# Recent evolution of glaciers in the Cocuy-Güican Mountains (Colombian Andes) and the hydrological implications

Juan Ignacio López-moreno, Francisco Rojas-heredia, Jorge Luis Ceballos, Enrique Morán-tejeda, Esteban Alonso-gonzalez, Ixeia Vidaller, Cesar Deschamps-berger, Jesús Revuelto

► To cite this version:

Juan Ignacio López-moreno, Francisco Rojas-heredia, Jorge Luis Ceballos, Enrique Morán-tejeda, Esteban Alonso-gonzalez, et al.. Recent evolution of glaciers in the Cocuy-Güican Mountains (Colombian Andes) and the hydrological implications. Land Degradation and Development, 2022, 33 (14), pp.2606-2618. 10.1002/ldr.4336. hal-04886447

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# Recent evolution of glaciers in the Cocuy-Güican Mountains (Colombian Andes) and the hydrological implications

Juan Ignacio López-Moreno<fnref n="1" /> | Francisco Rojas-Heredia<fnref n="1" />

<figure><img src="image_2.png" /></figure>

Jorge Luis Ceballos<fnref n="2" />

<figure><img src="image_3.png" /></figure>

Enrique Morán-Tejeda<fnref n="3" />

Esteban Alonso-Gonzalez<fnref n="4" />

Ixeia Vidaller<fnref n="1" />

Cesar Deschamps-Berger<fnref n="1" />

Jesús Revuelto<fnref n="1" />

**Correspondence**

Juan Ignacio López-Moreno, Instituto Pirenaico de Ecología, CSIC, Avda Montañana 1005. Zaragoza, Spain.

Email: nlopez@ipe.csic.es

**Abstract**

This study extends knowledge of the evolution of glacier shrinkage in the Cocuy-Güican Mountains since the maximum glacier extent of the Little Ice Age (LIA). Mass balance data for the Ritacuba Glacier since 2009 were acquired and compared with available data for the Conejeras Glacier (Los Nevados National Park). This study also investigated the hydrological significance of Colombian glaciers, which is still largely unknown because the available information is very limited. Glaciers in the Cocuy-Güican Mountains covered 13.2 km<fnref n="2" /> in 2019 compared with 127.8 km<fnref n="2" /> during the maximum LIA, representing a shrinkage of 89.7%. Analysis of glacier cover observations made in 1955, 1994, 2010, and 2019 revealed that the rate of ice loss was greatest from 1994 to 2010 (0.59 km<fnref n="2" /> yr⁻<fnref n="1" />), and was then almost halved from 2010 to 2019 (0.34 km<fnref n="2" /> yr⁻<fnref n="1" />). This slowing of glacier retreat is consistent with the moderate negative mass balance measured for 2009–2019, and an accumulated loss of 1766 mm w.e. (mm water equivalent). The progressive confinement of glaciers to higher elevations, ice accumulation in topographic locations providing shelter from solar radiation, and an absence of recent marked climatic anomalies could explain why the Cocuy-Güican glaciers have temporally reached a near equilibrium state conditions. This contrasts with the Conejeras Glacier, where 47,000 mm w.e. has been lost in the same period. The available data on runoff and isotope tracers of streamflow and precipitation suggest that precipitation rather than glacier melt water exerts primary control over the hydrological variability at high elevation sites.

**KEYWORDS**

Cocuy-Güican Mountains, Colombia, glaciers, mass balance, mountain hydrology

## 1 | INTRODUCTION

In response to global warming, most glaciers worldwide are undergoing shrinkage and wastage that has accelerated since the 1980s (Beniston et al., 2018; Huss et al., 2017; Huss & Hock, 2018). The speed at which glaciers are deteriorating is very variable, and mainly

depends on: (i) the local intensity and seasonal patterns of temperature increase; (ii) the occurrence of significant trends in snow accumulation during cold seasons; (iii) the elevation and hypsometry of glaciers in relation to the regional 0°C isotherm; and (iv) the specific topographic context of the individual glaciers, which modifies the impact of the regional climate on accumulation and ablation processes

This is an open access article under the terms of the [Creative Commons Attribution License](https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2022 The Authors. *Land Degradation & Development* published by John Wiley & Sons Ltd.

<footnote n="1">¹Instituto Pirenaico de Ecología, CSIC, Zaragoza, Spain</footnote>

<footnote n="2">²Instituto de Hidrología, Meteorología y Estudios Ambientales, IDEAM, Bogotá, Colombia</footnote>

<footnote n="3">³Universidad de Islas Baleares, Mallorca, Spain</footnote>

<footnote n="4">⁴CNRS-CESBIO, Toulouse, France</footnote>
(DeBeer & Sharp, 2009; Hock et al., 2019; Liu et al., 2021; Oerlemans & Reichert, 2000). Some mountain areas have been reported to now be at high risk of complete deglaciation in the next few decades, including mountains of the Mediterranean region (Gachev & Mitkov, 2019; Hughes, 2018); some of the North America Glacier National Park, the Olympic Mountains, and several volcanoes in Mexico (Luce, 2018; O'Neel et al., 2019; Veettil & Wang, 2018a); and most tropical glaciers. The latter have received much scientific attention because of the rapid glacier decline that has occurred in recent years. Tropical glaciers are generally characterized by their small size, their position below the equilibrium line altitude (ELA), and by very intense long- and short-wave radiation as a consequence of the low latitudes and high atmospheric humidity conditions (Rabatel et al., 2013; Vuille et al., 2018). In Peru, Bolivia, and Ecuador, there remain large glaciers that are expected to last for decades despite the extreme negative mass balance they have been subject to. However, in these countries there are also mountain ranges that have smaller glaciers that may disappear sooner (López-Moreno et al., 2014, 2019; Ramírez et al., 2001; Thompson et al., 2011). Glaciers in Africa, Australasia, and Venezuela are currently very reduced in extent, and various studies have projected their complete thaw before 2050 (Chevallier et al., 2010; Cullen et al., 2006; Morris et al., 2006; Veettil & Kamp, 2019; Veettil & Wang, 2018b). The situation for Colombian glaciers is intermediate, as the four main glaciated areas (Sierra Nevada de Santa Marta, Los Nevados National Park, Sierra de Cocuy-Güican, and Huyla) still covered up to 42 km² in 2016 (Rabatel et al., 2018). This extent is only 10% of the ice cover at the maximum of the Little Ice Age (LIA), and has decreased by 62% and 36% since the mid-1950s and mid-1990s, respectively. Rabatel et al. (2018) found very different rates of glacier shrinkage for these glaciated areas during the 2005-2016 period. It was greatest in the Santa Isabel Mountains (-66%), practically stationary in Nevado del Ruiz and Santa Marta (-2% and -6%, respectively), and there were losses of -25%, -30%, and -17% for Tolima, Huila, and Cocuy respectively. López-Moreno et al. (2020) has reported a recent slowdown in glacier shrinkage in Sierra Nevada de Santa Marta, while the Santa Isabel glaciers have shown an acceleration in shrinkage (Morán-Tejeda et al., 2018). Such spatial differences have been related to the contrasting climatic influences in each mountain region (Poveda & Pineda, 2009), and the elevation and hypsometry of the ice covered areas (López-Moreno et al., 2020). Nonetheless, some of the reported differences may also be because of the initial geometry of the ice bodies comprising the various glaciers. Thus, there are difficulties in comparing the response of glaciers to climate conditions based only on glacier surface area, which may be a poor proxy for their mass balance evolution (Vidaller et al., 2021).

The retreat of glaciers in Colombia (and other tropical mountains) provides a clear warning for local populations that climate warming is affecting their territory. The retreat also represents the loss of a unique landscape that, for many inhabitants, has deep cultural and spiritual meaning (Ceballos, 2012). However, it is unclear how the retreat and disappearance of these glaciers is impacting the hydrology and ecological function of associated lowlands. This is because the amount of water released by glaciers is smaller once

the melt peak flow has been reached (Huss & Hock, 2018), and can be largely offset by the high levels of precipitation that generally occur over these areas. However, it is thought that glacier melt dynamics has a significant influence on the hydrological cycle of the páramos (high plateau areas above the tree line; between 3500 and 4400 m asl; characterized by the presence of various shrub species of Espeletia and Espeletiopsis (Brown et al., 2007; Villacis et al., 2010), and it has been reported that very small glaciers can contribute to the daily and seasonal runoff patterns of high elevation tropical streams (López-Moreno et al., 2017; Morán-Tejeda et al., 2018).

The aim of this study was to extend knowledge of the evolution of glaciers since the LIA in the Cocuy-Güican National Park. In addition, we present two new datasets: one from the 2009 mass balance monitoring program for the Ritacuba Glacier; and another comprising two hydrological records, for the foreland of one of the glaciers and in the same catchment but downstream of the páramo area, together with monthly measurements of δ²H and δ¹⁸O isotopes in the runoff and precipitation within the catchment. These new data enabled comparison with the long-term Colombian mass balance monitoring program on the Conejeras Glacier in the Los Nevados National Park (Mölg et al., 2017), and assessment of the hydrological impact of glaciers in the downstream area.

## 2 | STUDY AREA

The Cocuy-Güican Mountains (named the Cocuy Mountains in earlier studies) are located in the northeast of Colombia (6°25' N; 72°20' W) (Figure 1); they form the largest glaciated mountain area in Colombia (15.5 km² in 2016). The area was declared a National Park in 1977 because of the large number of ecosystems it encompasses. It includes glaciers, numerous lakes of glacial origin, wide areas of páramos, and Altoandino rainforest (mountain rainforest between 2500 and 3400 m asl) having well-developed, high moisture forest patches as a consequence of continuous cloudiness and precipitation throughout the year. All these ecosystems occur together in one of the most highly biodiverse mountain areas in the country (Alcantara-Rodriguez et al., 2018). The mountain range has a north-south alignment. The eastern slopes drain to the Arauca and Casanare rivers; these are tributaries of the Orinoco River, which flows to the Atlantic Ocean. The western slopes drain to the Caribbean Sea via the Magdalena and Chicamocha rivers, which enter the Nevado River. The highest summit is the Ritacuba Blanco peak (5480 m asl), but the area includes a total of 11 peaks exceeding 5000 m asl.

Glaciers are a very central aspect of the mountain range, and are strongly linked to the beliefs of the indigenous inhabitants (u'was). It is forbidden to enter the glaciers except for research activities that the IDEAM (The Institute of Hydrology, Meteorology and Environmental Studies) carries out in the area. The maximum extension of glaciers in the area (2000 km²) occurred 27,000-24,000 years BP, and a later major glaciation occurred during the Antarctic Cold Reversal (14,500-
<figure><img src="image_4.png" /><figcaption>FIGURE 1 Location of the Cocuy-Güican and Conejeras Glaciers (a and b) [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

12,900 years BP; Jomelli et al., 2014), when the glaciated surface was approximately 1000 km² (Morris et al., 2006). The last cold pulse occurred during the LIA, between the 16th and 19th centuries, with the maximum expansion in Colombia estimated to have occurred around AD1850, when the glaciers covered approximately 148.7 km² (Flórez, 1992; van der Hammen et al., 1980). The suggested date of the maximum LIA provided for this area should be taken with caution, as other studies in the tropical Andes (Cordillera Blanca and the Bolivian Andes) have dated the maximum LIA between the 17th and 19th centuries (Jomelli et al., 2008; Rabatel et al., 2005, 2008; Solomina et al., 2007).

Weather station data indicate that a single peak of precipitation occurs during June–August in the eastern part of the range, resulting from deep convection of moisture transported from the Amazon basin as a consequence of the orographic barrier of the Andes. Two peaks of precipitation (Figure 2), in April–May and October–November, occur in the western sector as a consequence of the seasonal displacement of the Inter-Tropical Convergence Zone (ITCZ). Temperatures show a low level of seasonal variability, and the annual 0°C isotherm is estimated to occur at 4980 m asl (Rabatel et al., 2018).

## 3 | METHODS

### 3.1 | Change in glacier area in the Cocuy-Güican Mountains, and mass balance of the Ritacuba Glacier

The glaciated area at the maximum of the LIA (~1850, according to van der Hammen et al., 1980) was determined from geomorphological evidence, and the areas in 1955 and 1994 were based on aerial photographs taken by the Agustín Codazzi Geographic Institute in those years (Ceballos et al., 2006; Flórez, 1992). The surface area covered by ice in 1955 and 1994 was reported by Rabatel et al. (2018). To determine the maximum glacier extent during the LIA, Flórez (1992) used the main moraine deposits as a reference. Rabatel et al. (2018) noted that there is a relatively high degree of uncertainty in these estimates because of the lack of continuity of several morainic ridges. In our study, we slightly modified the shapefiles of the glacier extent delineated by Flórez (1992), taking advantage of the higher resolution of available satellite images and fieldwork reviews made by IDEAM staff. However, uncertainty associated with glacier extent estimates for this period remains high. For the years 2010 and 2019, the glaciers were delineated using ALOS (Advanced
<figure><img src="image_5.png" /><figcaption>**FIGURE 2** Monthly average temperature and precipitation for the Sierra Nevada del Cocuy weather station [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

Land Observing Satellite) images at 2.5 m spatial resolution. These images were acquired with almost complete absence of debris cover, topographic shadows, clouds, and fresh snow beyond the glacier limits. Thus, uncertainty in the surface area estimates was limited to the resolution of the images, and to georeferencing errors that were assumed to not exceed 0.26 m in the horizontal direction (Paul et al., 2013).

The IDEAM mass balance program for the Ritacuba Glacier commenced in 2009. The distribution of ablation measurement stakes was determined by the marked crevassed nature of this glacier. To overcome this problem, a safe vertical transect from 4850 to 5150 m asl was established in the central part of the glacier; this covered most of the accumulation and ablation area. Stakes were placed at approximately every 50 m of elevation. In most years measurements were made bi-monthly, and the annual mass balance was computed from surveys made in February, which is considered to be the beginning of the glaciological year under the prevailing climate of the region. The mass balance program at the Conejeras Glacier commenced in March 2006, and involved measurements made on a monthly basis (for a detailed description see Mölg et al., 2017). Both, the Ritacuba and Conejeras mass balance series are reported annually in the World Glacier Monitoring Services.

## 3.2 | Climatic and hydrological data

Daily precipitation and temperature data from the meteorological station at Güicán (3716 m asl; 6°25'46"N 72°22'23"W) were used to analyze the long-term evolution of temperature and precipitation in the region for the period 1981–2019. Data were averaged to annual values, starting from 1 February to maintain consistency with the glacier mass balance data. Data gaps affected 15% and 19% of the

temperature and precipitation series, respectively. Years having > 5% data missing were not used, and were instead filled using linear correlation with the nearest centroid of the ERA5-LAND reanalysis grid (Muñoz-Sabater et al., 2021), at a native resolution of 9 km. ERA5-LAND data have been shown to have differences from observed data, but in general terms it adequately represented the interannual variability of our dataset for temperature and precipitation, making it a useful data source to fill gaps in climatic series in the absence of high-quality data from stations nearby (Lompart et al., 2019).

Two gauging stations measure runoff directly flowing from the glacier. La Laja station (4307 m asl) is situated 1700 m from the glacier front, well above the upper limit of the *páramos* (Figure 1). There are several small lakes between the glacier front and the gauging station. Therefore, even if the residence time of water in the lakes is very short, these lakes do not facilitate analysis of sub-daily fluctuations in the water flow, as made by Morán-Tejeda et al. (2018) at the Conejeras Glacier. In the same stream, but at 3742 m asl, runoff is measured at the La Playa gauging station, which is located in the transition zone between the *páramo* and the Andean rainforest ecosystem. Runoff data from the La Laja station only covers two relatively short periods (2014–2015 and 2017–2018), while the La Playa station data covers the entire 2014–2020 period.

## 3.3 | Sampling of isotopes in water

Simultaneously with the bi-monthly acquisition of mass balance data, streamflow water samples were collected at four sites located in two rivers flowing from the Ritacuba Glacier (the Playitas and Cardenillo Rivers); a sample of water flowing directly from the glacier snout was also collected. For each river, samples were taken at two high mountain sites
(4556 and 4321 m asl), on the páramo (3946 m asl), and at the outlet of the páramo area where it meets the Andean rainforest (3732 m asl) (shown as S1, S2, S3, and S4 in Figure 1, respectively). In each river, the samples were collected on consecutive days (determined by fieldwork logistics). To reduce any impact of daily cycles in the isotope composition, on any sampling day the time between sample collection at the glacier snout (4870 m asl, S0 in Figure 1), at the high mountain sites, and from the outlet of the páramo did not exceed 2 h. In addition, at the checkpoint of the National Park of Cocuy at 3934 m asl, a totalizer gage was used to collect water from precipitation that occurred during the previous month. The sampling period was from February 2017 to October 2019, during which a total of 77 runoff samples and nine precipitation samples were collected. Water samples were kept cold during the transport to the Stable Isotopes Laboratory of the Colombian Geological Survey (SGC; Bogotá), where they were analyzed using a Los Gatos Research (LGR) DTL 100 off axis integrated cavity output spectrometer (OA-ICOS). The stable isotope values were calibrated against Vienna Standard Mean Ocean Water (VSMOW2) and Vienna Standard Light Antarctic Precipitation (SLAP2). Uncertainties based on an independent quality check standard (QC) were <0.3‰ for δ¹⁸O and <2.0‰ for δ²H.

<figure><img src="image_6.png" /><figcaption>**FIGURE 3** Temperature and precipitation evolution in the Güicán de La Sierra sector. Dotted lines are the linear trends. The *p*-values were estimated with a Mann-Kendall test. [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

# 4 | RESULTS

## 4.1 | Climate evolution during the 1981–2019 period

During the period 1981–2019 there was high interannual variability in temperature and precipitation (Figure 3). Temperatures during this period were higher than the average during the 1980s and from 2000 to 2006. Frequent negative anomalies occurred during the 1990s, while the period 2006–2019 was characterized by relatively low inter-annual variability and values close to the long-term average. Minimum, mean, and maximum temperatures showed almost identical interannual evolution; the three series showed a small positive linear trend, but in no case did this reach the threshold of statistical significance (*p* > 0.05).

Precipitation was above average during the 1980s and from 1993 to 1996, and a particularly wet period occurred from 2008 to 2010 (Figure 3), coinciding with a La Niña phase (Bedoya-Soto et al., 2019). The period 1997–2005 was the longest dry period recorded among the study years, with the lowest precipitation years being 2001, 2002, and 2005. From 2009 to 2019 the rainfall was below the long-term average, but with no extreme years; 2015 was the driest year in this period, and 2016 and 2017 where the wettest. Overall, the long-term series showed a negative linear trend, but this was not statistically significant (*p* > 0.05).

## 4.2 | Changes in glacier surface area and mass balance in the Ritacuba Blanco Glacier

The progressive loss of ice cover in the Cocuy-Güican Mountains from the LIA to 2019 is shown in Figures 4 and 5. During the LIA, glaciers covered 127.8 km², encompassing the main axis of the range connected by two main ice bodies (Figure 4a,b). The least ice cover was from 3900 to 4000 m asl, and most was found between 4300 and 5000 m asl, where glaciers covered more than 10 km² for each 100 m elevation interval (Figure 4c).

In 1955 the ice cover was markedly shrunken compared with the maximum LIA extent, with glaciers covering 39.3 km² and the ice cover having a more fragmented spatial distribution. Most ice cover was at elevations ranging from 4600 to 5100 m asl, with > 5 km² of ice cover for each 100 m interval of elevation, and the lowest elevation for ice presence was at 4400–4500 m asl In 1994 and 2010, the ice covered 25.8 km² and 16.3 km², respectively, with the lowest elevation of ice cover at 4600–4700 and 4700–4800 m asl, respectively, and most of the ice in the range occurred at elevations between 4900 and 5100 m asl. Compared with 1994, in 2010 there was markedly less ice at elevations of 4700–5000 m asl, but very similar ice distribution in the highest parts of the mountain range. In 2019, the ice area was 13.2 km², and most ice loss had occurred at elevations of 4700–5000 m asl. The rate of ice cover loss per year was 0.35, 0.59, and 0.34 km² per year for the periods 1955–1994, 1995–2010, and 2011–2019, respectively. In addition to marked changes in the hypsography of the ice cover in the Cocuy-Güican Mountains, the distribution of the
<figure><img src="image_7.png" /><figcaption>**FIGURE 4** (a) Changes in glacier surface area over the Cocuy-Güican Mountains. Delineation of glacier extent for various phases for the north and south sector of the mountain range respectively. (b) Zoom of the main glaciated area of a (south sector). (c) Hypsography of the glacier surface for the various phases analyzed. [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>
<figure><img src="image_8.png" /></figure>

**FIGURE 5** Polar plots showing the relative (%) distribution of ice cover in the Cocuy-Güican Mountains with respect to aspect and elevation (colours) in approximately 1850 (the maximum LIA), 1955, 1994, and 2019. [Colour figure can be viewed at wileyonlinelibrary.com]

ice covered surface varied over time, according to the aspect and slope (Figure 5). Thus, during the LIA maximum, the distribution of ice cover was similar for all mountain aspects, with only slightly more ice cover on slopes facing S-NW compared with those facing N-SE. In 1955, the distribution of ice cover varied markedly on differing slope aspects, with major loss of ice having occurred on east-facing aspects relative to SW, W, and NW aspects, which accounted for >60% of the total ice cover. This trend was more evident in 1994 and 2019, and now there has been almost complete loss of ice on slopes having eastward aspects, and an increase on westward-facing aspects. In 2019 the highest ice cover (28%) was on slopes having NW aspects, in contrast to 1994, when the W aspect dominated the ice cover was dominant.

The mass balance for the Ritacuba Glacier (in the Cocuy-Güican Mountains) for the period 2009–2019 alternated among positive, neutral, and negative years, but the cumulative loss was 1900 mm w.e. over that period (Figure 6a). The most negative years were 2009, 2010, 2013, 2015, and 2016 (losses ranging from 500 to 1000 mm w.e. yr⁻¹), and the most positive years were 2012, 2017, 2018, and 2019 (increases from 250 to 850 mm w.e. yr⁻¹). The mass balances underwent little change in 2012 and 2014. The contrasting interannual

mass balances for the glacier were also evident in values from individual ablation stakes for the period 2012–2019 (Figure 6c). The lowest elevation ablation stakes generally recorded the greatest ice losses, while above 5000 m asl the mass balance was positive in most of the years. Ablation over the entire transect occurred in only 2 years. It is notable that climatic anomalies recorded at the Sierra Nevada El Cocuy-Güican station did not appear to explain the observed anomalies in the mass balance. Thus, years with above average precipitation and low temperatures (2010 and 2016) showed negative mass balances, while warm years with near average precipitation (2012 and 2019) showed positive mass balances. The only clear pattern was that any year having a positive mass balance always had negative anomalies in precipitation. Stakes above 5000 m asl recorded accumulation in most of the years (Figure 6c). Data on mass balances in Colombian mountains were also available for the Conejeras Glacier (Los Nevados National Park; Figure 6b). During the same period, a negative mass balance was recorded for all years; this cumulatively represented a loss of 47,000 mm w.e. during the study period. Only in 2012 was there a moderate ice loss (−450 mm w.e. yr⁻¹), while in the other years the losses ranged from 2500 to 5800 mm w.e. yr⁻¹. The greatest losses
<figure><img src="image_9.png" /><figcaption>**FIGURE 6** Annual glacier mass balance (a and b), mass balance for individual ablation stakes (c and d), and temperature and precipitation anomalies (e and f) for the mass balance period (2009–2019) for Ritacuba (a, c, e) and Conejeras (b, d, f) glaciers. [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

occurring in 2015, 2016, and 2019, and none of the installed ablation stakes recorded positive mass balances during the study period (Figure 6d). Comparison of data from ablation stakes installed in the same elevation range in the Ritacuba and Conejeras glaciers (4700–4900 m asl) showed marked differences in the magnitude of negative values (more than double in Conejeras), and the occurrence of positive values for some years in the Cocuy-Güican Mountains. As for these

mountains, precipitation and temperature anomalies at the Conejeras
Glacier did not explain the interannual variability in the mass balances.
Thus, the most negative mass balance years (2015 and 2016) occurred
with a positive precipitation anomaly (associated with a strong El Niño
event), and these were not the warmest years. In contrast, 2011 had
the least ice losses, but was a warm year with precipitation levels
approaching the average for the period (Figure 6f).
<figure><img src="image_10.png" /><figcaption>**FIGURE 7** Hydrological variability measured at the La Laja and La playa gauging stations and its relationship with precipitation (a), and temperature and glacier mass balance (b). [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

## 4.3 | Hydrological and isotope features of the Ritacuba glacier

Comparison of common periods for which data were available showed that runoff at La Playa (3742 m asl, 26.3 km² of drainage area) was approximately four-fold that measured at La Laja (4307 m asl, 5.7 km² of drainage area) (Figure 7a). The glaciated areas of both drainage areas were similar. Both series closely followed the temporal distribution of precipitation, pointing to this factor as the main driver of the hydrological variability in the two analyzed catchments. Runoff at the La Playa station showed a slower hydrological response time, and inertia in the series resulted in some punctual anomalies in precipitation that are not reflected in the hydrogram. Generally, a 1-month time lag is observed in the La Playa streamflow compared with precipitation values, while runoff at La Laja show less inertia and no one-month lag was observed.

Figure 7b shows the average temperature and runoff for the periods between two consecutive mass balance measurements. This shows that

temperature did not control the mass balance, with marked negative mass balances under warmer conditions, and vice versa. It is notable that there was a positive relationship between the runoff series and mass balances at both sites, suggesting that a greater melt of the glacier is not translated into greater runoff. The main anomalies in mass balance were not translated into significant differences in runoff magnitude between the two sites, which are quite similar along the available common periods.

The similar hydrological response measured at the high mountain (La Laja) and *páramo* (La Playa) stations, both of which are located on the Playitas River, were reflected in the isotope composition of water samples (Figure 8) taken from the streamflow of the glacier at various elevations (4556, 4321, 3946, and 3732 m asl). As expected, depleted isotope values were found at lower elevations, with a progressive enrichment of isotopes upstream. However, the variations over time were very similar, with values in a similar range to those of precipitation samples collected at an intermediate elevation (3946 m asl). Water samples taken directly from the stream originating at the glacier front (at 4870 m asl) showed similar values to those in samples
<figure><img src="image_11.png" /><figcaption>FIGURE 8 (a) δ18O isotopic concentrations of streamflow from various elevations, and in precipitation at 3946 m asl for available sampling dates. (b) δ18O versus δ2H isotopic concentrations. Isotopic concentrations for the glacier front (4850 m asl) are represented by crosses. [Colour figure can be viewed at wileyonlinelibrary.com]</figcaption></figure>

collected in the lower areas, but the variability among sampling days was markedly higher, and the fluctuations were not as similar as those found for the lower sectors.

5 | DISCUSSION

This work provides knowledge of the glacier surface changes in the Cocuy-Güican Mountains, and provided mass balance data for the Ritacuba Glacier over the past 10 years (2009–2019). In addition, we have provided new data on hydrological runoff for two high mountain sites, located at approximately 4300 m asl and at the outlet of the páramo ecosystem (approximately 3742 m asl), and report the isotope composition of streamflow and precipitation collected during field surveys in 2017 and 2018.

From the LIA maximum to 2019, the glacier extent declined from 127.8 to 13.2 km² (89.7% loss), with the levels in 1955, 1994, and 2010 representing 66.4, 48.8, and 19% losses, respectively. Since 1955, the greatest rate of loss of ice cover (0.59 km² yr⁻¹) occurred

in the period 1994–2010. The ice loss rate in the period 1955 to 1994 (0.35 km² yr⁻¹) is consistent with an almost worldwide cold anomaly observed during the 1970s (Sgubin et al., 2017), and is similar to the 0.34 km² yr⁻¹ loss observed in the last decade. Studies conducted in the first decade of the 21st century have projected rapid and complete deglaciation of the Cocuy-Güican Mountains (Herrera & Ruiz, 2008; Morris et al., 2006; Poveda & Pineda, 2009). A slowing of glacier loss in recent years has been reported for several mountain areas of Colombia (Rabatel et al., 2018), and for the glaciers in Sierra Santa Marta (López-Moreno et al., 2020). This appears to be a consequence of the absence of significant climatic anomalies during the last decade (Figure 3), and the fact that glaciers have progressively been restricted to the highest elevations and those aspects most exposed to high humidity sources (SW, W, and NW; Figure 5). The slowing of glacier shrinkage is consistent with the mass balances measured for the Ritacuba Glacier for the same period. Although overall ice accumulation was negative (losing 1800 mm w.e.) for the 2009–2019 period, there were years of net mass gain and others that were almost neutral. In general, positive annual mass balances were recorded at ablation stakes located above 4950–5000 m asl This is in stark contrast with data for the Conejeras Glacier, the other site for which mass balance data are available in Colombian mountains, where a mass balance loss of 47,000 mm w.e. has been reported (Mölg et al., 2017), and with all studied years showing significant mass losses affecting the full elevation range of the glacier. These results indicate that the Conejeras Glacier is at extreme risk of disappearing in the near future (Mölg et al., 2017; Morán-Tejeda et al., 2018; Rabatel et al., 2018). Conversely, the life span expected for the Cocuy-Güican glaciers is difficult to project, but its disappearance seems to be far from imminent. The marked difference in mass balance between the Conejeras and Ritacuba glaciers is also evident in the dataset of elevation changes in South American glaciers derived from ASTER images for the period 2000–2018 (Dussaillant et al., 2019).

It is noteworthy that the interannual variability of temperature and precipitation is a very poor proxy for the evolution of the mass balance in both Cocuy-Güican and Conejeras glaciers. One explanation is that the distance and elevation gradient between the meteorological stations and the glacier lead to a poorly represented climatic conditions over the later. However, the good agreement between precipitation data and runoff series suggests that this hypothesis is questionable. Another plausible explanation is that the complexity of the energy balance in tropical mountains entails that temperature and precipitation not being representative of all the processes involved in the mass balance evolution of the ice bodies, and that other variables must be considered. In this context, Vuille et al. (2018) noted the important role of atmospheric humidity and cloudiness in determining the phase of precipitation and net longwave radiation, which are key to the energy balance of tropical glaciers. In recent years, the IDEAM has installed and managed automatic weather stations in the vicinity of these glaciers, but many technical problems have been encountered, mostly related to their remote location; these problems have interfered with collection of complete and long-term data records that are necessary to apply such physically based approaches. The results
of this study support the need to better characterize the response of Colombian glaciers to atmospheric conditions.

The available hydrological information is very limited and fragmented, and the runoff and precipitation sampling strategy is far from being sufficiently robust to clearly characterize the spatio-temporal variability of stable isotopes in the study area, or to derive data on glacier melt contributions to total runoff. However, the available information suggests that precipitation is a key driver of the hydrology of Cocuy-Güican Mountains, and that its importance far exceeds that of the hydrological role of glacier melting. First, a very high synchronicity can be observed between precipitation and runoff series at both the high mountain environment (La Laja) and at the outlet of the páramo sector (Playitas). It is somewhat surprising that given the high water storage capacity of the páramos (Célleri & Feyen, 2009; Flores-López et al., 2016; Lazo et al., 2019), the response to previously accumulated precipitation is almost direct, with a maximum lag time of 1 month (Figure 7). This response suggests that the soils of the páramos store large amounts of water, and are able to provide a consistent baseflow, even during dry periods. However, the arrival of new water inputs from precipitation displaces the existing water reserves through lateral and subsurface flow, leading to a relatively short time of response of the runoff to precipitation. Our results have also shown that despite the short distance from the high mountain gauging station (La Laja) to the glacier snout, and the nature of the intervening terrain (mainly bare rocks, boulders, and small new lakes), the fluctuations in runoff are not conditioned by the mass balance of the previous months, but follow closely the evolution of precipitation. We hypothesize that this is because of the high levels of precipitation that fall above 4000 m asl (probably twice the amounts measured at Güicán); this typically falls as rain over the glacier and surrounding area, or as snowfall that melts in the hours immediately following the precipitation event. Only the small area spanning 5000 and 5300 m asl stores precipitation as consolidated snowpack (see Figure 5c). The major contribution of precipitation to runoff compared with that of glacier melt was also suggested by the analysis of water isotopes in samples. Although the number of samples was limited and we lack complete daily cycles of water isotope data to provide full understanding of the dynamics, the isotopy in the high mountain site and at the outlet of the páramo (around 3700 m asl) showed very similar temporal fluctuations, and values close to the isotope composition of precipitation (Figure 8). The isotope depletion toward lower elevations must be related to increased evapotranspiration and water transit times (Gibson et al., 2005; Guo et al., 2019). However, water flowing directly from the glacier (at 4850 m asl) exhibits much higher temporal variability, and marked deviations from the runoff series measured immediately downstream. Isotope values for water flowing from the glacier do not differ substantially from those recorded downstream, probably because a significant amount of the water came from liquid precipitation or the melt of recent snowfalls over the glacier. Given the nature of the data available, these conclusions need to be treated with caution. However, they suggest the need to increase the monitoring of the climate and hydrology of the highest areas of Colombian glaciers. Moreover, the fact that glacier melt is probably not the main hydrological driver in Colombian mountains does

not mean that the disappearance of glaciers will not involve change in water quantity and quality, with important consequences for the ecology of streams and the páramos (Correa et al., 2020; Morán-Tejeda et al., 2018; Villacis et al., 2010). This also require scientific investigation and interpretation.

## 6 | CONCLUSIONS

In 2019, the glaciers of the Cocuy-Güican Mountains covered 13.2 km², implying a 89.7% shrinkage compared with the surface during the LIA maximum. After the period 1994–2010, when the highest rate of surface area loss was observed (0.59 km² yr⁻¹), the loss during 2009–2019 was markedly slowed (0.34 km² yr⁻¹). This finding was consistent with the mass balance data for the Ritacuba Glacier, which lost only 1800 mm w.e. during the same period, with an alternance of years of mass losses, gains, and neutrality occurred. Above 5000 m asl, mass accumulation dominated in most of the years. This recent stability has been associated with the absence of significant climate anomalies compared with the long-term records, and to the reported progressive retreat of remaining ice bodies toward elevations and aspects favorable for ice accumulation and shelter from incoming solar radiation. This has not occurred generally for all Colombian glaciers; during the same period the Conejeras Glacier shrank dramatically, and underwent an accumulated mass balance loss of 47,000 mm w.e., leading to it being at serious risk of disappearance. The very limited hydrological and isotope data available for the area suggest that precipitation is the major driver of hydrological variability, with relatively short hydrological response times characterize both the high mountain sectors and at the outlet of the páramo. This preliminary conclusion needs to be confirmed with longer hydrological series, more comprehensive monitoring of weather conditions, and further analysis of the isotopes in streams and precipitation. The region also needs focused studies about the impact of glacier melt on the ecology of the mountain streams and the páramo.

## ACKNOWLEDGMENTS

This study was funded by HIDROIBERNIEVE (CGL2017-82216-R), from the Spanish Ministry of Science, Innovation and Universities. The authors thank the staff of the Cocuy-Güican National Park and local communities for their support for the research. We also thank IDEAM staff for their help in providing data and discussing the results.

## DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## ORCID

Juan Ignacio López-Moreno ID https://orcid.org/0000-0002-7270-9313

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**How to cite this article:** López-Moreno, J. I., Rojas-Heredia, F., Ceballos, J. L., Morán-Tejeda, E., Alonso-González, E., Vidaller, I., Deschamps-Berger, C., & Revuelto, J. (2022). Recent evolution of glaciers in the Cocuy-Güican Mountains (Colombian Andes) and the hydrological implications. *Land Degradation & Development*, **33**(14), 2606-2618. https://doi.org/10.1002/ldr.4336