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2021 | Book

Arctic Hydrology, Permafrost and Ecosystems

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About this book

This book provides a comprehensive, up-to-date assessment of the key terrestrial components of the Arctic system, i.e., its hydrology, permafrost, and ecology, drawing on the latest research results from across the circumpolar regions. The Arctic is an integrated system, the elements of which are closely linked by the atmosphere, ocean, and land. Using an integrated system approach, the book’s 30 chapters, written by a diverse team of leading scholars, carefully examine Arctic climate variability/change, large river hydrology, lakes and wetlands, snow cover and ice processes, permafrost characteristics, vegetation/landscape changes, and the future trajectory of Arctic system evolution. The discussions cover the fundamental features of and processes in the Arctic system, with a special focus on critical knowledge gaps, i.e., the interactions and feedbacks between water, permafrost, and ecosystem, such as snow pack and permafrost changes and their impacts on basin hydrology and ecology, river flow, geochemistry, and energy fluxes to the Arctic Ocean, and the structure and function of the Arctic ecosystem in response to past/future changes in climate, hydrology, and permafrost conditions. Given its scope, the book offers a valuable resource for researchers, graduate students, environmentalists, managers, and administrators who are concerned with the northern environment and resources.

Table of Contents

Frontmatter
Correction to: Arctic Hydrology, Permafrost and Ecosystems

In an earlier version of this book, the affiliation of the volume editor “Daqing Yang” was incorrect. This has been corrected. Correct Affiliations is Daqing Yang, Watershed Hydrology and Ecology, Research Division, Water Science and Technology Directorate, Environment and Climate Change Canada, Victoria, BC, Canada

Daqing Yang, Douglas L. Kane

Arctic Climate and Greenland

Frontmatter
Chapter 1. Arctic Climate Change, Variability, and Extremes

Global warming over the past half century has been amplified in the Arctic, especially in the cold season. Other Arctic indicators, especially those of the cryosphere, show signals consistent with the warming of the past half century. This Arctic amplification of the warming arises from a number of processes in the climate system, including the feedbacks associated with the loss of sea ice and snow, the increase of atmospheric moisture, and the vertical temperature structure of the Arctic atmosphere. Ocean heat fluxes into the Arctic from the North Atlantic and North Pacific also appear to have contributed to the Arctic warming through a reduction of sea ice. Internal variability, which played a major role in Arctic warming during the early twentieth century, appears to have been a minor contributor to the more recent warming, which has also been associated with unprecedented extremes of Arctic temperature and sea ice. There is evidence for increased moisture content of the Arctic atmosphere and corresponding impacts on episodes of extreme warmth. The recent variations of Arctic temperature and associated variables fit well with the simulations of Arctic climate by global and regional climate models. Projected changes include a continued warming of the Arctic even under moderate mitigation scenarios, and an increase of Arctic precipitation consistent with the higher temperatures and atmospheric humidities.

John E. Walsh
Chapter 2. Precipitation Characteristics and Changes

Precipitation over the Arctic region plays a significant role in the water and energy cycle that sustains the Arctic’s unique ecosystem. Although a cold climate with strong seasonality in temperature and moisture predominates, there is large spatial variation due to the heterogeneity of the landscape and atmospheric processes that control local weather and climate. Long-term historical synoptic records exist for some regions providing very valuable information on how precipitation has been changing, yet there are many challenges to overcome. Inconsistency in instrumentation and measurement techniques, undercatch due to weather conditions and precipitation types, uneven spatial and temporal distribution of station locations, and the reliability of remote sensing products all have to be considered. Research on Arctic precipitation is mostly focused on a specific continent or geographical or political region using very diverse perspectives and approaches. Here we draw from many of these and remote sensing to piece together studies that illustrate a broader picture of Arctic precipitation conditions and reveal emerging and/or diverging patterns of change. This chapter will (1) introduce existing and forthcoming sources of data and their corresponding challenges across the Arctic; (2) describe the distribution of precipitation characteristics including total amount, intensity, and frequency over major land areas and the oceans; and (3) demonstrate past changes and future predictions in these precipitation characteristics and their extremes. This will provide a fairly comprehensive knowledge repository and a strong foundation to promote and inspire future research development on precipitation over the Arctic region.

Hengchun Ye, Daqing Yang, Ali Behrangi, Svetlana L. Stuefer, Xicai Pan, Eva Mekis, Yonas Dibike, John E. Walsh
Chapter 3. Snow Cover—Observations, Processes, Changes, and Impacts on Northern Hydrology

This chapter presents an overview of Arctic terrestrial snow cover and hydrology starting with the factors contributing to variability and change in large-scale snow cover extent and snow water equivalent (SWE), then moves to the local scale for a discussion of the processes and interactions responsible for the spatial distribution and physical properties of Arctic snow cover, most notably the roles of blowing snow and vegetation interactions. Snowmelt and runoff processes are subsequently covered with particular attention on liquid water infiltration through the snowpack and soil layers. The chapter concludes with an overview of Arctic snow observing systems, estimates of current and projected trends in Arctic snow cover extent and SWE, and potential hydrologic implications of the projected changes in snow cover. A key message from the Chapter is that the response of Arctic snow cover and snow hydrology to a changing climate is complex due to the numerous linkages and feedbacks within the coupled snow–soil–vegetation system.

Ross Brown, Philip Marsh, Stephen Déry, Daqing Yang
Chapter 4. Evaporation Processes and Changes Over the Northern Regions

Evapotranspiration (ET) is a key component in global water and energy cycles. This chapter presents and discusses recent research advances about ET over northern regions and watersheds. ET in northern regions tends to increase with the decrease of latitude. The largest ET typically appears in the forest ecosystem, while the grasslands and shrublands have small ET. While the seasonal variations in ET are usually high, the interannual variability in annual ET is usually low over the Arctic regions. Sublimation from snow cover accounts for about 15–25% of winter precipitation. Many factors, such as soil moisture, vegetation type and productivity, and ecosystem features affect ET over northern regions. In addition, precipitation plays a key role in impacting ET. ET is more sensitive to precipitation in the early growing season than in the late growing season. Furthermore, changes in freeze–thaw processes due to warming also affect land surface conditions and the ET processes. During 1983–2005, ET increased significantly in the Arctic region with a rate of 3.8 mm decade-1 because of regional warming and vegetation greening. Such an increase in ET may exert significant impacts on the regional hydrology and water resources. Advanced models can simulate past ET change over the large northern watersheds. Remote sensing has provided new ET data and information that support climate and hydrology research and applications. There is a key question: Will Arctic landscapes become wetter or drier as climate changes? According to global models and data analyses, annual ET has increased over the northern regions. In the future, summer PE is projected to decrease much of Canada, increase over Alaska, decrease over the western and northern Eurasian subarctic, and increase over parts of northeastern Russia. Over most of these areas, the sign of the projected change is not robust across the models at the 95% confidence level. Many factors contribute to the uncertainty in the projected changes in Arctic surface wetness. There is certainly a need to better quantify and narrow the uncertainties in global models in the northern regions.

Yinsheng Zhang, Ning Ma, Hotaek Park, John E. Walsh, Ke Zhang
Chapter 5. Greenland Ice Sheet and Arctic Mountain Glaciers

This chapter provides a review and update of meltwater and Arctic hydrology, and the impact of glacier and ice sheet mass balance contributions to sea-level rise and ocean circulation. It highlights the recent work and results of large-scale modeling of Greenland climate, glaciers, and ice caps and Greenland Ice Sheet (GrIS) mass balances, and Greenland spatiotemporal freshwater runoff to the surrounding oceans and seas (spatiotemporal runoff simulations based on SnowModel/HydroFlow generated individual drainage catchments for Greenland (n = 3,150), each with an individual flow network). The mass balance for the GrIS was close to equilibrium during the relatively cold 1970s and 1980s and lost mass rapidly as the climate warmed in the 1990s and 2000s. Since 2003, the average annual GrIS mass loss rate was 250–300 km3 yr−1 (equal to 250–300 Gt yr−1). This represents a GrIS loss rate equivalent to a eustatic sea-level rise contribution of 1.1 mm SLE yr−1, compared to a mean estimated global sea-level rise of 3.3 ± 0.4 mm SLE yr−1 from 1993 to 2009, and an average 4.8 mm SLE yr−1 for 2013–2018. Not only has the GrIS lost mass, the land- and marine-terminating outlet glaciers on the periphery of the GrIS have undergone rapid mass and area changes over the recent decades. For example, for the last decade (2000–2010) the average simulated Greenland runoff was 572 ± 53 km3 yr−1 (1.6 ± 0.2 mm SLE yr−1), where the simulations indicated that 69% of the runoff to the surrounding seas originated from the GrIS and 31% came from the land area.

Sebastian H. Mernild, Glen E. Liston, Daqing Yang

Hydrology and Biogeochemistry

Frontmatter
Chapter 6. Regional and Basin Streamflow Regimes and Changes: Climate Impact and Human Effect

Many large northern rivers contribute significant amount of freshwater and energy from land to the Arctic Ocean. Due to climate warming and human effect, basin hydrology changed very significant over the past decades. This chapter reviews the research progress of regional flow regimes and changes, and the results of watershed hydrology analyses, including climate impact and influence of human activities, particularly dam regulation. This chapter is closely linked with other chapters of basin snow cover hydrology, and freshwater and heat fluxes into the Arctic Ocean.

Michael Rawlins, Daqing Yang, Shaoqing Ge
Chapter 7. Hydrologic Extremes in Arctic Rivers and Regions: Historical Variability and Future Perspectives

This chapter provides an overview on the range of hydrologic extremes occurring in Arctic Rivers, consisting of extreme low winter flows; river-ice jam breakup spring floods; snowmelt-driven peak spring/early summer flows; and in some instances, rainfall-driven peak flows in summer. These extreme conditions are mainly influenced by climatological drivers, and in particular, warming climate and enhanced wetness is causing substantial changes in the magnitude, variability and timing of extreme events. The most prominent historical changes in the Arctic include increasing trends in mean annual flow and winter low flow, and earlier timing of peak flow, which are attributable to warming temperature and increasing precipitation, and resulting changes in snowpack storage. Winter low flow is further enhanced by permafrost degradation as it promotes increased soil infiltration and subsurface water movement. Snowmelt-driven annual maximum flow, primarily, has been decreasing, consistent with increased warming and decreased snowpack. Secondary peak flow events in late summer, driven by extreme summer rainfall and possibly enhanced by glacial melt, have been occurring more frequently in some areas of the Arctic, exceeding snowmelt-driven peak flow events. There is also evidence of nonstationary changes in streamflow extremes, such as increasing recurrence intervals of snowmelt-driven floods of a particular magnitude. Future projections indicate continued and enhanced warming, and strong increases in the high-latitude precipitation leading to enhanced annual flows and low flows. Future changes in peak flow remain unclear as peak flow could either increase or decrease depending on the region and interactions between precipitation change and temperature increases. Alterations in hydrologic extremes in the Arctic will have major social and economic implications; thus, focused research aimed at understanding, predicting, and projecting the Arctic streamflow extremes is recommended.

Rajesh R. Shrestha, Katrina E. Bennett, Daniel L. Peters, Daqing Yang
Chapter 8. Overview of Environmental Flows in Permafrost Regions

River ecosystems have adapted to a natural range of variability in magnitude, timing, duration, and predictability of key hydrograph components, such as high- and low-flow periods. However, the timing, magnitude, and variability of cold region flow regimes are changing in response to a warming climate, water abstraction, and building of impoundments. Changes in water quantity flowing down a river at a given time have the potential to adversely and/or positively affect habitat conditions and sustainability of ecological diversity within both the river and associated riparian and floodplain zones. There is a growing need to incorporate environmental flow assessments in the management of permafrost regions in response to changing flow regimes in order to preserve these diverse ecosystems. Environmental flows are defined as the quantity, timing, and quality of freshwater flows and levels necessary to sustain aquatic ecosystems. The goal of this Chapter is to present an overview of environmental flows for permafrost regions, with a focus on North America where information is most readily available. This goal is achieved via a review of (i) cold regions hydro-ecology, (ii) history and application of environmental flows internationally, (iii) environmental flow guidelines and policy in Arctic states, and (iv) riverine monitoring in northern regimes to support environmental flow frameworks. Several key recommendations to address knowledge and data gaps to better manage natural resources are provided.

Daniel L. Peters, Donald J. Baird, Joseph Culp, Jennifer Lento, Wendy A. Monk, Rajesh R. Shrestha
Chapter 9. Yukon River Discharge Response to Seasonal Snow Cover Change

We used remotely sensed Snow Water Equivalent (SWE) and Snow Cover Extent (SCE) data to investigate streamflow response to seasonal snow cover change over the Yukon watershed. We quantified the seasonal cycles and variations of snow cover (both SWE and SCE) and river streamflow, and identified a clear correspondence of river discharge to seasonal snow cover change. We also examined and compared the weekly mean streamflow with the weekly basin SWE and SCE. The results revealed a strong relationship between streamflow and snow cover change during the spring melt season. This relationship provides a practical procedure of using remotely sensed snow cover information for snowmelt runoff estimation over the large northern watersheds. Analyses of extreme (high/low) streamflow cases (years) and basin snow cover conditions indicate an association of high (low) flood peak with high (low) maximum SWE. Comparative analyses of weekly basin SWE versus SCE, peak snowmelt floods, and climatic variables (temperature and winter precipitation) show consistency among basin SWE, SCE, and temperature, but there is some incompatibility between basin SWE and winter precipitation. The inconsistency suggests uncertainties in determination of basin winter snowfall amounts and limitations in applications of the SWE retrieval algorithm over large watersheds/regions with different physical characteristics. Overall, the results of this analysis demonstrate that the SWE and SCE data/products derived from remote sensing technology are useful in understanding seasonal streamflow variations in the northern regions.

Daqing Yang, Yuanyuan Zhao, Richard Armstrong, Mary J. Brodzik, David Robinson
Chapter 10. Arctic River Water Temperatures and Thermal Regimes

Water temperature has an important impact on many aspects of basin hydrology and ecology. In the northern regions, the investigation of river thermal regimes and their changes over space and time is a challenge due to data limitations. This chapter determines the water temperature regimes and its changes at several locations within the Yukon, Mackenzie River, and Lena watersheds, and examines their relationship with air temperature. Yukon and Mackenzie Rivers have distinct water temperature dynamics. They remain near zero from freeze-up in the fall to ice break-up in the spring, and reach their peak temperature during mid-summer. For the locations examined, peak mean monthly water temperatures ranged from 9 to 15 °C, and mean July air temperatures ranged from 13 to 16 °C. The lags between water and air temperatures ranged from 1 to 40 days. The largest lag was found at the Great Bear River monitoring location, since water temperature at this site is strongly influenced by the heat storage of Great Bear Lake. Tests of three models, i.e., linear regression, logical regression (s-shape), and the physically based air2stream model, show that the air2stream model provided the best results, followed by logical regression. Linear regression gave the poorest result. Model estimates of water temperature from air temperature were slightly improved by the inclusion of discharge data. The water temperature sampling regimes had a considerable effect on model performance; long-term data provide a more robust test of a model. Comparisons of mean monthly water temperatures suggest significant spatial variability and some inconsistency between upstream and downstream sites, mainly due to difference in data collection schemes. Similar to the VIC model, the CHANGE model can simulate large basin water temperature pattern over the arctic regions as a whole. With this capability, it might be possible to reconstruct the water temperature records for the northern rivers without past observations. This review clearly demonstrates the need to improve water temperature monitoring in the northern regions.

Daqing Yang, Hoteak Park, Amber Peterson, Baozhong Liu
Chapter 11. Changing Biogeochemical Cycles of Organic Carbon, Nitrogen, Phosphorus, and Trace Elements in Arctic Rivers

Streams and rivers are critical components of Arctic watersheds, functioning as corridors for the movement of water, carbon, and other solutes from headwater streams to larger rivers, estuaries, and the Arctic Ocean. Recent climate change in the Arctic has altered stream and river discharge, temperature, and biogeochemical processes. In this chapter, we summarize the state of research linking watershed hydrology and biogeochemical cycling in Arctic rivers, and how these processes are changing in response to changing climate and disturbance regimes (e.g., permafrost thaw, wildfire). The chapter is divided into three main sections. First, we examine hydrologic controls on stream and river chemistry, including the roles of spring snowmelt and subsurface hydrology as mediated by permafrost characteristics. Second, we summarize recent findings from the literature that describe biogeochemical processes in Arctic rivers, with particular focus on the cycling of organic carbon, nitrogen and phosphorus species, and a suite of trace elements. Third, we identify uncertainties and current gaps in our knowledge of biogeochemical processes in Arctic rivers and recommend steps forward to address these uncertainties.

Jonathan O’Donnell, Thomas Douglas, Amanda Barker, Laodong Guo
Chapter 12. Arctic Wetlands and Lakes-Dynamics and Linkages

Arctic wetlands can occur as isolated patches with areas of 1–10 km2, or they can cover extensive areas in the landscape. Wetlands exert a strong influence on the hydrological cycle as they can both store and release water to streams, other wetlands (ponds) and replenish groundwater reserves. Arctic landscapes are also rich with lakes and their occurrence depends on geology, geomorphic or anthropogenic setting. Like ponds, lake sustainability over time depends on inputs exceeding losses. Hence, their capacity to hold water and the nature of shifting storage capacity especially in light of climate warming (shifts in precipitation/evaporation), or stream/river connectivity, together with growing expansion of mining, oil development are critical issues for northern ecosystems and communities. To survive over time, a wetland or lake needs positive water storage to maintain a high degree of saturation (wetland) or storage capacity (lake). Snow is particularly important, and for Arctic wetlands and lakes, it is the total winter snow accumulation that is of major hydrological consequence. Summer rainfall in most permafrost areas is not high, and often is insufficient to match evaporation rates in lakes. However, the frequency and duration of rainfall can be important for arctic wetlands. Climate warming has been tied to an increase in ground thaw, resulting in both the loss of lakes/ponds and expansion of ponds/lakes depending on permafrost conditions. The timing of ice cover on lakes can affect evaporation, where shallower lakes that experience bed-fast ice during the winter become ice-free sooner in the warm season, which leads to longer open-water seasons and greater amounts of evaporation. Northern lakes have shown shifts towards shorter ice cover duration during the cold seasons, resulting in longer open-water seasons. Lake ice modelling suggests continued shifts towards earlier break-up and later freeze-up may be expected.

Kathy L. Young, Laura Brown, Yonas Dibike
Chapter 13. River Ice Processes and Changes Across the Northern Regions

River ice is critical for northern hydrology and ecosystems, such as the magnitude and timing of hydrologic extremes, i.e., low flows and floods. Historical data analyses and model studies clearly show widespread decreases in river ice thinness and duration due to climate warming across the northern regions. Reductions in river ice jam flooding may have major positive benefits for communities and infrastructure along the river margins, but could also alter the ecology of deltaic riparian and coastal marine ecosystems. The reduction in river and lake ice will influence transportation opportunities in remote regions. In situ observations are important to monitor the ongoing changes in river and lake ice features across the northern regions. Modeling and remote sensing tools are very useful to the understanding of ice processes, attributions of past changes, and projection of future ice conditions in a warming Arctic. More effort is necessary to combine observations, models, and remote sensing technology to investigate ice hydrology over the broader northern regions.

Daqing Yang, Hotaek Park, Terry Prowse, Alexander Shiklomanov, Ellie McLeod

Permafrost and Frozen Ground

Frontmatter
Chapter 14. Permafrost Features and Talik Geometry in Hydrologic System

Permafrost is widely distributed in the high latitudes. This chapter discusses frozen (permafrost) and unfrozen states of the hydrological geometry in the northern regions. The hydrological activities are very active and dynamic not only in discontinuous permafrost zone but also in cold continuous permafrost areas. Water carries significant amount of heat in aquifer and talik system. Water locates in the depth below the maximum ice formation can develop an unfrozen layer underneath the water body (i.e., talik and thaw bulb). Taliks could be open to connect to the sub-permafrost layer, while the hydrologic gradient makes flow in upward or downward directions. The heat balance of the super-, inter-, or sub- permafrost generates unique unfrozen geometry in the permafrost. This chapter also reviews various cellars developed and used in the arctic regions by indigenous people.

Kenji Yoshikawa, Douglas L. Kane
Chapter 15. Ground Temperature and Active Layer Regimes and Changes

Permafrost is degrading worldwide due to climate, leading to serious consequences for regional hydrology, climate, and ecosystems. Over the past decades, field observations in most permafrost regions of the Northern Hemisphere showed a warming trend in ground temperatures. The warming magnitude of low-temperature permafrost was significantly higher than that of high-temperature permafrost. Measurements from the CALM network revealed that in 2016, the increasing trend in the active layer thickness at all Arctic sites was about 1.2–1.9 cm/year across circum-Arctic regions. This change is at or near the long-term maximum for the past 18–21 years. This chapter discusses and reviews permafrost observation networks/programs and datasets, ground temperature variations, active layer changes, effect of snow cover on ground thermal regimes, ground ice distribution, carbon storage in frozen ground, and InSAR application in the northern regions. It is important to emphasize that northern permafrost conditions have significantly changed and will continue to change in the future. In order to understand the past history and future of permafrost, we need to continue and expand the monitoring of the permafrost variables, particularly ground temperature and active layer thickness, via in situ and remote-sensing technologies.

Lin Zhao, Cangwei Xie, Daqing Yang, Tingjun Zhang
Chapter 16. Permafrost Hydrology: Linkages and Feedbacks

In the cold regions, hydrological regime is closely related with permafrost conditions, such as permafrost extent and thermal characteristics. Ice-rich permafrost has a very low hydraulic conductivity and commonly acts as a barrier to deeper groundwater recharge or as a confining layer to deeper aquifers. In regions underlain by permafrost, the active layer is the upper layer of the soil near the surface that undergoes thawing in the summer and freezing in the fall. The thawing starts from the surface in the spring, and the active layer reaches its maximum in late summer. The lower boundary of this layer is the top of the permafrost layer. The active layer is considered to produce base flow (or low flow) during the ice-free season. In this chapter, we discuss relationship between permafrost coverage and streamflow regime, detection of permafrost thawing trends from long-term streamflow data, determination of permafrost groundwater age, and water balance of northern permafrost basins.

Tetsuya Hiyama, Daqing Yang, Douglas L. Kane
Chapter 17. Permafrost Hydrogeology

Groundwater processes are often overlooked in permafrost environments, but subsurface storage and routing can strongly influence water and biogeochemical cycling in northern catchments. Groundwater flow in permafrost regions is controlled by the temporal and spatial distribution of frozen ground, causing the hydrogeologic framework to be temperature-dependent. Most flow occurs in geologic units above the permafrost table (supra-permafrost aquifers) or below the permafrost base (sub-permafrost aquifers). In the context of climate change, thawing permafrost is altering groundwater flowpaths and thereby inducing positive trends in river baseflow in many discontinuous permafrost basins. Activated groundwater systems can provide new conduits for flushing Arctic basins and transporting nutrients to basin outlets. The thermal and hydraulic physics that govern groundwater flow in permafrost regions are strongly coupled and more complex than those in non-permafrost settings. Recent research activity in permafrost hydrogeological modeling has resulted in several mainstream groundwater models (e.g., SUTRA, FEFLOW, HYDRUS) offering users advanced capabilities for simulating processes in aquifers that experience dynamic freeze-thaw. This chapter relies on field examples to review key processes and conditions that control groundwater dynamics in permafrost settings and presents an up-to-date synthesis of the mathematical representation of heat transfer and groundwater flow in northern landscapes.

Barret L. Kurylyk, Michelle A. Walvoord

Ecosystem Change and Impact

Frontmatter
Chapter 18. Greenhouse Gases and Energy Fluxes at Permafrost Zone

Energy, water, and greenhouse gas exchange in the permafrost zone play an important role in the regional and global climate system at multiple temporal and spatial scales. High-latitude warming in recent years has substantially altered ecosystem function, including biosphere–atmosphere interaction, which may amplify or dampen future high-latitude warming through a variety of feedback processes. In this chapter, we have reviewed the current state of energy, water, CO2, and CH4 exchange at the northern high-latitude permafrost zone, with synthesizing observed micrometeorological fluxes. Tundra has a higher summer and winter albedo with a longer snow period than boreal forests, resulting in that tundra less transfers sensible and latent energy to the atmosphere. Growing season length determines the spatial variability of the annual gross primary productivity and net growing season CO2 sink. In contrast, interannual variabilities of the annual CO2 budget at boreal forests are determined by ecosystem respiration, indicating an importance of ecosystem respiration in the boreal forests. The CO2 fertilization effect could be an important determinant of the long-term greenhouse gas budget at sites with a near neutral CO2 budget. In terms of annual greenhouse gas budget, CH4 emission is more important than CO2 budget for both boreal forest and Arctic wet tundra. Based on this synthesis, finally, we discuss future possible directions of study to reach a better understanding of changing high-latitude ecosystems, by synthesizing tower flux measurements in Alaska and Siberia and combining these in situ measurements with remote sensing data.

Masahito Ueyama, Hiroki Iwata, Hideki Kobayashi, Eugénie Euskirchen, Lutz Merbold, Takeshi Ohta, Takashi Machimura, Donatella Zona, Walter C. Oechel, Edward A. G. Schuur
Chapter 19. Spring Phenology of the Boreal Ecosystems

Ecosystem phenology, i.e., the timing of key biological events, is often considered as both a witness and an actor of climate change. Phenological interannual variations and decadal changes reflect climate variability and trends. Deciduous plant phenology also directly influences the carbon, water, and energy exchanges of the ecosystem with the atmosphere. In the northern forests, a trend to earlier spring has been widely reported, often based on remote sensing methods. This trend is suggested to explain a part of the residual carbon sink. However methodological issues, especially related to the combined effects of the vegetation and of the snow cover seasonal changes on the remote sensing signal, were found to affect the results. This chapter describes a remote sensing green-up retrieval method designed to avoid signal contamination by snow. The result validation with ground observations showed that the method catches the interannual variations in phenology of the plant community. Changes in the 1998–2017 period are analyzed and positioned in a longer term. This shows that the most persistent feature over the last decades is a large-scale shift in the green-up date at the end of the 1980s, and that the green-up date has not recovered yet to its status prior to 1987. Finally the green-up date maps were used to represent phenology in the northern ecosystem carbon budget simulations. No unidirectional effect of phenological changes in the annual carbon balance could be identified because of a complex interplay between vegetation, water resources and climate.

Nicolas Delbart
Chapter 20. Diagnosing Environmental Controls on Vegetation Greening and Browning Trends Over Alaska and Northwest Canada Using Complementary Satellite Observations

Tundra and boreal forest regions have undergone extreme environmental changes in recent decades. Many studies have documented these changes and associated ecosystem impacts using a variety of methods including field measurements, remote sensing and biophysical modeling. Combined observations from satellite optical-infrared and microwave remote sensing have also been used for regional assessment and monitoring of environmental change, ecosystem processes and biogeochemical cycles in the Arctic. Remote sensing derived vegetation parameters range from relatively direct observations of vegetation greenness and chlorophyll fluorescence to higher-level vegetation productivity estimates. However, satellite remote sensing of land surface conditions is particularly challenging at high latitudes due to seasonal variations in solar illumination, snow cover, persistent cloud cover and atmospheric aerosol contamination. Here, we used satellite-derived observations of vegetation greenness (EVI), sun-induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) to clarify regional patterns and recent variations in vegetation growth over the Arctic Boreal Vulnerability Experiment (ABoVE) domain. The annual non-frozen (NF) period and volumetric soil moisture (VSM) retrieved from satellite microwave remote sensing were used as proxies for growing season length and water supply controls to investigate the impacts of climate on vegetation growth. Positive trends in regional productivity generally coincide with a longer NF season. However, the benefit of a longer NF season to vegetation growth is reduced in soil moisture constrained regions, which have become more widespread in the recent decade over almost half (48.9%) of the domain. Our results document the influence of a changing environment on regional vegetation growth and the northern terrestrial carbon sink for atmospheric CO2.

Youngwook Kim, John S. Kimball, Nicholas Parazoo, Peter Kirchner
Chapter 21. Boreal Forest and Forest Fires

Boreal forest has played a role as sink of atmospheric CO2 due to the slow growth of black spruce; however, changes in source of atmospheric CO2 by forest fires and recent warming have significantly triggered modulation in physiological ecology and biogeochemistry over the boreal forest of Alaska. This chapter describes recent research findings in boreal forest ecosystem of Alaska: (1) the forest aboveground biomass (AGB) with field survey data and satellite data, (2) latitudinal gradients of phenology with time-lapsed camera and satellite data, (3) spatio-temporal variation of leaf area index (LAI) with the analysis of satellite data, (4) latitudinal distribution of winter and spring season soil CO2 emission, and (5) successional changes in CO2 and energy balance after forest fires. As a result, mapping of forest AGB is useful for the evaluation of vegetation models and carbon stock in the biogeochemical cycle. Latitudinal distribution of phenology understands the recent and future phenological changes including post-fire recovery forests. Interannual variation of LAI shows the leaf dynamics and near-surface remote-sensing approaches with the analyses of time-lapsed digital camera and satellite data. Spring carbon contributions are sensitive to subtle changes in the onset of spring. Vegetation recovery after forest fire is the major driver of the carbon balance in the stage of early succession. Increasing soil carbon emission in response to abrupt climate warming in Alaska is a significant driver of carbon balance.

Yongwon Kim, Hideki Kobayashi, Shin Nagai, Masahito Ueyama, Bang-Yong Lee, Rikie Suzuki
Chapter 22. Northern Ecohydrology of Interior Alaska Subarctic

Ecohydrology—as an interdisciplinary field—developed in and explores processes in warm semi-arid and arid ecosystems. This field is in its infancy with respect to arctic and subarctic systems in Alaska. However, similar to warm and dry regions, soil moisture storage is a driver of ecohydrological processes in these northern regions. The presence or absence of permafrost impacts soil moisture storage and determines whether ecological or hydrological processes drive water cycling. The arctic is in the zone of continuous permafrost distribution, and the subarctic is in the zone of discontinuous permafrost distribution. In the subarctic, hydrological processes are dominated by soil moisture storage in areas with permafrost and by ecological processes in areas without permafrost. Given the infancy of the ecohydrology discipline in arctic and subarctic systems, there are a number of knowledge gaps outlined at the end of this chapter.

Jessica M. Young-Robertson, W. Robert Bolton, Ryan Toohey
Chapter 23. Yukon River Discharge-NDVI Relationship

Similar to the Mackenzie River, a strong seasonal consistency between NDVI and discharge exists for Yukon River. The flow-NDVI association is particularly strong before June, discharge rapidly rises and reaches the peak the 1st half of June, while the NDVI in the period of April to June increases fastest and reaches the maximum in July. In the mid and late summer, both discharge and NDVI decline gradually. Similarly, two sensitive periods while NDVI significantly correlates to discharge variations were also found in this region. May to June is key time of vegetation relates to discharge, the NDVI on 2nd half of May and 1st half of June is significantly correlated to the 1st half of May discharge mainly in midstream zone. August is another sensitive period, the 2nd half of August NDVI closely related to the synchronous and previous half-month discharge. River discharge decreased during growing season except in May from 1982 to 2013 in Yukon Basin. The significant decrease about 8–15% of the average flow, but a significant increase with a trend above 34.2% occurred in May. The NDVI trends during the growing season from May to September almost inversely correspond to discharge changes with a weak increments about 5% of the mean NDVI. In addition, examination of extreme flow years and corresponding NDVI conditions also reveals that low runoff year was associated with a lower basin NDVI with an earlier maximum, while the higher flow year was linked with a higher NDVI and a longer growth season. It may imply the better water supply with higher flow in the spring will induce a higher vegetation production.

Weixin Xu, Daqing Yang

Cross-System Linkage and Integration

Frontmatter
Chapter 24. River Freshwater Flux to the Arctic Ocean

Various estimates of freshwater discharge to the Arctic Ocean with different methods and for different drainage areas have shown a good consistency in long-term mean runoff ranging from 200 mm/year to 226 mm/year. Most of the estimates are derived from available discharge measurements at the downstream gauging stations. According to the most recent assessment of the total discharge to the Arctic Ocean is approximately 4300 km3 year−1 and continental contributions to the river input into the Arctic Ocean for Asia, North America, and Europe are 55%, 28%, and 17%, respectively. The river flux to the Arctic Ocean has significantly changed with an increase of 210 km3 over 1936–2015 across Eurasia, and 36 km3 over 1964–2015 for northern Canada. These changes were especially pronounced during the last 30-years, associated with most intense warming of air temperature over the northern hemisphere and significant declines in sea ice extent over the Arctic Ocean. The significant increase in annual river flow is mainly due to increases in winter (60%) and spring (33%) discharge. Winter flows have a very consistent and significant increase throughout the Eurasian pan-Arctic. All six largest Eurasian Arctic rivers show a significant increase in winter river flows over the long-term period 1936–2015. Similar but less significant trends in winter and spring discharge were found for Canadian northern rivers. Seasonal discharge has been altered as the result of human activity, particularly reservoir regulation. Eliminating reservoir effect in the largest Arctic rivers of Yenisei, Lena, and Ob, using the hydrograph transformation model, show significant increase in annual discharge, i.e., increase in spring by 49%, winter by 31%, and summer-fall by 20%. These results are different from those obtained from the observational discharge data. Thus, for hydroclimatic analysis to understand possible changes in river flux to the Arctic Ocean, it is necessary to take into account human impact on the discharge regime and change. Sea surface salinity (SSS) links various components of the Arctic freshwater system, including river discharge. Analysis of remote sensed SSS data has shown that SSS distribution pattern in the Arctic Ocean during warm period is partly defined by river flux. There is a great potential of using remote sensing data for a better understanding of variability in the Arctic freshwater system.

Alexander Shiklomanov, Stephen Déry, Mikhail Tretiakov, Daqing Yang, Dmitry Magritsky, Alex Georgiadi, Wenqing Tang
Chapter 25. River Heat Flux into the Arctic Ocean

Long-term observations and data analyses of water temperatures and discharge over the northern regions determine water temperature regimes and quantify river heat flux into the ocean system. This chapter presents an overview of thermal regime and heat flux for the large rivers in northern regions. This chapter compares the results for the Siberian and North American arctic watersheds/regions, and highlights the differences and changes in water temperature and heat flux due to climate variation and human effect. Given the limited water temperature observations, this chapter is unable to discuss the variability and change in river thermal conditions over the northern regions of the North America. There is a knowledge gap in river temperature and heat contribution along the arctic coast of North America. Advanced hydrologic models and remote sensing data have provided opportunities to improve our understanding of river thermal characteristics across the northern regions. There is a need to continue to explore remote sensing data/products in the investigations of river water temperature and heat transport processes and to develop coupled land–ocean models, in order to better quantify land–ocean linkage and connections across the northern coastal regions.

Daqing Yang, Shaoqing Ge, Hotaek Park, Richard L. Lammers
Chapter 26. Cold Region Hydrologic Models and Applications

Over the recent decades, the warming in Arctic has affected changes in the terrestrial hydrologic processes. Unfortunately, the number of hydrometeorological observing stations in the region has decreased. To reduce the limitation in observation, a number of process-based and distributed models have been developed for simulating the hydrological processes in a changing climate. The current generations of models are able to reasonably reproduce the prominent cold region hydrologic processes, such as degrading permafrost, decreasing snow extent, increasing river discharge and evapotranspiration, and increasing streamflow temperature. These models enhance our understanding of the response of Arctic terrestrial processes to climate change and variation. However, the model representations for some of the Arctic hydrological processes are still not yet sufficient and need further improvements. This chapter provides an overview of changes in key processes and conditions of the Arctic terrestrial hydrology based on a synthesis of observations and model simulations, and presents recommendations for further development and improvement of cold region hydrologic models.

Hotaek Park, Yonas Dibike, Fengge Su, John Xiaogang Shi
Chapter 27. Regional Climate Modeling in the Northern Regions

Regional climate models (RCMs) are indispensable tools for dynamically downscaling climate projections to regional scales. Compared to statistical downscaling, RCMs provide a tool to investigate how regional scale climate evolves without assuming stationarity by explicitly representing the physical processes resolved by the RCMs. Studies using RCMs have investigated the climate change’s impacts on precipitation, temperature, floods, permafrost, wildfire, etc., over the northern regions of North America. As the computing capacity increases, RCMs with grid spacing less than 5 km can directly resolve convection and eliminate the need to parameterize one important process in the generation of precipitation and improves the simulation of convective precipitation. As the need for regional climate dynamical downscaling increases, further improvements of RCMs and incorporation of other components of eco-climate system are needed.

Zhenhua Li, Yanping Li, Daqing Yang, Rajesh R. Shrestha
Chapter 28. High-Resolution Weather Research Forecasting (WRF) Modeling and Projection Over Western Canada, Including Mackenzie Watershed

Weather Research Forecasting (WRF) model was run at a Convection-Permitting (CP) 4-km resolution to dynamically downscale the 19-member CMIP5 ensemble mean projection to assess the hydroclimatic risks in Western Canada under high-end emission scenario RCP8.5 by the end of twenty-first century. A retrospective simulation (CTL, 2000–2015) forced by ERA-Interim and a Pseudo-Global Warming (PGW) forced with the reanalysis plus the climate change forcing (2071-2100–1976-2005) were derived using CMIP5 ensemble. The surface air temperature of WRF-CTL, evaluated against gridded analysis ANUSPLIN, shows good agreements in the geographical distribution. There are cold biases east of the Canadian Rockies, especially in spring. WRF-CTL’s precipitation resembles the geographical distribution of CaPA and ANUSPLIN. The wet bias mainly resides near the British Columbia coast in winter and over on the eastern side of the Canadian Rockies in summer. WRF-PGW shows much larger warming over the polar region in the northeast during the cold season relative to WRF-CTL. Precipitation increases in most areas in spring and autumn, whereas unchanged or decreased precipitation in summer occurs in the Saskatchewan River Basin and southern Canadian Prairies. The flat precipitation changes cannot compensate the enhanced evapotranspiration over the region causing the water stress for the rain-fed agriculture during the growing season in the future. WRF-PGW projects lower warming than that by the CMIP5 ensemble throughout the year. The CMIP5 ensemble projects a much drier future over the Canadian Prairies with a 10–20% decrease of summer precipitation. The CMIP5 ensemble mean generally agrees with WRF-PGW except for regions with significant terrain, which may be due to WRF’s higher resolution can represent small-scale summer convection and orographic lifting better. A larger increase of high-intensity precipitation events compared to lower intensity events, which indicates a higher risk for extreme events and lower effective rainfall for agriculture. New bias correction methods need to be developed to capture the shift in the precipitation intensity distribution in the future. The study also reveals the urgent need for high-quality meteorological observation to provide forcing data and evaluation benchmarks in Western Canada. The high-resolution dynamical downscaling over Western Canada provides opportunities for studying local-scale atmospheric dynamics and providing hydroclimatic data for cold region ecosystems, agriculture, and hydrology.

Yanping Li, Zhenhua Li
Chapter 29. Responses of Boreal Forest Ecosystems and Permafrost to Climate Change and Disturbances: A Modeling Perspective

The north circumpolar region contains a large amount of carbon. This carbon storage is vulnerable due to permafrost degradation and wildfire disturbances under ongoing and projected climate change. Climate warming and wildfires change soil organic horizons gradually or abruptly, and modify permafrost thermal-hydrology and biogeochemistry, ecosystem structures, functions, and capability of sequestrating rising atmospheric CO2. Land models do not fully take accounts of these interactions and its complexity in the high latitude. This chapter describes a terrestrial ecosystem model with dynamic organic soil module (DOS-TEM) and its unique freezing-thawing algorithm, and presents key results of its applications mainly in boreal forests of Alaska. The DOS-TEM explicitly considers interactions of soil thermal and hydrological processes, permafrost degradation and the direct and indirect effects of wildfire disturbances, in addition to soil–plant C and N cycles. We first introduce four modules of DOS-TEM, focusing on its disturbance module and coupling with a dynamic organic soil module. Then we describe and validate DOS-TEM’s freezing-thawing algorithm and development based on two-directional Stefan algorithm (TDSA). Finally, we apply the DOS-TEM at site and region scales, with a focus on model ability to dynamically simulate soil organic thickness under warming and wildfires, and consequent impacts on permafrost in the Yukon River Basin. We conclude that land surface model development is urgently needed to include other critical landscape processes, such as thermalkarst and other disturbances, to synchronize thermal-hydrological-biogeochemical processes, and to incorporate an advanced understanding of biospheric feedbacks to atmosphere and ecosystems. Such a complexity of modeling scope is plausible with advancement of high performance computing.

Shuhua Yi, Fengming Yuan
Chapter 30. Future Trajectory of Arctic System Evolution

The Arctic climate system is undergoing changes in its multiple components, including its hydrologic cycle, as documented in the preceding chapters. The future trajectory of the Arctic climate system becomes a major issue for adapting to anticipated impacts ranging from local-scale impacts on water security (hydropower, infrastructure, and human health), to global-scale impacts such as greenhouse gas releases and sea level rise. Here we highlight projections of changes in key Arctic variables relevant to the Arctic freshwater cycle: precipitation, evapotranspiration, snow, river discharge, surface- and ground-water, and permafrost. We highlight key uncertainties arising from the future emission scenarios and across-model differences. Precipitation and evapotranspiration are both projected to increase, consistent with atmospheric warming and the Clausius–Clapeyron equation. The percentage increases of precipitation projected for the Arctic are among the largest in the world. Evapotranspiration is also projected to increase, although not enough to offset the increase in precipitation, so the freshwater runoff as river discharge is also projected to increase. The projected change signal of the river discharge increase is much greater than the model uncertainty. Projected changes in soil moisture are highly uncertain because of interactions with vegetation, topography, and permafrost, together with uncertainties in local net precipitation minus evapotranspiration. Snow cover duration and maximum accumulation are projected to decrease across most regions of the Arctic, with increased annual maximum accumulations only in high latitudes where increased snowfall dominates the decrease of snow season length. Near-surface permafrost is projected to thaw over large portions of the Arctic, with timing dependent on the rate of warming (emission scenario) and the effects of changes in snow cover. Projected changes become more sensitive to emission trajectories after about the middle of the twenty-first century with projected changes in many variables accelerating under a business as usual scenario in contrast to much slower rates of change where efforts are made to limit GHG emissions.

Kazuyuki Saito, John E. Walsh, Arvid Bring, Ross Brown, Alexander Shiklomanov, Daqing Yang
Metadata
Title
Arctic Hydrology, Permafrost and Ecosystems
Editors
Prof. Dr. Daqing Yang
Prof. Douglas L. Kane
Copyright Year
2021
Electronic ISBN
978-3-030-50930-9
Print ISBN
978-3-030-50928-6
DOI
https://doi.org/10.1007/978-3-030-50930-9