Over the Nadym and Pur basins, the relative area influenced by similar permafrost thawing and associated lake and hydrological effects appears (yet) too small to be clearly and systematically reflected in the basin-average indicators for these large basins. [ABSTRACT FROM AUTHOR]

Summary Climatic changes can profoundly alter hydrological conditions in river basins. Lake Baikal is the deepest and largest freshwater reservoir on Earth, and has a unique ecosystem with numerous endemic animal and plant species. We here identify long-term historical (1938–2009) and projected future hydro-climatic trends in the Selenga River Basin, which is the largest sub-basin (>60% inflow) of Lake Baikal. Our analysis is based on long-term river monitoring and historical hydro-climatic observation data, as well as ensemble mean and 22 individual model results of the Coupled Model Intercomparison Project, Phase 5 (CMIP5). Study of the latter considers a historical period (from 1961) and projections for 2010–2039 and 2070–2099. Observations show almost twice as fast warming as the global average during the period 1938–2009. Decreased intra-annual variability of river discharge over this period indicates basin-scale permafrost degradation. CMIP5 ensemble projections show further future warming, implying continued permafrost thaw. Modelling of runoff change, however, is highly uncertain, with many models (64%) and their ensemble mean failing to reproduce historical behaviour, and with indicated future increase being small relative to the large differences among individual model results. [ABSTRACT FROM AUTHOR]

This study simulates and quantifies the exchange and the pathways of deep and shallow groundwater flow and solute transport under different climate and permafrost conditions, considering the example field case of the coastal Forsmark catchment in Sweden. A number of simulation scenarios for different climate and permafrost condition combinations have been performed with the three-dimensional groundwater flow and transport model MIKE SHE. Results show generally decreasing vertical groundwater flow with depth, and smaller vertical flow under permafrost conditions than under unfrozen conditions. Also the overall pattern of both the vertical and the horizontal groundwater flow, and the water exchange between the deep and shallow groundwater systems, change dramatically in the presence of permafrost relative to unfrozen conditions. However, although the vertical groundwater flow decreases significantly in the presence of permafrost, there is still an exchange of water between the unfrozen groundwater system below the permafrost and the shallow groundwater in the active layer, via taliks. 'Through taliks' tend to prevail in areas that constitute groundwater discharge zones under unfrozen conditions, which then mostly shift to net recharge zones (through taliks with net downward flow) under permafrost conditions. [ABSTRACT FROM AUTHOR]

Summary: Permafrost responses to a changing climate can affect hydrological and biogeochemical cycling, ecosystems and climate feedbacks. We have simulated a model permafrost system in the temperature range associated with discontinuous permafrost focusing on interactions between permafrost and hydrology using a non-isothermal, three-phase model of water migration coupled to heat transport in partially frozen porous media. We explore the subsurface hydraulic property controls on the formation and dynamics of permafrost, and how this impacts seasonal variability of subsurface runoff to surface waters. For all subsurface conditions considered, the main common hydrological signal of permafrost degradation in a warming trend is decreasing seasonal variability of water flow. This is due to deeper and longer flow pathways with increasing lag times from infiltration or thawing through subsurface flow to surface water discharge. These results show how physically based numerical modelling can be used to quantitatively and qualitatively improve the understanding of how permafrost thawing relates to, and may be detected in, hydrological data. This is advantageous since hydrological data is considerably easier to obtain, may be available in longer time series, and generally reflects larger-scale conditions than direct permafrost observations. [ABSTRACT FROM AUTHOR]