Michael Rawlins - Academia.edu (original) (raw)

Papers by Michael Rawlins

Arctic Hydrology, Permafrost and Ecosystems, 2020

Many large northern rivers contribute significant amount of freshwater and energy from land to th... more 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. 6.1 Introduction Many large northern rivers contribute significant amount of freshwater and energy from land to the Arctic Ocean (Fig. 6.1 and table). Due to recent strong climate warming in the Polar Regions, arctic hydrology system and its key elements have significantly changed. It is important to point out that several community-based

15 The quantity and quality of river discharge in arctic regions is in uenced 16 by many processe... more 15 The quantity and quality of river discharge in arctic regions is in uenced 16 by many processes including climate, watershed attributes and, increasingly, 17 hydrological cycle intensi cation and permafrost thaw. We used a hydrological 18 model to quantify baseline conditions and investigate the changing character 19 of hydrological elements for Arctic watersheds between Point Barrow and just 20 west of Mackenzie River over the period 1981 2010. A synthesis of measure21 ments and model simulations shows that the region exports 31.9 km3 yr−1 of 22 freshwater via river discharge, with 55.5% (17.7 km3 yr−1) coming collectively 23 from the Colville, Kuparuk, and Sagavanirktok rivers. The simulations point 24 to signi cant (p < 0.05) increases (134 212 % of average) in cold season dis25 charge (CSD) for several large North Slope rivers including the Colville and 26

Remote Sensing, 2021

The Yukon River basin encompasses over 832,000 km2 of boreal Arctic Alaska and northwest Canada, ... more The Yukon River basin encompasses over 832,000 km2 of boreal Arctic Alaska and northwest Canada, providing a major transportation corridor and multiple natural resources to regional communities. The river seasonal hydrology is defined by a long winter frozen season and a snowmelt-driven spring flood pulse. Capabilities for accurate monitoring and forecasting of the annual spring freshet and river ice breakup (RIB) in the Yukon and other northern rivers is limited, but critical for understanding hydrologic processes related to snow, and for assessing flood-related risks to regional communities. We developed a regional snow phenology record using satellite passive microwave remote sensing to elucidate interactions between the timing of upland snowmelt and the downstream spring flood pulse and RIB in the Yukon. The seasonal snow metrics included annual Main Melt Onset Date (MMOD), Snowoff (SO) and Snowmelt Duration (SMD) derived from multifrequency (18.7 and 36.5 GHz) daily brightness ...

The Cryosphere Discussions, 2019

The quantity and quality of river discharge in arctic regions is influenced by many processes inc... more The quantity and quality of river discharge in arctic regions is influenced by many processes including climate, watershed attributes and, increasingly, hydrological cycle intensification and permafrost thaw. We used a hydrological model to quantify baseline conditions and investigate the changing character of hydrological elements for Arctic watersheds between Point Barrow and just west of Mackenzie River over the period 1981-2010. The region annually exports 28.1 km 3 yr −1 of freshwater via river discharge, with 51.9% (14.6 km 3 yr −1) coming collectively from the Colville, Kuparuk, and Sagavanirktok rivers. Our results point to significant (p < 0.05) increases (134-212% of average) in cold season discharge (CSD) for several large North Slope rivers including the Colville and Kuparuk, and for the region as a whole. A significant increase

Journal of Climate, 2016

This study used air temperatures from a suite of regional climate models participating in the Nor... more This study used air temperatures from a suite of regional climate models participating in the North American Climate Change Assessment Program (NARCCAP) together with two atmospheric reanalysis datasets to investigate changes in freezing days (defined as days with daily average temperature below freezing) likely to occur between 30-yr baseline (1971–2000) and midcentury (2041–70) periods across most of North America. Changes in NARCCAP ensemble mean winter temperature show a strong gradient with latitude, with warming of over 4°C near Hudson Bay. The decline in freezing days ranges from less than 10 days across north-central Canada to nearly 90 days in the warmest areas of the continent that currently undergo seasonally freezing conditions. The area experiencing freezing days contracts by 0.9–1.0 × 106 km2 (5.7%–6.4% of the total area). Areas with mean annual temperature between 2° and 6°C and a relatively low rate of change in climatological daily temperatures (<0.2°C day−) near...

Biogeosciences Discussions, 2015

Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong... more Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of methane emissions to environmental factors such as soil temperature and moisture has led to concerns about potential positive feedbacks to climate change. This risk is particularly relevant at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over the next 100 years. However, global models disagree as to the magnitude and spatial distribution of emissions, due to uncertainties in wetland area and emissions per unit area and a scarcity of in situ observations. Recent intensive field campaigns across the West Siberian Lowland (WSL) make this an ideal region over which to assess the per-Published by Copernicus Publications on behalf of the European Geosciences Union. 3322 T. J. Bohn et al.: Intercomparison of wetland methane emissions models formance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH 4 Intercomparison of Models Project (WETCHIMP), focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 21 models and 5 inversions over this domain in terms of total CH 4 emissions, simulated wetland areas, and CH 4 fluxes per unit wetland area and compared these results to an intensive in situ CH 4 flux data set, several wetland maps, and two satellite surface water products. We found that (a) despite the large scatter of individual estimates, 12-year mean estimates of annual total emissions over the WSL from forward models (5.34 ± 0.54 Tg CH 4 yr −1), inversions (6.06 ± 1.22 Tg CH 4 yr −1), and in situ observations (3.91 ± 1.29 Tg CH 4 yr −1) largely agreed; (b) forward models using surface water products alone to estimate wetland areas suffered from severe biases in CH 4 emissions; (c) the interannual time series of models that lacked either soil thermal physics appropriate to the high latitudes or realistic emissions from unsaturated peatlands tended to be dominated by a single environmental driver (inundation or air temperature), unlike those of inversions and more sophisticated forward models; (d) differences in biogeochemical schemes across models had relatively smaller influence over performance; and (e) multiyear or multidecade observational records are crucial for evaluating models' responses to long-term climate change.

Eurasian Arctic Land Cover and Land Use in a Changing Climate, 2010

Chapter 7 Interactions Between Land Cover/Use Change and Hydrology Alexander I. Shiklomanov, Theo... more Chapter 7 Interactions Between Land Cover/Use Change and Hydrology Alexander I. Shiklomanov, Theodore J. Bohn, Dennis P. Lettenmaier, Richard B. Lammers, Peter Romanov, Michael A. Rawlins4 and Jennifer C. Adam Abstract The water cycle is a vital component of the ...

JAWRA Journal of the American Water Resources Association, 2011

The potential impacts of climate change on northern groundwater supplies were examined at a fract... more The potential impacts of climate change on northern groundwater supplies were examined at a fractured-marble mountain aquifer near Nome, Alaska. Well water surface elevations (WSE) were monitored from 2004-2009 and analyzed with local meteorological data. Future aquifer response was simulated with the Pan-Arctic Water Balance Model (PWBM) using forcings (air temperature and precipitation) derived from fifthgeneration European Centre Hamburg Model (ECHAM5) global circulation model climate scenarios for extreme and modest increases in greenhouse gases. We observed changes in WSE due to the onset of spring snowmelt, low intensity and high intensity rainfall events, and aquifer head recession during the winter freeze period. Observed WSE and snow depth compared well with PWBM-simulated groundwater recharge and snow storage. Using ECHAM5-simulated increases in mean annual temperature of 4-8°C by 2099, the PWBM predicted that by 2099 later freeze-up and earlier snowmelt will decrease seasonal snow cover by one to two months. Annual evapotranspiration and precipitation are predicted to increase 27-40% (55-81 mm) and 33-42% (81-102 mm), respectively, with the proportion of snowfall in annual precipitation decreasing on average 9-25% (p < 0.05). The amount of snowmelt is not predicted to change significantly by 2099; however, a decreasing trend is evident from 2060 in the extreme ECHAM5 greenhouse gas scenario. Increases in effective precipitation were predicted to be great enough to sustain sufficient groundwater recharge.

Journal of Hydrometeorology, 2013

Daily synoptic observations were examined to determine the critical air temperatures and dewpoint... more Daily synoptic observations were examined to determine the critical air temperatures and dewpoints that separate solid versus liquid precipitation for the fall and spring seasons at 547 stations over northern Eurasia. The authors found that critical air temperatures are highly geographically dependent, ranging from −1.0° to 2.5°C, with the majority of stations over European Russia ranging from 0.5° to 1.0°C and those over south-central Siberia ranging from 1.5° to 2.5°C. The fall season has a 0.5°–1.0°C lower value than the spring season at 42% stations. Relative humidity, elevation, the station's air pressure, and climate regime were found to have varying degrees of influences on the distribution of critical air temperature, although the relationships are very complex and cannot be formulated into a simple rule that can be applied universally. Although the critical dewpoint temperatures have a spread of −1.5° to 1.5°C, 92% of stations have critical values of 0.5°–1.0°C. The cri...

Journal of Advances in Modeling Earth Systems, 2013

Environmental Research Letters, 2010

Wetlands are not only primary producers of atmospheric greenhouse gases but also possess unique f... more Wetlands are not only primary producers of atmospheric greenhouse gases but also possess unique features that are favourable for application of satellite microwave remote sensing to monitoring their status and trend. In this study we apply combined passive and active microwave remote sensing data sets from the NASA sensors AMSR-E and QuikSCAT to map surface water dynamics over Northern Eurasia. We demonstrate our method on the evolution of large wetland complexes for two consecutive years from January 2006 to December 2007. We apply river discharge measurements from the Ob River along with land surface runoff simulations derived from the Pan-Arctic Water Balance Model during and after snowmelt in 2006 and 2007 to interpret the abundance of widespread flooding along the River Ob in early summer of 2007 observed in the remote sensing products. The coarse-resolution, 25 km, surface water product is compared to a high-resolution, 30 m, inundation map derived from ALOS PALSAR (Advanced Land Observation Satellite phased array L-band synthetic aperture radar) imagery acquired for 11 July 2006, and extending along a transect in the central Western Siberian Plain. We found that the surface water fraction derived from the combined AMSR-E/QuikSCAT data sets closely tracks the inundation mapped using higher-resolution ALOS PALSAR data.

Arctic, Antarctic, and Alpine Research, 2003

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Journal of Geophysical Research, 2009

Discharge from large Eurasia rivers increased during the 20th century, yet much remains unknown r... more Discharge from large Eurasia rivers increased during the 20th century, yet much remains unknown regarding details of this increasing freshwater flux. Here, for the three largest Eurasian basins (the Ob, Yenisei, and Lena) we examine the nature of annual and seasonal discharge trends by investigating the flow changes along with those for precipitation, snow depth, and snow water equivalent. On the basis of a multiperiod trend analysis and examination of station data, we propose two characteristic regimes to explain the long-term discharge increase from these large Eurasian rivers. Over the early decades from approximately 1936 to 1965, annual precipitation correlates well with annual discharge, and positive discharge trends are concurrent with summer/fall discharge increases. The latter decades were marked by a divergence between winter/ spring flows, which increased, amid summer/fall discharge declines. A comparison of cold season precipitation (CSP) and spring discharge trends across subbasins of the Ob, Yenisei, and Lena shows limited agreement with one precipitation data set but good agreement (R 2 > 0.90) when a second is used. While natural variability in the Arctic system tends to mask these emerging trends, spatial and temporal changes can generally be characterized by increased solid precipitation, primarily to the north, along with a drier hydrography during the warm season.

Environmental Research Letters, 2021

Manifestations of climate change in the Arctic are numerous and include hydrological cycle intens... more Manifestations of climate change in the Arctic are numerous and include hydrological cycle intensification and permafrost thaw, both expected as a result of atmospheric and surface warming. Across the terrestrial Arctic dissolved organic carbon (DOC) entrained in arctic rivers may be providing a carbon subsidy to coastal food webs. Yet, data from field sampling is too often of limited duration to confidently ascertain impacts of climate change on freshwater and DOC flows to coastal waters. This study applies numerical modeling to investigate trends in freshwater and DOC exports from land to Elson Lagoon in Northwest Alaska over the period 1981-2020. While the modeling approach has limitations, the results point to significant increases in freshwater and DOC exports to the lagoon over the past four decades. The model simulation reveals significant increases in surface, subsurface (suprapermafrost), and total freshwater exports. Significant increases are also noted in surface and subsurface DOC production and export, influenced by warming soils and associated active-layer thickening. The largest changes in subsurface components are noted in September, which has experienced a ∼50% increase in DOC export emanating from suprapermafrost flow. Direct coastal suprapermafrost freshwater and DOC exports in late summer more than doubled between the first and last five years of the simulation period, with a large anomaly in September 2019 representing a more than fourfold increase over September direct coastal export during the early 1980s. These trends highlight the need for dedicated measurement programs that will enable improved understanding of climate change impacts on coastal zone processes in this data sparse region of Northwest Alaska.

Hydrological Processes, 2007

Comparisons between snow water equivalent (SWE) and river discharge estimates are important in ev... more Comparisons between snow water equivalent (SWE) and river discharge estimates are important in evaluating the SWE fields and to our understanding of linkages in the freshwater cycle. In this study we compared SWE drawn from land surface models and remote sensing observations with measured river discharge (Q) across 179 arctic river basins. Over the period 1988-2000, basin-averaged SWE prior to snowmelt explains a relatively small (yet statistically significant) fraction of interannual variability in spring (April-June) Q, as assessed using the coefficient of determination (R 2). Over all river basins, mean R 2 s vary from 0.20 to 0.28, with the best agreement noted for SWE drawn from simulations of the Pan-Arctic Water Balance Model (PWBM) that are forced with data from the National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP-NCAR) Reanalysis. Variability and magnitude in SWE derived from Special Sensor Microwave Imager (SSM/I) data are considerably lower than the variability and magnitude in SWE drawn from the land surface models, and generally poor agreement is noted between SSM/I SWE and spring Q. We find that the SWE vs. Q comparisons are no better when alternate temporal integrations-using an estimate of the timing in basin thaw-are used to define pre-melt SWE and spring Q. Thus, a majority of the variability in spring discharge must arise from factors other than basin snowpack water storage. This study suggests that SWE estimated from remote sensing observations or general circulation models (GCMs) can be evaluated effectively using monthly discharge data or SWE from a hydrological model. The relatively small fraction of Q variability explained by basin SWE warrants further investigation using daily discharge observations to more accurately define the snowmelt contribution to river runoff.

The pan-Arctic water cycle plays a central role in regulating Earth's climate and its role is inc... more The pan-Arctic water cycle plays a central role in regulating Earth's climate and its role is increasing with mounting evidence that it is today experiencing an unprecedented degree of change. To better understand these alterations it is important to explore potential signals of global climate change and to assess their feedbacks to regional hydrological systems and the global climate, and to their impacts upon humans. There is evidence of significant changes in the hydrological regime across the pan-Arctic, however, their causes could be due to climate change, direct human impacts or both. It is necessary to separate the natural change signal from the human impacts. We analyzed variability of the major water balance components across large pan-Arctic watersheds with a special focus on the river discharge regime. New naturalized river discharge time series were used to evaluate climate and human related changes in flow. The results of long-term trend analysis of hydrological and climatic characteristics across the pan- Arctic supports the conclusion that intensification of hydrological cycle is taking place and, more recently, this acceleration is increasing.

A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is describ... more A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described along with comparisons to observed data across the pan-Arctic drainage basin for the period 1980--2001. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The Pan-Arctic Water Balance Model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw/freeze model (TFM) driven by air temperature, modeled soil moisture content, and physiographic data. P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12 cm at 27 sites in Alaska, with many of the differences within the variability (1 sigma ) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400 mm year-1, with highest runoffs found across northeastern Canada, southern Alaska, and Norway. Lower simulated runoff is noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer/fall) runoff to the 10 Arctic sea basins (r = 0.84). Model water budgets are most sensitive to changes in precipitation and air temperature, while less affect is noted when other model parameters are altered. Increasing daily precipitation by 25 % amplifies annual runoff by 50 to 80 % for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model results in runoffs which are 7 to 27 % lower than the control run. The spatial and temporal variability of freshwater export along continental margins is also explored. This flux represents a merging of simulated discharge and observed data. The results of model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities---particularly climate time series---to better estimate terrestrial Arctic hyrological budgets.

Agu Fall Meeting Abstracts, Dec 1, 2006

Recent documented changes in polar, land-surface hydrology are consistent with assessments which ... more Recent documented changes in polar, land-surface hydrology are consistent with assessments which suggest that a major consequence of global warming will involve an intensification of the water cycle. Understanding the complex linkages and feedbacks among components of the arctic water cycle requires a synthesis of data such as river discharge, precipitation, air temperature, and landscape characteristics. An ability to predict future alterations is crucial given the potential for significant warming of the arctic atmosphere. In this study we employ traditional time series analysis methods as well as nonparametric statistics to uncover evidence of intensification across the pan-Arctic drainage basin. Analysis of data from both downstream sites and river subbasins are performed to provide a more complete picture of the spatial variability of extreme hydrological events. Linkages between these events and atmospheric forcings are examined using a flood-prediction methodology which incorporates seasonal precipitation, intensity of spring melt, and large-scale atmospheric patterns. For example, we seek to understand how recent increases in surface air temperature have impacted spring snow melt and resulting land-surface runoff, as well as the extent to which changes in seasonal precipitation have played a role. A comprehensive collection of spatially harmonious, arctic environmental data (ArcticRIMS) is leveraged to provide the fields which inform the prediction methodology and allow us to better understand the recent discharge changes. Limitations in our ability to understand and anticipate future discharge anomalies are also explored.

Several estimates of pan-Arctic freshwater flux to the ocean are made using observed river discha... more Several estimates of pan-Arctic freshwater flux to the ocean are made using observed river discharge data, modeled results, and a composite of the two. For observed data we report on an updated version of the R-ArcticNet river discharge database. This database now contains over 5000 gauges from Alaska, Canada, Scandinavia, and Russia. Modeled results use the Permafrost Water Balance Model (P/WBM) to characterize runoff, and other key hydrological variables, throughout the pan-Arctic region. The composite runoff field uses a hybrid of the observed data and modeled results to provide a "best guess" river discharge estimate. All estimates are carried out using the 25 km resolution digital river network based on the NSIDC Northern Hemisphere EASE grid. This river network contains over 3089 drainage basins within 18 Sea Basins throughout the pan-Arctic drainage system. An intercomparison of the different methods of estimating discharge to the ocean provides us with a range in expected outcomes which will yield those regions with increased uncertainty in discharge. The resultant database will be of use to Arctic Ocean modelers and those interested in the flux of freshwater continental shelves in the Arctic Seas.

Agu Fall Meeting Abstracts, Dec 1, 2002

In order to accommodate the growing need for timely estimates of the Arctic terrestrial hydrologi... more In order to accommodate the growing need for timely estimates of the Arctic terrestrial hydrological cycle we present the Rapid, Integrated Hydrological Monitoring System (ArcticRIMS). This system couples EOS-era satellites, numerical weather prediction (NWP) models and near real time observations of river discharge data with an atmosphere-land water budgeting scheme to compile operational fields (at 1-3 month time lags) of key hydrological cycle variables. The present research focuses on the land surface runoff and river discharge component of ArcticRIMS. A dual approach to the problem of estimating these values is taken through real time monitoring of river discharge and via near real time modeling of the water balance driven by modified NWP products. The land surface water budget model is a daily model which contains a simple snowmelt routine, a two layer soil component for root zone and deep soil, and active layer thaw based on a degree day approach. Fields of daily precipitation and air temperature, modified from NCEP re-analysis products, are used to drive the model from 1980 to the present. Local runoff surfaces and other spatial fields are estimated over the entire pan-Arctic domain. The runoff is then routed downstream to the monitoring gauges and to the Arctic Ocean and is compared to the observed river discharge record. Time lags of 1-2 months between the last date simulated and the present day are determined by lags in the availability of the NCEP data. The observational ArcticRIMS sites (the observed river discharge gauges) obtained in real time currently number 57 stations (16 in Russia, 10 in Canada, 19 in USA, and 12 in Norway). In total they cover a drainage area of 13.2 million km2, which is equivalent to 63% of total non-ice covered land area of the pan-Arctic or 79% of total Arctic Ocean drainage (not including Hudson Bay drainage and Greenland). The data for these gauges are supplied as provisional data, which means that normal adjustments to the data by the respective national agencies has not been implemented. Data is collected daily from the USGS and Environment Canada and weekly from Russia. This effort builds upon an existing pan-Arctic river discharge database, R-ArcticNET available over the Internet (http://www.R-ArcticNET.sr.unh.edu/) or on CD via the National Snow and Ice Data Center, Boulder, CO, USA. Future research will focus on an enhanced ArcticRIMS (E-RIMS) framework which will integrate Arctic Ocean-based data streams in cooperation with the Polar Science Center at the University of Washington.