changing climate and endangered high mountain ecosystems ......changing climate and endangered high...

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Changing climate and endangered high mountain ecosystemsin Colombia

Daniel Ruiz⁎, Hernán Alonso Moreno, María Elena Gutiérrez, Paula Andrea ZapataGrupo de Investigación ‘Gestión del Ambiente para el Bienestar Social—GABiS', Escuela de Ingeniería de Antioquia, Calle 25Sur No. 42-73,Envigado, Antioquia, Colombia

A R T I C L E I N F O

⁎ Corresponding author. Tel.: +57 4 339 3200; fE-mail address: [email protected] (D. Rui

0048-9697/$ – see front matter © 2008 Elsevidoi:10.1016/j.scitotenv.2008.02.038

A B S T R A C T

Article history:Received 20 July 2007Received in revised form15 February 2008Accepted 24 February 2008Available online 23 April 2008

High mountain ecosystems are among the most sensitive environments to changes inclimatic conditions occurring on global, regional and local scales. The article describes thechanging conditions observed over recent years in the high mountain basin of the ClaroRiver, on the west flank of the Colombian Andean Central mountain range. Local groundtruth data gathered at 4150m, regional data available at nearby weather stations, andsatellite info were used to analyze changes in the mean and the variance, and significanttrends in climatic time series. Records included minimum, mean and maximumtemperatures, relative humidity, rainfall, sunshine, and cloud characteristics. In highlevels, minimum andmaximum temperatures during the coldest days increased at a rate ofabout 0.6°C/decade, whereasmaximum temperatures during the warmest days increased ata rate of about 1.3°C/decade. Rates of increase in maximum, mean and minimum diurnaltemperature range reached 0.6, 0.7, and 0.5°C/decade. Maximum, mean and minimumrelative humidity records showed reductions of about 1.8, 3.9 and 6.6%/decade. The totalnumber of sunny days permonth increased in almost 2.1 days. The headwaters exhibited nochanges in rainfall totals, but evidenced an increased occurrence of unusually heavy rainfallevents. Reductions in the amount of all cloud types over the area reached 1.9%/decade. In lowlevels changes in mean monthly temperatures and monthly rainfall totals exceeded + 0.2°Cand − 4% per decade, respectively. These striking changes might have contributed to theretreat of glacier icecaps and to the disappearance of high altitude water bodies, as well as tothe occurrence and rapid spread of natural and man-induced forest fires. Significantreductions in water supply, important disruptions of the integrity of high mountainecosystems, and dramatic losses of biodiversity are nowa steadymenuof the severe climaticconditions experienced by these fragile tropical environments.

© 2008 Elsevier B.V. All rights reserved.

Keywords:High mountain ecosystemsPáramosGlaciersGlobal change

1. Introduction

The well-being of human societies is based on the sustaineddelivery of fundamental ecosystem services, such as (amongothers) ‘the regulation of the quality and quantity of watersupply, and the security in the face of future environmentalchange’ (Díaz et al., 2006). Regrettably, the consequences of theloss of these important goods and services ‘will be felt

ax: +57 4 331 7851.z).

er B.V. All rights reserved

disproportionately by the poor, who are the most vulnerableto such environmental problems’ (World Resources Institute,2005). Colombia is a good example. The United NationsFramework Convention on Climate Change received the firstColombian official communication in 2002 (NC1-2002).The future climate scenario suggests a nationwide increaseof 1–2°C in mean annual temperatures and variations inannual rainfall totals of about + 15% by 2050. The NC1-2002

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http://dx.doi.org/10.1016/j.scitotenv.2008.02.038

123S C I E N C E O F T H E T O T A L E N V I R O N M E N T 3 9 8 ( 2 0 0 8 ) 1 2 2 – 1 3 2

identified the Colombian high mountain ecosystems (HME) asone of the areas of primary concern (World Bank Group, 2006).

Colombia is host to the largest stretch of páramos life zonesin the planet (WBG, 2006). These are exceptional desolateregions located only in the Tropics between the highmountain Andean forests (the so-called bosque montano; ca.2000–3500m) and the areas of ‘permanent’ snow (ca. N 4500m).Their climatic conditions are characterized by average tem-peratures below 10°C, strong diurnal temperature range,cloudy skies, foggy days, high UV radiation amounts, strongwinds, and light rain. These fragile ecosystems have uniqueendemic flora and serve as important sources and reservoirsof water. Páramos habitats and towering snowcapped peaksconstitute the HME. It is expected that ca. 56% of Colombianpáramos are going to be seriously affected by increases intemperature by 2050 (WBG, 2006). As páramos ecosystems areonly endemic in high elevation regions (no way up) andmountain species exhibit a weak ability to adapt to changingclimatic conditions, climate change will undoubtedly result ina dramatic loss of biodiversity.

To further complicate matters glaciers in the areas of‘permanent’ snow (above 4500m) are also expected to beaffected by increases in temperature. In the NC1-2002, theColombian Institute of Hydrology, Meteorology and Environ-mental Studies (IDEAM) reported that the loss of the total

Fig. 1 –General location of the El Ruiz–Tolima Volcanic Massif. The30″-arc (924m×924m, left) and 90m×90m spatial resolutions (rig(USGS)—National Aeronautics and Space Administration (NASA) DInformation System HidroSig Java (Copyright: Postgrado en Aprovy Medio Ambiente, Universidad Nacional de Colombia Sede Med

Colombian glacier area had reached almost 80% since 1850.Sadly, it is expected that 78% of the remaining Colombianglaciers will be seriously affected by increases in temperatureby 2050 (WBG, 2006). The icecaps of these glaciers ‘feed’ highaltitude water bodies and permanent water-reservoir habitats(the so-called turberas) that contribute to the headwaters ofseveral rivers currently used by lowland populations to satisfythe water demand (a significant proportion of Colombiancommunities depend directly on highmountainswatersheds).Turberas are mainly colonized by mountain species withnarrow habitat tolerance and low dispersal capacity, and arelikely to be at high risk from the environmental effects ofclimate change. Hence, one of the major consequences of theglobal environmental problem could be the loss of environ-mental goods and services provided by these habitats,especially the water supply and basin regulation (Gutierrezet al., 2006; WBG, 2006). Unfortunately, dramatic land usechanges (i.e. clearing-off of highmountain Andean forests andpáramos) caused by extensive agriculture and livestock grazingare also threatening the existence of these fragile reservoirsand ecosystems, and could be producing severe local climaticanomalies. As the world is already facing the consequences ofa warmer climate, adaptation strategies are urgently neededto maintain considerable levels of environmental goods andservices in high mountain ecosystems.

topography is represented using Digital ElevationModels forht). The latter is based on the United States Geological Surveyigital TerrainModel andwas processed using the Geographicechamiento de Recursos Hidráulicos, Escuela de Geocienciasellín).

124 S C I E N C E O F T H E T O T A L E N V I R O N M E N T 3 9 8 ( 2 0 0 8 ) 1 2 2 – 1 3 2

In the international arena numerous studies have focusedon the impacts that changes in atmospheric circulation,temperature, precipitation, water vapor content, and cloudcover could have on, particularly, mountain glaciers andconsequently on discharge rates and timing in highland rivers(Kaser and Georges, 1997; Wagnon et al., 1999; Vuille et al.,2003). Due to their nature, such studies were focused onregional scales. Vuille et al. (2003), for instance, hypothesizedthat changes in temperature and humidity were the primarycause for the observed retreat of Tropical Andean glaciersduring the second half of the 20th century. Interestingly, theseauthors found that near-surface temperatures increasedsignificantly throughout most of the Tropical Andes, varyingmarkedly between the Eastern and Western Andean slopes,with a much larger temperature increase to the west.

In Colombia several studies have been conducted todetermine the most important variables forcing the retreat of

Fig. 2 –High-resolution digital terrain model of the Claro River batemperature (top right), annual minimum temperature (bottom leand maximum altitudes of the Claro River basin are approximattemperatures range from 18.5 to −2.5 °C and from 12.5 to −6.5 °C,almost −4.5 °C. The atmospheric pressure ranges from 820 to 56from 3.2 to 1.2 mm/day and from 2.2 to 1.2 mm/day, respectivelyfrom 15 to 4 hPa, from 17 to almost 6 hPa, and from 21 to 6 hPa, refrom 80 to 94%.

some glaciers (e.g. Euscategui and Ceballos, 1999; Euscategui,2002) and to quantify the water balance in high mountainecosystems (e.g. Diaz-Granados et al., 2005). Euscategui andCeballos (1999) and Euscategui (2002) focused their analyses onthe Nevado de Santa Isabel, located on the Colombian CentralCordillera, and supported their study on some evidences fromthe Sierra Nevada del Cocuy, a major glacier located on theEastern Andean Cordillera. The authors found ‘close relation-ships’ between local weather conditions and glacier reces-sions, and reported a ‘strong incidence’ of El Nino and La Ninaextreme events on glacier retreat. Diaz-Granados et al. (2005)focused on the hydrologic modeling of the upper Blanco Riverbasin, located on the Chingaza páramo, considered the majorsource of water for Bogotá, the Colombian capital city. Theseresearchers merged a horizontal precipitation model and aGeographic Information System to simulate the water supplyin the Blanco River basin, and to predict the potential impacts

sin (top left) and spatial distributions of mean annualft), and mean annual dew point (bottom right). The minimumely 1800 and 5200 m. The mean and minimum annualrespectively. The mean annual dew point varies from 14.5 to0 mb. The potential and actual evapotranspiration rates vary. The minimum, actual and saturation vapor pressures rangespectively. Finally, the mean annual relative humidity varies


that changes in vegetative cover and land use could have onwater balance. These studies, however, have not beenextensively reviewed by the international community, despitethe importance of their subjects.

All these reported evidences suggest that assessments ofchanges in local physical variables are extremely importantfor an improved understanding of the mechanisms andimpacts of climate change, and for calibration and verificationof general and regional circulation models. In order to under-stand evidences of changing climatic conditions and exploretheir potential implications on the integrity of high mountainecosystems, we aim to analyze several historical time series(ground truth data and satellite info) to detect significantchanges in the mean and/or the variance, and/or significanttrends in various climatic variables. Analyses focus on aspecific high elevation region located on the west slope of theColombian Andean Central Mountain Range (ACMR).

2. Study area and data

2.1. Study area

One of the most important high mountain ecosystems islocated on the ACMR in the ‘Los Nevados’ Natural Park, on theEl Ruiz–Tolima Volcanic Massif (see Fig. 1). Los Nevadosprotected area is distant 140km west of Bogotá, has an exten-sion of about 58,000ha, and has three ice-capped mountains(the El Ruiz, the Santa Isabel, and the El Tolima) and two highsnow-covered mountains with ephemeral snowfields (the ElQuindio and the El Cisne). These high peaks have summit

Table 1 – Historical time series (meanmonthly temperatures – toGlobal Historical Climate Network

WMO station

ID Name Latitude Longitude Elevation (m) Av

8014902 Chinchina 5.0N 75.6W 1360 Jan8014904 Chinchina 5.0N 75.6W 1360 Jan8014911 Chinchina 5.0N 75.6W 1310 Jan

WMO station

ID Name Latitude Longitude Elevation(m)

Avp

8014902 Chinchina 5.0N 75.6W 1360 Jan/Dec

8014904 Chinchina 5.0N 75.6W 1360 AprDec

8014911 Chinchina 5.0N 75.6W 1310 Jan/Dec

8021000 PereiraMatecana

4.8N 75.8W 1338 Jan/Dec

8021100 Armenia ElEden

4.5N 75.7W 1204 Jan/Mar

8021101 El Paso 4.5N 75.6W 3264 Jan/Dec

8021400 IbaguePerales

4.4N 75.1W 928 Jan/Dec

elevations ranging from 4900 to 5321m above sea level. Animportant watershed of the ‘Los Nevados’ Natural Park is thehighmountain basin of the Claro River, which is located on theWest flank of the Central Cordillera and is currently fed bynumerous mountain torrents originating high in the snow-fields of the El Ruiz and the Santa Isabel (see Fig. 2). This articledeals with the analysis of possible changing climatic condi-tions observed over recent years in the Claro River basin.

2.2. Data studied

2.2.1. Regional dataSeveral cloud characteristics, such as cloud amount, toppressure, top temperature, and optical thickness were ana-lyzed for multiple clouds (all types, high-level, middle-level,low-level, and deep convective clouds) occurring over theCentral Andean region. Datasets are available for the gridpoints ID 3556 (03°45′N; 76°15′W), ID 3699 (06°15′N; 76°47′W),and ID 3700 (06°15′N; 74°16′W) and for the period from July,1983 through August, 2001 (Rossow et al., 1996). Meanmonthlytemperatures and total monthly rainfall records from sevennearby weather stations of the Global Historical ClimateNetwork (GHCN) located on both flanks of the Andean CentralMountain Range were also processed (see Table 1; source:Baker et al., 1995). All these data were downloaded from theData Library of the International Research Institute for Climateand Society, IRI (http://iri.columbia.edu/).

2.2.2. Topography and climatic conditionsA detailed high-resolution digital terrain model of the ClaroRiver basin was created using cartography on a 1:25,000 scale,

p – andmonthly rainfall totals – bottom –) available from the

Monthly temperatures (°C) Trend in themean

(°C/decade)ailable period Mean SD Min Max

/1951–Dec/1970 18.9 0.6 17.4 20.5 +0.2/1951–Dec/1970 20.6 0.6 19.2 22.5 +0.4/1971–Dec/1980 21.0 0.8 19.3 23.6 (Only one decade)

Monthly rainfall total (mm) Annualtotal(mm)

Trend inthe

mean(%/

decade)

ailableeriod

Mean SD Min Max

1951–/1970

212.3 92.5 26.6 466.0 2,540 −6.0

/1950–/1979

192.5 107.1 0.0 608.0 2,280 −6.0

1971–/1980

213.4 91.2 9.0 505.9 2,560 (Only onedecade)

1951–/1993

176.8 89.7 5.0 496.0 2,090

1950–/1989

166.4 101.6 0.0 455.0 1,970

1950–/1979

152.4 99.8 1.0 572.0 1,810 −4.0

1955–/1993

157.3 88.4 1.0 494.0 1,900 −6.0

http://iri.columbia.edu/


available at the Colombian Geographical Institute. The spatialdistributions of the mean and minimum annual tempera-tures, mean annual dew point (see Fig. 2), and atmosphericpressure (not shown) were estimated using regression func-tions on altitude above sea level, according to the equationsdiscussed by Poveda et al. (2001) for the Andean region. Thepotential and actual evapotranspiration rates were estimatedthrough the equations proposed by the National CoffeeResearch Centre, CENICAFE (Chaves and Jaramillo, 1998),regionalized for the Colombian Central Andes. Finally, thespatial distributions of the actual vapor pressure, saturationvapor pressure, mixing ratio, saturation mixing ratio, andrelative humidity were estimated through the Clausius–Clapeyron equation, adapted to the Andean region.

2.2.3. Local climate dataTotal daily sunshine [h], total daily rainfall [mm], daily mini-mum temperatures [°C], daily maximum temperatures [°C],and mean daily relative humidity values [%] from a nearbyweather station (ID 2615515 Las Brisas, located at 04°56′N,75°21′W and altitude 4150m) were also processed. Data per-taining to thewindowperiod comprising from January, 1981 toDecember, 2005 were obtained for the analyses. Daily sun-shine allowed the estimation of the total monthly sunshine,the total number of cloudy and sunny days, the maximum,mean and minimum daily sunshine values, and the standard

Table 2 – Historical time series available from Las Brisas local w

Climatic variable Availableperiod

Total monthly sunshine [h] Jan/1982–Dec/2005

2Total days per month null sunshine [number]Total monthly sunny days [number]Daily maximum sunshine [h]Daily mean sunshine [h]Daily minimum sunshine [h]Standard deviation daily sunshine [h]Total monthly rainfall [mm] Jan/1981–Dec/

20032

Total dry days [number]Maximum daily rainfall [mm]Total annual rainfall [mm] 1981–2003 2Total annual dry days [number]Minimum monthly temperatures [°C] — warmestdays

Jan/1981–Dec/2003

2

Minimum monthly temperatures [°C]Minimum monthly temperatures [°C] — coldestdaysStandard deviation minimum temperatures [°C]Maximum monthly temperatures [°C] — warmestdays

Jan/1981–Dec/2003

2

Maximum monthly temperatures [°C]Maximum monthly temperatures [°C] — coldestdaysStandard deviation maximum temperatures [°C]Maximum monthly relative humidity [%] Jan/1981–Dec/

20032

Mean monthly relative humidity [%]Minimum monthly relative humidity [%]Standard deviation relative humidity [%]Maximum monthly diurnal temperature range [°C] Jan/1981–Dec/

20032

Monthly diurnal temperature range [°C]Minimum monthly diurnal temperature range [°C]Standard deviation diurnal temperature range [°C]

deviation of daily sunshine records. Daily rainfall totals wereused to estimate the total annual and monthly rainfall values,the total number of dry days per month and per year, and themaximum daily rainfall records. Daily minimum and max-imum temperatures were used to estimate the minimum andmaximum values during the coldest and warmest days, aswell as the standard deviation of daily temperature records.Daily minimum and maximum temperatures were also usedto estimate the maximum, mean and minimum monthlydiurnal temperature range, as well as the standard deviationof such climatic variable. Daily relative humidity was used tocalculate the maximum, mean and minimum relative humid-ity values, and the standard deviation of daily records. De-tailed information of available and missing periods, as well asthe mean, standard deviation, minimum and maximum va-lues of each climatic variable is presented in Table 2.

3. Results and discussion

3.1. Observed changes

The total amounts of all cloud types, high-level, middle-level,low-level, and deep convective clouds occurring over the pixelrepresented by the grid point ID 3556, reached average valuesof 80.6, 30.9, 34.8, 5.5, and 5.3%, respectively. The reduction in

eather station

N Total samplesize

Mean Standarddeviation

Min Max

88 202 71.9 30.0 17.3 165.84.9 3.4 0.0 17.0

24.5 3.8 13.0 31.08.1 2.1 3.1 11.72.5 1.0 0.6 5.50.0 0.1 0.0 0.62.3 0.7 0.8 4.0

76 239 120.1 61.7 6.5 326.9218 10.9 5.4 0.0 29.0

21.7 11.7 1.3 99.03 20 1417 231.4 1083 1806

20 118 30.6 37 17376 186 3.0 0.9 1.4 7.0

1.2 0.6 −0.6 3.1−1.0 2.0 −10.0 1.4

1.0 0.4 0.5 3.176 144 11.3 1.6 8.0 20.0

8.4 1.0 6.0 10.65.5 1.1 0.0 9.0

1.6 0.3 0.9 2.676 184 98.2 2.0 90.0 100.0

92.0 3.9 79.4 98.176.9 8.6 55.0 95.05.4 2.0 1.1 10.6

76 143 11.2 2.2 7.6 21.07.2 1.0 4.8 9.63.6 1.0 0.8 6.62.0 0.5 1.0 4.3

Fig. 3 –Historical time series of monthly (gray solid lines) and 3-month moving average (black solid lines) sunshine, temperature and relative humidity from the local weatherstation ID 2615515 Las Brisas for the window period comprising from January, 1980 to December, 2005. Top left panel: total number of sunny days per month (TSD) along withmaximum monthly temperatures – average – (ATmax) and maximum temperatures during the warmest (MTmax) and coldest days (mTmax). Top right panel: total number ofsunny days per month (TSD) along with minimum monthly temperatures – average – (ATmin) and minimum temperatures during the warmest (MTmin) and coldest days(mTmin). Bottom left panel: maximum (MRH), mean (ARH) and minimum (mRH) monthly relative humidity values. Bottom right panel: maximum (MDTR), mean (ADTR) andminimum (mDTR) monthly diurnal temperature range.

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the amount of such clouds reached 3.94, 1.95, 1.54, 0.76, and1.71%, respectively, over the 218-month observing period.Changes or trends in the time series of top temperatures andtop pressures are not present during the analyzed period.Trends in the mean of the historical time series of monthlytemperatures and monthly rainfall amounts are observed insome of the available regional records. Table 1 summarizesthe results for the GHCN weather stations.

Changes in the mean and the variance, as well assignificant trends in some of the historical time series ofsunshine, rainfall, maximum and minimum temperatures,and relative humidity were observed at the local weather sta-tion over the period from January, 1981 to December, 2005.Fig. 3 depicts some of the major findings of the exploratoryanalyses. Neither the total monthly sunshine nor the dailymean andmaximum sunshine historical time series exhibitedappreciable trends. However, the total number of days permonth of null sunshine (foggy days) slightly decreased duringthe period from January, 1982 through December, 2005, andhence, the total number of sunny days per month (TSD)increased by 2.1days over this period. The historical timeseries of total annual/monthly rainfall and total number of drydays per year/month, suggest that no changes in the meantook place during the period from January, 1981 throughDecember, 2003. Nevertheless, the maximum daily precipita-tion values exhibit an increased occurrence of unusuallyheavy rainfall events, particularly due to two unprecedentedevents of 99 and 85mm/day that happened in January, 1996and January, 1998, respectively.

The minimum monthly temperatures during the warmestdays (MTmin) decreased from 3.3 to 2.7°C over the period fromJanuary, 1981 through December, 2003. Conversely, the mini-mummonthly temperatures during the coldest days (mTmin)increased dramatically from almost − 2.0°C to − 0.3°C overthe same 23-year period (in the 1980s and the early 1990s,the minimum daily temperatures used to reach values ofalmost − 8.0 and − 10.0°C, but in recent years such tempera-tures have reached only values as cold as − 3.0°C). As aconsequence of these two opposite trends, the minimummonthly temperatures (ATmin) do not show significantchanges in the mean over the period from January, 1981through December, 2003. On the other hand, the maximummonthly temperatures during the warmest days (MTmax)increased noticeably from 10.7°C in the 1980s to almost 12.8°Cin the early 2000s (two unusual maximum daily temperaturesof 17.4 and 20.0°C were observed in May, 2001 and September,2002, respectively). The maximum monthly temperaturesduring the coldest days (mTmax) also increased from 5.1 to6.1°C during the period from 1981 through 2003. As aconsequence of these two similar trends, the maximummonthly temperatures (ATmax) exhibit a change from anannual temperature of about 8.0°C in the 1980s to almost 9.4°Cin 2003.

The maximum monthly relative humidity records (MRH)decreased from almost 100% in the 1980s to 96.5% in the early2000s. The mean and minimum monthly relative humidityvalues (ARH and mRH) also decreased from 96.1 to 88.2% andfrom 83.8 to 70.6%, respectively, over the same period. Inseveral instances during the 1990s and the early 2000s, thedaily minimum relative humidity reached values below 60%

(July, 1994; January, 1997; June, 1998; February, 2000; and July,2003). Finally, the maximum, mean and minimum diurnaltemperature range (MDTR, ADTR and mDTR) increased from10.6 to 12.1°C, from 6.5 to 8.1°C, and from 3.1 to 4.2°C, res-pectively, during the period from January, 1981 to December,2003.

Besides the observed changes in the mean of the men-tioned time series, the daily minimum sunshine values, themaximum daily rainfall totals, and the maximum tempera-tures during the warmest days exhibit increases in thevariance of their historical records. Moreover, the time seriesof ATmin and mTmin show decreases in the variance duringthe analyzed periods. Such changes are also evident in thetime series of the historical standard deviation (SD): max-imum daily temperatures and daily relative humidity valuesshow evidence of increased SD, whereas minimum tempera-tures exhibit decreased SD over the available 23-year periods.

3.2. Trends and potential driving mechanism

Based on the available period 1981–2003, records gathered at alocal weather station located on the west flank of El Ruiz–Tolima volcanic massif at an altitude above 4000m, suggestthatminimumtemperatures during the coldest days increasedat a rate of 0.6°C/decade (0.0055 ± 0.0018°C/month), whereasmaximum temperatures during the warmest and coldest daysincreased at rates of about 1.3 and 0.6°C/decade (0.0109 ± 0.0017and 0.0051 ± 0.0011°C/month), respectively. Estimated increas-ing trends in temperature in low levels (nearby weatherstations at around 1300m) ranged between 0.2 and 0.4°C/decade over the available period 1951–1970. The rates of in-crease inmaximum,mean andminimumdiurnal temperaturerange in the weather station located at an altitude above4000m reached 0.6, 0.7, and 0.5°C/decade (0.0054 ± 0.0024,0.0058 ± 0.0011 and 0.0040 ± 0.0011°C/month, respectively).Maximum, mean and minimum relative humidity recordsexhibit reductions of about 1.8, 3.9 and 6.6%/decade (− 0.0147 ±0.0019, − 0.0328 ± 0.0036 and − 0.0550 ± 0.0080%/month,respectively).

Increasing trends in temperature are likely to increaseprecipitation in the form of rain particularly over the areas of‘permanent’ snow, which used to have snowfall or only lightrain. Analyses suggest that, even though the local weatherstation exhibits no changes in the mean of annual andmonthly rainfall totals during the period 1981–2003, itevidences an increased occurrence of unusually heavy rainfallevents. One weather station located nearby at 3264m showsa decreasing trend in annual rainfall of 4%/decade duringthe period from 1950 through 1979. At altitudes around 1300m,regional weather stations show annual rainfall totalswith decreasing trends of about 6%/decade over the period1951–1970.

Changes inseveralother climaticvariableshavealsooccurredin the selected high mountain region: observations suggest thatthe reduction in the amount of all cloud types over the areareached 1.9%/decade during the period from 1983 to 2001.Accordingly, the totalnumberofdayspermonthofnull sunshine(foggy days) decreased significantly, andhence, the total numberof sunny days per month (TSD) increased by 2.1days over theperiod from January, 1982 through December, 2005.


All these trends could be driven by changes in circulationpatterns in the Colombian Andes Mountains. As depicted inFig. 1, the Andes Cordillera is divided in Colombia into threehigh branches (the Western, Central and Eastern Cordilleras)by two large rivers, the Rio Cauca and the Rio Grande de LaMagdalena. The climatology of the Central Andean Colombianregion is strongly influenced by the behavior of three majorclimate features: the Choco low-level westerly jet CLLJ (Povedaand Mesa, 2000; Vernekar et al., 2003), which blows from thePacific Ocean and enters the country at almost 5°N andbetween 850 and 1000mb; the Easterlies, which blow at al-titudes above 4000–5000m; and the Northeastern winds,which tend to blow from North to South along the valleys ofthe Cauca and Magdalena rivers. The intensity of the CLLJdepends on the difference between sea surface temperaturesin the Colombian Tropical Pacific Ocean (TPO) and El Nino 1 + 2region (Poveda andMesa, 2000). The inter-annual variability ofthis low-level jet is dominated by the El Nino–SouthernOscillation ENSO cycle: the CLLJs ‘is weaker in the warmphase of ENSO than in the cold phase’ (Vernekar et al., 2003).The dynamics and interactions between TPO, the CLLJ, theEasterlies, the valley currents, and the orography of the AndesMountains at these latitudes lead to complex local scalemotions, considered the major mechanisms controlling theformation of clouds and storms. The west upwind side of theAndean Central mountain range (CMR), exhibits importantcurrents of lifting incoming air during the afternoon andstrong movements of masses of sinking air during nighttime.

The diurnal counter-clockwise cell formed over the westflank of the Central Cordillera brings significant amounts ofwater vapor from low to high levels in the atmosphere,sometimes reaching altitudes of about 7000m. The moistconvection produced during this uplifting process plays asignificant role in the local climate effect of the high AndeanCMR. During the night, the upslope winds are reversed andblow from the peaks to the Cauca valley lowlands. Suchclockwise cell encounters a counter-clockwise cell comingfrom the opposite side of the valley, creating a zone of deep

Fig. 4 –High altitude water body in the headwaters of Santa BarbPark, Andean central mountain range, Colombia. High altitude wwas taken in September, 2005; picture on the right, two years ladisappearance of the water body.

convection that is associated with the occurrence of heavystorms over the Cauca River valley. These patterns are inaccordance with those by Vernekar et al. (2003), who analyzedthe variability of the lower tropospheric circulation andprecipitation on diurnal, intra-seasonal and inter-annualtimescales: they suggested that the CLLJ and the precipitationpatterns in the region show strong diurnal variability withnocturnal maximums during the long summer period Janu-ary–March. It is hypothesized, although not assessed here,that the currents of lifting incoming air during the afternoonsare weakening due to changes in the intensity of the CLLJ andthe valley currents, and due to increases in atmospherictemperatures and changes in vegetative cover of the Westflank. As a consequence, less water vapor is being producedover cloud forests and less fog is reaching high altitudes onthese mountains. Hence, current scenario shows that fogtends to be ‘trapped’ in low levels of the atmosphere, and onlyhigh-level clouds (which have the net effect of increasingsurface temperatures) are ‘covering’ these high mountainecosystems. Changes in atmospheric stability and the liftingcondensation level are consequently expected in these areas.

4. Conclusions

Changes in themean and the variance, and significant trends inhistorical timeseries ofminimumandmaximumtemperatures,relative humidity, rainfall events and sunshine were observedat the headwaters of the Claro River. Over the period fromJanuary, 1981 through December, 2003 minimum and max-imum temperatures during the coldest days increased at a rateof about 0.6°C/decade, whereasmaximum temperatures duringthe warmest days increased at a rate of about 1.3°C/decade.Interestingly, rates of increase in ambient temperatures in thehigh mountain region were significantly higher than thoseobserved at lowland weather stations. Maximum, mean andminimumdiurnal temperature ranges also increased at rates of

ara and Las Juntas creeks, Claro River, ‘Los Nevados’ Naturalater bodies exhibit a marked seasonality (picture on the leftter); the medium-to-long-term effect is, however, the


about 0.6, 0.7, and 0.5°C/decade. Maximum, mean and mini-mum relative humidity records, conversely, showed reductionsof about 1.8, 3.9 and 6.6%/decade. Finally, the headwaters of theClaro River experienced no changes in the mean of rainfalltotals, contrary to what was observed in lowlands where,generally speaking, it was detected a tendency towards drierconditions. However, the high elevation area evidences anincreased occurrence of unusually heavy rainfall events duringthe period 1981–2003.

Moreover, reductions in the amount of all cloud types ofabout 1.9%/decade were observed over the area during theperiod from 1983 to 2001. As a consequence of the reduction inthe number of foggy days, the total number of sunny days permonth increased by 2.1days over the period from January, 1982through December, 2005. These decreases in the amount ofcloudscouldhavecontributed to the retreat of glacier icecaps, aswell as to changes in local albedoand radiationbalance. The lossof icecaps causes ‘abrupt changes in stream-flow, because of thelack of glacial buffers during dry seasons’ (Bradley et al., 2006)and because of the shrinking anddisappearanceof highaltitudewater bodies and turberas (see pictureson Figs. 4 and5). Changesin the mean and the variance of minimum and maximumtemperatures, decreases in relative humidity, and increases in

Fig. 5 –Permanent water-reservoir habitats (turberas) in the headwbottom left), and Sietecuerales Creek (bottom right). The first thrand high altitude water bodies. The Sietecuerales turbera used tdisappeared in the 1980s.

the amount of days of significant incoming sunlight, lead toslow upward shifts in the transition between life zones. On afaster timescale, these climatic changes could favor theoccurrence and rapid spread of natural andman-induced forestfires, which could undoubtedly disrupt the integrity of highmountain ecosystems and cause dramatic losses of biodiversity(seepicturesonFig. 6). In summary, all these striking alterationsand their intrinsic feedback mechanisms are threatening thesefragile ecosystems, causing sudden losses of unique mountainspecies, and giving us steady signals of very adverse conditions.

High elevations are areas of primary concern because theyprovide as much as 90–100% of the freshwater resources fordrinking, irrigation, and industrial supply in surrounding aridand semi-arid lowlands, and because they are hotspots ofbiodiversity (Diaz et al., 2003). Bradley et al. (2004 and 2006)suggested that significant changes in high mountain regionscould be expected in the years to come, since temperatures inthese areas could rise more than those at lower elevations.Should such predictions effectively occur a significant propor-tion of Colombian communities are going to be seriouslyaffected: over 75% of Colombia's population lives in theAndean region; 5million people out of these 34million personslive in the surrounding areas of the Los Nevados Natural Park.

aters of Alfombrales Creek (top left), Claro River (top right andee turberas still receive water supply from mountain ice capso receive supply from El Cisne ice-capped mountain, which

Fig. 6 –Los Frailejones (Espeletia hartwegiana) Valley, headwaters of the Claro River. Pictureswere taken inMarch, 2006 (left) andMarch, 2007 (right). These unique mountain species grow at a rate of few millimeters a year.


People are settled in several large cities, villages, and towns inthe immediate lowlands because those temperate areasprovide moderate climates that offer enjoyable living condi-tions and because the rivers on the slopes of those mountainssupport their drinking water demand. Moreover, the econo-mies and activities of these communities depend directly onthese high mountain watersheds because they produce largehydroelectric power potentials and they satisfy the waterdemand of agricultural regions located in the interveningCauca and Magdalena valley lowlands. Accordingly, futureefforts will be focused on the economic assessment of theenvironmental goods and services provided by the páramos ofthe Los Nevados Natural Park, mainly water supply and basinrecharge, climate regulation, ecosystem integrity and biodi-versity. Short and long-term economic impacts of the loss ofsuch natural resources due to the ongoing changing climateshould be quantitatively estimated through direct and indirectassessments.

Undeniably, several gaps of knowledge remain in theunderstanding of changes in atmospheric stability and theirrole on the alteration of the local microclimate. A denser long-term monitoring network is extremely needed to fulfill suchgaps and improve our ability to simulate and forecast futureclimatic conditions. But we cannot wait until dramaticreductions in water supply take place in the region. Policies,strategies, and actions intended to ensure considerable levelsof environmental goods and services in Colombian highmountain ecosystems need to be implemented immediately,particularly because we are undoubtedly facing the ongoingglobal changing climatic scenario. Fortunately, Colombia iscurrently conducting an ambitious project aimed at definingspecific pilot adaptation measures and policy options to meetthe anticipated impacts of climate change on these areas.Among its major goals, the project is conducting severalactivities to maintain high levels of biodiversity in theseecosystems, as well as to ensure considerable levels of watersupply, extremely needed to satisfy human consumption,agriculture activities, industrial processes, and hydropowergeneration. Moreover, the project is strengthening the cap-ability of the Colombian government to produce and dis-seminate continuous and reliable climate information

relevant to high mountain ecosystems. We are preparingourselves, but the scenario is definitely adverse.

Acknowledgements

We thank Adriana Maria Molina, Sandra Cristina Arias, andCatalina Londoño Cadavid from Programa en IngenieríaAmbiental—Escuela de Ingeniería de Antioquia, Arnold Gor-don from the Lamont-Doherty Earth Observatory—ColumbiaUniversity in the City of New York, Alvaro Jaramillo from theCentro Nacional de Investigaciones de Café—CENICAFE, andKelly Cunningham and Juan Esteban Quiroz Giraldo for alltheir valuable comments. We thank the Unidad Adminis-trativa Especial del Sistema de Parques Nacionales Naturales(UAESPNN) de Colombia and the field team (Luis FernandoGiraldo and Alirio Tibaguy) for all their support. We also wishto thank two anonymous referees for their valuable sugges-tions. Current activities are being supported by Dirección deInvestigación, Escuela de Ingeniería de Antioquia.

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