Glacier changes in the Pascua-Lama region, Chilean Andes (29° S): recent mass balance and 50 yr surface area variations A. Rabatel, Hélène Castebrunet, V. Favier, L. Nicholson, C. Kinnard

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A. Rabatel, Hélène Castebrunet, V. Favier, L. Nicholson, C. Kinnard. Glacier changes in the Pascua- Lama region, Chilean Andes (29° S): recent mass balance and 50 yr surface area variations. The Cryosphere, Copernicus 2011, 5 (4), pp.1029-1041. ￿10.5194/tc-5-1029-2011￿. ￿hal-01871525￿

HAL Id: hal-01871525 https://hal.archives-ouvertes.fr/hal-01871525 Submitted on 11 Sep 2018

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | S, 0 19 ◦ S), the ◦ 4 Discussions S to 33 ◦ W; 5000 m a.s.l.), ◦ The Cryosphere S/70 ◦ , and C. Kinnard 3 ` eres, France S): recent ´ eophysique de l’Environnement ◦ S (Escobar et al., 2000), on Piloto Glacier, , L. Nicholson 0 1 2308 2307 35 ◦ 21% of their 1955 surface-area, and that the rate ± ` eres, France ¨ , V. Favier at Innsbruck, Innsbruck, Austria 2 ´ etude de la Neige, Saint Martin d’H , H. Castebrunet 1 ´ e Joseph Fourier, Laboratoire de Glaciologie et G ¨ ur Geographie, Universit ˜ no Southern Oscillation and to the Pacific Decadal Oscillation. W) is very close to the arid diagonal, and coincides with an apparent northerly 0 ´ eo France, Centre d’ 01 ´ et ◦ This discussion paper is/has beenPlease under refer review to for the the journal corresponding final The paper Cryosphere in (TC). TC if available. Centro de Estudios Avanzados en Zonas Aridas (CEAZA), La Serena, Chile Institut f M Universit of the Pascua-Lama region.found on The Echaurren nearest Glacier, study Chile, sites 33 from this subtropical region are evolution of the cryosphere (including glaciers,is rock a glaciers major and seasonal concern snowous for cover) hydrological local (e.g. Favier populations et due al.,Vuille 2009) to and and the climatological Milana, impact (e.g. 2007) Masiokas on etedge studies water al., of carried resources. 2006; glaciological out processes Previ- in at70 high this elevation. region The highlight Pascua-Lama the regionlimit (29 of lack glaciation of in knowl- tertropical Chile; north zone. from Glacier this mass-balance area measurements glaciers are are not almost available in absent the until vicinity the in- to El Ni 1 Introduction In the arid to semi-arid subtropical region of Chile and Argentina (27 we present: (i)ice-bodies 6 in years the of area, glaciological includingglacierets a surface and discussion mass-balance of characterization measurements themass-balance of from nature variability; the of 4 the and importance studied (ii)gion of glaciers changes since and winter in 1955, mass-balance surface-area reconstructedshow to of that from 20 annual ice-bodies aerial ice-bodies have in photographsof lost surface-area the 44 and shrinkage re- satellite increased images, inpresent the which an late interpretation 20th of century. inter-decadal From glacier these changes, datasets which we appear to be linked Since 2003, aglacierets in the monitoring Pascua-Lama region program ofpermitting the Chilean has the Andes (29 study beenhigh-elevation of conducted area glaciological where on processes no measurements several on were glaciers ice-bodies previously in available. and a In this subtropical, paper arid, Abstract 4 Received: 30 August 2010 – Accepted: 23Correspondence October to: 2010 A. – Rabatel Published: ([email protected]) 2 NovemberPublished 2010 by Copernicus Publications on behalf of the European Geosciences Union. 3 The Cryosphere Discuss., 4, 2307–2336,www.the-cryosphere-discuss.net/4/2307/2010/ 2010 doi:10.5194/tcd-4-2307-2010 © Author(s) 2010. CC Attribution 3.0 License. 2 (LGGE), UMR5183, Saint Martin d’H Glacier changes in the Pascua-Lama region, Chilean Andes (29 mass-balance and 50-year surface-area variations A. Rabatel 1 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C ◦ 5.5 − ). Finally, W) retreated 0 43 ´ on de Atacama). ◦ S, 69 0 www.glims.org 32 11.4% of its 1955 surface- ◦ erent in this transition zone − ff for 2008, Golder Associates, in 2007 and the ice is gener- 1 2 − W), Ginot et al. (2006) obtained a 0 S (e.g. Wagnon et al., 1999; Francou ◦ 55 1.2 m a ◦ 1500 km north on Zongo and Chacaltaya 16 ± ∼ ∼ S, 69 2310 2309 0 08 ◦ C, and basal temperature at 112.5 m depth was ◦ 6.2 W) changed little from 1981 to 1997. Rivera et al. (2002) used 0 − 50 ◦ 120 m (Table 1). All these ice-bodies are comprised of cold ice and S (Leiva et al., 2007) and ∼ 0 S, 69 0 27 er until now only limited knowledge of current local mass-balance pro- ◦ over the 1955–1984 period which represents ff 10 ◦ 2 Glacier monitoring of several glaciers and glacierets in the Pascua-Lama region was This paper focuses first on the results of the glacier mass-balance monitoring pro- and ice flow, where2009). it exists, Their is surface-area ranges minimalally from (2.0 thin 0.04 except to in the 1.84 km where case it of reaches a few largerare glaciers thought like Estrecho, to Ortigas be 1in cold-based or an Guanaco throughout; ice-core depth-averaged borehole icein drilled November temperature at 2008 measured 5161 was m a.s.l.(Ginot, personal in communication, the 2009). central part of Guanaco Glacier tribution is mainly controlled by topography, withern all slopes ice bodies of being the found onet highest the summits, al., south- spanning 2009). athe range This of redistribution distribution 4780–5485 of m is a.s.l snow aof (Nicholson by peaks consequence and predominantly of crestlines. shading northwesterly All from winds ice-bodies solar to have radiation relatively the smooth, and leeward gently side sloping surfaces 2 Study area 2.1 Pascua-Lama glaciers/glacierets network Figure 1 shows the studiedest ice part bodies of in the the HuascoA Pascua-Lama River small region basin located (southern number in part ofdeemed the of glaciers, ice-bodies high- while the the Chilean shows others Regi are surface more properly features referred indicative to as of glacierets. Their flow dis- and can be and GLIMS (Globalglacier Land changes Ice over Measurements theclimate. last from fifty The Space, contribution yearsshed are of is discussed glacier examined by ablation within Gascoin to the et al. the context (2010). hydrological of regime regional of the water- both of which represent significant additions to glaciological databases such as WGMS gram in the Pascua-Lamawithin region this to subtropical better zone. understand Then the it documents climate/glacier glacier relationship changes over the last 50 years, area in this regiongain is an very understanding of small. glacier behaviour Theseconditions. and studies its relation need to to present be and future complemented climate in orderinitiated to in 2003. Theor term avalanching “glacieret” snow, defines which an shows ice-bodyService, no formed WGMS). surface primarily signs by of blowing flow (World Glacier Monitoring by 0.52 km area. At Cerrorecord of Tapado summit net accumulation (30 bedrock, over the which 20th showed century largeNicholson from et interannual an al. variability ice (2009) core but showed drilled in no a down significant recent to inventory trend. the that the Finally, total extent of glacierized and studying the glaciersthe of hydrological this cycle. region is2006) Paleoglaciological crucial studies can to (e.g. o understand Kull thecesses, et role patterns al., and of relationship glaciers 2002; withations in Ginot local and climatology. et relationship Previous al., between work glaciersfour on and studies. glacier climate vari- In in 1999, this Leivagentina transition showed (30 zone that consists the of terminusaerial of the photographs Agua to Negra determine Glacier that in Tronquitos Glacier Ar- (28 glaciers in the Bolivian intertropicalet al., Andes, 2003). Climate conditionsthose are considerably observed drier 450 in km the south Pascua-LamaAndean region on divide than Echaurren on Glacier Pilotoa or Glacier consequence, (Falvey on glaciological and the processes Garreaud, Argentinian are 2007; side likely Favier to of et be the al., di 2009). As Argentina, 32 5 5 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (1) C and ◦ C, while ◦ 0.6 1 − + S) to Mediter- ◦ et al., 2002). Annual ff C for annual means over ◦ 6.8 − , for which surface-area is denoted i C and ◦ 5.3 − ˜ no Southern Oscillation (ENSO) and the Pa- 2312 2311 . e . S) (e.g. Falvey and Garreaud, 2007). The region is bounded ◦ in m w ˜ nez, 1997; Favier et al., 2009), and slightly increasing temperature
S  i s is the annual mass-balance of an area i is the total ice-body surface-area. The ice-body surface-area was subdivided i b S C for monthly means, and between b ◦ 5 m in average. X ± = , is calculated as: Climate variability over the 20th century has been characterized by decreasing pre- Precipitation shows a marked seasonality: 90% occurs in winter between May and Automatic weather stations (AWS) operated within the Pascua-Lama mine site show , and 10.9 a a i B homogenised measurement network. TheB annual mass-balance of the whole glacier, monitored (Esperanza, Toro 1, Toro 2 andcho Guanaco). and In 2005, Ortigas two 1) other were glaciers2) (Estre- added was to added. the networkmeasurements The and obtained in winter 2007 by mass-balance a a issite further combination glacieret calculated on of (Ortigas from the snow snow ice-bodies,pits cores depth and are and and sampled depending probing density on onmined at each the from each glacier(et) size in elevation stake of changes earlysmall the spring. measured size ice-body, at of Summer one the bamboo mass-balance ice-bodies or stakes is and two inserted deter- absence snow of in crevasses the or ice. seracs allow a The relatively well Annual surface mass-balancefloating-date measurements system (Paterson, usingAssociates 1994) the S.A, have and been glaciological sinceAvanzados carried method en 2007 out Zonas and by since Aridas the 2003 (CEAZA). glaciology Initially, by three group Golder glacierets of and the one Centro glacier were de Estudios are 3 Methods and data where s manually to allocate eachrepresentative. stake This a surface-area division portion was ofvation, carried with glacier out additional primarily surface consideration on for of thecover which where basis were transient it of persistent snow ele- was surface cover, penitents deemed features.using or Glacier a debris surface digital topography elevation was modelof reconstructed (DEM) a stereographic computed pair by of the 2005the Ikonos INFOSAT images, middle society so of on the the the DEM existing corresponds basis mass-balance to conditions time-series. in Vertical and horizontal precisions secular drying trend (Vuille and Milana, 2007). temperatures can be slightly positiveannual for a mean few temperatures hours remain a negative− day year in round summer, (ranging but monthly between and the 2002–2008 period), so that precipitation at this elevation occurscipitation only (Santiba in solid form. (CONAMA, 2007). Causes forbut a in reduced addition precipitacion to are ENSOfrom not variations the yet Amundsen (Escobar clearly Sea and understood, region Aceituno, may 1998), provide an high-latitude additional forcing explanation for the observed in this region of Chile (Escobar and Aceituno, 1998). that temperature seasonality is(Fig. linked 2). to At the “Laat annual Olla” “Frontera” cycle station station of (4927 (3975 m m solar a.s.l.), a.s.l.) radiation which annual intensity coincides mean with temperature the is lower limit of glaciation, circulation is characterized by prevailingthe westerly winds, flow with along a the southwardaverage deflection Chilean relative of side humidity remains of below the 40% mountain and range clear skies (Kaltho predominate. August (Fig. 2). Small precipitationmer events (February can occur and at March)precipitation high is due elevation mainly in to driven the convectivecific by late activity. Decadal the sum- Oscillation El (PDO), The Ni with inter-annual warm phases variability associated of with higher precipitation Climate in northernranean Chile in varies the from south extremelyby (33 arid the in Pacific Ocean the6000 m to north a.s.l.), the both (26 West of and which by exert the an influence Andes on Cordillera climate to conditions. the East Synoptic (reaching scale 2.2 Climatic conditions 5 5 15 10 25 20 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | = erent ff 1:60 000) = ´ etrico (SAF), and from Ikonos satel- ects the delineation of the edge of the ff 2314 2313 1:60 000), 31 May 1978 (SAF, scale 1:50 000). Satellite images were acquired on the = = software. For each data source, a margin of uncertainty on the delin- ® C), so melt water from diurnal fusion refreezes during the night and superimposed ◦ Accumulation processes result mainly from snow precipitation during winter. How- Ablation processes will be discussed in detail in a separate paper on the SEB data. Additional glaciological and climatological data sources used for the discussion of Surface energy balance (SEB) measurements were also conducted by CEAZA with Glacier surface-area was computed from aerial photographs taken by the Hycon 20 beyond the focus of the current paper. in ice temperature. ever, formation of superimposed ice wasspring also observed and during summer field campaigns seasons. oversured the on During Guanaco the and ablation− Ortigas season, 1 surface glaciers temperature drops mea- ice below is zero accreted during to the glaciertribution night ice of and (down snow. mass-balance to The over importance the of ice-bodies this is phenomenon in hard the to dis- quantify and its estimation is We just mention here that:summer (i) snowfall ablation events occurs have by asurface both by strong melting halting influence melting and (due sublimation; on tocreased and ablation increased turbulence (ii) processes albedo), associated by with at limiting reduction the sublimation ofthe (due glacier the glacier to roughness from de- length) and incident by radiation isolating positive contribution which allows a rapid decrease 4.1 Mass-balance analysis 4.1.1 Accumulation and ablation processes atThe the glaciological glacier surface year inmarily this during region the is winter fromfrom season, April October i.e. to to March. April March. Exceptionally toand dry September, solid Accumulation or accumulation whereas occurs wet is ablation pri- years possible dominates can at modify any this time simple of scheme, year. changes since the mid-20th century areof presented. glacier Finally, changes we over discuss the possible last causes current decades glacier in mass-balance light monitoring of theries. and knowledge other acquired glaciological, through and the climate data se- they have the longest data series available (6 years). Secondly, glacier surface-area ize the climate-glacierglacierets relationship (Esperanza, Toro in 1 and semi-arid Toro 2) climate and Guanaco conditions. Glacier are considered, Only since the three corresponds to the totalthe uncertainty ice-body (Perkal, on 1956; the Silverio delineation and Jaquet, multiplied 2005). by theglacial perimeter changes over of recent decades are given in Table 3. 4 Result and discussion Firstly, we present and discuss results of the mass-balance monitoring to character- to identify the glacieraccurate contour; identification of and the (4) edgeerrors a of for possible the each glacier, residual estimated year snow visually.independent and cover Table the errors). 2 preventing details resultant the the This totalglacier uncertainty total throughout (quadratic uncertainty its sum a contour. of the The di uncertainty in the calculation of the surface-area 1:70 000), 5 April 1956 (Hycon,and scale 26 November 1996 (SAF, scale 1 of March 2005cally and corrected the and 26 georeferenced to March the 2007 2005Geomatics Ikonos (1 m image using resolution). the commercial Alleation PCI images of were ice-bodies geometri- wasor estimated. digital This photograph; (2) results thewith from: process manual (1) of delineation the geometric of correction; pixel the size (3) outline, the of which error the depends associated image on the pixel size and the ability 3 AWS on Guanaco andbe Ortigas presented in 1 a glaciers forthcoming and publication on and the will Toro not 1Society be Glacieret. discussed and The here. the SEB Chilean will lite Servicio images. Aerofotogramm The aerial photographs were taken on the 27 April 1955 (Hycon, scale 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 0.71 = r 0.75 with 01 ( 01) is found = . . 0 0 r ρ < ρ > 41%) and the mean = cient between annual ffi cient of variation, CV, is ffi 12 with . 0.80 with 0 = = r 2 erent colour and measurements r ff 72%). Hence, the large winter mass- 0.65 m w.e. (CV = ± 0.68 m w.e.) than the biggest glacier of the 1.58 ± 2316 2315 − 1.16 − 01). . 0 0.43 m w.e.). ˜ no years, the whole glacier remains covered by snow ± 0.44 m w.e. (CV ρ < 01) for the glacierets and ± . 0 0.41 − 0.55, ρ < = 2 r 0.42 m w.e. in average for the 4 ice-bodies). This quasi-balanced ± 0.76 with = 0.05 01) for Glaciar Guanaco. This means that for the glacierets (glacier), 56% . − r 0 0.70 m w.e. The glacierets (Toro 1, Toro 2 and Esperanza) show more neg- ± 01 ( ˜ . no conditions, which are known to bring heavy snow accumulation (Escobar and ρ < 0 A weak, but not significant, negative correlation ( Similarly, there is no relation between winter mass-balance and altitude (Fig. 4b). In Over the 2003–2009 period, all ice-bodies show large annual mass-balance variabil- Within the study period, the 2005–2006 year has the least negative annual mass- 0.97 winter mass-balance and summerrole mass-balance of winter are mass-balance not variability on independent annual mass-balance variables. variability appears The to be 4.1.4 Relationships between mass-balance terms Figure 5 shows thebalance respective on influence of themass-balance summer annual mass-balance and mass-balance. and winter winterρ < mass-balance mass- The (summer correlationwith mass-balance) coe is (64%) of the mass-balance variability isand produced 58% by (51%) variations by of summer winter mass-balance. mass-balance Note that the sums exceed 100% because may result frombe stronger more melt sheltered at fromsurrounding low valley high elevation. sides, winds both and Lowerpothesis favouring needs receive melting parts to during increased be of the long confirmed the ablation by wave SEB season. ice-bodies radiation measurements. may This from hy- glacier surface is predominantly snow-free,end or of only the patches ablation of season.tions snow/firn on These remain the remaining at ice-bodies, snow/firn the winter patches where snow are pack, wind which in redistribution is sheltered not ofsequently, related posi- concepts snow to of the generates accumulation/ablation altitude a zone but andbe to locally the equilibrium-line easily thicker glacier applied. altitude topography. cannot Con- between summer mass-balance and altitude (ablation decreasing with altitude) which meaningless for the ice-bodies in this area. fact, during wet years,even i.e. at El the Ni end of2003 the year, J. melt Schmok, season personal and communication, is 2008). therefore Conversely, an for most accumulation years area the (e.g. 2002– annual mass-balance and altitude. The concept of mass-balance gradient is therefore presented, but to improve clarity,made on each Glaciar year Guanaco has are circled. a It di clearly appears that no relation exists between Aceituno, 1998; Masiokas et al.,considered 2006). ice-bodies In is a significantly general correlatedLama way, with annual base mass-balance precipitation camp for recorded ( the at Pascua- 4.1.3 Relationships between mass-balance terms andFigures altitude 4 a, b andwinter c mass-balance respectively and show the summer relationship mass-balancesurements between with made annual altitude. at mass-balance, On each these stake figures, on mea- the 4 ice-bodies over the 2003–2008 period are all balance ( situation is linked to higher2009 than average normal recorded precipitation at (1.7El Pascua-Lama times base Ni higher camp than at the 3800 2001– m a.s.l.) associated with ative annual mass-balance values ( area, Guanaco Glacier ( ity, which appears to73% increase for with the the 4 glacierbalance ice-bodies size measured and on (the the 106% coe 4 ice-bodies forwinter is Guanaco mass-balance Glacier). is 0.61 Thebalance mean variability summer has mass- a dominant influence on the annual mass-balance variability. Figure 3 presentsice-bodies in the the measuredable. Pascua-Lama surface region Over mass-balance where− the 6 data 6 years years, for of the the measurements average annual 4 are mass-balance avail- selected for the 4 ice bodies is 4.1.2 Annual mass balance and inter-annual variability 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | for for 1 1 − − ects, lower ff 0.22% a 0.14% a ± ± 9%). 0.26 m w.e. for Guanaco). 21%, with a maximum of ± ± ± 0.73 − = s B 2318 2317 for the 14 glacierets and 0.27 1 for the 14 glacierets and 0.18 − 1 − 16%), than for the glaciers (19 0.63% a ± ± 0.49% a ± (1.37 1 (0.56 01) between these variables. The systematic observation of peni- − . 0 1 − 0.46 m w.e. for the glacierets and ± ρ < 0.73% a ± 1.86 0.46% a 0.64, − ± = = s The aerial photographs and satellite images used allow analysis of 3 periods of 2 r B 0.47 the 6 glaciers). During the last period, mean annual surface-area loss for all the evolution: 1955/56–1978 (23/22years). years), Other 1978–1996 aerial (18 photographssnow years), exist, cover e.g. and 1981, precludes 1996–2007 but thenual (11 they were surface-area identification taken loss of in for glacierface. spring each when outlines. period, The first expressed Figureof as period 6 1.09 a shows shows function a thethe of mean an- the annual 6 1955/56 surface-area glaciers). loss sur- for all Over the the ice-bodies second period, mean annual surface-area loss falls to Surface-area changes of 6 glaciersbeen and reconstructed 14 glacierets from in the theimages mid-20th Pascua-Lama (see region century Sect. have using 3).mean aerial surface-area Results photographs loss are and for presented satellite 79% all in for Toro the Table 2 4. ice-bodies glacieretlarger reaches and Over for a 44 the the minimum glacierets whole of (54 period, 9% for the Ortigas 1 glacier. The loss is much The role of penitents hasripio been and discussed Purves, in several 2005).process studies (e.g. in Lliboutry Lliboutry, a 1954; (1954) Cor- favourable field mentions to melting, that of the melting penitents. presence is ofsummer penitents mass-balance the Thus, could on main partly the by ablation explain glacierets. creating the more and negative maintaining4.2 conditions more Glacier surface-area changes than clean-snow surfaces. Theyinfrared also and suggest that infrared high wave-lengthswavelengths intensity are are likely of crucial to radiation be for atsion higher near- from the at the heated start boder surrounding of ofwe rocks the observed (e.g. penitent ice-bodies that Francou due growth; on et to Guanaco these al., a Glacier larger 2003). most emis- of Unlike the the surface glacierets, is not covered by penitents. snow form penitents more readily, and have penitents with larger peak separations can be influenced byresults dust (Bergeron deposition et from al., the 2006) unglaciated have surroundings. demonstrated that Laboratory surfaces covered with dusted elevation-driven temperature-dependent contrast between thePossible causes ice-bodies of are enhanced ablation needed. onsurface the albedo glacierets are due stronger to edge natural e on dust the deposition glacierets and than penitents the whichitent glacier. are height Comparison all of at more measured evident 28 summer( ablation ablation stakes and pen- on thetents 6 on ice-bodies the showed glacierets asurface in significant as summer correlation they is are probably small related to ice-bodies dust and deposits therefore on a their larger whole portion of their surfaces of the glacierets (Sect. 4.1.2)( is mainly due toThis a more more negative negative summer summer mass-balance mass-balancetion of might stakes be on partly thebut attributable glacierets to as extending the to the distribu- atemperatures lower altitude-dependence elevation are compared of persistently to sub-zero ablation the at glacier, is this elevation, very additional weak explanations to (Sect. an 4.1.3; Fig. 4), and conclusions can be drawn whenbodies comparing with the glaciers results of obtained theis on Arctic the Pascua-Lama region dominant ice- where factor the in variability the of annual summer mass-balance mass-balance variability4.1.5 (Koerner, 2005). Causes of higher summer ablationComparison on glacierets ofglacierets winter and Guanaco mass-balance Glacier shows that and the more summer negative annual mass-balance mass-balance between the on interannual mass-balance variations, e.g.explains in only the 10–15% French of Alps,batel the winter annual et mass-balance mass-balance al., variabilityboth (Vallon 2008). et the al., higher This 1998; variabilitymer Ra- characteristic of mass-balance winter of (41%) mass-balance Pascua-Lama in (72%) ice-bodies and this lower may subtropical variability result area of compared from sum- to mid-latitudes. Similar higher than for mid-latitudes glaciers where summer mass-balance is the main control 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − 1.32% a ± 2.06 m w.e. = a B for the 6 glaciers). 1 − 0.61% a ± ˜ no events, which are in their turn associ- 2320 2319 1.2 m w.e. on Guanaco Glacier with an uncertainty = a B for the 14 glacierets and 0.96 01). Note that this correlation analysis includes a highly positive an- . 1 − 0 erencing (e.g. ff ˜ na events and so with precipitation deficits. Quintana and Aceituno (2010) ρ < 1.20% a 0.75, ± = On a longer time scale, surface-area changes of the small Pascua-Lama ice-bodies According to Escobar and Aceituno (1998) and Quintana and Aceituno (2010), pre- In Fig. 7, we present the cumulative annual mass-balances of Echaurren Glacier be- Glacierets consistently experienced a greater percentage surface-area loss over all 2 r a positive phase of the PDO. Note that the recent negative phase since 1998 is not so ment with more pronouncedwell glacier as surface-area negative loss measured inis annual thus the mass-balances not Pascua-Lama during surprising region recentIndeed, as that although years the limits (Sect. surface-area of 4.1). retreat the(imposed periods appears by It considered the to for available be the aerialPDO related glacier photos to shifts, surface-area and changes the satellite a PDO. images)glacier first do surface-area not qualitative change strictly insight and matchized PDO reveals the by regime. good greater The consistency surface-areathe first loss, between second and correspond period, the third to associated rate periods, a with character- negative of lower phase rate of of surface-area the change, PDO, corresponds while to Echaurren Glacier, locatedEchaurren 450 km Glacier further was South. quasi-stablelow between rate of 1975 The surface-area loss and cumulative recordedphase 1993, mass-balance on of the in the of Pascua-Lama PDO agreement ice-bodies index. and withnegative Since the the mass-balance the positive late values 1990s, associated Echaurren Glacier with has a shown generally negative PDO phase and in agree- GPR profile di of 15%, J. Schmok,this personal method communication, to 2008). determinemethod, this annual Despite estimated mass-balance the positive ingood lower annual comparison accuracy mass-balance agreement with value of with on theglaciological the Guanaco glaciological method Glacier highly for is the positive same in annual year on mass-balance Echaurren Glacier: measuredshow using close the agreement with the cumulative annual mass-balance record of the larger reflects the relationship betweenprecipitation the (Escobar annual et mass-balance al., atmass-balance 2000). series Echaurren from Glacier Echaurren Although and and the Guanaco( glaciers period are considered significantly correlated isnual short, mass-balance for annual the year 2002–2003 estimated on Pascua-Lama ice-bodies from an overall agreement between the PDO and mass-balance variations. Actually, this link tween 1975 and 2009 and the PDO data between 1955 and 2009. These data reveal cipitation in the Chilean subtropical zoneis is linked associated to with PDO frequent phase.ated and A positive with intense PDO high El phase precipitation Ni amounts,merous whereas La a Ni negative phase isshowed that associated during with the nu- 1950s, 1960snormally and low, 1970s, the but frequency this ofthe changed humid years 1980s into was and abnormally ab- the high2000s. early frequency 1990s, of humid becoming years low during again during the late 1990s and early 1977 (change to positive phase),although and commonly accepted 1998 is (change still toif debated negative in the phase). the lack climate The community of laststrong mainly shift perspective as because the on previous the changes. data sets and because it does not appear to be as graphic factors also influence the surface-area changes. 4.3 Possible causes of glacier evolutionFigure since 1955 7 presents thewith mean glaciological, surface-area climatological data loss series ofof and all PDO Pacific variations. the climate The studied variability PDOyears). ice-bodies is that The in a PDO shifts pattern parallel is phase detectedon as at Fig. positive/warm a 7). or negative/cool multi-decadal The phases most time (red/blue recent boxes scale regime shifts (20 occurred in to 1946 30 (change to negative phase), ice-bodies increases to(2.74 over twice the rate ofthe the periods first than period, glaciers.pronounced at In with addition, 2.34 increasing the scatter mean between surface-area individual loss glaciers is (Fig. more 6), suggesting that topo- 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 0.44, = 2 C/decade r ◦ 0.19 + 21% of the 1955 area. After the first ± ˜ nez, 1997; CONAMA, 2007), rather than tem- S) have been presented in this study. This 2322 2321 ◦ 01) and El Indio precipitation series ( . 0 ρ < 0.62, = C annual isotherm and so melting remains limited and hence, ◦ 2 r 2 − 01). These findings strengthen our hypothesis of a link between Pascua-Lama Under such climatological and geographical conditions,mains where negative year-round air due temperature to re- the high elevation, glacier annual mass-balance period, 1955–1978, annual equivalent glacierdown surface-area between recession 1978 rate and slowed 1996, anda has rate accelerated as since high the as late experienced 1990s during toThe the reach 1955–1978 mass-balance period. recordmass-balance of and surface-area Echaurren changesthe Glacier ice-bodies at are shows Pascua-Lama 450 km despite notable apart. the similarities fact to that is more strongly linked to variability inThe precipitation average than glacier air temperature. surface-arearegion recession over for the the 1955–2007 period 20 was studied 44 ice-bodies in the . 0 – – – All these considerations support the hypothesis that, in this region of the Andes, In contrast, no link between glacier surface-area loss and temperature evolution Since precipitation is driven by the PDO and represents a key factor at Echaurren in the sub-tropicalmonitoring Andes allows of us to Chile improveglaciers our (29 under knowledge semi-arid, and high-elevation understanding conditions. of the behaviour of glacier surface-area changes over recent decadesdecreasing trend were in mainly precipitation driven (Santiba byperature the observed changes. 5 Conclusions Results from a newof glacier glacier mass-balance surface-area monitoring changes program since and the the mid-20th reconstruction century on glaciers and glacierets glacier surface-area loss does notover seem the to be last closely 50firmed related years. to in temperature the However, evolution next ifthe decades, the mass loss the trend and increase of consequently in the rising melting rate summer of at temperatures glacier glacier retreat is surface in con- could this region. increase altitude above the related to the fact that, as mentioned above, Pascua-Lama ice-bodies are found at an Both summer and annualdata present averages a of slight, NCEP/NCARfor summer but 500 mb temperature not over temperature statistically thethe 1958–2007 reanalysis significant, period). strongest positive Although mean trend the annual ( consistently last surface-area decade positive loss shows temperature for all anomalies,temperature anomalies the we (2003 studied and observed 2006) ice-bodies arebalances that and associated observed the with more the on highest positive Pascua-Lama annualbalance summer mass- ice-bodies. data for the Despite year2005–2006 the 2002–2003, suggest lack the summer that of mass-balance ablation summer values was measured mass- for reduced on the 4 ice-bodies. This is probably ice-bodies changes and precipitation over recent decades. over the last 50temperature years anomaly at emerges. the 500ice-bodies) Figure mb for pressure 7 the level shows Pascua-Lama (approximately region the the computed elevation summer from of NCEP/NCAR (November the reanalysis to data. March) 3130 m a.s.l.; about 100geous km for this south). analysis, duringtain Although the several years longer positive with PDO time-series positive phasedard precipitation would (1977–1998), deviations. anomalies both Mass-balance be sometimes series time in advanta- series excess con- comparison of at with 2 Pascua-Lama are stan- precipitation too records. shortboth for sites, However, statistical Echaurren despite Glacier the mass-balanceprecipitation large is series distance significantly ( correlated between withρ < La Laguna precipitation during the hydrological year 2002–2003. Glacier (Escobar et al.,Figure 2000), 7 we shows analysed precipitation anomalies precipitationPascua-Lama at region variability two (El in high Indio the elevation Mine; sites study 3870 located m area. a.s.l.; close about to 50 the km south; and La Laguna; strong as the 1955–1976 negative phase, showing for example a pronounced peak in 5 5 15 25 10 20 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | S, J. ´ on de ◦ ´ on nival en ¨ urauf, J., Novoa, J.-E., ˜ na-like conditions) coin- ´ S), Clim. Change, 52, 359–381, atica en Chile para el Siglo XXI, S), Wat. Res. Res., 45, W02424, ´ on de Atacama, Recopilaci ◦ ◦ ¨ aggeler, H. W.: Glacier mass bal- n (CEAZA) as well as all those who took ı ´ ´ opez, D.: On the origin of water resources ´ omeno ENSO sobre la precipitaci ´ osfera, Informe 0792155016-3.0-IT 005, 2009. 2324 2323 ˜ no-like conditions) coincides with decreased glacier n, C.: 25-year record of mass balance of Echaurren glacier, ı ´ a Minera Nevada. ı ´ ˜ n S, J. Geophys. Res., 108(D5), 4154, doi:10.1029/2002JD002959, ◦ ´ Area de Pascua Lama, Tercera Regi We thank R. Garrido and J. Mar -Gauss, I., Fiebig-Wittmaack, M., Fiedler, F., Th ff ect of snow penitentes, in: Climate and Hydrology in Mountain Areas, edited nea base actualizada de la cri ff ı ´ , N., Bischo ff Glacier surface-area changes over the last decades result mainly from a decreas- A comparison between glacier changes andment: the PDO negative variation phases shows of good the agree- cide PDO with (associated periods with of La high Ni PDO glacier recession (associated rate, with whereas the Elrecession positive and Ni phase even of steady-state the situations. ing trend in precipitation observedrather than in from the air subtropical temperature region changes. over the last century, – – variations in the Central Andesinfluences of and Argentina and implications Chile, for 1951–2005:2006. water large-scale resources atmospheric in the region, J. Clim., 19(24), 6334–6352, 169–177, doi:10.1016/S0921-8181(99)00034-X, 1999. glacier, Las Cuevas river2007. basin, Mendoza, Argentina, Global Planet. Change, 59, 10–16, Ann. Glaciol., 42(1), 417–423, 2005. climatological conditions in the north2002. Chilean Andes (29–30 ance reconstruction by sublimation induced enrichment(Chilean of Andes), chemical species Clim. on Past, Cerro 2, Tapado 21–30, doi:10.5194/cp-2-21-2006, 2006. Pizarro, C., Gallardo, L.,Appl. and Meteorology, 41, Rondanelli, 953–970, 2002. R.: Mesoscale wind regime in Chile at 30 contribution to flow in twoChile, high-altitude The streams Cryosphere of Discuss., the accepted, semi-arid 2010. Huasco Basin, north-central estudios de l recorded by a glacierChacaltaya, in the Bolivia, central 16 Andes2003. during the last decades of the twentieth century: 27(3), 753–759, 1998. central Chile, and itsference relation on with Southern ENSO HemisphereApril events, Meteorology 2000, in: and American Oceanography, Proceedings, Meteorological Santiago Society, Sixth Santiago de International de Chile, Chile, Con- 3–7 118–119,meteorological 2000. conditions and orographic influences, J. Hydrometeo., 8, 171–193, 2007. from high altitude area of Chile’sdoi:10.1029/2008WR006802, Norte 2009. Chico region (29–33 Andes: the e by: de Jong, C., Collins, D., and Ranzi, R.,el Wiley & sector Sons, andino London, de 15–27, Chile 2005. Central durante el invierno austral, Bull. Inst. Fr. Etudes Andines, Phys. Rev. Lett., 96(9), 098502, doi:10.1103/PhysRevLett.96.098502, 2006. by DGF/UCH for CONAMA, CONAMA report, 2007. Lliboutry, L.: The origin ofMasiokas, penitents, M. J. H., Glaciolo., 2(15), Villalba, 331–338, R., 1954. Luckman, B. H., Le Quesne, C., and Aravena, J. C.: Snowpack Leiva, J. C., Cabrera, G. A., and Lenzano, L. E.: 20 years of mass balances on the Piloto Leiva, J. C.: Recent fluctuations of the Argentinian glaciers, Global Planet. Change, 22(1–4), Kull, C., Grosjean, M., and Veit, H.: Modelling modern and late Pleistocene glacio- Koerner, R. M.: Mass balance of glaciers in the Queen Elizabeth Islands, Nunavut, Canada, Ginot, P., Kull, C., Schotterer, U., Schwikowski, M., and G Kaltho Golder Associates S. A.: Gascoin, S., Ponce, R., Kinnard, C., Lhermitte, S., MacDonell S., and Rabatel, A.: Glaciers Francou, B., Vuille, M., Wagnon, P., Mendoza, J., and Sicart, J. E.: Tropical climate change Falvey, M. and Garreaud, R.: Wintertime precipitation episodes in central Chile: associated Escobar, F, Casassa, G., and Gar Favier, V., Falvey, M., Rabatel, A., Praderio, E., and L Escobar, F. and Aceituno, P.: Influencia del fen Corripio, J. G. and Purves, R. S.: Surface energy balance of high altitude glaciers in the central CONAMA: Resultados Proyecto Estudio de la variabilidad Clim Bergeron, V., Berger, C., and Betterton, M. D.: Controlled irradiative formation of penitents, References Acknowledgements. part in field measurements.were provided by Project the funding Compa and logistical support in the Pascua-Lama area 5 5 30 25 20 15 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ´ atico ´ ostico clim ` ere, France, J. Glaciol., ´ on en Chile, in: Diagn 2325 2326 ´ eguilly, A., and Vincent, C.: Twenty-five years (1981- 20 12 36 120 – – – Toro 1 Toro 2 Esperanza Guanaco Estrecho Ortigas 1 Ortigas 2 Glaciarete Glaciarete Glaciarete Glaciar Glaciar Glaciar Glaciarete ´ on en Chile, edited by: Soto, G. and Ulloa, F., CONAF, La Serena, Chile, n, J., Lopez, D., Rabatel, A., Bown, F., and Rivera, A.: Glacier inventory ı ´ ˜ na, C., Casassa, G., and Bown, F.: Use of remote sensing and field data to a ) 0.071 0.066 0.041 1.836 1.303 0.874 0.071 2 sites measured by Golder Associates S.A. (2003–2005), the other numbers represent the number of Geographical and topographical characteristics of the monitored glaciers in the = ˜ nez, F.: Tendencias seculares de la precipitaci b west coast of South America,2007. Geophys. Res. Lett., 34, L23703, doi:10.1029/2007GL031899, ance of Zongo Glacier,doi:10.1029/1998JD200011, 1999. Cordillera Real, Bolivia. J. Geophys. Res., 104(D4), 3907–39023, (Peru) using satellite imagery, Remote Sens. Environ., 95, 342–350, 2005. climatic change from 1844(146), years 93–96, of 1998. observations on Glacier d’Argenti estimate the contribution of2002. Chilean glaciers to sea level rise,de Ann. la Glaciol., desertificaci 34,1997. 367–372, coast of South America (Chile) during the 20th century,2005) submitted to of J. equilibrium-line Clim., altitude 2010. French and Alps mass using balance remote307–314, reconstruction sensing 2008. on methods Glacier and Blanc meteorological in data, the J. Glaciol., 54(185), 1994. of the upper Huascocomparison valley, to Norte central Chico, Chile, Chile: Ann. Glaciol., glacier 50(53), characteristics, 111–118, 2009. glacier change and Location(UTM19S, WGS 84)Surface area (km Max. elevation (m a.s.l.) 401Min. 085 elevation E (m a.s.l.)Max thickness (m) 5235 400 530 E 6 754 775 N 5080 6 399 755 340 055 E N 5200 6 755 010 N 401 495 E 5025 6 753 070 N 401 600 E 6 758 580 5145 N 6 397 4965 748 800 600 E N 6 748 000 N 398 900 5350 E 4985 5485 5030 5225 4775 5245 4975 AspectNumber of ablationstakes First year of mass-balance survey (5) 9 2003 SSW (5) 5 2003 SSW 4 2003 S (5) 14 2003 SSE (7) 14 2005 SE (4) 9 2005 SW 2007 1 S In brackets 2004 Wagnon, P., Ribstein, P., Francou, B., and Pouyaud, B.: Annual cycle of energy bal- Vuille, M. and Milana, J. P.: High-latitude forcing of regional aridification along the subtropical stakes measured by CEAZA. a – means nob data are available Vallon, M., Vincent, C., and Reynaud, L.: Altitudinal gradient of mass-balance sensitivity to Silverio, W. and Jaquet, J.-M.: Glacial cover mapping (1987–1996) of the Cordillera Blanca Table 1. Pascua-Lama region (in 2007). Rivera, A., Acu Santiba Rabatel, A., Dedieu, J.-P., Thibert, E., Letr Quintana, J. M. and Aceituno, P.: Changes in the rainfall regime along the extratropical west Perkal, J.: On epsilon length, Bull. Acad. Pol. Sc., 4, 399–403, 1956. Paterson, W. S. B.: The physics of glaciers, 3rd Edn., Butterworth-Heinemann Ltd, 496 pp., Nicholson. L., Mar 5 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | N 1958–2007 W, 3870 m) W, 3130 m) E W) 0 0 0 0 0 75 02 02 25 ◦ 08 ◦ ◦ ◦ ◦ 28 − ; ; 291 S, 70 S, 70 S, 70 0 0 0 0 0 25 75 ◦ 35 51 12 ◦ ◦ ◦ ◦ 31 − 288 (29 (30 ) 2328 2327 size (m) correction (m) (m) cover (m) (m) ´ ´ on General de Aguas Echaurren glacier 1975–2009 on General de Aguas La Laguna dam 1965–2006 http://jisao.washington.edu/pdo/PDO.latest (http://climexp.knmi.nl) source size to the pixel the geometric delineation possible snow uncertainty Photo/Image Scale/Pixel Error due Error due to Error in the Error due to a Total Additional data sources. Note that for NCEP/NCAR temperature reanalysis data, the Detail of errors associated with the images for each year. The largest error is related 195519561978 Hycon1996 Hycon2005 SAF 1:70,0002007 SAF 1:60 000 Ikonos Ikonos 1:60 000 1 1:50 000 4 1 m 1 m 1 2 20 1 14 1 15 8 3 4 / 7 3 4 10 0 3 3 0 0 23 15 0 0 15 9 3 8 temperature 500 mb NCEP/NCAR reanalysis DataAnnual mass-balance Chilean Direcci Pacific Decadal SourceOscillation Joint Institute for the(PDO) Study (Escobar, of personal the communication) Atmosphere – and Ocean (JISAO, Univ. Washington, (33 1955–2009 Location Duration Precipitation Barrick Gold Corporation El Indio Mine 1981–2005 Precipitation Chilean Direcci Table 3. period before 1958 was not considered because of large inhomogeneities. Table 2. to the geometric correction.consequently the All latter does images not have contain been error due rectified to on this the correction. basis of the 2005 image, Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and a a Glaciar (a) (in grey 5% 9% 3% 6% 5% 8% 9% 5% 4% 6% 4% 8% 9% 8% 9% 12% 11% 10% 12% 15% = Ortigas 1, ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 9 9 = 57 26 33 34 64 78 79 72 15 48 53 . Underlined − − 33 22 60 48 63 42 30 − − − − − − − − − − − − − − − − − − Glaciar Tronquitos, = ´ on de Atacama Guanaco, 18 www.glims.org Regi = ) 1955/56 and 2007 Glaciar Piloto, G.E. 2 = 0.010 0.017 0.030 0.024 0.011 0.007 0.006 0.005 0.007 0.010 0.027 0.006 0.006 0.003 0.006 0.005 0.013 0.040 0.005 0.020 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Toro 1, 9 = Glacier surface area Loss between 2330 2329 Toro 2, 8 = ˜ nitos 0.810 Glaciar Agua Negra, G.P. = Esperanza, 7 = GLIMS Id. Local Name in 2007 (km weather stations. Some glaciers of the area were not considered as they were Estrecho, 6 (b) Ortigas 2. For all the numbered glaciers, surface-area evolution since the mid-20th Surface-area of 20 glaciers in the Pascua-Lama region and their change since the = = Location of the Pascua-Lama region in the administrative Cerro Tapado, G.A.N. ◦ N 1920 G289957E29394S G289966E29393S Ortigas 2 0.071 0.757 1 G289986E29298S Estrecho 1.303 23 G290006E29297S4 Los G289999E29303S Amarillos5 G289953E29325S6 Amarillo G289957E29329S 1.077 7 G289963E29330S8 G289976E29330S Esperanza9 G289981E29332S 0.286 10 G289985E29348S Toro 211 G289932E29352S 0.041 Toro 112 G289939E29352S Guanaco13 G289946E29351S 0.049 14 G289963E29358S 0.066 0.038 G289969E29359S15 1.836 0.071 G289980E29360S1617 G289986E29367S18 G289933E29381S G289948E29387S Ca 0.053 0.140 Ortigas 1 0.030 0.048 0.071 0.873 0.205 0.048 = loss between 1978 and 2007 = not covered by theor aerial west photographs from (for glacier example 18). north from glacier 2, east from glacier 20 and 19 century has been reconstructed“Frontera” (refer to Table 4). Black squares indicate “La Olla” Fig. 1. on the left map). OnC.T. the left, the central and northern parts of Chile (G.T. values correspond to 1956. a Echaurren). On the right, glaciersin studied red: by CEAZA 1 in the Pascua-Lama region are numbered Table 4. mid-20th century. Numbers ofhas the been first generated column using refer to the Fig. GlimsView 1. software The available GLIMS on Id for each glacier Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) s B 3800 m a.s.l.). Temperatures ∼ ) and summer mass-balance ( w B 2332 2331 ), winter mass-balance ( a B Mean annual cycle (2001–2009) of monthly average precipitation (grey bars) and of Annual mass-balance ( over the 2003–2009 period on Toro 1, Toro 2, Esperanza and Guanaco (in m w.e.). Fig. 3. are recorded at “La Olla”(black (grey line; line; “b” “a” on on Fig. Fig. 1; 1; 4927 3975 m m a.s.l.) a.s.l.). and “Frontera” weather stations Fig. 2. monthly average temperature (lines)from recorded manual in measurements the at Pascua-Lama Pascua-Lama area. Mine base Precipitation camp comes ( Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Same (b) Same comparison (b) Same comparison but with summer mass- (c) 2334 2333 values shown are for the linear best fit of stakes measured on all 4 ice bodies. 2 r Comparison of annual mass-balance measurements with altitude on Toro 1, Toro Comparison of annual mass-balances and winter mass-balances computed on Toro Fig. 5. (a) 1, Toro 2, Esperanza glacierets and Guanaco Glacier between 2003 and 2009. comparison with summer mass-balances. but with winter mass-balance measurements. Fig. 4. (a) 2, Esperanza and Guanaco ice-bodies overbalance the measurements. 2003–2008 Lines and period. circlesfor each highlight year. measurements made on Guanaco Glacier Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 standard deviations interval. ± 2336 2335 Glacier surface-area loss (average per period of all the studied ice-bodies) com- Annual surface-area loss per period for 6 glaciers and 14 glacierets of the Pascua-Lama Fig. 7. pared with: (1) Echaurrenbalance; (blue (2) line) annual and variation Guanaco of (redboxes); the (3) line) PDO precipitation glaciers (violet anomaly cumulated line) annual recordedmer and mass- at temperature its anomaly El negative/positive of Indio phases NCEP/NCAR Mine (blue/red 500precipitation mb and and temperature La temperature reanalysis Laguna anomalies data. data dam; Grey represent boxes and for the (4) sum- region in percent of theirgraph; 1955–1956 lines surface-area. plotted Error-bars are are linear not best shown fits for for legibility each of period. the Fig. 6.