Mother Pelican
A Journal of Sustainable Human Development

Vol. 7, No. 8, August 2011
Luis T. Gutiérrez, Editor
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Increased Climatic Stress on High-Andean Ecosystems
in the Cordillera Central of Colombia

Daniel Ruiz Carrascal, María del Pilar Arroyave Maya,
María Elena Gutiérrez Lagoueyte, and Paula Andrea Zapata Jaramillo

Originally published in Herzog S.K., R. Martinez, P.M. Jørgensen, and H. Tiessen (Eds.)
Climate change and biodiversity in the Tropical Andes
MacArthur Foundation, Inter-American Institute of Global Change Research (IAI)
and Scientific Committee on Problems of the Environment (SCOPE),
São José dos Campos, Brazil, and Paris, France

The upper range of the northern Andes harbors unique neotropical alpine wetland ecosystems known as páramos. These occupy the narrow elevational belt above Andean cloud forests (ca. 2,000-3,500 m) and below areas of “permanent” snow (above ca. 4,500 m). Páramos provide valuable environmental goods and services such as a sustained water supply for domestic, agricultural, and industrial use (Buytaert et al. 2006). Historical climatic conditions of these high-elevation environments are characterized by average temperatures below 10°C, frequent cloud cover and fog, high UV radiation, low atmospheric pressure, strong winds, and precipitation in the form of drizzle (Castaño 2002, Gutiérrez et al. 2006, Ruiz et al. 2008). Some of these conditions have changed dramatically over recent decades. Human activity at local, regional, and global scales has begun to introduce anthropogenic stress on high elevation environments (Foster 2001, Diaz et al. 2003). In Colombia, for instance, rapid environmental changes and disruptions in the integrity of páramo ecosystems have been observed in recent years (Castaño 2002, Gutiérrez et al. 2006, Ruiz et al. 2008). Likely changes induced by human activities include, among others, water stress during dry seasons due to receding glaciers and the disappearance of high-elevation water bodies, abrupt loss of biodiversity, frequent occurrence and rapid spread of natural and human-induced fires, and increased erosion. We here review available information.

The Páramos of Los Nevados Natural Park

One of the most representative Colombian páramos is located in Los Nevados Natural Park (04°25'to 05°15'N, 75°00' to 76°00'W) on the El Ruiz-Tolima Volcanic Massif in the Cordillera Central of the Colombian Andes. Los Nevados is a protected area located in the Alto Cauca hydroclimatic region. Numerous streams originating in the snowfields of the El Ruiz (5,321 m) and Santa Isabel (5,100 m) ice-capped mountains of the Cordillera Central feed the high- elevation watersheds of the Claro, Otún, and Chinchiná rivers, which provide a continuous water supply to communities in the adjacent lowlands. The orography of the El Ruiz-Tolima volcanic massif and the two inter-Andean Cauca and Magdalena river valleys extends from tropical to nival elevational belts. Historical climatic conditions provide for the presence of eleven Holdridge (1987) life zones in such a small spatial domain: from tropical moist forest (Tmf) to alpine rain tundra (Art). In terms of the Cuatrecasas (1934) system, historical climatic conditions in the area of the Claro River watershed support moist Andean forest, wet high Andean forest, rainy subpáramo, wet subpáramo, rainy páramo, and rainy superpáramo. Data from elevational experimental plots (Ruiz et al. 2009) show that many unique plant species inhabit the headwaters of the Claro River basin. Key species and potential bio-indicators of likely changes in the elevational location and distribution of life zones include: Miconia salicifolia (Melastomataceae) and Berberis rigidifolia (Berberidaceae) in the subpáramo; Espeletia hartwegiana (Asteraceae), Plantago rigida (Plantaginaceae), and Valeriana plantaginae (Valerianaceae) in the páramo; and Senecio canescens (Asteraceae), Loricaria colombiana (Asteraceae), and Lycopodium crassum (Lycopodiaceae) in the superpáramo.

Observed and Inferred Changes in Historical Climatic Conditions

Climatic patterns have changed in the central region of the Cordillera Central (Ruiz et al. 2008). Observed trends in minimum and maximum near-surface temperatures, rainfall amounts, relative humidity, cloud characteristics, sunshine, and diurnal temperature range suggest that climatic stress is increasing in high-Andean ecosystems of the Cordillera Central. Observed changes appear to be consistent with changes occurring worldwide (see temperature trends plotted below) and at national and regional spatial scales. Some key aspects of the observed changes in historical climatic conditions are discussed below.

Changes in Near-Surface Temperatures, Rainfall, and Relative Humidity

Studies on changing climatic conditions in páramo life zones are limited due to the lack of long- term historical records. However, there is considerable evidence suggesting that significant changes in near-surface ambient temperatures and annual rainfall have occurred in these tropical environments. Bradley et al. (2006), using temperature records gathered from several stations along the tropical Andes, concluded that the rate of increase in air temperatures was +0.11°C/decade over the period from 1939 to 1998. For Colombia, Pabón (2003, 2004) showed that mean annual ambient temperatures over the period 1961-1990 increased at a rate of about +0.1 to 0.2°C/decade. More recent analyses (Departamento de Geografía, Universidad Nacional de Colombia 2005) have suggested that increases in near-surface temperatures in the Alto Cauca hydroclimatic region reached +0.12°C/decade over the same period. Our recent studies support these findings. Analysis of weather station data (see nationwide scale in Ruiz et al. 2009) suggests increases of up to +0.3°C/decade in mean near-surface temperatures along the Andean mountain ranges. On a regional scale, most historical time series of mean annual near-surface temperatures observed at weather stations located along a 5° latitudinal transect, show increasing trends that could reach 0.4°C/decade on all mountain flanks.

With regard to rainfall (see nationwide scale in Ruiz et al. 2009), most stations along the mountain ranges show decreasing trends over the past 25 years. Stations located in the inter- Andean valleys exhibit increasing trends. Regional rainfall also shows important changes:

Annual global land temperature anomalies (AGLTA; source: NOAA Satellite and Information Service-National Environmental Satellite, Data and Information Service) and annual local near-surface mean temperature anomalies (ANSMTA, observed at stations XII-2615502 Cenicafé and I-2615515 Las Brisas). Anomalies are defined as departures from the 20th-century average (1901-2000). Linear trends in near-surface ambient temperatures observed in the area of the Claro River watershed exhibit rates of increase of about 0.22-0.25°C/decade.

Increases have been observed over recent years on the western flank of the Cordillera Occidental, where total annual rainfall is strongly influenced by the orographic uplift of the westerly Chocó low-level jet (Poveda and Mesa 2000, Vernekar et al. 2003). By contrast, historical time series over the eastern flank of the Cordillera Central, where rainfall amounts are influenced by the behavior of the easterlies and the low-level jet to the east of the Cordillera Oriental (Vernekar et al. 2003), show general tendencies toward drier conditions. In the inter-Andean valleys some stations exhibit increasing trends in rainfall while others have seen decreases. Along these valleys rainfall amounts are affected by elevation and show influences of the northeasterly trade winds, which in the area become valley currents that blow southward.

In the areas surrounding Los Nevados Natural Park, most of the climatic variables that control the integrity of high-elevation ecosystems also show statistically significant changes (see local scale in Ruiz et al. 2009 for specific rates of change). These variables include total annual rainfall, maximum daily rainfall, minimum temperatures during the coldest days, maximum temperatures during the warmest days, and minimum relative humidity. Analyses suggest that in Los Nevados and at higher elevations on the western flank of the Cordillera Central, total annual rainfall at elevations above the pluviometric optimum (ca. 1,500 m) is decreasing. Below this elevation, some weather stations report slowly increasing trends. Daily precipitation records suggest, in general, an increased occurrence of unusually heavy rainfall events. Minimum temperatures on the coldest days show increasing trends at all elevations, suggesting that below- freezing temperatures and cold days are becoming less frequent. Increases in minimum temperatures at higher elevations are greater than those observed at lower elevations. Maximum temperatures on the warmest days are also rising and, much like minimum temperatures, exhibit faster increases at higher elevations. Finally, analyses suggest that minimum relative humidity values have significantly decreased at higher elevations.

Changes in Cloud Characteristics, Sunshine, and Diurnal Temperature Range

One of the key factors of increased climatic stress in Colombian páramos is the change in cloud cover (Ruiz et al. 2008). Cloud amounts are highly dependent on regional and local processes: coupled interactions between sea surface temperatures (SSTs), wind patterns, and the latitudinal displacement of the Inter-Tropical Convergence Zone drive regional cloudiness conditions on intra-to inter-annual timescales. Satellite data show important reductions in cloud cover over the high-elevation region over the last two decades of the 20th century. Observed changes in the region seem to reflect these changes in cloud cover. Most of the weather stations on the western flank of the Cordillera Central at elevations around the pluviometric optimum, exhibit statistically significant decreasing trends in the total annual sunshine and the maximum, minimum, and mean daily sunshine values. Such decreases in sunshine are consistent with statistically significant increases in the total number of foggy days and decreases in the total number of sunny days. By contrast, the total number of foggy days per month at higher elevations has decreased slightly over the past decades. Finally, homogeneity analyses conducted for Los Nevados Natural Park suggest that maximum, mean, and minimum diurnal temperature range (minDTR) at higher elevations have increased over the past decades. Maximum DTR, in particular, show statistically significant increasing trends at higher elevations, whereas lower elevations show decreasing trends. The upward trend at higher elevations is a consequence of the difference between the aforementioned rates of increase in minimum and maximum temperatures.

Water Balance, High-Elevation Water Bodies, and Ice Caps

Changes have also occurred in hydrological regimes. Besides rainfall, water inputs to the hydrological cycle in high-elevation watersheds include outflow from water bodies and aquatic micro-habitats, mist, glaciers, and snowmelt. Our analysis of intra-annual cycles of the mean streamflow of the Claro, Otún, and Chinchiná rivers suggest that water discharges follow the bimodal annual cycles of rainfall observed in the surroundings of Los Nevados Natural Park, but with a one-month time lag. Periods of high mean water discharge are usually observed during April-May-June and October-November-December. Periods of low streamflow tend to occur during January-February and July-August. Although minimum streamflows show similar intraannual distributions, observed records exhibit important differences during the dry periods January-February and July-August. During these months meltwater runoff from snow fields and glaciers, as well as water inputs from high-altitude water bodies and turberas (bogs) increase surface streamflow (i.e., streamflow is greater than would be expected from rainfall amounts alone due to meltwater runoff). This effect is particularly pronounced in the Claro and Otún river basins. By contrast, in the Chinchiná River, which does not receive meltwater runoff, and where aquatic microhabitats are limited to a few areas at its headwaters, reductions in streamflow during the critical dry months are considerable. during the critical dry months are considerable.

Decreases in annual rainfall observed at elevations above the pluviometric optimum and increases in near-surface temperatures, particularly at higher elevations, are likely to decrease streamflow. Exploratory analyses suggest decreasing trends in annual maximum and mean streamflow values in the Otún and the Chinchiná rivers over the past 40 and 20 years, respectively, although these trends are not statistically significant. Minimum discharges during the critical months January-February and July-August show changes in the available historical time series that are statistically significant. In the Otún River, minimum water discharges and minimum streamflows during the driest period January-February exhibit decreases of ca. 1.0% and >6.0% per decade, respectively, over the past 40 years.

Are these trends related to changes in the extent of high-elevation water bodies and icecaps? Water bodies in the Los Nevados Natural Park have experienced reductions in surface area over recent years, and some have already experienced natural sediment-filling and drying processes, accompanied by a gradual colonization by local vegetation. However, water bodies also exhibit a marked seasonality driven by regional climatic conditions. Increases in their water levels are common during April-May and October-November, whereas decreases typically occur during December-January-February and July-August-September. On inter-annual timescales, high-elevation water bodies show dynamics related to the warm and cold events of the El Niño– Southern Oscillation. Specifically, significant drought-induced shrinkages with respect to “past” reference shorelines are observed after above-normal summers that commonly accompany the El Niño warm events.

On the other hand, the Molinos glacier on the western flank of El Ruiz Nevado and the Conejeras glacier tongue on the western flank of the Santa Isabel Nevado have retreated dramatically over recent years (Euscategui 2002, Ceballos et al. 2006, IDEAM 2008). These retreats have been forced by volcanic activity, changes in climatic conditions, and changes in local surface albedo. Although there is limited information to infer the potential impacts of the changes in the extent of high-elevation water bodies and ice-caps on the ecosystem as a whole, the disappearance of water bodies and turberas and the retreat of mountain glaciers are probably undermining the integrity of páramo ecosystems. It is likely that the change in water availability has and will continue to have a sizable effect.

High-Elevation Fires

Fire events are one of the most serious threats to the integrity of high-Andean ecosystems and one of the most critical challenges for the conservation of protected areas. At higher elevations, fires cause numerous and almost-irreversible damage to páramo soils, wetlands, fauna, and flora. Fire-induced changes in the structure and composition of páramo ecosystems affect their provision of several environmental goods and services. In the surroundings of Los Nevados, lower-elevation areas and buffer zones are inhabited by smallholder farmers whose main productive activities include grazing dairy cattle and the cultivation of potato crops. Fires are usually set to regenerate grass for livestock, prepare land after harvesting crops, and expand cultivated land areas. These burns are not controlled appropriately and often spread into “nontarget” natural vegetation in páramo zones. Fires are particularly hazardous during the dry season given the high to very high vulnerability of páramo habitats to the occurrence and rapid spread of fires during this period. fires during this period.

Historical records of fires in Los Nevados extend back to 1994 (source: Unidad Administrativa Especial del Sistema de Parques Nacionales Naturales). These records include the worst ecological disaster that has occurred in protected Colombian high-elevation ecosystems, namely the fire of unprecedented severity that took place in the surroundings of the Laguna del Otún in July 2006 (Lotero et al. 2007). This event lasted for almost eight days and affected more than 4% of the of the park. Sadly, since 1994 the annual number of fire events, the total area affected per year, and the average fire duration show strong increasing trends. This is the result of several factors such as a weak institutional capacity to react to fires, more combustible material in the area, and climatic conditions more favorable to the spread of fires. Most events have been induced by or are related to human activities, but it is likely that changing climatic conditions have favored their rapid spread. Increases in the number of events and affected areas seem to correlate with the increasing and decreasing trends observed in temperature and relative humidity records (see above), respectively, gathered at nearby weather stations.

This link does not appear to be a coincidence. Testimonies of local experts and park guards support the links between the current rapid spread of fire events and the observed changes in climatic conditions in the area. Also, an association between the timing of fire events, the total area affected per month, and the intra-annual cycles of climatic conditions in the area of Los Nevados has been observed. Most fire events occur during the dry seasons June-July-August (JJA) and December-January-February (DJF). Higher values of maximum temperatures linked to lower relative humidity and rainfall set the stage for a potential increase in the spread of “small- scale” fire events during these trimesters. The maximum number of events and greatest area affected per month are observed during the trimester JJA. However, when excluding the unprecedented fire event of July 2006, the highest value of total area affected per month occurs during DJF. In summary, although changing conditions are not directly causing an increase in high-elevation fires, drier conditions may favor their rapid spread. Thus, larger affected areas and greater duration of fires are early warnings of the páramo ecosystems' increasing vulnerability.

Model Projections

Model projections consistently suggest future climatic conditions will be unfavorable for páramo life zones (Vuille et al. 2003, Diaz et al. 2003). Hulme and Sheard (1999) used the outputs of six Global Climate Models (GCMs) to propose future climate scenarios for the Northern Andes. According to their results, the total annual rainfall in the central region of the Cordillera Central is expected to be above the 1961-1990 normal annual value for all emission scenarios. They also suggest that increases in mean annual temperatures are expected throughout the region. Giorgi and Bi (2005) used atmosphere-ocean coupled GCM simulations for northern South America to predict increases in rainfall during future wet seasons and decreases during dry seasons. Also, near-surface temperatures are predicted to be above historical normal conditions. Bradley et al. (2006) used GCM results to suggest that, at 5°N and at elevations of 3,000-5,000 m, mean annual temperatures are expected to increase over this century under emission scenario A2 of Meehl et al. (2007). For Colombia recent statistical downscaling techniques of GCM outputs were used to estimate future climatic conditions under a 2xCO2 emission scenario (Departamento de Geografía–Universidad Nacional de Colombia 2005). On a national scale and for the Alto Cauca hydroclimatic region, total annual rainfall is expected to change up or down depending on the model, but mean annual ambient temperatures are consistently expected to be above the past mean.

GCM outputs indicate an increase in the elevation of clouds under a future warmer world (Meehl et al. 2007). They also suggest that most tropical areas will experience a decrease in net cloud cover over all layers. Based on our analyses of January SST anomalies (Ruiz et al. 2009), we suggest that a significant decrease in cloud cover in the high-elevation region is likely to occur over the next 50 years under normal conditions. Our predicted decrease of 6.8% in total cloud cover, relative to the period 1984-2001, is 1.4 times greater than (but consistent with) the 2.0% annual mean change suggested by Meehl et al. (2007) for the period 2080 to 2099, relative to 1980 to 1999. We also argue that if a strong El Niño event were to occur by 2050, the reduction in January monthly average cloud cover could be more critical.

Changes in the structure, composition, integrity, and extension of high-elevation ecosystems inhabiting the Claro River watershed and nearby areas are likely to occur over the first half of this century. Ongoing changes in climatic conditions could force upward shifts in the transitions between life zones, which would lead to the appearance of new environments, the expansion of some others, and reductions in the extent of the subalpine (páramo), alpine (superpáramo), and nival (glacial) elevational belts. The future distribution of these ecosystems will depend on their capacity to adapt to the expected climatic changes. Our analyses suggest that by 2050 climatic conditions in the watershed and the region will likely be suitable for the colonization of lower montane dry forest (LMdf) and montane moist forest (Mmf). A 56% increase in the montane wet forest (Mwf) surface area could also occur. On the other hand, subalpine rain páramo (SArp), alpine rain tundra (Art) and nival (N) life zones could experience reductions of about 31%, 53%, and 80%, respectively, by 2050. In terms of the Cuatrecasas classification, reductions in the areas of subpáramo, páramo, superpáramo, and nival zones could be 83%, 22%, 53%, and 80%, respectively. With respect to the entire páramo zone, such reductions correspond to a total decrease in area of about 54%.

Potential Impacts on Ecosystem Integrity

Although their impacts on the integrity of high-elevation habitats are very difficult to assess, changing climatic conditions could lead to the disruption of páramo and cloud forest ecosystems. Some of the expected impacts include:

  • Upward migration of low-elevation plant species are expected to occur, reducing the extent of páramo habitats. As the climate warms and ice caps melt a shift in life zones to higher elevations could be expected as, over long time intervals, these zones would maintain their relationships to the snow line. However, the inferred rapid upward changes in the Lifting Condensation Level and field-observed retreats of snowline (both considered good approximations of upward shifts in the transitions between life zones) suggest that several high-elevation plant species will most likely be unable to migrate upward. Changes in temperature could favor the upslope migration of many montane species, but might also have a devastating impact on those species that have adapted to and become dependent on extreme conditions at high altitudes.
  • Elevational changes in sunshine and rainfall could contribute to an increase in the rate of desertification of montane habitats, which today house an important fraction of global biodiversity.
  • Areas where only snow or drizzle used to fall could be experiencing heavy rain due to the rapid upward shift of the freezing level. Glacier margins may be at increasing risk of retreat, contributing to a continued diminution of the self-regulation capacity of the hydrological system.
  • Decreases in the amount of cloud and fog cover, driven by changes in atmospheric stability, will have significant impacts on the net radiation balance. As a consequence, glacier mass, high-elevation water bodies and mountain species could be further affected.
  • Finally, higher solar energy is expected to accelerate the hydrological cycle and increase evapotranspiration, having strong effects on water bodies and aquatic microhabitats.

Combined, these impacts constitute a serious threat to unique páramo habitats and, consequently, to the water supply in the region. In the foreseeable future it will be more expensive to supply water for human consumption, power generation, and agriculture (Vergara et al. 2007, Vergara 2009). Ambitious sustainable management strategies are now urgently required to protect these unique, rich, fragile, and highly endangered environments.

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Daniel Ruiz Carrascal is a Principal Investigator on hydroclimatology, 'Gestión del Ambiente para el Bienestar Social' (GABiS), at the School of Engineering in Antioquia, Colombia. He is currently a Graduate Research Assistant and PhD candidate at the International Research Institute for Climate and Society, Columbia University. For more on the work of this author, click here.

María del Pilar Arroyave Maya is Director, 'Gestión del Ambiente para el Bienestar Social' (GABiS), at the School of Engineering in Antioquia, Colombia. For more on the work of this author, click here.

María Elena Gutiérrez Lagoueyte and Paula Andrea Zapata Jaramillo are research assistants, 'Gestión del Ambiente para el Bienestar Social' (GABiS), at the School of Engineering in Antioquia, Colombia.

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