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Arctic Climate and Water Change: Information Relevance for Assessment and Adaptation Arvid Bring Department of Physical Geography and Quaternary Geology Stockholm University Stockholm 2013 c Arvid Bring ISSN: 1653-7211 ISBN: 978-91-7447-638-5 Cover: Bank of the Ob River at Salekhard, Russia. Layout: Summary: Arvid Bring based on a LATEX template by Rickard Petterson. Papers II and IV: Arvid Bring using LATEX. Paper I: Wiley Blackwell. Paper III: Springer. Paper V: AGU. Reprinted with permission. Printed by Universitetsservice US-AB, 2013 Doctoral dissertation 2013 Arvid Bring Department of Physical Geography and Quaternary Geology Stockholm University Abstract. The Arctic is subject to growing economic and political interest. Meanwhile, its water and climate systems are in rapid transformation. Relevant and accessible information about water and climate is therefore vital to detect, understand and adapt to the changes. This thesis investigates hydrological monitoring systems, climate model data, and our understanding of hydro-climatic change, for adaptation to water system changes in the Arctic. Results indicate a lack of harmonized water chemistry data, which may impede e↵orts to understand transport and origin of key waterborne constituents. Further development of monitoring cannot rely only on a reconciliation of observations and projections on where climate change will be the most severe, as they diverge in this regard. Climate model simulations of drainage basin temperature and precipitation have improved between two recent model generations, but large inaccuracies remain for precipitation projections. Late 20th-century discharge changes in major Arctic rivers generally show excess of water relative to precipitation changes. This indicates a possible contribution of stored water from permafrost or groundwater to sea level rise. The river contribution to the increasing Arctic Ocean freshwater inflow matches that of glaciers, which underlines the importance of considering all sources when assessing change. To provide adequate information for research and policy, Arctic hydrological and hydrochemical monitoring needs to be extended, better integrated and made more accessible. This especially applies to hydrochemistry monitoring, where a more complete set of monitored basins is motivated, including a general extension for the large unmonitored areas close to the Arctic Ocean. Improvements in climate model parameterizations are needed, in particular for precipitation projections. Finally, further water-focused data and modeling e↵orts are required to resolve the source of excess discharge in Arctic rivers. Keywords: Arctic, hydrology, monitoring, climate change, water management, general circulation models, adaptation. Svensk sammanfattning Arktis är för närvarande föremål för ett tilltagande intresse, både från ekonomiskt och politiskt håll. Samtidigt genomgår den arktiska regionen snabba och genomgripande förändringar i klimat och miljö. Dessa förändringar kommer inte bara att påverka Arktis, utan också ge upphov till långtgående globala e↵ekter. Vatten har en central roll i många av de mest uppmärksammade förändringar som nu observeras. Som exempel kan nämnas den kraftigt minskande utbredningen av sommaristäcket i Norra ishavet, och den tinande permafrosten i delar av Sibirien och Alaska. I och med vattnets sammanlänkande roll är det av stor vikt med relevant och tillgänglig information om förändringar i vatten och klimat. I denna avhandling undersöks hydrologiska övervakningssystem och data från globala klimatmodeller för Arktis, med avseende på vår förståelse för de förändringar som nu pågår och vår förmåga att anpassa samhället till dem. Resultaten visar bland annat på en brist av sammanställda och jämförbara vattenkemiska data för de floder som rinner ut i Norra ishavet. Detta kan försvåra försök att förstå hur ämnen transporteras i Arktis, och vad deras ursprung är. För att prioritera en utveckling av vattenövervakningen behövs robust information om vilka områden som kommer att beröras mest av förändringar i klimatet. I det här avseendet pekar dock observationer och modeller i olika riktningar, vilket gör att det inte tillförlitligt går att identifiera särskilt utsatta områden dit övervakningen bör prioriteras. Globala klimatmodellers projektioner av temperatur och nederbörd har förbättrats mellan två successiva generationer av modeller, men stora avvikelser finns fortfarande i deras simuleringar av nederbörd. Även om nederbördsprojektionerna skulle bli mer noggranna finns det andra svårigheter i att översätta nederbörden till prognoser för förändringar i vattenflödet. Under senaste delen av 1900-talet har ett antal stora arktiska floder nämligen uppvisat ett överskott på vatten i jämförelse med de förändringar som observerats i nederbörd. Detta indikerar ett möjligt bidrag från grundvattenförråd eller permafrost till floderna, och en förbättrad förståelse behövs för dessa komplexa samband i vattensystemet. Under de senaste decennierna har sötvatteninflödet till Norra ishavet ökat, både från floder, glaciärer och den grönländska inlandsisen. Ökningen av flödet från floderna är av samma storleksordning som ökningen i glaciäravsmältning, vilket understryker vikten av att ta hänsyn till alla källor när man söker en fullständig förståelse av förändringarna. För att bidra med bättre information för forskning och policybeslut behöver övervakningen av vattensystemet i Arktis förstärkas. En bättre integration mellan olika system och databaser skulle bidra till ökad tillgänglighet och överblick. Detta gäller i synnerhet för vattenkemi, där stora områden nära Norra ishavet idag är helt oövervakade. För att få en mer representativ bild av förändringarna behöver sammansättningen av de avrinningsområden som övervakas också bli mer heltäckande. Vad gäller klimatmodeller krävs en fortsatt förbättring, i synnerhet av hur nederbörd simuleras. Det är också motiverat med ytterligare ansträngningar som fokuserar på vattendata och modellering av vattensystemet, för att förstå ursprunget till överskottet på vatten i arktiska floder. Arctic Climate and Water Change: Information Relevance for Assessment and Adaptation Arvid Bring This doctoral dissertation consists of this summary and the following papers, which are referred to by their roman numbers in the text. I Bring, A. & Destouni, G., 2009. Hydrological and hydrochemical observation status in the pan-Arctic drainage basin. Polar Research 28, 327–338. II Bring, A. & Destouni, G., 2013. Hydro-climatic changes and their monitoring in the Arctic: Observation-model comparisons and prioritization options for monitoring development. Accepted for publication in Journal of Hydrology. III Bring, A. & Destouni, G., 2011. Relevance of hydro-climatic change projection and monitoring for assessment of water cycle changes in the Arctic. Ambio 40, 361–369. IV Bring, A. & Destouni, G., Manuscript. Evaluation of IPCC AR4 climate model performance over 14 major Arctic watersheds. Appendix to Paper III. V Dyurgerov, M.B., Bring, A. & Destouni, G., 2010. Integrated assessment of changes in freshwater inflow to the Arctic Ocean. Journal of Geophysical Research 115, D12116. The co-authorship of the papers reflects the collaborative nature of the underlying research. For Papers I–IV, I was responsible for all analysis and had the main responsibility for designing the study and writing the paper. For Paper V, I had the main responsibility for the design, analysis and writing of the river component of the paper, and contributed to the interpretation and writing of the remainder of the paper. Other related peer-reviewed publications by the author: Karlsson, J.M., Bring, A., Peterson, G.D., Gordon, L.J. & Destouni, G., 2011. Opportunities and limitations to detect climate-related regime shifts in inland Arctic ecosystems through eco-hydrological monitoring. Environmental Research Letters 6, 014015. Rennermalm, Å.K., Bring, A. & Mote, T.L., 2012. Spatial and scale-dependent controls on North American pan-Arctic minimum river discharge. Geographical Analysis 44, 202–218. Jarsjö, J., Asokan, S.M., Prieto, C., Bring, A. & Destouni, G., 2012. Hydrological responses to climate change conditioned by historic alterations of land-use and water-use. Hydrology and Earth System Sciences 16, 1335–1347. Abbreviations AHC Arctic Hydrological Cycle AR4 Fourth Assessment Report AR5 Fifth Assessment Report CRU Climate Research Unit GCM General Circulation Model GRIS Greenland Ice Sheet IPCC Intergovernmental Panel on Climate Change MG&IC Mountain Glaciers and Ice Caps PADB Pan-Arctic Drainage Basin SAON Sustaining Arctic Observation Networks SRES Special Report on Emission Scenarios TAR Third Assessment Report UNECE United Nations Economic Commission for Europe Introduction A multitude of global-scale changes, including climate change, are currently transforming the Earth system. This is clearly evident in the Arctic, where temperatures over the last half-century have increased at a rate 50% higher than the Northern hemisphere average (McBean et al., 2005), and where future climate change is expected to be most pronounced (Kattsov et al., 2005). Coupled to the changes in the physical environment, the Arctic is also increasingly becoming a focal point of economic and geopolitical interest. These transformations present a considerable challenge. The critical role of the Arctic in the global climate system implies that Arctic changes will have far-reaching consequences for, and feedbacks to, the Earth system (McGuire et al., 2006). To understand the changes, and to the degree possible, adapt to them, is therefore of large importance to the global community. Water is a key integrating, propagating and regulating factor, and therefore plays a central role in the changing Arctic and the wider global climate system. It is a shared component in the most important and recognized Arctic indications of global change. These indications include rapidly diminishing extent of sea ice (Comiso et al., 2008; Stroeve et al., 2012a), increased mass loss from glaciers (Kaser et al., 2006; Gardner et al., 2011), increasing river flows (Peterson et al., 2002; 2006; McClelland et al., 2006; Shiklomanov & Lammers, 2009; Overeem & Syvitski, 2010) and increasing groundwater contribution to those flows (Smith et al., 2007; Lyon and Destouni, 2010), permafrost degradation (Hinzman et al., 2005; White et al., 2007; Brutsaert and Hiyama, 2012), ecosystem regime shifts (Smol et al., 2005; Karlsson et al., 2011), and shorter extent of snow cover season (Brown et al., 2010; Callaghan et al., 2011). In order to observe, assess and plan for adaptation to the changes to the Arctic Hydrological Cycle (AHC) over the Pan-Arctic Drainage Basin (PADB), it is vital that observation systems and models can provide adequate information of relevance to scientists, environmental managers and policymakers. The importance of data and observation systems in particular has recently been emphasized at intergovernmental summits (GEO, 2010) and recognized as one of five ”grand challenges” for Earth system science and science policy over the next decade (Reid et al., 2010; ICSU, 2010). Assessing previous and ongoing change in the water system requires observations of river discharge, as well as sediment and water chemistry data to estimate the waterborne mass fluxes of important global cycle constituents such as carbon, nitrogen and phosphorus. The collection of such hydrological and hydrochemical data is normally conducted through continuous monitoring programs by various government agencies. However, in many countries, hydrological observation systems have been in decline during recent decades. The extent of monitoring generally peaked around 1980, after the significant increases in monitoring e↵orts during the International Hydrological Decade 1965–1974. Since then, budget constraints and failure to maintain existing systems have resulted in a general decline of monitoring, which has been reported in several studies (Brown, 2002; Fekete & Vörösmarty, 2002; Maurer, 2003; Hannerz, 2008; FAO, 2009). The global trend of declining discharge monitoring is also evident in the Arctic (Lammers et al., 2001; Shiklomanov et al., 2002; Hinzman et al., 2005; Walsh et al., 2005, Arctic-HYDRA consortium, 2010). However, the particular situation in the Arctic has received relatively much attention in the scientific community, partly due to the rapid changes and the general scientific interest in the region. Also, the accessibility to discharge data has been improved more in the Arctic than in many other parts of the world, due to concentrated international e↵orts and collaborations, in particular at the University of New Hampshire. In contrast to discharge monitoring, a clear picture of the status of water chemistry data for that discharge has been lacking. Previous e↵orts have tried to establish a status for particular parameters (e.g., Holmes et al., 2000; Holmes et al., 2002; Raymond et al., 2007), and estimated the quality of existing data (Zhulidov et al., 2000; Holmes et al., 2001; Zhulidov et al., 2003). Although particular data sets have been made accessible for parts of the PADB (e.g., Holmes et al., 2000; Holmes & Peterson, 2002), and in at least one case for the wider PADB (McClelland et al., 2008; data at http://www.arcticgreatrivers.org), no international repository and data host exists for all accessible Arctic water chemistry data. Neither has any initiative yet been launched to develop a common set of indicators, such as the Millenium Development Goals-related UN Federated Water Monitoring System (FWMS) and its Key Water Indicators Portal (KWIP). The decline in station numbers and the lack of integrated hydrological and hydrochemical information, together with the grand challenge of improving Earth observation systems, constitute an imperative 1 ARVID BRING to develop Arctic hydrological monitoring networks, and to ensure their relevance under conditions of climate change. To formulate a rational strategy to improve monitoring in the Arctic, one then either has to rely on some degree of certainty in the distribution of future changes, or acknowledge that other potential bases for prioritization may exist and try to harmonize them. Despite its importance for robust improvement of monitoring networks, this question has so far received little attention. To address this problem, and also the direct adaptation-central issue of projecting present and past hydro-climatic changes to the future, relevant and robust climate data are required. The primary information basis for global climate projections is the Intergovernmental Panel on Climate Change (IPCC) ensemble of general circulation models (GCMs), which form the basis for the IPCC assessment reports. The two most recent reports are the Third Assessment Report (TAR; 2001) and the Fourth Assessment Report (AR4; 2007). The fifth report (AR5) is scheduled for release in 2013. The performance of GCMs in the Arctic has been the subject of intensive discussion. Assessments of TAR and AR4 model performance in the Arctic have shown improvements between successive generations of models, but also indicated that significant shortcomings remain in simulating observed climate parameters (Christensen et al., 2007). There have been several assessments of simulations of sea ice processes (Zhang & Walsh, 2006; Overland & Wang, 2007; Stroeve et al., 2007; Eisenman et al., 2007, Holland et al., 2010, Stroeve et al., 2012b), the surface radiation budget (Sorteberg et al., 2007, Boé et al., 2010) and surface temperature (Lui et al., 2008) over the Arctic Ocean, while there are fewer studies explicitly examining GCM performance related to hydrological components of the Arctic hydrological cycle over drainage basin scales. Kattsov et al. (2007) analysed the output of the AR4 model ensemble for four major basins in the PADB, and Roesch (2006) evaluated AR4 simulations of snow cover. Holland et al. (2007) investigated ten AR4 GCMs to estimate change in freshwater budget of the Arctic Ocean, including pan-Arctic scale runo↵, and Rawlins et al. (2010) used the same GCMs combined with reanalysis and observational data in a pan-Arctic analysis of Arctic hydrological cycle intensification. However, no basin-wise investigation and comparison of GCM results between the TAR and AR4 has been performed for a larger set of basins within the PADB, and no benchmark of AR4 GCM performance over such a set of basins exists for comparison with the upcoming AR5 set of models. 2 Climate data Water information Water flow data Glacier change data Paper I Paper II Paper III Paper IV Paper V Figure 1. Integrative links between water information and other components of climate and water change understanding. Connections investigated in this thesis are shown with arrows, which are colored according to the appended papers where the analyses are carried out. Potential subsequent assessment and adaptation applications that derive from water information, and apply to the understanding of changes across other terrestrial, atmospheric and marine systems, are illustrated with dashed arrows. Assessment of AHC change, including projection of hydro-climatic system changes to the future, is central to adaptation. It has also been a question of considerable scientific interest in the recent decades. Component studies and integrative system assessments (e.g., Vörösmarty et al., 2001; Serreze et al., 2006; Slater et al., 2007; Rawlins et al., 2009; 2010) have greatly improved understanding of the AHC, but several inconsistencies, understanding gaps and open questions remain (Arctic-HYDRA consortium, 2010). The importance of the water system in Arctic and global change implies that the hydrological drainage basin is a fundamental and relevant unit of scale, both for water management, adaptation and basic research (Pahl-Wostl, 2007; UNECE, 2009). This thesis links and analyses several components required to provide reliable water information for change adaptation and assessment (Figure 1), consistently at drainage basin scales. This basin-scale water information and understanding then also has important ensuing applications in understanding coupled ARCTIC CLIMATE AND WATER CHANGE changes across other terrestrial, atmospheric and marine systems (e.g., Karlsson et al., 2011), illustrated in Figure 1 by dashed arrows from the water information box. The thesis is centered on the following two overarching research questions: 1. Are current surface water system observations representative, accessible and relevant for assessing changes to the Arctic environment and connections to global systems? What critical gaps and key limitations exist, and is there a basis to robustly prioritize how to address these limitations? 2. Are climate model results and our understanding of water budget changes in major Arctic basins and the wider pan-Arctic ocean drainage system sufficient for adaptation of society to climate and other global change? Methods and data The hydrological drainage basin has been the fundamental basis when investigating the research questions of this thesis. The drainage basin constitutes a physically consistent boundary for closing the flow balance of water and the mass balances of constituents transported by water, which makes it a relevant scale for addressing both scientific and management-related problems. The study area of the thesis is centered on the 14 largest Arctic watersheds in the PADB, covering an area of at least 200,000 km2 each and with a combined drainage of 13.8 million km2 (see map of study area in Figure 2). These basins are common to the analysis in Papers II–IV. In Paper I, the entire PADB is included. For paper V, the analysis focuses on the central Arctic Ocean drainage, a subset of the PADB, and includes 17 basins, of which 11 are in common with the 14 major basins and the remainder are smaller ones. Paper V also separately incorporates mountain glaciers and ice caps (MG&IC) that contribute water directly to the Arctic Ocean, as well as the Greenland ice sheet (GRIS). Figure 3 shows the characteristic temperature and precipitation conditions, and recent observed changes for those parameters, in the 14 major basins. Basin-scale climate data in the form of observations and GCM projections were analyzed for the 14 major basins in Papers II–IV. Papers III and V contain synthesis and analysis of discharge data for the basins included in the respective studies. Paper I also includes a characterization of basin properties based 180° 120°W Ma Ne 120°E Ko Yu Le In Ol Ch Ya Ye Kh Ob Pe 60°W SD 60°E 0° Watersheds included Glaciers (Paper V) Papers II-V MG&IC Papers II-IV Paper V GRIS Remaing PADB Figure 2. Map indicating studied areas of the PADB. Basins common to Papers II–V are shown in red, and additional studied basins in blue (Papers II–IV) and green (Paper V). Paper I includes all areas within the PADB, demarcated by the combined area of all colored basins and the dark gray area. The glaciers (crosses) and the GRIS (light blue) are also included in Paper V. Basin names are abbreviated as Ne: Nelson, Ch: Churchill, Ma: Mackenzie, Ko: Kolyma, Kh: Khatanga, Ol: Olenek, Le: Lena, Ya: Yana, In: Indigirka, Ye: Yenisey, SD: Severnaya Dvina, Pe: Pechora, and Yu: Yukon. Lambert azimuthal equal-area projection; approximate scale 1:150 000 000. on a range of data sources, and Paper V includes analysis of glacier change data. Climate observation data were in the form of global gridded datasets of temperature and precipitation at half-degree resolution. For paper III, the Climate Reseach Unit (CRU) TS 2.1 dataset (Mitchell & Jones, 2005) was used, and for Papers II and IV both the CRU TS 3.10 (Harris et al., in review) and the Willmott & Matsuura 3.1 (method first described in Willmott & Matsuura, 1995; data available at http://climate.geog.udel.edu/ climate) datasets were used. For climate projections in Papers II–IV, IPCC TAR (Paper III only) and AR4 global climate model 30-year means from the IPCC data distribution center (http://www.ipcc-data.org) were used. 3 ARVID BRING Summary of papers Paper I Bring, A. & Destouni, G., 2009. Hydrological and hydrochemical observation status in the panArctic drainage basin. Polar Research 28, 327– 338. Figure 3. Climate characteristics of the 14 major Arctic basins. The top panel shows average annual temperature; the bottom one shows annual average precipitation, for the periods 1961–1990 and 1991–2009. Data from CRU (Harris et al., in review) and Willmott & Matsuura (http://climate.geog.udel.edu/⇠climate). Paper I presents a synthesis of all accessible discharge and water chemistry data for the PADB, with lists of data sources and specifics of each data set. The extent of accessible data is further presented in map form, illustrating the maximum length of time series and latest data year for the PADB. Characteristics of monitored and unmonitored areas are summarized for, and compared between, North America, Europe and Asia. The general picture derived from the analysis in Paper I shows a considerable di↵erence between accessible water chemistry monitoring and discharge monitoring, both in terms of total extent and characteristics of the data. In general, discharge data are available for a wide range of di↵erent basins, from small catchments of a few square kilometers in size to the major river basins in the PADB. In contrast, accessible water chemistry monitoring is limited to a much smaller set of stations, which cover a significantly smaller area and also a much less complete range of basin sizes. Figure 4 shows a summary of the accessible length of time series for discharge, sediment and carbon monitored areas. The average length of time series for the various parameters, and the corresponding share of the PADB that is monitored, is further summarized in Table 1. Table 1. Average length of time series and monitored share of total area for discharge, carbon and sediment data in the PADB. Parameter For Papers III and V, discharge data from the RArcticNET (Lammers et al., 2001) and ArcticRIMS (http://rims.unh.edu) databases were used. Paper V also includes discharge data from the Water Survey of Canada HYDAT database (Environment Canada, 2004). Glacier data in Paper V consist of data on annual direct mass balance observations carried out for MG&IC (Dyurgerov & Meier, 2005; Glazovsky & Macheret, 2006; Fluctuations of Glaciers (FoG), 2008), and of several recent modeling studies for the GRIS (Rignot et al., 2008; Hanna et al., 2008, 2009; Box et al., 2006; Mernild et al., 2009). 4 Discharge Sediment Carbon Average timeseries length (years) 29 7 5 Area monitored 73% 63% 51% Results from Paper I also show a marked di↵erence in characteristics of monitored and unmonitored areas (Figure 5). For example, monitored areas are distinctly dominated by the taiga eco-region, while unmonitored areas are generally strongly defined by tundra type vegetation. This tendency is particularly evident for discharge monitoring in all regions, and for all monitoring parameters in Asia. The most balanced monitoring, in terms of eco-region proportions, ARCTIC CLIMATE AND WATER CHANGE a c b 1 - 10 21 - 40 11 - 20 41 - 70 71 - partly monitored unmonitored or not accessible Figure 4. Overview of the maximum length of accessible data series (years) for the pan-Arctic monitoring of (a) water discharge, (b) sediment, and (c) carbon. Cells containing stations with drainage areas smaller than five cells are indicated as partly monitored. Figure 5. Distribution of terrestrial eco-regions in monitored (M) and unmonitored (U) areas, by monitoring parameter and continent. is for carbon monitoring in Europe, while the most unbalanced monitoring is found in North America and Asia. Such regional monitoring di↵erences complicate the interpretation of observation data di↵erences between di↵erent parts of the PADB. Paper II Bring, A. & Destouni, G., 2013. Hydro-climatic changes and their monitoring in the Arctic: Observation-model comparisons and prioritization options for monitoring development. Accepted for publication in Journal of Hydrology. In this paper we analyze the prioritization basis for planning of monitoring development under conditions of climate change. We formulate two alternate final stages of possible climate change in the next half-century by selecting the five warmest or wettest models from the most severe IPCC Special Report on Emission Scenarios (SRES) scenario (A2), and the five coldest or driest models from the least severe scenario (B1). For these two cases, we analyze the relative distribution of climate change severity across the 14 largest Arctic drainage basins, and compare this distribution with hitherto observed changes. 5 ARVID BRING Temperature change mm!yr Precipitation change 100 Warm!wet A2 50 Cool!dry B1 0 Nelson Churchill Mackenzie Kolyma Khatanga Olenek Lena Yana Indigirka Yenisey Ob S.Dvina Pechora Yukon Observations Nelson Churchill Mackenzie Kolyma Khatanga Olenek Lena Yana Indigirka Yenisey Ob S.Dvina Pechora Yukon K 6 5 4 3 2 1 Figure 6. Changes to temperature (left) and precipitation (right) from 1961–1990 to 1991–2009 for observations and to 2040–2069 for GCM projections across 14 major Arctic basins. Error bars indicate one standard deviation of di↵erent GCM results from the model ensemble mean for each basin. Results from Paper II indicate that observations and projections of climate change severity across the pan-Arctic are not in agreement, when comparing the relative order of basins (rank correlations of basin orders are close to zero, or negative; Table 2). Both directional (in the case of precipitation) and temporal shifts are required to bring observed changes in line with projections (Figure 6). Some continued directional changes are naturally expected, however, as observations and projections concern di↵erent time periods. In Paper II, we also analyze how the present distribution of hydrological monitoring network density relates to observed and projected climate change. Results from this analysis show that current network density is more adapted to prioritize monitoring capacity for the so far observed precipitation changes than the observed temperature changes, or the projected future changes in either temperature or precipitation. Table 2. Spearman’s correlation of GCM-projected climate change ranking with observed climate change ranking. Scenario Temperature Cool B1 Hot A2 ⇢ 0.01 -0.03 Scenario Precipitation Dry B1 Wet A2 ⇢ -0.10 -0.23 Paper III Bring, A. & Destouni, G., 2011. Relevance of hydro-climatic change projection and monitoring for assessment of water cycle changes in the Arctic. Ambio 40, 361–369. 6 Paper III first presents a comparison of IPCC TAR and AR4 GCM projections for precipitation and temperature in the 14 largest Arctic basins. Areaweighted basin average projections were summarized and compared with observed changes. Paper III results also include a comparison of precipitationdischarge changes for the studied basins, as well as an analysis of the evolution of the discharge-monitoring network in relation to projected climate changes. Figure 7 illustrates GCM projections and CRU observations for the 14 major basins. Temperature projections seem compatible with observed changes during the late 20th and early 21st century, both for the TAR and AR4, while precipitation projections indicate an increase that is hitherto not evident in observations. The absolute GCM results compare well with observations for temperature, but the models considerably overestimate precipitation. A further result of Paper III is that the responses in discharge to changes in precipitation vary widely for the major basins in the PADB (Figure 8). The majority of basins exhibit excess flow changes in relation to precipitation changes; that is, discharge has so far increased more (or decreased less) than precipitation within each basin. These disagreements between precipitation and discharge changes are in some cases large; therefore, an essential question for forthcoming investigation is: where does the extra water come from? Finally, Paper III presents an analysis of the development of the discharge monitoring system in relation to projected climate change. A comparison of monitoring station density between the period of peak extent of monitoring and a recent period shows that the weight of discharge monitoring systems has shifted towards the basins where the ex- 2 -2 4 -4 ⇥⇤ Êχ 6 ⇥ Ê ⇤ Ï 800 800 700 700 600 ⇥ 600 Ê Precipitation mm⇤yr⇥ Precipitation HmmêyrL Temperature °C⇥ Temperature H°CL ARCTIC CLIMATE AND WATER CHANGE ARCTIC CLIMATE AND WATER CHANGE ‡ 500 500 -6 400 400 8 -8 1961 1991 1961- 19911990 2002 1990 2002 2010 20102039 2039 ⇥ Ê ‡ ‡ ⇤ Ï 1961 19611990 1990 ⇤ Ï 1991 19912002 2002 TAR models TAR AR4models models AR4 models Observations Observations 2010 20102039 2039 Runoff change mm yr 1 ⇥ Figure . .Changes temperature (left) (left)and andprecipitation precipitation (right) from 1961–1990 to 1991–2002 for Figure77 Changes to to temperature (right) from 1961–1990 to 1991–2002 for obobservations and to 2010–2039 for GCM projections across the 14 major Arctic basins. Error bars indicate servations and to 2010–2039 for GCM projections across 14 major Arctic basins. Error bars indicate one one standard deviation of di↵erent GCM results the model ensemble standard deviation of di↵erent GCM results fromfrom the model ensemble mean.mean for each basin. Ol Pe 50 SD Yu In Ya 0 Ma R 2 ⇥0.46 1:1 line 50 Le Ko Ne Ye Ob Ch 40 20 0 20 Precipitation change mm yr 1 ⇥ Figure 8. Changes from 1961–1990 to 1991–2002 in observed 8annual average corresponding Figure . Changes fromprecipitation 1961–1990 toand 1991–2002 in obruno↵ for 13 major Arctic basins. The dashed line indiserved annual average precipitation and corresponding catesfor a 1:1 precipitation and dashed runo↵. The runo↵ 13 change major in Arctic basins. The line solid indiline is a linear best-fit regression of actual changes in all cates a 1:1 change in precipitation and runo↵. The solid basins except the Ch (Churchill) watershed, which is afline is a linear best-fit regression of actual changes in all fected by major artificial water diversions. Abbreviations basins except the Ch (Churchill) watershed, which is afof basin names are the same as in Figure 2. fected by major artificial water diversions. Abbreviations of basin names are the same as in Figure 6. pectedIV changes to temperature and precipitation are Paper the smallest. If one aims to follow up and capture the Bring, & Destouni, G. change Manuscript. Evaluation actualA. e↵ects of climate on the AHC, this is of IPCC AR4 climate model performance over not a desirable development. 14 major Arctic watersheds. Appendix to Paper III. Paper Paper IVIV is an appendix to and extension of the analysis made in Paper III. Here, we perform an exBring, A. & Destouni, G. Manuscript. Evaluation plicitoferror of IPCC IPCCand AR4performance climate modelanalysis performance over AR4 GCMs over the 14 largest Arctic watersheds. 14 major Arctic watersheds. Appendix to Paper Mean III. Error (MAE), Mean Bias Error (MBE) Absolute and a dimensionless index of model performance (dr ; Paper et IVal., is an appendix to and extension of the Willmott 2012) are evaluated against observaanalysis made in Paper III.precipitation Here, we perform anreferextions of temperature and for the plicitperiod error and performanceWe analysis of IPCC AR4 ence of 1961–1990. also analyze the corGCMs over the 14ranking largest of Arctic watersheds. Mean relation between model performance for Absolute Error Mean simulations. Bias Error (MBE) temperature and (MAE), precipitation andResults a dimensionless of model performance (dr ; is from thisindex analysis indicate that there Willmott et al., 2012) are evaluated against observaa large spread in error and relative performance betions of and precipitation refertween thetemperature models forming the basis for for the the AR4 (Figence period of 1961–1990. We also analyze the corure 9). For some basins, and for the pan-Arctic in relation between ranking of model performance for general, an above-average model performance in temtemperature and precipitation simulations. perature simulation does not correlate particularly Results from this analysis indicate that there is strongly with performance in simulating precipitaa large spread in error and relative performance betion (MAE and drforming rank correlations Table tween the models the basis for negative; the AR4 (Fig3). implies choosing a ”best” model is in difureThis 9). For somethat basins, and for the pan-Arctic ficult if one wants to have consistently good perforgeneral, an above-average model performance in temmance in simulating over the Arctic. perature simulation both does parameters not correlate particularly strongly with performance in simulating precipitation (MAE and dr rank correlations negative; Table 3). This implies that choosing a ”best” model is difficult if one wants to have consistently good performance in simulating both parameters over the Arctic. Table . Spearman rank correlation coefficient ⇢ bePaper3V tween the pan-Arctic temperature and precipitation Dyurgerov, M., Bring, A. & Destouni, G., 2010. values ofIntegrated MAE, MBE and dr . of changes in freshwater assessment inflow to the Arctic Ocean. Journal of Geophys⇢MAE ⇢MBE ⇢d r ical Research 115, D12116. -0.29 0.37 -0.29 7 7 Cumulative deviation from 1961-1992 mean Hkm3 L ARVID BRING 2500 2000 1500 MG&IC GRIS Rivers 1000 500 0 -500 1960 1970 1980 1990 2000 year Figure 9. Mean Absolute Error (MAE; top panel), Mean Bias Error (MBE; middle panel) and model performance index (dr ; bottom panel) for 14 GCMs across the PADB. In this paper we perform an integrated analysis of freshwater inflow to the Arctic Ocean, and separately assess the contribution of rivers and glaciers to this inflow over the period 1961–2006. We specifically investigate the periods 1961–1991 and 1992– 2006, where the break coincides with a shift in magnitude of glacier mass loss (Lemke et al., 2007). Results from this assessment are generally in line with other studies that indicate an increase in freshwater inflow to the Arctic Ocean. However, our analysis also highlights that the magnitude of the increase in inflow from the 1961–1991 to the 1992– 2006 period is similar for the river contributions and the glacier contributions (Figure 10). This underlines the importance of also accounting for river discharge Table 3. Spearman rank correlation coefficient ⇢ between the pan-Arctic temperature and precipitation values of MAE, MBE and dr . ⇢ 8 MAE -0.29 MBE 0.37 dr -0.29 Figure 10. Above: Total meltwater runo↵ and total river runo↵ into the Arctic Ocean. Below: Cumulative deviations in annual freshwater flows from MG&IC, GRIS, and rivers relative to average values for 1961–1992. changes that are not related to glacial melt water changes as a potentially contributing source for sealevel rise and the freshening of the Arctic Ocean waters. Discussion Robust scientific understanding of climate and water systems is a prerequisite for informed policy decisions in assessing and adapting to the large-scale environmental changes currently transforming the Arctic and other regions. This in turn requires access to relevant information on changes to flows of water and waterborne constituents. This thesis has aimed to contribute to a more complete picture of several important components required for AHC change monitoring and adaptation planning. This has been done by investigating two overarching research questions pertaining to the adequacy and information relevance of water monitoring systems, and of climate model and hydro-climatic change understanding, for change assessment and adaptation. ARCTIC CLIMATE AND WATER CHANGE Regarding the first research question on the relevance of hydro-climatic data, the results from Papers I–III point to some important shortcomings, but also to certain opportunities and results of relevance for future research and monitoring improvement e↵orts. The synthesis of monitoring data in Paper I indicates a lack of water chemistry data, compared with the more extensively accessible discharge data. The range of basin sizes, sampling frequency, and length of time series for water chemistry data overall compare negatively with corresponding attributes for discharge data. Together, these shortcomings imply that the full potential of translating the existing discharge data to also calculate mass fluxes of important constituents is hindered. Furthermore, the di↵erence in characteristics of monitored areas found in Paper I indicate that existing monitoring data are not representative of the PADB as a whole. This constitutes a limitation to the value and reliability of the modeling that must be used for interpreting and projecting changes in the AHC in unmonitored areas. From the perspective of an integrative pan-Arctic analysis, the limited accessibility to water chemistry data is remarkable, given the high profile of and international commitment to research into Arctic environmental changes. While discharge data have been compiled into pan-Arctic datasets (most importantly, R-ArcticNET (Lammers et al., 2001) and the ARDB (http://ardb.bafg.de)) and also made accessible in near-real time through the ArcticRIMS project (http://rims.unh.edu), water chemistry data remain fragmented, although the recent continuation of the PARTNERS project as the Arctic Great Rivers Observatory (http://www.arcticgreatrivers.org) constitutes an important improvement. Several factors may explain these results. Firstly, although the research community emphasizes a system perspective on the pan-Arctic domain, no international body has formal responsibility for an integrated monitoring system. Instead, monitoring efforts must build upon undertakings by separate government agencies in at least the eight di↵erent nations of the Arctic Council, and for hydrology also Mongolia and Kazakhstan, which constitute parts of the PADB. Even if all national hydrometeorological agencies were committed to promoting a coordinated Arctic observation e↵ort, domestic budget limitations and conflicting information goals may still interfere with ambitions being met. Secondly, public agencies that apply costrecovery principles to their environmental data may be reluctant to undermine this rule by freely sharing their data with international repositories. Thirdly, in a previously isolated Arctic that is now rapidly becoming more accessible to activities such as natural resource exploration, shipping and tourism, water data may be viewed as increasingly sensitive information from both political and economic perspectives. Occasionally, pressure from international organizations on member states to disclose water chemistry information viewed as sensitive has rebounded and instead caused delays in the progress of sharing other water data (Vladimir Ryabinin, personal communication). All the same, member states of the Arctic Council have in the Tromsø Declaration recently committed to facilitate data access, as a legacy of the International Polar Year during 2007–2009. The organizational form for this commitment is the Sustaining Arctic Observation Networks (SAON) process, which is currently in its implementation phase. The European Commission has also expressed support for SAON (European Commission, 2008; 2012). It remains to be seen to which extent the SAON process can contribute to increased accessibility to monitored water chemistry data in the PADB, but it is now established as a platform for policy dialogue on Arctic monitoring issues, for example through recurring Arctic Observation Summits. Whether through institutional pan-Arctic initiatives or through other channels at various levels and scales, any remediation of the present-day monitoring system shortcomings identified in Paper I requires a strategy to improve observation networks under conditions of climate change. This issue is investigated in Paper II, which centers on the prioritization of hydro-climatic change monitoring across the Arctic. Improvements of monitoring and observing capacity in the Arctic, and elsewhere, must incorporate climate change projections in order to take the nonstationary nature of the environment into account (Milly et al., 2008). For the case of the Arctic, however, results from Paper II indicate that the relative distribution of climate change severity, as simulated by GCM projections, does not agree with the distribution of actually observed changes across the major Arctic basins, which places obstacles for a robust prioritization strategy based on reconciliation of observations and projections for an assessment of which basins that will be most a↵ected by climate change. An alternative strategy to the aforementioned one could be to prioritize basins where the disagreement between observations and projections is particularly large, as such a strategy would yield important information on the hydro-climatic system functioning and changes regardless of whether there is actual convergence of observations and projections in the end or not. Alternatively, one could argue 9 ARVID BRING for prioritizing monitoring of basins with greater observed changes so far, as these are actual experienced changes where increased e↵orts at understanding and adaptation can be intrinsically motivated. Such a prioritization is to some degree evident in the present distribution of monitoring, specifically with respect to precipitation changes, although this situation is most likely not by design but by coincidence. The divergent rationales and prioritization bases that can be argued for based on the results of Paper II underline the importance of attempting to formulate win-win or no-regret solutions in any strengthening of hydro-climatic monitoring e↵orts under climate change conditions (UNECE, 2009), incorporating also other relevant parameters, in addition to the temperature and precipitation data studied here, and explicitly identifying set information goals to be achieved. The results presented here can inform observation assessments connected to strategic Arctic initiatives and programs, such as SAON and the upcoming Third International Conference on Arctic Research Planning (ICARP III) in 2015, where continued evaluation of monitoring e↵orts will be a priority. The second research question about climate model and water budget change understanding is explored in Papers III–V. Paper III highlights improvements in basin-scale climate model simulation of temperature and precipitation, but also identifies some key remaining limitations, which are further examined in Paper IV. Also in Paper III, some challenges to water system understanding through the precipitation-discharge change relation are presented, and Paper V extends the discharge assessment of these changes to a full Arctic Ocean freshwater inflow synthesis, including a glacier-independent river change component in addition to the change contributions from melting glaciers, ice caps, and the Greenland ice sheet. Considerable improvements have been made between the two successive generations of model ensemble runs that underlie the most recent IPCC Assessment Reports, the TAR and the AR4. Examples include improved parameterization of land surface schemes and snowpack, as well as the inclusion of canopy processes in most models (Randall et al., 2007). However, important uncertainties remain in the representation of cryospheric feedbacks, which explain part of the range of model responses at mid and high latitudes (Randall et al., 2007). These improvements are evident in that Paper III results indicate a lower spread among the ensemble members for the AR4 models, and in the case of precipitation, a marked improvement in the agreement with absolute observed values. However, despite the improvement in precision, accuracy remains insuffi10 cient for precipitation projections, which, even if they were correct, are still difficult to translate to subsequent changes in the water cycle without further and finer resolved hydrological modeling. It should be noted that observations also are associated with uncertainty, for example gauge undercatch of primarily solid precipitation due to wind (e.g., Yang et al., 2005; Tian et al., 2007), which may explain part of the remaining di↵erence between observations and the improved AR4 results. Based on a global precipitation bias adjustment by Adam & Lettenmaier (2003), the annual e↵ect seems generally to be about 10–25% over the latitudes of the whole PADB, but may amount to higher values in the most northern parts of some basins. The large span in model performance, evident from the explicit error and performance analysis of AR4 models in Paper IV, also indicates that large uncertainties and shortcomings remain for reliable simulations of hydro-climatic parameters on basin scales. The analysis furthermore underlines that models may yield good output results on these scales for the wrong reasons. For example, the panArctic bias error of both temperature and precipitation for the GIER model is close to zero, which would place it at the top of a basin-scale simulation performance ranking. At the same time, the absolute error and the performance index for the same model are among the worst of the ensemble, implying large deviations from observations at individual grid points, even though the deviations happen to almost cancel out across the PADB. Overall, the evaluation in Paper IV can serve as a benchmark for evaluating the performance change against the subsequent generation of climate models, which underlies the forthcoming IPCC AR5 report. Notwithstanding further improvement in GCM simulations, full understanding of hydro-climatic change, and transfer of this understanding back into model development, requires basin-scale understanding of precipitation-discharge change patterns. In the Arctic, certain counterintuitive hydro-climatic changes have caused intense investigation and discussion in the scientific community. The fact that most of the rivers analyzed in Paper III can be termed so-called ”excess” rivers (that is, the increase in discharge has been greater than the increase in precipitation) is consistent with findings by Milliman et al. (2008) for a related set of Arctic rivers. This, and other studies (e.g., Dyurgerov & Carter, 2004; McClelland et al., 2006; Smith et al., 2007; Lyon et al., 2009; Brutsaert & Hiyama, 2012) indicate that both specific climatic and subsurface processes pertaining to the Arctic, such as permafrost degradation, as well as other anthropogenic changes, and ARCTIC CLIMATE AND WATER CHANGE general atmospheric patterns such as increased moisture transport from outside the PADB, are responsible for the range in discharge patterns, but the relative importance of the di↵erent contributing factors is not definitely established. Undercatch of snow, in combination with increases in winter precipitation (Bulygina et al., 2009; Rawlins et al., 2009), is also a potential contributing factor. The wide spread in discharge responses to precipitation changes indicate a need for further concerted modeling and field investigation e↵orts aimed at increasing the process knowledge of hydrological regimes particular to the Arctic domain, including simulations of evaportranspiration and permafrost processes, considering also e↵ects of scale (Rennermalm et al., 2012). Improved parameterization, in particular with precipitation focus, is also critical to the development of GCMs, and continued water-balance assessments and closure experiments in Arctic catchments are motivated. The extended water budget changes of the entire PADB and its Arctic Ocean drainage including glacier contributions, studied in Paper V, also has implications for global climate system changes, and sea level rise influencing both the Arctic region and the wider Earth system. The fact that increases in river freshwater contribution are of the same order of magnitude as increases from MG&IC and GRIS underlines the importance of accurately understanding the reasons for river flow changes, and the potentially contributing components of frozen and liquid water storage changes in major Arctic basins (e.g., Muskett & Romanovsky, 2009). Such changes could have large implications on the pan-Arctic hydro-climatic system, but also on scales beyond the Arctic through contribution to sea level rise or thermohaline circulation functioning. The review of literature and analysis in this thesis confirms a picture of advances in our knowledge about the Arctic environment and its functioning during recent decades. International efforts at making discharge information accessible, e.g. through the ArcticRIMS project, have contributed to a more timely access to river flow data for a number of important basins and sub-basins. Similarly, the PARTNERS monitoring campaign (http://ecosystems.mbl.edu/partners), now semipermanently established as the Arctic Great Rivers Observatory (http://www.arcticgreatrivers.org) has provided a multi-season dataset of concentrations of a range of important water chemistry constituents for six major Arctic rivers. Climate model advances have improved in precision and alignment with observations in the Arctic, and numerous studies have contributed to a fuller understanding of hydro-climatic changes. These developments, which coincide with a time of increasing focus on the Arctic as an arena for important changes, imply improvements also in our ability to understand the AHC and the associated PADB. Nevertheless, considerable challenges for understanding and managing the rapidly changing Arctic water system still remain. A critical priority must be to continue improving the accessibility to water data, in particular for water chemistry, for the PADB. Observations must be made at the right places, and improvements should be based on clearly stated information goals, striving in their achievement for winwin and no-regret approaches that do not rely on a single most likely scenario of future hydro-climatic conditions. Improved coverage of unmonitored areas in the northern rims of the PADB is also motivated, particularly as these areas are expected to become increasingly accessible and also subject to exploration with a warming climate (Andreeva, 1998). In addition, improved monitoring here may yield information on the unclear role of these areas in the total flux of water chemistry constituents to the ocean, as near-ocean catchments have in other regions been shown to contribute an unproportionately large share of coastal pollution in relation to the drainage basin as a whole (Destouni et al., 2008). Conclusions This thesis has investigated the adequacy of water flow and water chemistry observations and climate model projections in the PADB, with the purpose of establishing a quantitative picture of the status of these observations and model results for understanding and management of water cycle changes in the Arctic. The main findings of the thesis can be summarized in the following conclusions: • There is a lack of long-term and accessible water chemistry data for large regions of the PADB, and discharge data is also limited for considerable areas. The data that are accessible do not constitute a representative sample of the PADB environment. • There is a need to extend monitoring and to make data more accessible, in particular for the relatively unmonitored but large areas on the northern rim of the Eurasian continent. • Establishing regional priorities for hydrological monitoring systems with regard to the specific issue of climate changes in the Arctic can currently not be achieved based solely on a reconciliation of observations and projections. When 11 ARVID BRING taking di↵erent data and system/change perspectives as starting points, di↵erent conclusions about what constitutes rational priorities, and related strategies, arise. • The precision in predicting precipitation and temperature change on drainage basin scales has improved between successive generations of the IPCC model ensemble. However, that improvement is relatively unimportant next to the large inaccuracy that still remains in precipitation projections. Individual model performance varies greatly, and models can be right for the wrong reasons when relatively large errors cancel out on basin scales for some models. Further investigation and benchmarking of model performance in the GCMs underlying the IPCC AR5 could indicate whether certain hydro-climatological model shortcomings in the Arctic have been addressed. • Hitherto observed changes in precipitation do not translate into similar changes in discharge even over the large scales of the studied basins. The discrepancy between precipitation and discharge changes, and the fact that this discrepancy principally is expressed as excess in discharge compared to available precipitation, indicate that a component of the variation in discharge may be due to changes in permafrost or groundwater storage. • Even though the increase in river inflow to the Arctic Ocean during 1993–2006 is small in relative terms compared to the average flow for 1961–1992, in absolute terms it is of the same order of magnitude as the meltwater increase from glaciers, which underlines the importance of also accounting for river discharge changes as a potentially contributing source for sea-level rise and Arctic Ocean freshening. Financial support The research in this thesis has been funded through grants from the Swedish research council Formas (project number 2007-1263) and the Swedish Research Council (VR; project number 2007-8393), and has been linked to the Bert Bolin Centre for Climate Research (in turn supported by VR and Formas through a Linneaus grant) and the strategic research project EkoKlim at Stockholm University. I gratefully acknowledge travel support from the Graduate Research School of the Bolin Centre, C F Liljevalchs foundation, Knut and Alice Wallenbergs foundation, 12 L & E Kinanders foundation, John Söderbergs foundation, the government of the Yamalo-Nenets Autonomous Okrug, and the Arctic Research Council of the U.S. Acknowledgements I am very grateful for the invaluable support I have had from my main advisor, Georgia Destouni. Without your insight, enthusiasm and guidance, Gia, this thesis would not have come about. You have always had time for extensive comments and feedback on my work, and I appreciate all the discussions we’ve had, on the specific research issues at hand but particularly also on the larger picture, strategic science matters and science-policy interactions. I have also much appreciated collaboration and discussions with my co-supervisors Jerker Jarsjö, Steve Lyon, Garry Peterson, and with my co-authors Johanna Mård Karlsson, Line Gordon and Mark Dyurgerov. Sadly Mark passed away too soon, before we had an opportunity to continue our collaboration. Åsa Rennermalm I would like to thank for stimulating discussions at my first international scientific meeting in Washington, DC, and the collaboration that followed. A special thanks to Johan Kuylenstierna for introducing me to the world of international environmental negotiations. I would also particularly like to thank Fredrik Hannerz, Christoffer Carstens and Klas Persson for many enjoyable lunches with inspiration on water-related topics. I’ve always enjoyed going to work at the Department of Physical Geography & Quaternary Geology. Thanks to everyone for your contribution to a stimulating work environment. A particular thanks to the technical and administrative sta↵, who are invaluable in keeping things together, and to the whole community of PhD students, past and present, for the support and discussions. Unfortunately I have been able to join all too few pub nights! I also want to acknowledge the interdisciplinary group for environmental science PhD students. The atmosphere at our gatherings really stimulated an academic discussion, and remains one of my best memories from the doctoral studies at Stockholm University. I am very glad for the continued network that we have established, and for the perspectives on my research you have given. The Association of Polar Early Career Scientists (APECS) also played an important role during my PhD studies. Stina and Sussie got me involved with APECS and have continued to be good friends and colleagues. Thanks to you and all other wonderful ARCTIC CLIMATE AND WATER CHANGE APECS people I have had the opportunity to get to know and work with. To my sisters and brother, Nina, Torun, Hedda and Johan, and all other friends, thank you for the important support and encouragement. I would also like to thank my parents Lena and Axel. Your erudition remains a paragon to me, and I can only hope that age shall endow me too with some sagacity. Since I started work on this thesis, I have had two wonderful sons, Valter and Tage. The two years I spent at home with them I would not trade for any career outcome in the world. But I have been away, too, particularly at conferences around the world. At these times, my wife Eva has had much support from my parents-in-law Helena and Weine, for which I (and Eva) are very grateful. And to Eva, with whom I’ve shared ten wonderful years and hope to share many more, thank you, above all—for all the days, of love, light and joy. References Adam, J.C. & Lettenmaier, D.P., 2003. Adjustment of global gridded precipitation for systematic bias. Journal of Geophysical Research 108, 1–14. Andreeva, E.N., 1998. The Russian Arctic coastal zone management problems: Past lessons and new realities. Ocean & Coastal Management 41, 237–256. Arctic–HYDRA consortium, 2010. The Arctic hydrological cycle monitoring, modelling and assessment programme: Science and implementation plan. ISBN 978–9979–9975–0–4. Boé, J., Hall, A. & Qu, X., 2009. Current GCMs’ unrealistic negative feedback in the Arctic. Journal of Climate 22, 4682–4695. Box, J. E., Bromwich, D. H., Veenhuis, B. A., Bai, L.-S., Stroeve, J. C., Rogers, J. 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