ClimatWarmingdue to Overgrazing on the Tibetan PlateauExample at Damxu - PDF document

ClimatWarmingdue to Overgrazing on the Tibetan PlateauExample at Damxung in the entral art of the Tibetan PlateauMingyuan DSeiichiro YONEMURAXianzhou ZHANGYongtao HJingshi Land Shigeto KAWASHIMAAbstract: Many studies have shown that the increase in air temperature on the Tibetan Plateau is greater than that for the Northern Hemisphere and the same latitudinal zone. 119(201 Journal of Arid Land Studies "ICAL 1 / DT X" * Corresponding Author: dumy@affrc.go.jp 3 Kannondai, Tsukuba, Ibaraki, 3058604 Japan1) Department of AgroMeteorology, National Institute for AgroEnvironmental Sciences, Japan2) Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, China 3) Institute of Tibetan Plateau, Chinese Academy of Sciences, China4) Kyoto University, pan The main topography over the Tibetan Plateau (up) and observation stations (down)The Tibetan Plateau is shown as the shaded region where elevation is higherthan 3000 m a.s.l.Black contour lines show topography with an interval of 1000 m(up) and 100m (down)The triangles indicate the observation stations.meteorological elementsincluding short and longwave radiations, wind speed and direction, air temperature and humidity, soil temperature and water content etwere measuredthere by usingmeasurementsystem of Campbell Scientific, IncData were recorded with a datalogger(CR10X; CSI) at min intervalsMeasurement system on the other 10 stations are Hobo weather stations (Onset Computer CorporationBourne, MA, USAsettled at 4300m, m, 465m, 4800m, 4950m, 5100m, 5200and 5530m on a south slopetations atm are located on a wet land. Stations at 5300m and 5530m are located on a bare land and others are located in the pastureAir temperature and humidity at 2m and soil temperature and soil water content at 5cm, 20cm and 50cm are sampled at 1 min intervals and the mean value wererecorded with a datalogger at30 min intervalsThe air temperature data from August2005 to July,are usedin this study. Data and methodDaily mean of air temperature(T)minimumand maximumair temperature(Tmin and Tmax), air pressure(P), absoluteand relative humidity (e and RH), low and totaamount(Cl and C), wind speed (V), surface temperature (Ts), precipitation (Rain), sunshine hour (S) and pan evaporation (Et) of the Damxung meteorological observatory stationfrom Observed Air temperature variation during 1962 to 20Damxung.August 1, 1962 to June 30, 2009 are used.Stepwise linearregressionmethod was used for getting relationship between daily mean air temperatureon theslope and the meteorologicalelements of theDamxung meteorological observatory stationy usingSAS software(SAS institute inc., Cary, NC, USA) with testat statistical significancedetermined at the P 0.05 levelDue that the mechanismof local temperature varies for differentseasons, we get therelationships for eachmonthTherefor Tcal here, Tcalis estimated air temperature for station month =1, 10; =1, 12) . and ijkare regressioncoefficients of station month for meteorological elements =T, Tmax, Tmin, P, e, RH, Cl, C, V, Ts, Rain, S, Et). We assumethat the relationship between daily mean air temperatureon theslope and the meteorologicalelements of theDamxung meteorological observatory should reflect the effects of land degradation by overgrazingand may be the same in the past47 years. Therefore, we can use the relationship to reconstruct the daily mean air temperature during 1962 to 2004 on the slopeand then to calculate the 18 years mean temperature for 19621980 due to there was almosttemperature increaseduring this period as shown in FigureTherefore, we can compare the temperature differencesbetween the observed mean of 2005 to 2010 and the estimated mean of 19623. Results and Discussion3.1. Climate warmingat DamxungAs shown in Figure 2, observed air temperature at Damxung meteorological observatory shows statisticallysignificant increase trend for each month, especially in wintertime (0.02/year in July and 0.087/year in January)Increase in daily minimumair temperatureis learer(0.022/year in July and 0.114/year in January)Annual air Vertical distribution of vegetation coverage and root biomass along the south sloperedraw from Ohtsuka et al., 2008 and data at 4300m is with personal communicationtemperature at the meteorological observatory has increased about 2 degrees during past 47 yearsThis increase in air temperature is higherthan other places on the TP at similaraltitudeand surroundingarea.vergrazingand vegetationver changeFigure 3shows the distribution of vegetation coverage and and relation between root biomassand elevationalong the south slopein 2005It can be seen that both vegetation coverage and root biomass at the lower part of the slope (between 4400m a.s.l.) was smaller than that at the middle part of the slope and that in the lley(4300This is due to the overgrazing there. The middle part of the slope has been used as summer pasture and the valley wet land has been used as winter pasturewhile the lower part of the slope is been used throughout a yearbecause most of herdsmen are living at the lower part of the slopeInterviewwith theherdsmen let us know that this overgrazing was occurredaround 1980 and becoming more and more remarkawith the increase in livestock numbers as shown by Du t al. (2004)Air temperature distribution along the slope and its changesAs shown in igure 4observation data (mean of 2005 to 2010) along the slope shows auniform lapse rate about 072ºC/100m along the slope, in summerseasonlapse rate is greater than that of averaged over the TP(Du et al., 2010)However, there is ainversion layerat lower partof slope (below 4800m) and a relatively larger lapse rate about 0.79ºC/100mat higher partof the slope in wintertimeThis is due to strong radiation cooling based on lower humidity and cold air runoff from a higher mountain region into the valley by a local circulation, the air temperature in the valley becomes lower and lower during night in wintertimeThis process occurred and a temperature inversion layer exited almost occurredeveryday during wintertimeas Du et al. (2009) Observed and estimated air temperature variation along the slope during 2005 to 2010 and 1962 to 1980.describedHowever, air temperature at the lower part of the slope is little bit higher than the lapse ratepredicted (right up the lapse line shown in Figure) in summertimeand higher in winter partly due to the temperature inversionFigure 4 also shows the estimatedmean temperature (1962 1980) distribution along the slopeIt shows a similar distribution patternas observed one (mean of 2005 to 2010withsignificant increase of air temperature throughoutthe slope, especially in JanuaryHowever, there isevidently high value of the temperaturein the overgrazed lower part of the slopeTherefore, the lapse rate in summer changes from ºC/100m to 0.69ºC/100though this value is still larger thanthat of averaged over the TP, this value can be treatedas a natural environmental, which do not induced landdegradationLapse rate at higher partof the slopechanges from 0.79ºC/100m to 0.72ºC/100m in wintertimRelationship between overgrazing and climate warming at Damxungand degradation by overgrazing can affect climatechange (e.g. Jackson and Idso, 1975Balling, Du, 1996Many researchers have found that decrease invegetation coverreduces evapotranspiration therebyallowing an increase in local temperature levelsBalling (199) hasrevealed that overgrazing and consequently land degradationin semiarid areas of northern Mexico resultedin significantly air temperaturesincrease oth in northern Mexico and in its adjacentArizona, USADamxung meteorological observatoryis located very near to the overgrazing pastureTherefore, air temperature increase has coincided withthe progress of overgrazing since1980 as shown in Figure Moreover, the land degradation effect were reflectedupon not only the air temperature but also all the observedmeteorological elementsat Damxung meteorological observatoryFor example, humidity (e and RH) and cloudamount (C and Cl) have decreased and sunshine hour (S) has Table 1.Comparison of regressioncoefficientsof station 4400 m and 5300 m. TmaxTmin 4400m Jan.-1.7980.8290.342 5300m Jan.-13.5930.3410.8040.036 4400m Jul.-58.4510.0940.7680.196 5300m Jul.-182.8730.2870.8330.187-0.337 (Continue of Table 1.) RainEt 4400m Jan.-0.182 5300m Jan.-0.266-0.086 4400m Jul.-0.018 5300m Jul.0.015-0.027 Station &month aij bij Station &month bij increased slightlyAir temperature at the pasture and surroundingarea has been also affected by the land degradationThese variationave effects on air temperature at different area of the slope pasturewith the relationship obtained by the stepwise linearregressionTable 1shows the comparison of regreion coefficients for July and January of staion 4400and station As shown in Table 1despite the regressioncoefficientsdifferences, there are two more elements (RH and Sin January, Tmin and C in July) selected for station 5300Sinceand Caredecreased andTmin and S is increased and air temperature at 5300m is directproportionto RHand Cand inverseproportionto S and Tmin, this is one of the reasons of increase amount of air temperature at 5300m is smaller than that at 44004. Conclusion (or Recommendation)Both observed air temperature at the meteorological observatory and estimated air temperature at the overgrazed pasture at Damxung has increased about 2 degrees during past 47 years and this extreme air temperature increase is mainlcaused by the land degradation due to overgrazingby following reasons(1)47 years observed air temperatureat the meteorological observatoryhas increasedsince 1980 which coincideswiththe progressof the overgrazing.(2)5 year observed air temperature at the pasture shows relative higher valueat the overgrazed area(3)Estimated air temperature at the pasture shows more increase amount at the overgrazed areathan other areaReferencesBalling Jr.R.C., KlopatekJ.M., HildebrandtM.L., MoritzC.K.,C.J. 1998Impacts of land degradation on historicaltemperature records from the Sonoran Desert. ClimaticChange669681.M. Is it a global change impact that the climate isbecoming better in the western part of the arid region ofChina?Theor. Appl. Climatol.139., Kawashima Yonemura, Zhang Chen S. (2004): Mutual influence between human activities and climate change in the Tibetan Plateau during recent yearsGlobal andPlanetary Change241M., KawashimaS., YonemuraS., YamadaT., ZhangZ., LiuJ., LiY., GuTangY. (2007): Temperature distribution in the high mountain regions on the Tibetan PlateauMeasurement and simulation. Oxley,L. and Kulasiri, D. edsMODSIM 20072146M., Liu Zhang Li Tang Y. 2010: Changes of spatial patterns of surfaceairtemperature on the Tibetan Plateau. Latest Trends on Theoretical and Applied Mechanics, Fluid Mechanics and Heat & Mass Transfer. Mechanical Engineering Series, WSEAS Press (ISSN: 17924359, ISBN: 0), FrauenfeldW., Zhang SerrezeC. (2005): Climate change and variability using European Centre forMediumRange Weather Forecasts reanalysis (ERA40) temperatures on the Tibetan PlateauJ. Geophys. Res.110D02101,doi:10.1029/2004JD005230.JacksonR.D., IdsoS.B. Surface albedo and desertification.Science1012KanWu You Flugel Pepin N. Yao T. (2010): Review of climate and cryospheric change in the Tibetan PlateauEnvironmental research letters, 5 015101, doi:10.1088/17489326/5/1/015101.LiuX., ChenB. Climatic warming in the Tibetan Plateauduring recent decades. Int. J. Climatol.(14)1729H., LiuG. (2010): Trends in temperature and precipitation on theTibetan Plateau, 1961Climate Research43Ohtsuka, T.HirotZhang Shimono Senga Du Yonemura , Kawashima Tang 2008: Soil organic carbon pools in alpine to nival zones along an altitudinal gradient (44005300 m) on the Tibetan Plateau. Polar Science,