PUBLICATIONS Journal of Advances in Modeling Earth Systems REVIEW ARTICLE Modeling modern glacier response to climate changes along 10.1002/2015MS000482 the Andes Cordillera: A multiscale review Key Points: Alfonso Fernandez 1,2,3 and Bryan G. Mark1,2 Models allow process understanding and supplement existing data 1Department of Geography, The Ohio State University, Columbus, Ohio, USA, 2Byrd Polar and Climate Research Center, on Andean glacier changes The Ohio State University, Columbus, Ohio, USA, 3Department of Geography, Universidad de Concepcion, Concepcion, Variety of approaches are identified, but their application does not seem Chile to follow spatial pattern Deficit of continental scale studies precludes global to local linkages Abstract Here we review the literature preferentially concerned with modern glacier-climate modeling of glacier change trends along the Andes. We find a diverse range of modeling approaches, from empirical/statistical models to rela- tively complex energy balance procedures. We analyzed these models at three different spatial scales. First, Correspondence to: we review global approaches that have included the Andes. Second, we depict and analyze modeling exer- A. Fernandez, [email protected] cises aimed at studying Andean glaciers as a whole. Our revision shows only two studies dealing with gla- cier modeling at this continental scale. We contend that this regional approach is increasingly necessary Citation: because it allows for connecting the ‘‘average-out’’ tendency of global studies to local observations or mod- Fernandez, A., and B. G. Mark (2016), els, in order to comprehend scales of variability and heterogeneity. Third, we revise small-scale modeling, Modeling modern glacier response to finding that the overwhelming number of studies have targeted glaciers in Patagonia. We also find that climate changes along the Andes Cordillera: A multiscale review, J. Adv. most studies use temperature-index models and that energy balance models are still not widely utilized. Model. Earth Syst., 8, 467–495, However, there is no clear spatial pattern of model complexity. We conclude with a discussion of both the doi:10.1002/2015MS000482. limitations of certain approaches, as for example the use of short calibration periods for long-term model- ing, and also the opportunities for improved understanding afforded by new methods and techniques, Received 20 MAY 2015 such as climatic downscaling. We also propose ways to future developments, in which observations and Accepted 17 JAN 2016 models can be combined to improve current understanding of volumetric glacier changes and their climate Accepted article online 21 JAN 2016 Published online 23 FEB 2016 causes. 1. Introduction Glaciers result from climatic and topographic conditions that define a dynamic equilibrium between accu- mulation and ablation. Thus, the volume of any given glacier depends on the amount of snow that nour- ishes the accumulation zone, the rate of mass loss due to melting, and the characteristics of the underlying lithology that partially controls the ice flow [Cuffey and Paterson, 2010]. In this context, a detailed under- standing of glaciers as indicators of climate changes requires employing a variety of techniques to account for such multifaceted controls, for instance snowpits and stakes to monitor accumulation and ablation rates [Rivera et al., 2005], remote sensing to map changes on glaciers’ shape [Poveda and Pineda, 2009], and numerical models to simulate the behavior of glaciers according to a range of past and future climatic sce- narios [Roe and O’Neal, 2009]. Currently available observations of glacier changes show generalized shrinkage that is linked to a global trend of temperature increase [Ohmura, 2011; Marzeion et al., 2014]. However, this global increase in tem- perature is not positively correlated to glacier volume loss everywhere, which underscores the importance of regional and local factors that may modify the impact of changes detected in the majority of observa- tions. A good example is the positive mass balance that some Norwegian glaciers showed between 1980 VC 2016. The Authors. and 2000, which led to frontal advance [Chinn et al., 2005; Nesje et al., 2008]. Those changes are thought This is an open access article under the terms of the Creative Commons to have resulted from increased precipitation as a consequence of strengthened westerly flow, as well as Attribution-NonCommercial-NoDerivs the onset of a period of lower temperatures [Chinn et al., 2005]. Such apparently anomalous glacier behavior License, which permits use and testifies to the complex relationship between glaciers and climate, whereby global-scale forcing like trends distribution in any medium, provided in temperature and precipitation may be modified by local factors impacting glacier mass balance and the original work is properly cited, the response time to climatic perturbations. This attests to the need for compiling databases that account for use is non-commercial and no modifications or adaptations are local factors, such as topoclimatic conditions, in order to understand the processes leading to glaciers’ volu- made. metric fluctuations, including the temporal scale in which changes in climatic elements (e.g., temperature FERNANDEZ AND MARK MODELING ANDEAN GLACIERS 467 Journal of Advances in Modeling Earth Systems 10.1002/2015MS000482 and precipitation) occur [Kuhn et al., 1985; Roe, 2011; Pedersen and Egholm, 2013]. Thus, compilation efforts such as the Global Terrestrial Network of Glaciers (GTN-G), established during the 1990s, are invaluable sour- ces of observations of glacier state, including mass balance, outlines, and thickness, among others [Zemp et al., 2009]. Such organized structures for compiling and delivering data (see Haeberli [1998] for a detailed historical description of how these efforts have been organized since 1894) allow scholars to rapidly and accurately evaluate the quality of available records and the need for new ones [e.g., Braithwaite, 2002; Pfeffer et al., 2014]. On the contrary, no similar compilation currently exists to comparatively assess the approaches and results of glacier modeling studies, excluding those in Antarctica and Greenland. In fact, the glacier community has only recently begun to perform intercomparison studies of modeling (GlacierMIP, see http://www.climate- cryosphere.org/activities/targeted/glaciermip). This suggests that we need more progress within the scien- tific community to produce a unified source of glacier modeling approaches. In order to contribute to a better assessment of glacier modeling approaches, here we review studies deal- ing with modeling of glacier mass balance and related indicators such as the equilibrium line altitude (ELA) in the Andes. Outside Antarctica, the Andes concentrate the largest glacier surface area in the Southern Hemisphere [Pfeffer et al., 2014]. Yet among all major glacierized regions, the modern (twentieth century) Andean cryosphere is one of the least comprehensively studied, featuring a low density of observations Zemp et al. [2008], compared to the longer tradition of paleoglacier research in the region, which has con- tributed to understanding the complexity of glacier-climate interactions at millennial scales [Vuille et al., 2008a; Rodbell et al., 2009]. 1.1. The Observational Record in the Andes and the Role of Modeling The modeling of glacier surface mass balance and volumetric changes, as consequence of fluctuations in cli- matic elements, has been facilitated by recent enhances in computing power, process-based studies, and availability of data at the global scale. The latest modeling studies have expanded earlier simple sensitivity analyses to simulations of glacier volumetric changes, assessment of climate drivers, and the consequences of glacier change [e.g., Marzeion et al., 2012]. But glacier models have also been employed to fill gaps in mass balance observations [Vuille et al., 2008b], understand topoclimatic controls responsible for observed trends in glacier parameters such as the equilibrium line altitude (ELA) [Cook et al., 2003] and, in the case of inverse modeling, to reconstruct temperature trends from glacier length records [Leclercq and Oerlemans, 2012]. The best source of information about glacier mass balance is measurements taken in the field. Also known as the glaciological method, this technique utilizes a series of stakes and snowpits to record ice/snow sur- face lowering, or ablation, and surface thickening, or accumulation, at annual or biannual scales [Cogley et al., 2011]. Further measurement accuracy is achieved when snow density and ice displacement are recorded (more details on the method can be found in Benn and Evans [2010]). Therefore, direct mass bal- ance monitoring programs are key to understanding the relationship between glacier mass balance and cli- mate changes [Braithwaite, 2002]. In the Andes, mass balance programs are scarce, and most of them provide short time series. Figure 1a demonstrates that, of approximately 27,500 glaciers represented in the Randolph Glacier Inventory (RGI) [Pfeffer et al., 2014], only one glacier has been continuously measured for more than 30 years (Echaurren Norte, Chile) while most of the other field programs cover less than 10 years. Over the last decade, newly established programs display a wide regional distribution (Figure 1a), improving the potential to sample glaciers located in different Andean climates. Nevertheless, the main issue is the lack of long-term