The Effects of Changes in Climate and Other Environmental Factors on Permafrost Evolution
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THE EFFECTS OF CHANGES IN CLIMATE AND OTHER ENVIRONMENTAL FACTORS ON PERMAFROST EVOLUTION By Elchin Jafarov RECOMMENDED: Advisory Committee Chair ~JJ--ril Chair, Department of Geology and Geophysics APPROVED: ean of the Graduate Sc <2-f/'~At~ , Date THE EFFECTS OF CHANGES IN CLIMATE AND OTHER ENVIRONMENTAL FACTORS ON PERMAFROST EVOLUTION A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Elchin Jafarov, B.S., M.S. Fairbanks, Alaska May 2013 iii Abstract Permafrost is a product of a past colder climate. It underlies most of the terrestrial Arc- tic, where it influences landscape hydrology, biogeochemical environments and human activity. The current thermal regime of permafrost is mediated by different environmental factors, including snow, topography, vegetation and soil texture. The dependence of per- mafrost on these factors greatly complicates the modeling of permafrost thermodynam- ics. Accurate modeling of permafrost is critical for evaluating potential impacts of climate change on permafrost stability. The objectives of this study were to a) improve modeling of ground temperature during snow season; b) analyze the effects of post-fire environ- mental changes on permafrost thermal stability; and c) predict 21st century ground tem- perature dynamics in Alaska with high spatial resolution. To achieve the proposed objec- tives, near-surface air and ground temperatures were measured at permafrost observation stations across Alaska. Measured ground temperatures were used to evaluate simulated ground temperatures, which were generated with the Geophysical Institute Permafrost Laboratory (GIPL) numerical transient model. The GIPL model takes into account cli- mate, snow, soil texture, soil moisture, and the freeze/thaw effect. To better model ground temperatures within the soil column, it was necessary to improve the parameterization of snow layer thermal properties in the model. To improve ground temperature simulations during snow season, daily snow thermal properties were estimated using an inverse ap- proach. Modeling bias was improved by including ground temperatures simulated using estimated daily snow thermal conductivities. To address the effects of fire disturbance on permafrost thermal stability, we applied the GIPL model to lowland and upland boreal for- est permafrost environments. The results indicate that permafrost vulnerability depends on pre-fire organic soil layer thickness and wetness, the amount of organic matter burned during the fire, and post-fire soil organic layer recovery rates. High spatial resolution permafrost maps are necessary for evaluating the potential impacts of permafrost thaw- ing on Arctic ecosystems, engineering facilities, infrastructure, and the remobilization of soil carbon. Simulated ground temperatures in Alaska during the 21st century indicate widespread permafrost degradation in the discontinuous permafrost zone. High ground temperature warming trends are projected for most of the continuous permafrost zone north of the Brooks Range. iv Table of Contents Page SignaturePage...................................... i TitlePage.......................................... ii Abstract........................................... iii TableofContents .................................... iv ListofFigures ...................................... vi ListofTables....................................... ix Acknowledgements................................... x 1 Introduction 1 1.1 PermafrostdistributioninAlaska . ....... 1 1.2 Factorsthatdeterminepermafrostthermalstate . .......... 2 1.2.1 Snow..................................... 3 1.2.2 Topography................................. 4 1.2.3 Vegetation.................................. 4 1.2.4 Organicandmineralsoils . 4 1.2.5 Openwaterbodies ............................. 5 1.2.6 Wildfires................................... 6 1.2.7 Anthropogenicinfluences . 7 1.3 Permafrostunderawarmerclimate . .... 7 1.4 Researchobjectives .... ...... ..... ...... ...... ... ... 9 1.5 Researchquestions ............................... 9 1.6 OutlineofChapters............................... 10 1.7 Bibliography.................................... 13 2 The effect of snow: How to better model ground surface temperatures 19 2.1 Introduction .................................... 19 2.2 Physicalmodel ................................... 21 2.3 Dataassimilationtechnique . ..... 23 2.4 Methodevaluation ................................. 25 2.5 Abriefdescriptionofthesites. ...... 28 2.6 Results ........................................ 29 v 2.7 Discussion ...................................... 31 2.8 Conclusions ..................................... 33 2.9 Acknowledgements................................ 33 2.10Figures ........................................ 34 2.11 Bibliography................................... 45 3 The effects of fire on the thermal stability of permafrost in lowland and upland black spruce forests of interior Alaska in a changing climate 50 3.1 Introduction .................................... 50 3.2 Methods ....................................... 52 3.3 Results ........................................ 55 3.4 Discussion ...................................... 58 3.5 Conclusions ..................................... 59 3.6 Acknowledgements................................ 60 3.7 Tables......................................... 61 3.8 Figures ........................................ 62 3.9 Bibliography.................................... 72 4 Numerical modeling of permafrost dynamics in Alaska using a high spatial res- olution dataset 78 4.1 Introduction .................................... 79 4.2 Mathematicalmodel ................................ 81 4.3 Methods ....................................... 82 4.4 Modelcalibrationandvalidation . ..... 85 4.5 Optimizationofgroundthermalparameters . ....... 87 4.6 Results ........................................ 89 4.7 Discussion ...................................... 90 4.8 Conclusion...................................... 91 4.9 Acknowledgements................................ 92 4.10Tables......................................... 93 4.11Figures ........................................ 94 4.12 Bibliography................................... 107 5 General Conclusions 113 vi List of Figures Page 1.1 SpatialmapofpermafrostinAlaska . ..... 3 2.1 Three cases experiment set up to evaluate proposed method......... 34 2.2 Estimated and prescribed snow thermal conductivities for three cases ex- periments. ...................................... 35 2.3 The estimated snow density (black solid curve) and calculated uncertainties (solid cyan)forthereconstructedsnowdensities . ........ 36 2.4 Evaluation ofthereconstructedsnowdensities . .......... 37 2.5 The estimated snow thermal conductivities [Wm−1K−1] (black solid curve) attheDeadhorsepermafroststation . 38 2.6 The estimated snow thermal conductivities [Wm−1K−1] (black solid curve) attheFranklinBluffspermafroststation . ...... 39 2.7 The estimated snow thermal conductivities [Wm−1K−1] (black solid curve) attheBonanzaCreekpermafroststation . 40 2.8 The estimated snow thermal conductivities [Wm−1K−1] (black solid curve) attheSmithLakepermafroststation . 41 2.9 Averaged snow thermal conductivities (solid black curve) obtained from av- erageofroundedthermalconductivities . ..... 42 2.10 The root mean square errors between measured and simulated ground sur- facetemperatures.................................. 43 2.11 The compasion between calculated from measured heat flux and estimated snowthermalconsuctivities . 44 3.1 Climatological data from the Fairbanks International Airportstation . 62 3.2 The postfire dynamics rates of (A) moss, (B) fibrous, and (C) amorphous organicsoillayers.................................. 63 3.3 Simulations of the active layer thickness for the (A) upland and (B) lowland boreal forest sites for different warming scenarios . ......... 64 vii 3.4 Simulations of the permafrost table depth for the (A) upland and (B) low- land boreal forest sites for different fire severities . .......... 65 3.5 Simulations of the permafrost table depth for the (A) upland and (B) low- land boreal forest sites for different fire severities during stable climate . 66 3.6 Simulated permafrost table dynamics with and without changes in the soil moisturecontent .................................. 67 3.7 Contour plots of the ground temperature dynamics with depth over time forthelowlandpermafrostsite . 68 3.8 Freeze-up time for (A) the upland permafrost site after 15 cm of the organic layerburn ...................................... 69 3.9 Simulated permafrost table dynamics after (A) 15 cm of the organic layer burn 70 3.10 Simulated permafrost table dynamics after 100 % organic layer burn for the uplandborealforestpermafrostsites . ..... 71 4.1 Permafrost observation station locations and 18 ground temperature zones 94 4.2 Measured (solid) and calculated (dashed) monthly averaged temperatures at2mabovethegroundand0.05,0.3and0.82mdepths . 95 4.3 Measured (solid) and calculated (dashed) monthly averaged temperatures at2mabovethegroundand0.03,0.4and0.86mdepths . 96 4.4 Measured (solid) and calculated (dashed) monthly averaged temperatures at2mabovethegroundand0.08,0.38and0.84mdepths . 97 4.5 Simulated and measured MAGTs at different depths from 3 to 30 m during 2007-2009IPYyears................................. 98 4.6 Simulated and measured MAGTs from 1 to 6 meters depths during 2009 . 99 4.7 Comparison