Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussions The Cryosphere 2 1740 1739 , and V. Hochschild 2 ˇ cek ([email protected]) , S. Hoerz ´ a 3 , F. Chen 1,2 ˇ cek ´ a This discussion paper is/has been under review for the journal The Cryosphere (TC). Please refer to the corresponding final paper in TC if available. Institute for Cartography, Dresden University of Technology, Helmholzstr. 10, Department of Geography, University of Tuebingen, Ruemelinstr. 19–23, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, 18 Shuangqing Rd., heat source and moisture2003; Sato sink and during Kimura, 2007). the It summer impacts the (Ueno monsoon et circulation as al., a 2001; barrier to Hsu zonal and Liu, freeze onset and water cleanfreeze-up of and ice break-up day dates appear in to case of be the more studied thermally lakes. determined than 1 Introduction Tibetan Plateau (TP) wasto identified changes as in one climate ofproperties, (Liu the and TP most Chen, sensitive has 2000). regions a At of strong the the impact same world time, on because the of global its climate unique system, acting as a large by inspection of highand/or resolution optical high data. salinity Mild arederived winter the by seasons, most linear large likely water regressionA explanations. volume for correlation Trends all in of the the iceconditions phenology ice studied variables showed cover lakes with a duration show parameters high a describing thermal high climatic dependency and variation of local in the space. ice regime. It appears that the The ice phenology of 59 largeResolution lakes Imaging on the Spectroradiometer Tibetan (MODIS) Plateaufrom was 8-day 2001 derived composite from to Moderate data 2010. forstudied Duration region the of due period to the both icecover climate cover and were appears local calculated factors. to for Mean have values fourIn for a groups the each high of duration group variability of lakes ice in definedperiod. several the as lakes Possible distinct reasons showed geographic for anomaliesmany regions. such in lakes anomalous do ice behavior not cover are freeze duration discussed. up in Furthermore, completely the during studied some seasons. This was confirmed Much attention has recentlyPlateau. been paid This to remote the andbasin) impact harsh lakes. of region Ice climate includes phenology change i.e. aof at the the large the ice timing cover Tibetan system of may of provide freeze-up valuable endorheic and information about break-up (closed climate and variations in the this duration region. Abstract The Cryosphere Discuss., 6, 1739–1779,www.the-cryosphere-discuss.net/6/1739/2012/ 2012 doi:10.5194/tcd-6-1739-2012 © Author(s) 2012. CC Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. 1 01069 Dresden, Germany 2 72070 Tuebingen, Germany 3 Beijing 100085, China Received: 5 April 2012 – Accepted: 24Correspondence April to: 2012 J. – Krop Published: 21 May 2012 Analysis of ice phenology ofTibetan lakes Plateau on from the MODIS data J. Krop 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C. ◦ ˇ cek et al., ´ a ciently long time period. Ap- erent regions is often biased ffi ff C for a su ◦ C. They also report a sensitivity of ice phe- ◦ 1742 1741 ects water bodies in high latitudes and altitudes where the ff erences in definition of variables describing the duration of lake ff cult accessibility call for the use of remote sensing methods. Variations in climate Since there are di An important indicator of changes in climate derived from satellite data is lake ice ffi in Canada. Thethat air influences temperature the has ice been phenology for suggested instance as by the Livingstone (1997) most and significant Kourayev et factor 1.2 Factors influencing the lake iceSensitivity phenology of lake phenologyauthors. It to was climate proved variablesUsing that have a BU/FU been numerical are simulation highly investigatedup a sensitive by delay to dates several of changes has as in beenreaction much air to as found temperature. change 4 by in weeks air-temperature Listonnology in for to and 4 freeze-up a and Hall decrease break- (1995) in wind for speed, St which Mary amounts for Lake 2 in weeks for Canada Great in Slave Lake variables as climate indicatorthat varies FU and among BU authors. togetherclimate Liston change, with while and maximum Latifovic ice and Hall Pouliot thicknessof (1995) (2007) are use break-up suggest useful the in end indicators of their ofchoice freeze-up regional analysis and was the influenced of end by lake the ice availability of phenology comparable in in-situ Canada data. instead. However their ice cover a comparison(Brown of and ice Duguay, phenology 2011). records Herecover: Duration for we of di use Ice Cover two (DI)Duration variables which of describing results Complete from the Ice subtraction Cover duration ofFU. (DCI), the of Many which WCI ice lakes is and on defined FO as and theup the plateau in period freeze between December up BU or asof and late simplicity November as since is in it counted January belongs to or to February. ice the A cover same freeze- of ice cycle. the The following choice year of for lake sake ice phenology up Date (FU) in thisbelow study. An the increase ice of in temperature spring ofAppearance leads the of to air a above a detectable and thinning ice of ofoccurs, free the the is water water ice surface, called and after eventually Break-up whichleads to date no to the more an (BU) ice total eventual break in disappearance freeze up. the of up ice following. denoted Further as deterioration Water Clean of of the Ice ice (WCI) . date of the end of the freeze- up period, when the total ice cover is denoted as Freeze- study. The ice formation begins alongduring the the shore formation of of shallow bays. a Ice new growth, thin especially ice, can be interrupted by strong wind events. The 1.1 Lake ice phenology Ice phenology deals withand periodic changes formation in and its decay timing ofFormation as ice of a cover ice over result cover water oftemperature a bodies seasonal during and cold inter-annual season variation fallspearance in below of 0 climate. ice isThe initiated date when when the detectable lake ice surface appears water is temperature referred falls to below as 0 the Freeze Onset (FO) in this ice phenology allows estimateslakes on of the local TP climaticrological are variability stations distributed (Walsh are mainly et concentrated2000). in in al., Derivation the of the 1998). lake central eastern ice The andknowledge phenology part of about western of Tibetan the part, lakes impact the could while of plateau therefore climate meteo- fill (Liu change a in and gap this in Chen, remote our region. in this area arerecords reflected such by as several snow phenomena distribution that2010), (Shreve et are changes al., well in 2009; documented glacier Xu bylake et extent satellite area al., (Ye et (Bianduo 2009; Krop et al., al., 2006; 2009) Bolch that et can al., be therefore 2010)phenology. seen This or as fluctuations has climate in indicators. beenteenoja, proved 1986; in Barry a andglobal Maslanik, number scales 1993; (Walsh of et Duguay recent al., et 1998; studies al., Menguson on 2006; at Che regional al., et 2000). (Ruos- Interannual al., variation 2009) in and lake studies have been focused onour various aspects knowledge of of climate its changeanalysis mechanisms impact of on and the the regional TP impact variations but ground of is measurements. the still Sparseness changing limited. of climatedi An meteorological on unbiased stations, the rough TP conditions is often and hindered by lack of and meridional air motion (e.g. Kurzbach et al., 1993; Barry, 2008). Recently many 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 | ect ect ff ff ˇ cek et ecting ´ ff a ect. ff ect has been ff ect is well known in case of the ff ˇ cek et al. (2011a). ´ a 1744 1743 ´ enard et al. (2002) for instance showed that lake C change in mean air temperature corresponds to a ◦ ects the amount of on-lake evaporation since the lake ice ff ects of lake ice phenology on local or regional climate ff Ground observations of lake ice phenology on the remote TP with harsh winter con- A deep lake such as Nam Co can supply a large amount of heat energy to the ice phenology events from MODISof 8-day lakes snow on composites the for TP a that representative allows group calculation of duration of ice cover period. The relation on the TP is to our knowledge still missing. ditions are not available.the Such case cost of intensive large lakes observationsstation where are (Walker the and further whole Davey, lake 1993). complicated surface Thefor in cannot number instance be of observed in such from stations Canada aof is from shore the globally 140 decreasing, 1990s. sites Obviouslysatellite in the observations. mid-1970s analysis This to of study less lake is than ice focused 20 on phenology sites the on by derivation the the of TP end a has time to series rely of on lake et al. (2000) and Dibikeproaches, et respectively, do al. not (2011) based includelarge on the lakes ground TP. on So observations the far and TPby analysis modeling has of Che ap- been the et carried ice out: al.Nam regime Qinghai Co (2009), of Lake in using two on the the data Centraland NE TP from optical by margin satellite a Ye of data. et the An passive al. overview TP (2011), microwave of using lake satellite combination ice instrument, of phenology passive of and microwave at least the largest lakes determined snow cover in Namsatellite Co and Basin passive has microwave been data compared by on Krop time series1.4 of optical Objectives So far little attentionison has with been high paid latitudesphere to lake lakes. the ice Both cover ice as the regime a of response of to comprehensive lakes changing analyse on temperature of presented the by Northern TP Magnuson in Hemi- compar- large Lurentinan Greatdescribed Lakes in (Eichenlaub, the case 1970). ofplateau For Nam (Li et Co, TP al., which the 2009) is andal. a lake has (2010). large been e This saline analyzed exchange by lake remote process inmore sensing warmer the is data open central obviously by water part Krop interrupted is of by available. the The lake relation freeze-up of when the no lake freeze-up and lake e fall on the downwind shore. This so called lake e atmosphere in the post-monsoonover period a (Haginoya large et relatively al., warmer 2009). open Air water masses area passing during winter can lead to heavy snow While the lake ice phenologyturn is impacted influence by the climate local change,cesses or the lead lake even ice to the regime an regional can abrupt climate.mass in change The and of freeze-up energy the and exchange lake break-up betweenact surface pro- lake as properties water heat (e.g. and albedo), sinks atmosphere.variation a in The in summer lakes ice and basically phenology heat a blocks the sources water-air in interface winter and (Haginoya the et sublimation does al., not 2009). compensate The this e modeling of thedepth lake is ice a cover. determinant M thermodynamic of lake freeze-up ice date model. for Canadian lakes using1.3 a one-dimensional E climate that determines theboth ice the regime duration of ofdivided lakes. ice into There cover local are and and severalinclude the factors climate wind that factors. timing speed Apart a of andof from ice snow snow temperature phenology cover, cover climate which events thus related acts(Kouraev which results et factors as in can al., an thicker be 2007). ice insulating Theare: cover layer. local lake and The bathymetry, factors salinity, this altitude, that absence shape leads have ofregarding a in the the relation shoreline turn importance and to to of lake the area. later particular ice Some break-up factors facts regime for of the lakes lake ice regime can be proved by Hemisphere showed thatchange a of 1 about 5 daysson in et the al., duration 2000). of However theof Weyhenmeyer ice et temperature cover al. season and (2004) (Skinner break-up suggestedof 1993, that Magnu- date ice the break-up is relationship date non-linear, to leading temperature to changes more in sensitive cold reactions regions. However it is not only al. (2007). Analysis of ice phenology of numerous lakes and rivers in the Northern 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 er- − ff 3g l < C while it ◦ erent tran- ff ˇ cek et al., 2011b). ´ a their number reaches al- , out of which 1260 lakes 2 2 ering in size, salinity, altitude ff due to the retreat of mountain ff 1746 1745 C in the northern part of the plateau (Fig. 2). The mean annual tem- ◦ (Jiang et al., 2008). This makes the TP to one of the largest lake sys- distributed mainly in the SW part of the plateau out of which 4 exceed 2 2 . So far there is little known about the bathymetry of even the largest lakes 2 ˇ cek et al., 2011b). Furthermore,the lake shore may have shifted for even hun- ´ a C (Xu et al., 2008). Analysis of meteorological records over the last decades reveals Levels and extent of lakes on the TP experienced high oscillations as a reaction to Most of the lakes on the TP are brackish or saline. An overview of salinity in three There are an enormous number of lakes on the TP di The climate of the study region is characterized by wet summers and dry and cold ◦ dreds of meters duringThese the oscillations last were 40 related yrglaciers to by (Bianduo Yao an et et al. increased (2007), al., runo whoconfusion analyzed 2009; in several the catchments Krop in terminology Tibet. caused Therethe by is same parallel a usage lake. lot of of Often severalscriptions more versions from of than names Tibetan two for often versionsadhere via are to Chinese used a increase in convention the introduced Tibetan by confusion.2007) while the Here compiled di Map we of by decided the the lakes to CAS). and Institute glaciers of on the TP TP (Yao, Research, Chinese Academy of Science (ITP, period of salty lakes inclimate, comparison elevation with etc. freshwater lakes under the same condition i.e. changes in climate conditionsKrop in the past (Zhang and Liu, 2011; Phan et al., 2011; the total sum of ionsof dissolved in inland water. drainage Most basins of and theSW are lakes therefore part on salty. Only the of several TP the lakes representLakes plateau e.g. a in Taro are termini highly Co arid through-flow in basins the lakes withinstance containing little surface the freshwater inflow case (salinity may become of hypersaline Chabyeror which is Caka Lagkor for Co (Zabuye in Lake) the investigatedmelting SW by temperature part Wang of of et the the al. lake Plateau.decreases (2002) water. Salinity The with indeed magnitude influences an of the the increase freezing and freezing of point salinity. depression This leads in turn to shortening of ice cover classes is presented by(Yao, the 2007), “Map while of zoning thedescribed in of Lakes Zheng and and Tibetan Liu Glaciers lakes (2009).lakes Additionally on are according several figures dispersed the on to in Tibetan salinity literature. of their Nevertheless Plateau” salinity the a of Tibetan hydrochemical comprehensive lakes data on type set the describing is TP the is not available. Salinity in the context of limnology represents 1000 km (Wang et al., 2010). southwestern part follows theeastern same part trend of but the with TP smaller turns amplitude, warmer while and the drierand north- (Niu shape. et Putting al., the 2004). most limit of 6880, the covering minimum inexceed area total 1 to km an 0.1 km areatems of on around the 43 000 Earth km than 500 unique km in the high elevation conditions. There are 7 lakes larger perature in the South5 in area aroundthat Lhasa, both that temperature contains and precipitation onlyXu show a an et few increasing al., trend lakes (Liu 2008). exceeds, ences and This Chen, across 2000; general the climate TP. The trend southeastern appears part to of feature TP some becomes regional warmer di and wetter, the 2 Study area The TP has amountain mean ranges elevation Karakorum exceeding 4500 andNorth m Himalaya extending a.s.l. to in and a the it length South of is several and bordered hundreds by of by kilometers. thewinters. Kunlun high Mean Shan in temperatures the southern on part the of TP thedrops decreases TP to towards has below 0 a north. mean The annual western temperature between and 0 and 5 assess the potential of iceally phenology a for trend the in indication durationlakes of of is climate the derived. oscillation. ice Addition- cover in the period from 2001 to 2010 for the studied of ice phenology to (i) local factors and to (ii) climate variables is analyzed in order to 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 | ¨ oll 2004), which as 1748 1747 erences in the ice regime of lakes in such a large area the ff were selected. This resulted in 65 lakes which are well distributed over the 2 erence Snow Index (NDSI) and several other criteria tests that minimizes the impact ects. Instead we used an adaptive approach. The dataset was first divided by a me- Global Lakes and Wetlands Database – GLWD (Lehner and D For the extraction of ice phenology events from MODIS data lakes larger than The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument is carried ff ff was calculated from MODIS images covering autumn period after the monsoon and lakes were divided intodenoted four by regions abbreviations Northwest, NW, Northeast, NE,DI, Southwest DCI, SW, phenology and SE dates Southeast respectively and (see trends Fig. for these 1). groups Mean werea values calculated global of and dataset compared. createdthe as definition a of combination the ofchecked spatial various against extents available the of sources, MODIS the wasediting lakes. images. used of The for In the shorelines some shoreline from had instancesaccount the to for a small GLWD be certain were variations involved of amount i.e. the shifts of lake or manual shapes shape caused adjustments. by In mixed order pixels, to a mean image TP (Fig. 1). Out ofChabyer this Caka group and 6 Ringinyububu Co) lakes hadtoo (Yinmar, to Yamzhog noisy Yumco, be Nau for sorted Co, a Gyeze outhas Caka, since reliable highly their extraction histograms complex of were tentacle-like ice shapeder phenology. that to For account results for instance in regional the an di Yamzhog extremely Yumco noisy signal. In or- with the values abovemean median values corresponding were to calculated unfrozenthen from conditions. applied both to In datasets. the the The range nextrange limited thresholds step 0–100 by 5 %. these % This calculated and mean helpedcation 95 values % us of instead to were of shallow suppress the water whole theused as influence lake class outlines of ’No and mixed snow’ the pixels, and real misclassifi- shorelines. remaining discrepancies between100 km the phenology dates. Factors 5thresholds % for and the 95 identification % offluence for the of the ice noise. area phenology Such eventse of in absolute open order threshold water to would were excludedian the be chosen into in- two insensitive as parts: to one various below median disturbing corresponding to frozen lake and the other one reasons a threshold for the ice/water extent had to be set in order to detect the ice estimates than querying thesince number of it pixels accounts belonging better to for classes lake miss-registrations ice between and MODIS snow scenes. For practical of cloud cover. The classification schemefollowing matches five the classes: needs of Snow, No this study snow, as Lake, it Lake contains ice and3.2 Cloud Derivation of ice phenology datesThe from frozen the MODIS lake 8-day surface composite8-day is data composites. represented We by adopted classesa the Lake measure percentage ice for of and the pixels Snow classified frozen in as the status class MODIS of water the as lake. This approach provides more accurate the entire Earth’s surface everymorning) 1 and to Aqua 2 satellites daysa (in in reasonable the 36 level afternoon). in spectral In this bandsal., order by study 2007) to both we instead keep Terra used (in the ofand the the data primary MODIS is amounts snow spectral a at product bands. compositeDi MYD10A2 This classification (Hall product image et has over a a resolution 8-day period of 500 based m on a Normalized the case for instance of highthe latitude medium Canadian resolution lakes optical (Howell data, et whichhundred al., have meters, 2009). spatial allow Furthermore resolution for in the derivationis order of in of ice contrast several phenology to passive forkilometers microwave tens data, which of with are lakes spatial useful on resolutionswe the only in used TP. for the This MODIS the order data of largest for tens the lakes of derivation (Che of et lake ice al.,by phenology 2009). two of In polar Tibetan this orbiting lakes. study satellites Terra and Aqua. The system is able to acquire data of 3.1 MODIS instrument and data description The study area features favorably lowthe cloud data cover during acquisitions winter by and optical spring instruments periods are and not hindered by polar darkness as it is 3 Data and methods 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 | erences in days. A RMS error ff erence in days between each point ff 1750 1749 ˇ cek et al., 2011b) during the study period. These variations usually do not exceed ´ a erence as low as 1.2 days proves that there is no systematic error in the open water In order to identify correctly the FU in case of multiple intersections of the open water In the next step histograms were extracted from all MODIS images in the time series ff it is related to thermal inertia of the lake. gons due to concaveRadar shape Topography Mission of (SRTM) digital theA elevation shore. simple model Lake shape using altitude the indexbe edited was was easily centroids. defined identified retrieved as from in a theof the ratio GIS the Shuttle between shore. layer Lakes of perimeter with lakes. and asequence This area, complex a index shape which lower describes are can likely thermal shape to inertia complexity Lakes have a in with lower high comparison depth shape with and index a asup are a rounded usually likely con- lake starts. to of Also provide the the more same shallow parameter size. bays lake where area the itself freeze- is a proxy of the lake volume and In an attempt totracted identify ice the phenology main datators. drivers was The compared of local with the factors which data icelongitude, were describing regime possible elevation, local to of area describe and the and by climateGLWD available study shape. fac- using data area Latitude were: automatically the latitude, and generated ex- manually longitude centoids shifted were of inside retrieved lake the from polygons. lake the in The several centroids cases were when they fell outside the lake poly- with the same percentagecalculated of as open root water meanequal was square to derived. error 9.6 An of days overall was thesedi accuracy obtained time from was di twenty then validationarea images estimation. for Nam Co. Mean time 3.4 Correlation of the lake phenology with the local and climate factors and they are from variousdata), satellite Landsat, sensors TerraSAR-X and including SPOT. Envisat/ASAR Foropen (wide each water swath validation mode area image a was percentagedata derived which of and was the compared interpolated for with eachrepresenting the day. the A water validation time curve image di and from a MODIS corresponding 8-day point on the interpolated curve images. These images cover various phases of freeze-up and break-up processes The accuracy of theday derivation composites of was the estimated open by water a area comparison for with a a lake number from of the reference MODIS satellite 8- possible early freeze up. FromAnalogously this all point the the other first iceof threshold phenology the crossing dates open were was water identified searched (Fig.obtained has for. 3). 8-day as Since sampling, a the the linear points identified exact interpolation day points of of representing the each the first iceopen ice point water phenology curve phenology below date for and was dates a above were visual the check. plotted threshold. together All 3.3 with the Validation of open water area derived from MODIS 8-days composites induced by classification uncertainty. Thevariation magnitude of of the the noise watercloud becomes cover. curve evident during as the summer period, whichcurve does with not the threshold, complement which is mainly due to noise a point has been set well before separately for each lake.for Graphs the of whole percentage time of period.as open The intersection ice water phenology area of events were the wereIt constructed then was curve identified observed representing automatically that openand multiple water intersections break-up with with period. thresholds thresholdsrefreezing This occur 5 during % during can the the and occur freeze-up break-up 95 dueday %. compositing period to approach. or ice Another by reason retreat is cloud caused the cover presence by not of wind accounted noise events in for the and by time the series 8- shape between single acquisitionsvector data. was Another used source as ofconnected a to the the base size lake volume/size variation layer oscillations isKrop (Bianduo for et probably adjustments al., a 2009; of shoreline Wu and displacement the the Zhu, 2008; pixel size of MODIS. before the lake freeze-up. This image which shows in one layer spatial variations of 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 | erence ff erences in ff ect of mixed pixels. ff erence between the DI erences in the behavior ff ff erence in DCI between the two northern ff erence can be seen between the southern ff 1752 1751 cients were calculated between variables describ- ffi erence in DCI between the corresponding southern and ff erences between the trend in DCI and the trend in DI for the erences in ice regime over the TP.DCI and DI feature a high ff ff erences in altitude of the lakes. Each of these two regions contains ff erence in the ice cover duration in terms of both DCI and DI for the studied ff ect impacts more strongly smaller lakes and lakes with complex shape. Since cult to set a threshold of certain minimal lake size as a clear limitation of the ff ffi The northern regions feature higher variations in both the DCI and the DI. This is For characterization of the climate for the selected lakes it is not possible to sim- same region. This reflectsand variation in it duration is of also the highly freeze-up and influenced break-up by periods no complete freeze-up events. The di 4.2 Trends in duration of iceTrends cover in in the DCI four and regions year DI (Fig. for 6). all They(Table regions 2). are were The listed standard fitted together deviations toof reveal with the mean lakes the magnitude values in corresponding of calculated each di suggests standard for that group. deviations there every The in is especially ain high strong this region. influence standard There of are deviation the di in local factors case on of the ice group regime NE of lakes Bangong Co (4227 m a.s.l.)in in the the lake ice NWlakes cover region. along duration Another a in reason parallel both for decreasingand of the the DCI the for range lower southern all of variation the regions latitude.of studied is The mean lakes durations di the is of distribution on freeze-up of and average the 49 break-up days periods. which corresponds to the sum of around 10 degrees. Thenorthern di regions amountswest-east approximately direction one is and muchand lower half the as months. two the The southern di respectively. gradient regions amounts in for the two weeks anddue in to DI a only higher di 6one lake and of 13 distinctly days lower altitude Ayakkuh Lake (4261 m a.s.l.) in the NE region and There is a di regions (Table 1). The mostand remarkable the di northern regions whichirradiation indeed with corresponds the to decreasing the latitude. gradient The in studied the lakes Earth span over surface a latitude di 4.1 Duration of ice cover for lakes in the four regions the water, for instance Ulan Ul Lake. figures for the whole TP wouldble not to be extract representative. the For several ice lakesthe phenology it MODIS due was not to 8-day possi- a composites. highThis This level e was of noise most in likelythe the due lower signal to obtained limit from the ofbe e the di used method inmethod. terms In of the lake case size ofMODIS 8-day some is composites, lakes shape which open can dependant, water be it was probably would explained mis-classified by as a class high land sediment load in in the 4 Results and discussion The lake ice phenology forof 59 MODIS lakes 8-day on composites the for TP theoverview period has of from been the 2001 regional extracted to from di 2010. thevariation This time amongst allowed series us the to four get geographical an regions (Tab. 1). This means that any general et al., 2005). Thismaximum temperature data for the set period contains fromused 1950 the monthly maximum to precipitation temperature 2000 and interpolated and theof to calculated mean, the a cumulative 1 1 minimum, above km km zero square grid. and temperature identified We lake by basin the climate. lake Correlation polygon coe centroiding for ice the phenology characterization and of the those describing the local and climate factors (see Table 3). ply rely on measurementssparseness. of The nearby density ground of stations meteorologicalern decreases stations part towards because West, of of leaving theGyaring the their plateau Co whole west- have with a someits ground five lake meteorological shore. stations. station Instead To we located our rely in knowledge on the temperatures only from immediate Nam the vicinity WorldClim Co of database and (Hijmans 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 | C ◦ (Ta- 2 respectively. However there is a high vari- 1 − 1754 1753 erences in salinity and depth. The shortest ice cover in ff C (Fig. 2). These climatic conditions are reflected by a ◦ 2 − ect of snow cover slowing up the break-up, changes in albedo etc. ff The trend in duration of lake ice period is positive in terms of both DCI and DI (Ta- this group appart of Gyeze Caka has Longmu Co with the mean DI of only 94.9, while during the wholeduration period of from ice cover 2001 bothup to in completely. terms Gyeze 2010. Caka of In even DI appearedthe addition and ice studied DCI Longmu free and period. with Co in no Theas some has signs reason 42.3 seasons of m very could did freezing by short not up be Yao (2007) during freeze- salty the and lake depth the in hypersalinity in Tibetan). in It the thevariation is case case indeed of of of also ice Gyeze due Bangong cover Caka to in (cakaaltitude Co the means range this influence given and group of likely these is also three high di lakes (Table that 1). the Other factors are a relatively high This group is locatedthe in Kunlun the Mountains very and(Table western it B1). part contains The of lowest fourteenan and the lakes elongated the TP with shape. largest bordered an On lake from altitudeDCI average is range the 118.0 lakes Bangong and of north in Co DI 840 by this m groups at 186.4 region (Table 1). days the Two feature lakes: with Indian Bangong a the Co border long and highest Gyeze with ice Caka variability did cover in not period: comparison freeze-up completely with the other to have a rapid increaseUlan, in Ayakkuh the Lake, ice Lixi cover duration Oidaima in Co high terms and of variation Yaggain the Canco. inUlan DI: All ice and Dogai of Yaggain Coring, cover Canco, these Xijir duration both lakesimpacted the (Table have A1). by increasing also occurrence trend In of and the no the case freeze-up high events variation of in are Dogai the4.4.2 strongly studied Coring, period. a Xijir Region Northwest 2002. ble 2) and amounts foration 2.5 of and trend 3.0 days in yr bothtrend the of DI DI and while DCI for (Table 2). the Eight rest lakes of of the the lakes group it have is a negative. positive Four lakes in this region appear Canco and Dogai Coring did not freeze up completely during the seasons 2001 and features remarkably short meanof DI the group of mainly 88.3 due days to in its comparison low with elevation the (4161 m average a.s.l.). DI Lakes Xijir Ulan, Yaggain This group contains in totalble A1). fifteen The lakes ice out regime ofwith of which lakes annual five in are mean this region larger below long is than determined duration 300 km by of cold ice continentalation climate cover of (DCI both 131.6 DCI daysmore and and than DI one DI (Table thousand 1). 180.2 metersportant A days). (Table factors large 1) There that and range contribute is a of to a large this elevations high range high in variation of vari- this of latitude group, ice are which cover indeed duration. is im- Lake Ayakkuh in the relevant periods.confirmed The in presence this of way for open a water number during of usual lakes4.4 (see ice-on Table 3). season was Results for the four geographic4.4.1 regions Region Northeast 4.3 Validation of the no completeIt freeze-up appears events that there wasmay no be complete surprising freeze-up in intemperatures. an some This area years occurs with for also several harshCo. in lakes. climate This In the and case order with of a tothe some data, long exclude large quick-looks period the of lakes of Landsat possibility like below scenes for that 0 were instance the checked Taro for phenomena the presence is of only open random water noise in events, isolating e Both northern regions appear toof have negative the trends ice in both coverBoth DCI decreases and the rapidly DI. The northern for duration one regionsHowever apart to on from two the the and SE contrary half region feature the days variations a per are positive year exceeding on trend the calculated average. in trend. both variables. duration of the freeze-up and break-up periods may be caused by snow fall and wind 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | com- 2 N and this ◦ in this group 1 − 2 days yr − respectively. All but three 1 − 1.1 days yr − 1756 1755 1.8 and − respectively (Table 2). The overall positive trend given in lake 1 − ect can be excluded since this lake while having an outlet towards Chabyer ff The lake ice cover in this region with an average DCI of 67.6 days and a DI of There is a positive trend in the ice cover duration in terms of both DCI and DI which seasons, for instance Bam Co inbut 2009, two Npen lakes Co have in negative 2006 trend and in Ringco Ogma DI in which 2006. is All on average It is probably due to aone lower of mean the temperatures reasons (Fig. for 2).other the The regions lowest low (Table 1). variation altitude Pangkog of range Co, is which iceling is likely cover Co, located duration has immediately in the to comparison longest theby with lake east a the from ice Ser- period. high This elevation, anomalous whilethe behavior with group. cannot the A be altitude explained possible ofbined explanation with 4529 would m a high be a.s.l. salinity it a andare is a relatively available. low the small Several depth. third lakes size Unfortunately, no lowest in of bathymetry lake this measurements 100.7 of km region do not freeze over completely during some This group of sixteen lakesble includes D1). the Apart two from largest Puma lakesof Yumco, Nam this which Co group is and are an Serling located isolatedNyainqentanglha Co in lake Mts. (Ta- the further The central in part lakes the of inwith SE, the a this the plateau mean lakes region north elevation span of from 4608 anson the m with elevation Gangdise a.s.l. the range Although and SW the of region the mean 560 ice m elevation cover is a.s.l. is lower longer in (DCI compari- of 92.4 days and a DI of 140.4 days). is negative indicated by bothMean DCI trend and in DI with DCIlakes a have and relatively negative DI low trend variation in reach DI in DI. in DI This the (Table would 2). region suggesttrend. but that the there variation is of a trend significant trend amongst in the4.4.4 lake of the Region group Southeast exceeds the southern part (Wang et al.,on 2010). this In e the caseCaka of is Taro a Co, fresh the water influence lake59.2 of (Wang days et high (Paiku al., Co) salinity 2002). to The 179.9that DI days it (Palung of Co). froze lakes In over in case completely. this The of region mean Paiku varies Co trend from it in was ice only cover in duration 2008 of this group of lakes the northern part that reaches a depth of 214 m which is circa 100 m deeper than the or not at allary as 2008 seen and on 15 Landsat March images 2010). (for instance This on is 31 obviously March caused 2007, by 27 a Febru- heat accumulation in Yumco (Manasarowar Lake) andconnected La’nga by Lake surface are stream forming freshwaterin together lakes. the an past These endorheic they lakes system, drained are towards but the it west seems to that Sutlej127.7 River days Basin. is the shortestXuru of Co, the Monco four Bunyi regions. and Lakes DajiaYumco, Taro Co which Co, did is Tangra not Yumco, Paiku regarded freeze Co, as up completely theinto in deepest northern some lake years. and on Tangra southern the parts TP by (Wang a et narrow al., strait. 2010), The is northern divided part freezes over later regions SE and SW was thuslake decided arbitrarily numbers in and order also to obtain toWest groups allow direction. of the This comparable region comparison has oflakes fourteen lake on lakes ice the (Table TP C1) phenology e.g. including along Zhari manyfor the Namco, of Mapam Ngangla East– the Ringco, Yumco Tangra largest and Yumco and La’nga Tarofrom Co. Co Except Gangdise Mountains, all which lakes acts are as a in barrier the to central monsoon circulation. part Both of Mapam the plateau north negative trend in DIthe (Table B1). high trend The of positive two trendin lakes: 2001 in Aksayqin and DCI and 2003. North is Heishi also with highly extremely influenced low4.4.3 by values of DI Region Southwest Lakes in thislake region pattern are continues towards distributed the approximately East in along the the SE region parallel (Fig. 30 1). The border between and Gozha Co (5070 m a.s.l.). is 3.1 and 1.0 daysice y cover duration doesvariation not of the seem trend to between the be lakes representative, and taking the fact into that account six the lakes of high the group have a the longest ice cover of 241 days was observed in two lakes: Bairab Co (4952 m a.s.l.) 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 | ect ff (18 lakes 2 leads to a increase 2 ect the smaller lakes ff may be due to generalized 2 300 km > ected by the shape complexity even in ff cient. This confirms high thermal deter- 0.41) with latitude is in fact related to de- ffi erence) derived from MODIS 8-day snow ff r > 1758 1757 ects the ice phenology in particular the freeze-up ff cient to 0.78 to 0.89. In both cases the cumulative temperature C derived from Worldclim database feature a high correlation co- ffi ◦ 0.79 in case of duration of complete ice cover (DCI). This shows that = r cient from 0.63–0.69. The selection of lakes larger than 300 km The analysis revealed much higher dependency of FO and WCI to the climate and While there is only a weak correlation of ice phenology variables with the perime- High correlation of ice cover duration ( ffi The obtained resultsity, imply shape that or despite wind some exposure, the influence ice of phenology local of settings Tibetan e.g. lakes salin- is to a high degree comparing the correlation of BUbe and more FU thermally with determined, temperature,who it which found is contradicts the the to FU BUcase that findings to of appears of Canadian be to lakes. Duguay the et more al. robust (2006) indicator of climate5 oscillations than FU Conclusions in Ice phenology was derived for 59 lakes on the TP from MODIS 8-day composite data. wind or the localthe conditions same way lead the to FOby a and WCI; systematically higher or, higher variation the inaccuracy spatial ofthe variation in FU FO of BU and BU and and and BU, WCI FUcomposites but FU (respective is appears don’t estimation. DI purely to a caused as Whatever be the their a reason, di better indicator for changes in climate on the TP. While the case of thephenology large variables lakes. for The all lakes lower thanshapes correlation to of of the lake lakes the shorelines perimeter/areamore. in index Only with the a ice GLWD weak database, correlationrameter which with area. may ice a This phenology variables suggestsrespective was volume that calculated and a for thermal the capacity. large pa- area does notlocal always parameters than mean in a case of large FU depth and BU. This can be caused by two factors. Either ter/area index for allachieving lakes there isthe shape a complexity strong significantly a correlationprocess providing for shallow the bays selectedthe for break-up large the process lakes development seems of to be an largely early una ice. On the contrary dates for smaller lakes with noisy time series of the satellite data classifications. crease of temperature towardscontinental the climate. There North is duelead probably to to no an strong a East–West driver lower gradientvealed of total between in the the ice irradiation ice ice phenology and regime, phenology sinceto which variables due only and would change to a longitude. with weak Ice altitude correlation coverair duration was due pressure appears re- which to can alarge be decrease lakes expressed of leads by to temperature temperaturetude. a connected lapse This significant can rate. to increase be The decrease likely of selection caused of dependency by of an of the inaccuracy ice in cover determination duration of lake to ice alti- phenology of the correlation coe features higher values of themination of correlation lake coe phenology reportedThe by dependency many studies of for ice afreezing number point phenology of depression on lakes caused worldwide. thermal by salinity variables could would have been be taken likely into higher account. if the cal parameters was carriedthe out sensitivity for of all theintroduced analysis 59 by to studied mixed lake lakes pixels, selection which (Tablesmaller and 4). obviously lakes, to the play In suppress same a order analysis the morein to was influence important total repeated assess of (Table role for 5)). noise lakes in Results largercover the of than duration case the 300 (DCI analysis of km and showed DI) thattemperature with there above temperature. 0 is Both a mean high temperaturee correlation and of cumulative ice but the variation of trend amongst the lake of4.5 the group is Correlation still of high. ice phenology variablesStatistical with analysis climatic and of local the parameters dependency of ice phenology variables on climatic and lo- (Table 2). This would again suggest that there is a significant trend in DI in the region 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 | doi:10.5194/tc- ´ enard, P.:Recent , 2010. erences in salinity, which could not ff C temperature averaged over the pe- ◦ 1760 1759 erences in geographical location such as alti- ff doi:10.1177/0309133310375653 ect snow fall during Autumn. ff This work has been carried out within the frame of the DFG (Ger- , 2010. ects on the local climate during the cold part of the year, for instance by complex ice cover and lake-water thermal25, structure 2942–2953, patterns 2011. to a changing climate, Hydrol. Process., trends in Canadian lake ice cover, Hydrol. Process., 20, 781–801, 2006. microwave remote sensing low frequency data, Chinese Sci. Bulletin, 54, 2294–2299, 2009. 4-419-2010 Progr. Phys. Geogr., 34, 5, 671–704, Basin, Tibet, and glacier changes 1976–2009, The Cryosphere, 4, 419–433, tion in north Qinghai-Tibet Plateau in last 30 years,Schneider, J. C.: Geogr. A Sci. glacier 19, inventory 131–142, for 2009. the western Nyainqentanglha Range and the Nam Co Data Rep., 92, GD-25, 66–79, 1993. ISBN 978-0-521-86295-0, 506, 2008. It has been observed that cumulative above 0 The available time series of MODIS data allowed us to derive a trend in ice cover du- ff Duguay, C. R., Prowse, T. D., Bonsal, B. R., Brown, R. D., Lacroix, M. P.,and M Dibike, Y., Prowse, T., Saloranta, T., and Ahmed, A.: Response of Northern Hemisphere lake- Che, T., Li, X., and Jin, R.: Monitoring the frozen duration of Qinghai Lake using satellite passive Brown, L. C. and Duguay, C. R.: The response and role of ice cover in lake-climate interactions, Bolch, T., Yao, T., Kang, S., Buchroithner, M. F., Scherer, D., Maussion, F., Huintjes, E., and Bianduo, B., Li, L., Wang, W., Zhaxiyangzong: The response of lake change to climate fluctua- Barry, R. G.: Mountain Weather and Climate, Cambridge University Press, Cambridge, UK, Acknowledgements. man Research Foundation)Ecosystems”. Priority This study Program was(No. 1372 supported 41001033). by – The the MODIS National “Tibetan dataCenter Natural were (NSIDC). Plateau: Science gratefully Foundation provided Formation-Climate- of by the China National Snow and Ice Data References Barry, R. G. and Maslanik, J. A.: Monitoring lake freeze-up/break-up as a climatic index, Glaciol. would make any general conclusionFor about the a extraction trend of in a ice trendTP phenology significant a on for longer the the time assessment TP series of dubious. changes of in observations climate would on be the needed. regions. These facts together with the relatively short evaluation period of ten years ation remains even after the derivation of mean values for the geographically compact riod from 2001 to 2010 representsmaximum a temperature. better This proxy indicates for that the cumulativeter lake above ice zero proxy regime temperature than of is the a annual theof bet- the accumulation freeze-up of process. energy Thise lake-atmosphere in interaction water may mass havemechanisms some which of additional lake is e an important driver ration for the studied lakes, which appeared highly variable over the TP. The high vari- four regions than DCI. Additionallynot the estimation freeze of up DCI completely. isacterization It hindered when can of the be the lakes thus do iceappears, concluded regime that that from FO DI and MODIS allows WCIthe 8-days are more studied composites more lakes. reliable for thermally char- lakes determined on than the FU and TP. It BU in case of while comparing them. Thistude reflects and latitude, di local settings andbe probably also checked di due to theber unavailability of of reference Tibetan data. lakesinteresting This do study phenomena showed not and that freeze its aregime up num- consequences should completely for be during local paidused some climate as a winter including measure proper seasons. snow of attentionindicator, This cover duration although in of DI further appeared the research. to ice be Both cover, more DI of stable and the in DCI variables, terms can of be variation used in three as of a the climate sults from other cold regionsof of Tibetan the lakes world. can This indicate suggests variationsthe that in area changes regional in is climate. ice This only phenology isan sparsely highly important covered valuable role since by in ground regional observationsaveraged and over and global climate. the at The acquisition the ice period same phenology of features time the a plays studied high lakes variation both in the regions and determined by climate, especially the air temperature which is in agreement with re- 5 5 25 20 15 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ´ emy, F.: , 2003. , last access: ´ esy, B., and R doi:10.5194/hess-13-2023- doi:10.1029/2003GL017909 doi:10.1016/j.jag.2011.10.001 1762 1761 , 2009. , 2011. , 2004. ect snowfall to the lee of the Great Lakes: Its role in Michigan, B. 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R.: Lake Ice Conditions as a Cryospheric Indicator for Detecting Climate Variability Shreve, C., Okin, G., and Painter, T.: Indices for estimating fractional snow cover in the western Sato, T. and Kimura, F.: How does the Tibetan Plateau a 5 5 30 15 25 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | of DI σ trend DI of DCI σ σ 1.12.3 1.8 2.1 − − 1766 1765 trend DCI Trend DI σ 1.8 4.9 2.4 2.0 − − ) of both the variables, which is a measure of variation of ice cover σ altitude (m) range(m) region Trend DCI NWNESW 3.1 2.5 5.4 4.4 1.0 3.0 2.6 5.5 SE NWNESWSE 4850 4714 4731 840 4608 1060 118.0 131.6 186.4 660 180.2 560 67.6 127.7 68.6 92.4 55.7 140.4 69.0 47.7 52.9 26.8 38.2 22.1 region mean altitude DCI DI Trends in days/year in DCI – duration of complete ice cover and DI – duration of ice Duration of complete ice cover (DCI) and duration of ice cover (DI) in days calculated Table 2. cover in the periodcalculated from for every 2001 year. to Thethe corresponding 2010 variation standard for of deviations each of trends group trends in gives determined each an region. as idea a about trend of mean values Table 1. as a mean valueand for standard each deviations of ( theamongst four the geographical lakes regions in over each the group. period from 2001 to 2010 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Seasons of no complete freeze-up from MODIS 2003-5, 2008-10 2003, 2005-7, 2009-10 2001, 2009 2001-3, 2005-6 0.63 0.65 0.63 0.65 0.57 0.02 − − − 0.04 0.23 0.20 − − − Mean BU from MODIS (region) 24 Jan (15 Apr) 6 Feb (15 Apr) 4 Apr (29 Mar) 25 Jan (18 Apr) 0.30 0.30 0.20 0.00 − − − 0.27 0.22 0.19 0.310.51 0.05 0.34 0.13 0.27 0.12 0.03 0.11 − − − − Mean FU from MODIS (region) 18 Jan (7 Jan) 21 Jan (7 Jan) (27 Dec) 29 Dec (7 Dec) (8 Dec) (14 Apr) 2001-10 1768 1767 0.69 0.59 0.63 0.53 0.22 0.29 − − − cient exceeding 0.5 is in bold numbers. DCI DI FO FU BU WCI 0.68 0.63 0.31 ffi − − − ) + C) ◦ C) ◦ Dates (% of ice coverTM from and Landsat ETM 3/3/2009 (60 %),18/2/10 (80 %), 6/3/10 2/2/10 (90 %) (30 %), (40 %), 15/03/2010 (40 %) (20 %), 23/3/2003 (20 %), 23/2/2005 (20 %) 28/3/2005 (0 %), 2/3/2010 (10 %) cumul ( max ( altitude (m a.s.l.)t 0.41 0.46 longitude (deg) 0.21 0.17 latitude (deg)t 0.52 0.47 area (sq. km) perim/area 0.19 0.15 Validation of the no complete freeze-up events detected by MODIS data for selected Correlation of ice cover duration (DCI – duration of complete ice cover and DI – dura- Lake name (region) Ice Cover from Landsat, Taro Co (SW)Tangra Yumco 6/2/09 (SW) (40 %), 11/02/2010 (5 15/2/2009 %), 27/02/2010 (60 %), Nam Co (SE)Xijir Ulan (NE) 5/2/2001 (70 %), 26/4/2001 (60 %)Bangoing 16/3/2001 Co 13 (20 %), (NW) Feb 19/3/2002 22/2/2004 (0 %), 7 Jan 2005 (60 %), tion of ice cover)59 and studied ice lakes. phenology Correlation dates coe with climate and local parameters calculated for all Table 4. Table 3. lakes by Landsat data. Percentagefalling of to ice the cover was period determined of from usual available ice Landsat cover images determined for the particular region. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 0.63 0.63 0.50 0.50 0.05 0.08 − − − − mean mean mean mean 0.16 0.32 0.28 0.38 − − σ cient exceeding 0.5 is in bold ffi 0.36 0.31 0.47 0.47 0.07 0.14 − − − mean DI σ 0.63 0.52 0.33 0.180.54 0.11 0.49 0.43 0.26 − − − − 1770 1769 0.89 0.81 0.80 0.69 0.49 0.27 0.31 − − − 0.61.9 146.9 131.5 6.50.4 27.0 180.8 194.2 176.90.3 10.4 13.42.8 22 Nov 18.9 18 Nov 166.0 7 Dec 4 211.1 188.2 Jan0.1 35.9 3 16 May May0.4 7.1 13.1 22 31 May May 237.9 7 144.8 Nov 213.6 14.2 156.6 23 Nov 29.1 12.9 21 20 Oct May 16 Nov 6.0 26 Nov 221.9 30 7 Nov Jun 11 May 199.5 9.4 16 7 Jun Jun 11.0 17 Oct 18 Jun 22 4 Nov Nov 17 Apr 2 Dec 27 May 8 May 23 May − − − − − − − DCI DI FO FU BU WCI 0.75 0.73 0.84 0.78 0.79 0.32 4.3 5.50.6 13.16.21.6 26.7 2.51.2 1.2 36.7 195.0 102.8 184.9 34.0 60.3 10.9 24 Dec 249.9 29 Dec 228.0 15.5 25 Jan 19.6 20 Oct 25 Oct 15 6 Nov Apr 24 29 Nov May 28 May 27 Jun 10 Jun 0.9 − − − − − − − − − − (18 largest lakes). Correlation coe 2 C) ◦ C) ◦ (m a.s.l.) Fig. 1 DCI DI (days) of DCI (days) of DI FO FU BU WCI cumul ( max ( latitude (deg)altitude (m a.s.l.) 0.46 0.45 longitude (deg) 0.28 0.29 t t perim/area area (sq. km) Derived lake ice phenology for lakes in the group NE. Correlation of ice cover duration (DCI – duration of complete ice cover and DI – du- nameYaggain CancoDorsoidong CoMigriggyangzham ElevationDogai Coring 4872 labelAqqik in Kol 4935 4929Ayakkuh trend Lake inJingyu 45 trend inLixi’Oidaim 47 Co 4818 46 mean DCI Xijir Ulan Lake 8.9Ulan 3876 Ul Lake 4251Taiyang 48 4870Hoh 15.5 Xil Lake 50Huiten 4772 Nur 49 4713 2.5Dorge Co 52 117.0 4855Hoh Sai 4.6 Lake 53 2.4 51 7.3 51.3 4886 4881 7.5 54 4.0 4753 136.8 1.2 3.3 56 33.4 4475 55.0 4688 55 7.2 3.4 57 41.5 1 30.7 Dec 140.6 59 58 124.7 6 18.9 Dec 12.3 90.8 25.9 2 40.8 Apr 1.9 176.4 88.3 31 Dec 17 171.6 Apr 15.0 8.0 28.5 16 1 Dec 16 Jan Nov 15 Nov 28 Nov 3 4 Jan Feb 9 Dec 18 Apr 14 Feb 1 12 Apr 11 Apr May 15 Mar 5 May Table A1. Table 5. ration of ice cover)lakes and ice larger phenology than dates 300 km with climate and local parameters calculated for numbers. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | mean mean mean mean mean mean mean mean σ σ mean DI mean DI σ σ 1772 1771 4.21.01.5 71.6 109.22.1 144.3 23.50.1 8.32.7 16.9 124.8 114.90.4 167.04.0 16.7 83.3 179.9 101.1 5.30.1 16.9 17.2 9 Jan 18 97.4 Nov 9.4 40.7 16 Nov 172.31.9 24 2 Dec 3.8 Feb 44.01.2 15.5 30.6 3 121.8 156.0 Dec 12 15 Apr Apr 12 Nov 12.0 31.9 27 37.3 Apr 155.8 7.8 16.0 10 4 5 Dec May May 15 16 31.0 6 92.3 May Dec Dec 14 59.5 21.9 Apr 106.8 29 Nov 16 Jan 4 13.3 26.7 21.4 Jan 31 4 Dec May 27 Apr 29 24 Mar Dec 95.1 3 Feb 132.6 12 8 May Apr 17 12.4 17 Jan Apr 6 8.1 Jan 13 17 4 Jan Feb May 26 10 Nov Jan 21 10 Jan Apr 9 Dec 4 6 Apr Feb 11 Mar 18 Apr 8 Apr 1.4 145.3 19.70.4 197.40.3 10.60.2 13 153.3 Nov 169.1 28 Nov 9.7 51.8 22 15.0 Apr 30 May 52.9 204.6 232.8 14.8 13.2 176.5 15 Nov 26 Oct 21.7 8 Dec 19 16 Nov Nov 10 May 26 Dec 8 May 16 7 Feb Jun 16 Jun 11 May 1.03.5 160.2 190.9 55.7 24.3 228.6 230.9 9.1 15.1 5 Nov 21 Oct 17 2 Nov Dec 26 11 May May 22 Jun 9 Jun − − − − − − − − − − − − − − − − − 5.6 0.7 2.0 2.5 0.29.5 3.4 6.0 8.91.2 102.4 10.9 12 Jan 18 Jan 24 Jan 24 Apr 0.2 2.1 60.8 35.1 154.3 25.5 10 Dec 25 Jan 27 Mar 13 May 3.6 7.51.6 0.7 24.11.2 32.3 94.9 30.5 11 Jan 16 Jan 9 Feb 16 Apr 2.1 0.4 0.7 169.7 37.1 241.0 14.6 23 Oct 3 Dec 22 May 21 Jun − − − − − − − − − − − − − − (m a.s.l.) Fig. 1 DCI DI (days) of DCI (days) of DI FO FU BU WCI (m a.s.l.) Fig. 1 DCI DI (days) of DCI (days) of DI FO FU BU WCI Derived lake ice phenology for lakes in the group SW. Derived lake ice phenology for lakes in the group NW. nameAksayqinChem Co Elevation label inGozha Co trend in 4844Geyze Caka trend inBamgdog 4961 Co meanLamaqangdong DCI 1 5080 4525 2 4812 4904 10.5 0.2 5 6 8 7 2.1 2.4 – 2.6 106.3 2.0 57.1 2.8 – 192.2 165.6 12.1 169.1 16.3 8 Nov 0.0 21.6 3 240.9 Dec 0.0 219.8 19.0 20 Mar 16.3 19 9 May Nov 4 Nov 28 0.0 Dec 25 Nov 12 0.0 Jun 14 May 11 8 Jun Jul – – – – Bangong CoLongmu Co 4239 5004Memar CoAru 3 CoHeishi 4 0.0 4920 1.0 4937 9 5049 10 0.0 11 0.0 12.9 125.4 15.6 17 Dec 1 Jan 1 Jan 21 Apr Yang 4778 14 8.3 0.0 146.1 62.7 224.4 16.6 29 Oct 27 Nov 22 Apr 10 Jun JianshuiBairab 4889 4960 12 13 Mapam YumcoNgangla RingcoPalung CoTaro 4585 Co 4716Dawa CoZhari Namco 16 Geysa Co 17 5101Dajia CoPaiku Co 4567 4612Monco Bunnyi 4623 18 Xuru Co 5198Tangra Yumco 19 21 20Ngangzi Co 4684 5145 4580 22 4535 0.8 0.7 25 23 4714 24 4685 27 10.7 26 0.0 28 3.0 0.0 1.2 5.2 8.6 69.1 15.9 1 Feb 9 Feb 15 Feb 12 Apr nameLanga Co Elevation label in trend in 4570 trend in mean DCI 15 Table C1. Table B1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

29 Dogze 45

Region SE: mean mean mean mean Region NE: σ mean DI 15 Langa Co, 16 Mapam Yumco, 17 Yumco, 15 Langa Co, 16 Mapam σ Co, 53 Xijir Ulan Lake, 54 Ulan Ul Lake, g Co, 32 Co Ngoin, 33 Serling Co, 34 37 Nam Co, 38 Bam Co, 39 Npen Co, 40 Co, 38 Bam 37 Nam 45 Yaggain Canco, 46 Dorsoidong Co, 47 Mi- ngdong Co, 9 Memar Co, 10 Aru Co, 11 North ngdong Co, 9 Memar ggyangzham Co, 48 Dogai Coring, 49 Aqqik ggyangzham NW, SW, SE and NE. Selected lakes are SW, NW, 1774 1773 Region SW: 15 Langa Co, 16 Mapam Yumco, 17 Ngangla Ringco, 1.21.71.2 92.3 104.62.9 13.33.0 7.75.6 76.0 132.63.9 89.3 21.0 132.21.1 91.3 8.1 150.5 26.83.2 9.7 26 Nov 113.20.6 65.8 9.5 106.0 6.9 126.0 6 Dec 9 Dec 8.8 50.12.9 28.8 50.3 16 142.0 27.6 Dec 11 30 Mar Dec 204.85.3 29 73.3 Nov 31 12.5 Mar 29.4 18 152.63.5 19.8 Jan 26 8 128.2 Dec Apr 41.6 18 42.4 18.0 87.9 Apr Dec 23 Oct 25 110.0 4 Mar 130.8 Apr2.1 8.7 25 Nov 17 Nov 3 28.8 132.2 28 12.4 Jan 80.7 22 Dec 30 19.2 Apr 4 Dec 123.7 Apr 17 12.2 Apr 12 5 127.2 Jan 4 23.8 Apr Jan 128.3 6 16 Mar May 10.1 160.5 6 Dec 28 13 Apr 15.2 25 Feb Apr 27 22.7 Apr 7.8 140.9 9 145.6 8 6 Jan Dec May 4 Apr 22.5 4 Nov 22 25 Mar 161.6 Dec 15-May 8.3 14 Nov 8 Dec 23 17 Mar 11 Apr 7.7 Dec 1 Dec 28 Mar 16 22 Apr 10 Nov 2 Dec Mar 14 Apr 13 6 Apr Dec 4 Apr 13 26 Apr Apr 3 May − − − − − − − − − − − − − − − Region NE: 1.60.6 0.11.7 0.8 5.7 57.03.3 23.85.2 2.7 116.42.7 4.5 7.9 2.84.1 31 Dec3.0 20 Jan1.7 84.7 18 Mar 26 31.3 Apr 130.5 17.8 22 Dec 10 Jan 05 Apr 1 May 1.2 0.7 1 Aksayqin, 2 Chem Co, 3 Bangong Co, 4 Longmu Co, 5 Gozha 3 Bangong Co, 4 Longmu Co, 1 Aksayqin, 2 Chem − − − − − − − − − − − − − − − Region SW: Region NW: 29 Dogze Co, 30 Urru Co, 31 Gyarin 1 Aksayqin, 2 Chem Co, 3 Bangong Co, 4 Longmu Co, 5 Gozha Co, 6 Geyze Study area divided into four regions (m a.s.l.) Fig. 1 DCI DI (days) of DCI (days) of DI FO FU BU WCI Derived lake ice phenology for lakes in the group SE. Heishi, 12 Jianshui, 13 Bairab, 14 Yang; highlighted. Co, 6 Geyze Caka, 7 Bamgdog Co, 8 Lumaqa Ngangla Ringco, 18 Palung Co, 19 Taro Co, 20 Dawa Co, 21 Zhari Namco, 22 Geysa Co, 23 28 Ngangzi Co; Dajia Co, 24 Paiku Co, 25 Monco Bunnyi, 26 Xuru Co, 27 Tangra Yumco, Region SE: Pung Co, 41 Dung Co, 42 Co Nag, 43 Zige Tangco, 44 Kyebxang Co; Fig. 1. Yumco, 36 Puma Pangkog Co, 35 Ringco Ogma, Yaggain Canco, 46 Dorsoidong Co, 47 Migri Kol, 50 Ayakkuh Lake, 51 Jingyu, 52 Lixi'Oidaim 55 Taiyang, 56 Hoh Xil Lake, 57 Huiten Nur, 58 Dorge Co, 59 Hoh Sai Lake Study area divided into four regions NW, SW, SE and NE. Selected lakes are highlighted. Gyaring Co 4649 31 Pung Co 4529 40 nameNgangzi CoDogze Co ElevationUrru Co label in 4685 trend inCo Ngoin trendSerling 4465 in CoPangkog mean Co 28 DCI 4554Ringco Ogma 29 Puma Yumco 4563 4539Nam Co 4527 30 4656Bam Co 5013Npen 32 Co 33 34 35 Dung Co 36 1.1 4724Co Nag 4560Zige Tangco 4666Kyebxang Co 37 38 4551 4568 39 4615 4585 0.4 41 43 44 42 18 Palung Co, 19 TaroCo, Co, 20 25 Dawa Monco Co, Bunnyi, 21 26 Zhari Xuru Namco, 22 Co, Geysa 27 Co, Tangra 23 Yumco, 28 Dajia Ngangzi Co, 24 Co; Paiku griggyangzham Co, 48 Dogai Coring, 49Co, Aqqik 53 Kol, Xijir 50 Ulan Ayakkuh Lake, Lake,Co, 51 54 59 Jingyu, Ulan Hoh 52 Ul Lixi’Oidaim Sai Lake, Lake. 55 Taiyang, 56 Hoh Xil Lake, 57 Huiten Nur, 58 Dorge Fig. 1. Region NW: Caka, 7 Bamgdog Co, 8shui, Lumaqangdong Co, 13 9 Bairab, Memar 14 Co, 10 Yang; Aru Co, 11 North Heishi, 12 Jian- Co, 30 Urru Co, 31 Gyaring36 Co, Puma 32 Yumco, 37 Co Ngoin, Nam43 33 Co, Serling 38 Zige Co, Bam Tangco, 34 44 Co, Pangkog 39 Kyebxang Co, Co; Npen 35 Ringco Co, Ogma, 40 Pung Co, 41 Dung Co, 42 Co Nag, Table D1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

(middle) and clouds (middle) ” for FU, “*” for BU and ed with symbols: 'x' for FO, 'x' ed with symbols: + l ice cover is often caused by

elow), ice and snow 28 t Autonomous Region (after Xu et al., 2008) t Autonomous

rare in the winter period on the TP. 27 1776 1775 ke ice phenology events are mark ' for WCI. The noise in the tota ' ◊ An example of curves water (b for open An example

Fig. 3. (Lake Yumco data for Mapam MODIS 8-days composite (above) derived from la Manasarowar). The identified '+' for FU, '*' for BU and ' confusion with clouds which are actually Contours of mean temperature in the Tibet Autonomous Region (after Xu et al., 2008). An example of curves for open water (below), ice and snow (middle) and clouds (above)

” for WCI. The noise in the total ice cover is often caused by confusion with clouds which are 740 741 742 743 738 739 ♦ derived from MODIS 8-days compositetified data for lake Mapam ice Yumco phenology (Lake Manasarowar). events The are iden- marked with symbols: “x” for FO, “ Fig. 3. “ actually rare in the winter period on the TP. Fig. 2. Contours of mean temperature in the Tibe temperature Contours of mean

Fig. 2.

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the area of open water for Nam Co derived Co derived Nam water for the area of open

om high resolution satellite images (Landsat, om high resolution satellite images 29 arison of the open water curve with points arison of the open water duration of break-up period as heights of the

on the TP showing duration of freeze-up 30 1778 1777 bar symbols whereas the total size of the bar represents the represents size of the bar total whereas the bar symbols Validation of the time series representing series representing Validation of the time Validation of the time series representing the area of open water for Nam Co derived Ice cover duration for the studied lakes on the TP showing duration of freeze-up period,

Envisat/ASAR, TerraSAR-X and SPOT). Envisat/ASAR, TerraSAR-X and SPOT). Fig. 4. MODIScomp 8-day composite data by from fr representing the area of open water extracted

Ice cover duration for the studied lakes

duration of complete ice covertively (DCI) colored and sections duration of of barof break-up symbols ice period whereas cover as the (DI). heights total of size of the the respec- bar represents the duration Fig. 5. from MODIS 8-day compositesenting data the by comparison area of ofvisat/ASAR, the open TerraSAR-X and open water SPOT). water extracted curve from with high points resolution repre- satellite images (Landsat, En- Fig. 4.

Fig. 5. period, duration of complete ice cover (DCI) and respectively colored sections of duration of ice cover (DI).

749 745 746 747 748 744

755 751 752 753 754 750 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

terms of DCI and DI for all four regions. terms 31 1779 trends in the lake ice cover duration in Trends in the lake ice cover duration in terms of DCI and DI for all four regions.

Fig. 6. Fig. 6.

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