Toward an imminent extinction of Colombian glaciers?

Antoine Rabatel1, Jorge Luis Ceballos2, Natan Micheletti3, Ekkehard Jordan4, Michael

Braitmeier4, Javier Gonzales4, Nico Mölg5, Michael Zemp5, Christian Huggel5

(1) Univ. Grenoble Alpes, CNRS, IRD, Institut des Géosciences de l’Environnement (IGE), Grenoble, France

(2) IDEAM, Bogota, Colombia

(3) Institute of Earth Surface Dynamics, University of Lausanne, Switzerland

(4) Heinrich-Heine-Universität, Düsseldorf, Germany

(5) Institute Department of Geography, University of Zurich, Switzerland

Suggested journal: Geografiska Annaler: Series A, Physical Geography

Corresponding author:

Dr. Antoine Rabatel

Institut des Géosciences de l’Environnement

54 rue Molière,

38400 Saint Martin d’Hères, France

E-mail: antoine.rabatel@univ-grenoble-alpes.fr

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ABSTRACT. (< 250 words)

This study documents the current state of the glacier coverage in the Colombian Andes, the

glacier shrinkage over the 20th century and discuss indications of their disappearance in the

coming decades. Satellite images have been used to update the glacier inventory of Colombia

reflecting an overall glacier extent of about 41 km2 in 2016 distributed in four glacierized

mountain ranges. Combining these data with older inventories, we show that the current

extent is 40% less than in the mid-1990s, and 65% less than in the mid-20th century, and

almost 90% less during LIA maximum extents.

Focusing on the Nevado Santa Isabel in the Parque Nacional de los Nevados, aerial

photographs from 1987 and 2005 combined with a terrestrial Lidar survey show that the mass

loss of the former ice cap, which is nowadays parceled into several small glaciers, was about -

2.5 m w.e. yr-1 during the last three decades. Radar measurements performed on one of the

remnant glaciers, La Conejeras glacier, show that the ice thickness is limited (about 20 m in

average) and that with such a mass loss rate, the glacier should disappear in the coming years.

At the scale of the Colombian Andes, due to their imbalance with current climate conditions,

their limited altitudinal extent and their relatively low uppermost altitude (i.e. < 5400 m a.s.l.),

most of the Colombian glaciers will most likely disappear in the coming decades and only the

largest ones located on the highest summits will probably persist until the mid-21 st century

although very reduced.

KEY WORDS. Glaciers, surface area changes, tropical Andes, Colombia

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1. INTRODUCTION

Glaciers in Colombia are more than ice on mountains: they indeed are key components of the

landscapes lived by the Colombian society (Ceballos et al., 2012). For peasants, indigenous,

mountain climbers, artists, scientists and city dwellers, glaciers in Colombia fulfill different

functions within their territories and are part of their daily practices in different ways: from

sentinels of global climate changes, local water resources, local-to-regional sources of hazards

as glaciers in the Cordillera Central of Colombia are frequently located on active volcanoes

(Thouret, 1990; Huggel et al., 2007). The increasing ice loss of Colombian glaciers since the

late 1970s, (Ceballos et al., 2006; Morris et al., 2006; Poveda and Pineda, 2009), like

everywhere in the tropical Andes (Rabatel et al., 2013a), has strengthened the necessity of a

glacier monitoring combining repeated inventories at the national scale and in-situ

measurements on reference benchmark glaciers located in the two mostly glacierized

mountain ranges of Colombia (e.g., Ceballos et al., 2012; Mölg et al., 2017). Such a

monitoring strategy is in line with the international strategy for glacier monitoring defined by

the Global Terrestrial Network for Glaciers (GTN-G, gtn-g.org). Nowadays, in-situ

measurements are conducted by the Instituto de Hidrología, Meteorología y Estudios

Ambientales (IDEAM). These activities are part of different international programs: the joint

international laboratory GREAT-ICE (Sicart et al., 2015) financed by the French Institut de

Recherche pour le Développement (IRD), the World Glacier Monitoring Service (wgms.ch),

and the CATCOS project (Capacity Building and Twinning for Climate Observing Systems)

financed by the Swiss Agency for Development and Cooperation (SDC).

The aims of this paper are: 1) to present the current state of glaciers in Colombia, with the

results of a new glacier inventory from 2016; 2) to draw a multi-decadal perspective of

changes in glacier surface-area using repeated glacier inventories since the mid-20 th Century

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and LIA maximum extents; and 3) to estimate the future evolution of glaciers in Colombia on

the basis of the up-to-date inventory and current surface-area and mass loss rates.

2. STUDY AREA

Glaciers in Colombia are located in four main areas (Fig. 1): from North to South: Sierra

Nevada de Santa Marta (about 10°50’ N; 73°40’ W), Sierra Nevada de El Coquy (about

6°25’ N; 72°20’ W), Cordillera Central: cadena Ruiz-Santa Isabel-Tolima (about 4°45’ N;

75°20’ W), and Cordillera Central: Nevado Huila (about 2°55’ N; 76°00’ W). In the two

northernmost areas, small slope glaciers can be found, whereas in the two southernmost areas,

small ice caps lying on more or less active volcanoes (e.g., Nevado del Ruiz, Nevado del

Huila) are the dominant glacier type.

Figure 1: Glacierized areas in Colombia. The spectral bands combination used

for the Landsat8 images involves the bands #6 (middle infra-red: MIR), #5

(short-wave infra-red: SWIR) and #3 (green).

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Table 1 lists the main characteristics of the glacierized areas of Colombia, with the glacier

cover in 2016, the maximum ice thickness estimate -where it exists- together with the year of

the estimate. One can note that the averaged maximum elevations of the glacierized summits

range typically between 5,100 and 5,400 m a.s.l. which is rather low in comparison with the

other glacierized areas in the tropical Andes of Equador, Peru and Bolivia where the highest

elevations frequently exceed 6,000 m a.s.l. (Rabatel et al., 2013a).

Glacierized areaGlacier

cover (km²) in 2016

Max. elevation(m a.s.l.)

Mean elevation(m a.s.l.)

Min. elevation(m a.s.l.)

Max thickness (m) and year of estimate

S.N. de Santa Marta 7.2 5342 5167 5005 //

S.N. de El Coquy 15.5 5054 4912 4750 //

V.N. del Ruiz 8.8 5330 5126 4706 190, 2000

V.N. de Santa Isabel 1 4852 4804 4745 120, 2000

V.N. de Tolima 0.7 5192 5103 4946 70, 1998

V.N. del Huila 7.8 5306 5019 4710

Table 1: Colombian glacierized areas with the most up-to-date glacier cover surface-area

and topographic features of the glaciers. Note that the elevation data are averaged

considering all the glaciers in the different areas. S.N. = sierra nevada, V.N. = volcán

nevado.

From a climatological point of view, Colombia belongs to the inner tropics (Troll, 1941) with

almost unchanged humidity, homogeneous temperature and almost constant incident solar

radiation throughout the year. At the seasonal scale, the displacement of the inter-tropical

convergence zone (ITCZ) strongly controls the annual regime of precipitation which results to

be contrasted from one region to the other at the country scale (e.g., Poveda et al., 2005). The

central and western parts of Colombia (glacierized areas C and D on Fig. 1) experience a

bimodal precipitation regime with two periods of high precipitation (April-May and October-

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November) and two periods of less precipitation (December-February and June-August). On

the other hand, the Caribbean coast (glacierized area A on Fig. 1) and the Pacific coast of the

isthmus with Panama show a unimodal precipitation regime (May-October), resulting from

the northernmost position of the ITCZ. The eastern side the eastern Andes (glacierized area B

on Fig. 1) also experiments a single precipitation peak occurring during June-August which

results from deep convection of the moisture transported from the Amazon basin due to the

orographic barrier of the Andes.

The inter-annual variability of atmospheric conditions is dominated by the El Niño-Southern

Oscillation (ENSO). Although the climate characteristics of La Niña/El Niño events are not

uniform at the scale of a country, El Niño years (warm phase of ENSO) tend to be warmer

and drier, while La Niña years (cold phase of ENSO) are associated with colder and wetter

conditions in the mountains.

3. METHODS AND DATA

3.1. Quantification of glacier surface-area

Former studies have documented the glacier surface-area changes since their maximal extent

during the Little Ice Age (e.g., Florez, 1992; Ceballos et al., 2006; Poveda and Pineda, 2009;

Herrera and Ruiz, 2009). Note that the Little Ice Age maximal extent has not been dated in the

Colombia Andes as it was the case in the other countries of the tropical Andes (e.g., Rabatel

et al., 2005, 2008; Jomelli et al., 2009), but we can assume that it lasted between the mid-17th

and the early 18th centuries. The former studies on the extent of Colombian glaciers in the past

are based on the moraines (reflecting the Little Ice Age maximal extent), aerial photographs

from the late 1940s until the late 1970s early 1980s, and using Landsat TM and ETM Mid

1980’s until early 2000s. In the current study, an update of the glacial coverage in the

Colombian Andes has been realized using images from the following satellites: QuickBird

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(2007 for all the Colombian glacierized areas), ALOS (2008, 2009 for Sierra Nevada de El

Coquy), RapidEye (2010 for all the Colombian glacierized areas) and Landsat8 OLI (2016 for

all the Colombian glacierized areas, Fig. 1).

On the basis of Landsat8 images from late January-early February 2016, a detailed inventory

was performed and a database was generated according to the design of the GLIMS glacier

relational database. For an extensive description of the database content, the reader will refer

to the GLIMS website (http://www.glims.org/MapsAndDocs/db_design.html). The 2016

Landsat8 images provide the perfect conditions for a glacier inventory: no cloud cover on the

mountains, no snow cover outside the glaciers. These images have a spatial resolution of 30 m

in multispectral mode and 15 m in the panchromatic mode. Due to the small size of the

glaciers and their limited number, the delineation of the glaciers outline has been made

manually. This allows getting a better accuracy than automatic delineation methods which

generally fail at detecting snow and ice covers in the shadowed parts (Gardent et al., 2014).

Note that debris-covered glaciers are negligible in Colombia, either because the glaciers are

small ice caps, or remnants of ice caps, or slope glaciers; and in every cases, rock walls

overhanging the glaciers are limited or absent.

3.2. Quantification of glacier volume

Ice thickness measurements have been acquired on La Conejeras glacier (Nevado Santa

Isabel) using an ice penetrating radar (IPR) during field campaigns in January-February 2014.

Our IPR is a geophysical instrument specially designed by the Canadian company Blue

System Integration Ltd in collaboration with glaciologists to measure the thickness of glacier

ice (Mingo and Flowers, 2010). It comprises a pair of transmitting and receiving 5 MHz

antennas that allow continuous acquisition, and is georeferenced with a GPS receiver.

14 cross profiles and two longitudinal profiles have been acquired on this small glacier (0.19

km² in 2014, Fig. 2), which is a remnant of the Santa Isabel ice cap (Fig. 3). From the in-situ

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GPR continuous acquisitions, 200 measurements have been picked up (Fig. 2) where the

reflected signal was the clearer. This represents an average density of 1 pt / 100 m². Note that

these data have been integrated to the glacier thickness database (GLATHIDA 2.0, WGMS,

2016).

Figure 2: GPR measurements acquired in

Jan-Feb 2014 on La Conejeras glacier.

3.3. Quantification of surface elevation changes

Changes in glacier-surface elevation can be computed by the difference of digital elevation

models (DEMs) realized by topography (DGPS, LiDAR) or using aerial photographs or

satellite images. However, such accurate DEMs are not available for all the Colombian

glaciers. Nevado Santa Isabel is one of the exceptions as realized a photogrammetric

restitution of this summit on the basis of 1987 and 2005 aerial photographs (Fig. 3). All the

technical details about these restitutions can be found in Braitmeier (2003) and Gonzalez et al.

(20XX). Figures 3A and 3B show the orthophotos from 1987 and 2005 respectively. The

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orthophoto from 2005 shows the extent of the Santa Isabel ice cap in 1987, 2005 and 2016

(also overlaid on the orthophoto from 1987 in Fig. 3A)

Figure 3: A) Orthophoto of Nevado Santa Isabel with glacier extent in 1987 and 2016. B)

Orthophoto from 2005, with the outline of the ice cap in 1987 (in dark grey) and the outline of

the remnant glaciers in 2005 and 2016 (light blue and red respectively).

During the January-February 2014 field campaign for glacier thickness measurements on La

Conejeras glacier (as previously mentioned this glacier is a remnant of Santa Isabel ice cap,

see Fig. 3B), a complete topography of the glacier surface was realized using a terrestrial

LiDAR. An ultra-long-range RIEGL VZ-6000 device was used (Fig. 4A). This system emits a

near-infrared laser beam at 1064 nm ideal for glacial studies. Ten reflector targets with 5 cm

diameter were fixed on stakes or rocks around the glacier for georeferencing purposes. Their

position has been measured using differential GPS. Three distinct scan positions were set to

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achieve good coverage of the whole glacier and its surroundings. The LiDAR data were

processed using the software RiSCAN PRO. The main processing steps included a filtering of

points (e.g., due to atmospheric reflections caused by dust or moisture), a unification of the

point clouds from the different scan positions, and the georeferencing of the final grid using

the target reference points. Figure 4B provides an illustration of the final point cloud. The

resulting DEM has a homogeneous resolution of 0.5 m and was reprojected to MAGNA

Colombia Bogotá (EPSG 3116), the official georeference system of Colombia.

Figure 4: A) RIEGL VZ-6000 operating at

the front of La Conejeras glacier. B) Scanned

point cloud of La Conejeras glacier.

The changes in glacier surface elevation have been quantified by subtracting the different

DEMs. This was possible at the scale of the entire Santa Isabel ice cap for the period 1987-

2005, and for the La Conejeras glacier only for the periods 1987-2014 and 2005-1987 using

the 2014 LiDAR data.

From these surface elevation changes, the geodetic average annual mass balance has been

quantified considering the average surface area between the two considered dates, the time

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between the two DEM and an average ice density of 0.9900 kg m3 . For more details about the

geodetic method the reader may refer dedicated publications (e.g. Rabatel et al., 2006;

Cogley, 2009; Basantes Serrano et al., 2016).

3.4. In situ glacier surface mass balance data

Two glaciers in Colombia are monitored with in-situ measurements to quantify their surface

mass balance: La Conejeras glacier on the Nevado Santa Isabel, Ritacuba glacier in the Sierra

Nevada de El Coquy (Ceballos et al., 2012). Accumulation and ablation measurements are

performed at the monthly scale with the classical glaciological method (snow pits and ablation

stakes) since 2006 for La Conejeras and 2008 Ritacuba glacier. Recently, the entire monthly

surface mass balance data series of La Conejeras glacier has been reanalyzed by Mölg et al.

(2017). The reader will refer to this publication for more details on the monitoring network

and the results of this 10-yr monitoring program.

4. RESULTS

4.1. 2016 Colombian glaciers inventory

Table 2 gives an overview of the distribution of glaciers according to size classes for the 2016

inventory for the whole Colombian glaciers and considering the four main glacierized areas:

Sierra Nevada de Santa Marta, Sierra Nevada de El Coquy, Parque Nacional Los Nevados

(including los nevados del Ruiz, de Santa Isabel and de Tolima) and Nevado del Huila.

Glaciers of the Colombian Andes covered 41 km2 in early 2016 with 7.2 km² in the Sierra

Nevada de Santa Marta, 15.5 km² in the Sierra Nevada de El Coquy, 10.5 km² in the Parque

Nacional Los Nevados and 7.9 km² for the Nevado del Huila. The size of the glaciers ranged

from 0.01 km² (minimum size considered in the inventories) to 8.85 km² (ice cap covering the

Nevado del Ruiz in the Parque Nacional Los Nevados). At the scale of the Colombian Andes:

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mean glacier size was 0.48 km² (median = 0.18 km², indicating that the distribution is clearly

dissymmetric toward small-size glaciers); glaciers < 0.5 km² represented 76% of all glaciers

and 26% of the total glacierized area; one glacier is bigger than 5 km² and accounted for 22%

of the glacierized area. Glaciers > 1 km² accounted for 84%, 66%, 16% and 14% of the

glacierized area in the Parque Nacional Los Nevados, Sierra Nevada de El Coquy, Sierra

Nevada de Santa Marta and Nevado del Huila respectively.

Size class (km²) Colombia

Sta Marta

El Coquy

P.N. Los Nev. Huila

<0.1 Number 29 13 6 10Number (%) 34 46 24 59Area (km²) 1.65 0.74 0.37 0.54Area (%) 4 10 2 5

0.1-0.5 Number 36 11 11 6 8Number (%) 42 39 44 35 53Area (km²) 9.11 2.70 2.54 1.11 2.76Area (%) 22 38 16 11 35

0.5-1 Number 12 3 3 6Number (%) 14 11 12 40Area (km²) 8.88 2.61 2.28 4.00Area (%) 22 36 15 51

1-5 Number 7 1 5 1Number (%) 8 4 20 7Area (km²) 12.55 1.13 10.28 1.14Area (%) 31 16 66 14

> 5 Number 1 1Number (%) 1 6Area (km²) 8.85 8.85Area (%) 22 84

Total Number 85 28 25 17 15Area (km²) 41.0 7.2 15.5 10.5 7.9

Table 2: Summary statistics (number and area) on glaciers in Colombia for the 2016 inventory.

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Glacier minimum, maximum, and mean altitudes have been computed from the ASTER

GDEM V2. This global DEM has been realized from ASTER images dating from the period

2000-2010. The exact dating for each region is unknown but it can be considered that the

elevation provided by this DEM is representative of the 2000s. The mean altitude has been

computed from the area-altitude distribution. Indeed, such mean altitude can be considered as

a proxy of the balanced-budget equilibrium-line altitude corresponding to the glacier extent

(Rabatel et al., 2013b; Braithwaite, 2015). Considering the different glacierized regions, the

average of the mean altitude of each individual glacier are 5167 m a.s.l., 4912 m a.s.l., 4923 m

a.s.l. and 5019 m a.s.l. for Sierra Nevada de Santa Marta, Sierra Nevada de El Coquy, Parque

Nacional Los Nevados, and Nevado del Huila respectively.

The maximum altitude of the glacier is an interesting variable, because when compared to the

equilibrium-line altitude it allows computing the altitudinal extent of the accumulation zone,

and together with the glacier-area distribution the accumulation-area ratio. The highest

altitudes of glaciers’ top can be found in the Sierra Nevada de Santa Marta where they range

between 4970 and 5678 m a.s.l. On the Nevado del Huila, the altitude of glaciers’ top ranges

between 5160 and 5425 m a.s.l. In the two other glacierized areas, the uppermost elevations

are lower, ranging between 4784 and 5346 m a.s.l. for the Sierra Nevada de El Coquy and

between 4775 and 5315 m a.s.l. in the Parque Nacional Los Nevados.

In terms of altitudinal extent (difference between the minimum and maximum elevations of

the glacier), the Colombian glaciers span over limited ranges: 600 m on the Nevado del Huila,

340 m in the Sierra Nevada de Santa Marta, 300m in the Sierra Nevada de El Coquy and 200

m in the Parque Nacional Los Nevados.

4.2. Historical glacier surface area changes

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Table 3 presents the surface area changes in the different glacierized areas of the Colombian

Andes. Note that the Parque Nacional Los Nevados encompasses the three volcanos Ruiz,

Santa Isabel and Tolima (Fig. 1C). These changes are also illustrated in Figures 5A and 5B

including the rates of mean annual surface area loss in %/yr for each glacierized area since the

mid-20th century.

Santa Marta El Coquy Ruiz Santa Isabel Tolima Huila Total(km²) (km²) (km²) (km²) (km²) (km²) (km²)

LIA max 82.6 148.7 47.5 27.8 8.6 33.7 348.91939 21.41946 10.8 3.11954 19.41955 38.9 108.91958 2.71959 21 9.4 17.51965 16.31975 19.61981 16.1 15.41985 18.7 87.91986 31.5 171987 6.4 1.61989 121990 14.1 13.91994 23.71995 11.1 67.51996 5.3 13.31997 11.8 1.22001 12.92002 8.4 10.3 3.3 1 55.82003 19.82007 7.7 18.6 10 2.6 1 10.8 50.72008 17.72009 17.42010 7.4 16 9.7 1.8 0.7 9.7 45.32016 7.2 15.5 8.8 1.0 0.7 7.8 41

2007-2016 -14 % -17 % -12 % -62 % -33 % -27 % -22 %1995-2016 -40 % -35 % -25 % -81 % -45 % -41 % -41 %1985-2016 -59 % -51 % -53 % -84 % -59 % -49 % -55 %1955-2016 -66 % -60 % -58 % -89 % -76 % -55 % -64 %LIA-2016 -92 % -90 % -81 % -96 % -92 % -77 % -89 %

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Table 3: Surface area changes since the Little Ice Age maximum. For each glacierized area

the surface area (km²) for each date is presented as well as the loss for different periods (in %

of the initial surface area for the considered period).

The overall glacierized surface area in the Colombian Andes decreased by ~90% since the

Little Ice Age maximal extent (undated). Considering the glacierized surface area in the mid

20th century (about 110 km²), the current extent is about 65% lower. In the last two decades

(i.e. since 1995) the glacierized surface area has decreased by about 40%.

However, Figure 5 illustrates that the trend has not been homogeneous since the mid-20 th

century, both temporally and spatially. Indeed, the mean annual surface area loss rate has

remained close to -1% per year from the 1940s till the mid-1970s, even with a slight decrease

between the mid-1960s and the mid-1970s. Since the mid-1970s, the mean annual surface

area loss rate has increased continuously, reaching -3% per year during the current decade in

average for all the Colombian glacierized areas. On the other hand, this retreating trend is

spatially highly contrasted, with the most important loss rate found for Santa Isabel and

Tolima volcanoes, which is in agreement with their lowest elevations.

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Figure 5: A) Glacier surface area

changes in the different glacierized

areas of Colombia since the 1940s.

B) Rates of mean annual area loss in

%/yr for each glacierized area. The

black curve and grey area represent

the average with 1 st-dev. interval.

The average has been smoothed

using a polynomial fit.

4.3. Glacier volume estimation from field data at La Conejeras glacier

The 2014 ice thickness data from the 14 cross profiles and two longitudinal ones acquired on

La Conejeras glacier (Fig. 2) have been interpolated using the software PCI-Geomatica

(MQSINT: multiquadratic spline interpolation). Figure 6 presents the resulting raster with a

spatial resolution of 15 m (pixel size). The maximum ice thickness located in the central part

of the glacier was slightly above 50 m in 2014. The estimated total ice volume was estimated

to 4.325 x106 m3, which corresponds to 3.893 x106 m3 of water equivalent (using an ice

density of 0.9). Considering a surface area of 0.199 km², the average ice thickness of La

Conejeras glacier was about 22 m in 2014.

Considering an uncertainty of 2 m in the in situ ice thickness measurements with the radar, the

uncertainty in the mean thickness and glacier volume estimates are about 10%.

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Figure 6: Map of ice thickness in 2014 at La

Conejeras glacier.

5. FUTURE CHANGES OF COLOMBIAN GLACIERS AND CONSEQUENCES

In-situ mass balance measurements over the last decade on La Conejeras and Ritacuba

glaciers, respectively in the Parque Nacional Los Nevados – Nevado Santa Isabel and in the

Sierra Nevada de El Coquy, have shown a clear unbalanced situation (Ceballos et al., 2012).

Indeed, the balacance-budget Equilibrium Line Altitude (ELA0, cf. Cogley et al. 2011)

derived from the surface mass balance measurements for La Conejeras glacier is about 4920

m a.s.l., thus 160 m above its mean altitude (i.e. 4760 m a.s.l.), and 120 m above the mean

altitude of the glaciers located on the Nevado Santa Isabel. This is the same for the Sierra

Nevada de El Coquy where the mean altitude of the glaciers is 4910 m a.s.l., 120 m below the

ELA0 derived from in situ measurements on Ritacuba glacier.

Reanalyzing the 10-yr monthly mass balance time series of La Conejeras glacier, Mölg et al.

(2017) have shown that the mean annual mass balance has been close to -3 m w.e. yr-1 over

the period 2006-2015 (Fig. 7 where annual mass balance are plotted). Mölg et al. (2017) also

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showed that the annual ELA was on average close to the glacier maximum altitude during the

monitoring period, with an accumulation-area ratio of about 4%, i.e. almost no accumulation

zone.

On the other hand, the comparison between the 2014 Lidar DEM and the photogrammetric

DEM from 1987 (see section 3.3) showed that the glacier-surface elevation has lowered by 80

m at 4700 m a.s.l. (altitude of the glacier surface in 2014) between the two dates. The geodetic

mass balance was -2.56 m w.e. yr-1 for the period 1987-2005 and -2.46 m w.e. yr-1 for the

period 2005-2014 (Fig. 7). Note that the in situ surface mass balance averaged over the closest

period (i.e. 2007-2014) was -2.45 m w.e. yr-1. This very good agreement between the two

independent methods shows that the well distributed network of in situ measurements at the

surface of La Conejeras glacier allows an accurate quantification of the mass balance using

the glaciological method. Computed at the scale of the entire Santa Isabel ice cap, the

geodetic mass balance between 1987 and 2005 was -2.69 m w.e. yr-1, i.e. slightly more

negative than considering La Conejeras glacier only.

Figure 7 also shows the evolution of the volume of La Conejeras glacier computed on the

basis of the ice thicknesses measured in 2014, the annual changes in surface-area and the

surface mass balances in situ measured since 2006. Extrapolating linearly the glacier volume

changes of the last decade for the future La Conejeras glacier would disappear in the first

years of the 2020s, and so will probably do the other glaciers of Nevado Santa Isabel.

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Figure 7: Surface mass balance and volume changes of La Conejeras glacier. Red squares

show the annual surface mass balance with the average for the period 2006-2015 (red line)

from Mölg et al. (2017). The green lines illustrate the average glacier-wide annual mass

balance computed from the difference between the 1987, 2005 and 2014 DEM. The blue

diamonds show the annual glacier volume computed on the basis of 2014 estimate (dark blue

diamond) using thickness measurements; the black line shows the linear regression.

At the scale of the Colombian glaciers, although the mass balance measured on La Conejeras

glacier cannot be directly extrapolated to the other glaciers, as neighboring glaciers under

similar climate conditions can show different mass balances in relation with the dynamic

response of glaciers to a change in climate forcing (e.g., Rabatel et al., 2016), the important

shrinkage of the Colombian glaciers since the mid-20th century, which is increasing since the

mid-1970s, clearly shows that these glaciers are strongly unbalanced with the current climate

conditions.

Assuming linear trends on the observed glacier shrinkage in the different glacierized areas of

Colombia during the last decades (Fig. 5A) allows a rough estimation of their future changes

and disappearance. Accordingly, glaciers on the Nevado Santa Isabel and Nevado de Tolima

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will likely disappear before 2030, and most of the glaciers in the Sierra Nevada de Santa

Marta and Sierra Nevada de El Coquy before 2050. Only the few largest glaciers with the

highest maximum elevations on Nevado el Huila, Nevado del Ruiz and in the Sierra Nevada

de Santa Marta and Sierra Nevada de El Coquy will probably persist after the mid-21st century

although strongly reduced. Our results suggest that glacier extinction in Colombia happens

much faster than the corresponding estimates in the 4th IPCC report (Magrin et al. 2007:

“within the next 100 years”), but not as dramatic as suggested by Poveda and Pineda (2009:

“by the late 2010-20 decade”). The latter estimates are based on LandsatTM and ETM+

images from 1989-2007 and result in slightly smaller total areas for 2004-07, and

correspondingly higher loss rates, than the present study.

Conversely to other regions of the tropical Andes where glaciers represent a non-negligible

water reservoir for human consuming, for example in La Paz - Bolivia where the water

coming from the glaciers represents up to 30% of the runoff during the dry season (Soruco et

al., 2015), their potential impact in Colombia is mainly related to the Páramo ecosystems

(Brown and others, 2007), as well as for local agriculture and tourism. However, the

glacierized volcanos in Colombia remain – at least for the next few decades - a natural

hazards, as dramatically shown with the example of the post-eruption and particularly to

lahars with the dramatic example of the Nevado del Ruiz in 1985 (Thouret, 1990). Because

the Nevado del Ruiz presents the largest ice coverage in Colombia (8.85 km²) with an

estimated ice volume of 765 x106 m3 (measured maximum thickness of 190 m in 2000, J.

Ramirez, pers. Com.), the risk of lahar will still persist for several decades. As a consequence,

to better estimate the potential water release resulting from an eruption of the Nevado del

Ruiz and to prepare potential impact scenarios, an accurate mapping to the ice thickness and

distribution, as we presented here for La Conejeras glacier, is urgently recommended.

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5. CONCLUSION

In this study we presented the results of a new glacier inventory of the Colombian Andes

performed using 2016 Landsat images, in combination with in situ measurements of glacier

thickness using radar and of glacier surface topography using lidar and aerial photogrammetry

on the well studied La Conejeras glacier located on the Nevado Santa Isabel in the Parque

Nacional de Los Nevados.

The main results showed that:

- The glaciations is very reduced in Colombia, with a total ice covered in 2016 of 41 km².

The mean glacier size was 0.48 km², and small size glaciers largely predominate (76 % <

0.5 km²).

- The glacier shrinkage is strong since the mid-1970s and almost constantly increasing

reaching a mean annual area loss rate of -3% yr-1 during the last years.

- Mass loss on the Santa Isabel ice cap has been strongly negative over the last three decades

with an average annual mass balance of about -2.5 m w.e. yr-1 since 1987 quantified using

aerial photogrammetry and terrestrial lidar.

Considering the imbalance of the glaciers in Colombia with the current climate conditions and

the relative low altitude of the Colombian glaciers, most of them will most likely disappear in

the coming decades and only the largest ones located on the highest summit will persist until

the mid-21st century.

Author contribution statement

A. Rabatel conducted the GPR monitoring on La Conejeras glacier, realized the 2016 glacier

inventory, analyzed the data wrote the manuscript and produced the figures and tables. N.

Micheletti conducted the LiDAR measurements on La Conejeras glacier and produced the

DEM. J.L. Ceballos (with colleagues from IDEAM) performed ten years of mass balance in-

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situ measurements on La Conejeras glacier and analyzed the data with N. Mölg. J.L. Ceballos

and C. Huggel made the glacier mapping from the satellite images from 2007 to 2010. E.

Jordan, Michael Braitmeier and Javier Gonzales realized the photogrammetric DEMs of

Nevado Santa Isabel for 1987 and 2005. M. Zemp led the Andean part of the CATCOS

project and together with J.L. Ceballos managed the 2014 field campaign. All the co-authors

revised the manuscript.

ACKNOWLEDGEMENTS

This study was conducted in the context of the project Capacity Building and Twinning for

Climate Observing Systems (CATCOS) supported by the Federal Office of Meteorology and

Climatology MeteoSwiss, contract no. 7F-08114.1, between the Swiss Agency for

Development and Cooperation (SDC) and MeteoSwiss, by the Swiss State Secretariat for

Economic Affairs (SECO). NASA/METI/AIST/Japan Space systems, U.S./Japan ASTER

Science Team are acknowledged for the release of the ASTER GDEM V2. Antoine Rabatel

aknowledges the contributions of the SNO GLACIOCLIM (use of the IPR), the LMI

GREAT-ICE (Institut de Recherche pour le Développement, IRD) and the Labex

OSUG@2020 (Investissements d'avenir – ANR10 LABX56).

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