, 李稚, 方功焕, 邓海军中国科学院新疆生态与地理研究所 荒漠与绿洲生态国家重点实验室,乌鲁木齐 830011
Impact of climate change on water resources in the Tianshan Mountians, Central Asia
CHENYaning, LIZhi, FANGGonghuan, DENGHaijun收稿日期:2016-08-24
修回日期:2016-11-1
网络出版日期:2017-01-20
版权声明:2017《地理学报》编辑部本文是开放获取期刊文献，在以下情况下可以自由使用：学术研究、学术交流、科研教学等，但不允许用于商业目的.
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1 引言
山区作为一个独特的地理单元,是干旱、半干旱区大多数河流的发源地,尤其在干旱区,几乎所有的河流发源于山区[1]。山区降水相对丰富,以冰川、积雪、冻土等形式储水于山上,为世界上约20%的人类的生存提供淡水资源[1-2]。全球变暖加速了水循环,加剧了极端气候水文事件,降低了水资源有效性,加大了水系统的脆弱性[3-4],尤其干旱区以冰川、积雪融水和降水混合型补给为主的河流,对气候变化响应敏感,气温和降水的变化使得河流水文过程变得更为复杂[2]。天山被誉为“中亚水塔”,横亘于欧亚大陆腹地,长约2500 km,南北宽平均250~350 km,由一系列高大山地、山间盆地和谷地组成,是世界上距离海洋最远的山系,也是世界上现代冰川最发育的山系之一[5]（图1）。山区丰富的冰川、积雪作为中亚干旱区水资源的重要组成部分,对气候变化非常敏感。气候变暖引起的山区冰川/积雪变化直接影响河川径流过程与水资源量的改变。中亚干旱区主要河流均发源于山区,水资源的形成、补给、转化等方面的特点鲜明,在世界干旱区都具有很强的代表性[2, 6]。
显示原图|下载原图ZIP|生成PPT图1中亚天山地理位置图
-->Fig. 1Location of the study area (the Tianshan Mountains in Central Asia)
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研究结果显示,自1998年开始,全球出现升温滞缓现象（Global Warming Hiatus）[7-8]。在当今CO2浓度不断增加的情况下,为什么会出现增温滞缓?其原因和机制尚无定论。然而,值得关注的是,在全球增温滞缓背景下,中亚天山山区的气温却在1998年之后的15年间一直处于高位震荡状态,而同时降水呈微弱增加趋势[9]。在这种气候变化背景下,中亚天山山区的降水形式、降水总量、雨雪比以及冰川、积雪等又都发生了怎样变化?水文过程与水资源又如何响应?这些问题尚不得而知。
天山山脉连接着中国新疆以及中亚的哈萨克斯坦、吉尔吉斯斯坦和乌兹别克斯坦等国家。由于多国多民族的政治复杂性与自然地理单元的完整性叠加在一起,分散的政治主体割裂了天山科学研究的完整性,导致天山区域性研究成果的局限性。气候变化引起的天山山区水循环和水系统的改变,可能引起水资源数量变化,加剧水文波动和水资源的不确定性,从而导致中亚地区间、国家间的水事争端和绿洲经济与荒漠生态两大系统的水资源供需矛盾加剧,影响中亚区域国家之间关系以及丝绸之路经济带建设。为此,深入研究气候变化对天山山区的水资源影响,准确掌握水资源的数量及变化,不仅对科学管理水资源、服务于国家丝绸之路经济带建设具有重要意义,同时为中国在中亚地区国际河流水资源谈判中争取主动权提供重要的科技支撑。
2 气候变化对水资源的影响
在过去的半个多世纪,全球增温速率为0.175 ℃/10a[10],而中亚地区升温达0.36~0.42 ℃/10a[11],明显高于全球或北半球同期平均增温速率。利用CRUTS 3.23数据分析了中亚天山的气候变化,发现中天山、东天山一带温度升高最为显著,升温速率最高可达0.45 °C/10a[12]。详尽分析中亚天山的温度变化还发现,年平均气温在1998年出现了“突变型”升高（图2）,统计气温突变升高以来的约15年间（1998-2013年）,气温较其之前的30年升高了约1.0 ℃,并且自1998年以来一直处于高位震荡[9]。而这期间,中亚天山山区的降水量变化比较平稳,略有增加,增加速率为8.4 mm/10a,略高于全球和北半球平均水平。其中,西天山和北天山的部分地区增加明显,增率达8.5~12.3 mm/10a;中天山和东天山降水呈微弱增加趋势,增加速率仅为6.1~7.0 mm/10a。在全球变暖,尤其当前气温持续高位震荡影响下,势必导致降水的时空分布和降水形式改变,加快以冰川、积雪为主体的“固体水库”的消融和萎缩,改变水资源构成和径流组分,对天山山区的水资源系统产生重要的影响。
显示原图|下载原图ZIP|生成PPT图21960-2014年间全球、北半球和中亚干旱区气温和降水变化趋势
-->Fig. 2Trends of temperature and precipitation of the world, Northern Hemisphere, and Central Asia during 1960-2014
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2.1 气候变暖导致山区降雪率变化
山区径流的形成不仅受气温和降水影响,还与山区降水形式和降雪率变化有着密切联系。在气候变暖背景下,降水形式、季节分配、冰川积雪时空分布等也随之会发生变化,并影响山区水循环过程,如河流补给类型、径流季节分配、径流量等[2]。2.1.1 降雪率降低 在气候变暖和气温持续高位态波动状态下,山区降水的时空分布、海拔变化及雨雪比等都会发生相应变化,出现降雪初日推迟、终日提前、降雪（日数、量）减少、降雨增多的现象[2]。气温升高导致山区不仅仅是降水量的变化,同时可能会对降水形式（如雨雪比）产生影响,从而改变山区的产汇流过程。本文结合中国气象局（data.cma.cn/）和全球历史气候网（Global Historical Climatology Network, GHCND）（ncdc.noaa.gov/ghcnm/）的气象站点实测数据,对天山山区4个不同区域过去50年的降雪率变化进行了分析,研究结果显示,天山山区气温急剧升高,降水也呈增加趋势,降雪率却呈现总体降低趋势,天山山区的降雪率从1960-1998年的11%~24%降低到2000年以来的9%~21%。这与Guo等[13]对中国境内天山的研究结果是一致的。其中,在天山山区1500~2500 m的中海拔地区降雪率减少最为显著,而在>3500 m的高海拔地区变化幅度不甚明显。在昆仑山、瑞士阿尔卑斯山及美国大陆等地区,也发现了降雪日数相对于降雨日数的降低和降雪率降低等现象[14-16]。如美国大陆,降雪率总体呈降低趋势,特别是在日均温为-5 ℃左右、增温幅度在0~3 ℃的地带,降雪率的降低不仅受到太平洋年代际涛动的影响,而且受到气候长期变暖的影响[14]。值得一提的是,在全球变暖背景下,虽然降雪率有降低趋势,但是极端降雪量却没有相同的变化趋势。例如在北美洲气温0 ℃以下、海拔<1000 m的区域,虽然平均降雪量减少了65%,但极端日降雪量增加了8%[17]。
2.1.2 降雪率变化的影响 降雪率变化不仅影响冰川物质的积累、消融过程,而且显著影响径流过程和水资源变化。降水形式的改变会影响水文过程,但如何影响径流量变化尚不确定[18]。有研究者通过Budyko水热平衡假设分析了降水形式变化对径流量的影响,指出山区径流的形成和多寡不仅受气温和降水影响,还与山区降水形式和降雪率变化有直接关系[19]。山区降雪率大与径流水平高有密切的联系,降雪率下降,可能导致河川径流量减少。然而,在山区降水量不变甚至有所增加的情势下,降雪率变化是如何影响水资源、抑制径流过程,其机理尚不明确[19]。在融雪径流补给为主的地区,降雪向降雨的转变会显著影响流域水文过程,导致径流季节分配变化,径流峰值向春季移动,而不再集中于需水量最高的夏秋季节[2]。在有些地区,降雪率降低还可能引起夏季的水资源短缺或洪水灾害[20]。这对预估未来不同情景下的水资源变化趋势至关重要。
2.2 气候变暖加速山区冰川积雪消融
冰川、积雪作为“固态水库”储水于山区,是山区水资源的重要组成部分,气候变暖及持续高位震荡加快了天山山区的冰川退缩,加剧了山区冰川、积雪和冻土等固态水体的消融,加快了“中亚水塔”的萎缩[1, 5, 21]。2.2.1 冰川退缩严重 中亚天山山区共有冰川10778条,总面积约为13566.6 km2（glims.org/RGI/index.html）。在1961-2012年间,约有97.52%的冰川表现为退缩状态,有2.14%的冰川呈增加趋势,0.34%的冰川没有明显变化[21]。本文对天山山区不同区域两个阶段20世纪60年代-2000年、2000-2012年的典型冰川变化情况进行了分析,结果显示,在20世纪60年代-2000年期间,西天山的冰川递减速率最大,达-20%;其次是中天山,递减速率为-15%;北天山和天山东部的博格达山区的冰川递减速率分别为-13%、-3.1%。而在2000年以来,西天山和中天山冰川的递减速率明显减缓,分别为-8.1%、-10.1%;而北天山和天山东部的博格达山区冰川的递减速率增大,分别达到-13.8%、-7.45%。总体表现为天山西部地区（西天山、中天山西部及北天山西部）近10年来的冰川退缩速率要明显低于前一阶段,而天山东部（中天山东部、北天山东部及博格达山）冰川退缩速率要明显快于前一阶段。
对不同海拔高度的冰川变化分析对比显示,几乎所有海拔范围内的冰川面积都呈减少的趋势,只是分布在低海拔区域冰川较高海拔区域的冰川退缩更为明显。如在北天山的Karatal河流域,1989-2012年冰川的平均最低海拔分布高度上升了47 m,从3288 m上升到3335 m[22]。分布在海拔3600 m以下高度的冰川退缩速率约为-27%,而分布在海拔3600 m以上冰川的退缩速率约为-16%。比较1989年、2001年及2012年3个时段的冰川变化显示,在过去的20余年间,该流域的冰川由1989年的243条减少到2012年的214条,冰川面积也由142.8 km2减少到109.3 km2,减少了23.45%（表1）。
Tab. 1
表1
表1中亚天山Karatal River流域冰川变化[
Tab. 1Changes of glaciers in the Karatal River Basin of Tianshan Mountians
| 分区 | 冰川面积(km2)/数目(条) | 面积变化(%)/年平均变化率(%) | ||||||
|---|---|---|---|---|---|---|---|---|
| 1956年 | 1989年 | 2001年 | 2012年 | 1956-1989年 | 1989-2012年 | 1956-2012年 | ||
| Terisakkan | 14.1/36 | 8.4/21 | 6.5/21 | 5.1/17 | -40/-1.22 | -39/-1.68 | -63/-1.13 | |
| Koksu | 108.6/167 | 75.3/149 | 64.1/140 | 56.1/135 | -31/-0.93 | -26/-1.11 | -48/-0.86 | |
| Shyzhyn | 8.7/19 | 4.9/11 | 4.2/10 | 3.8/10 | -44/-1.32 | -22/-1.32 | -56/-1.0 | |
| Kora | 49.3/66 | 50.8/62 | 45.6/55 | 42.7/52 | -22/-0.68 | -21/-0.91 | -39/-0.69 | |
| Total | 198.9/285 | 142.8/243 | 122.2/226 | 109.3/214 | -28/-0.86 | -23/-1.02 | -45/-0.81 | |
| Glaciers <0.1 in 1956 | 3.6/73 | 2.36/77 | 0.76/39 | 0.59/34 | -34/-1.0 | -75/-3.2 | -83/-1.5 | |
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2.2.2 积雪面积减少 山区积雪的变化对干旱区水资源情势有着直接影响。根据MODIS积雪数据,分析了2002-2013年10余年间中亚天山的最大积雪面积与最小积雪面积的变化。结果显示,2002-2013年间天山山区的积雪面积总体呈减少趋势。其中,中天山的积雪面积减少最为明显,最大积雪面积和最小积雪面积减少值分别为-672 km2/a、-60 km2/a,西天山的积雪面积有所增加,最大积雪面积和最小积雪面积增加值分别为2.3 km2/a、16 km2/a。进一步比较不同区域的最大/最小积雪覆盖面积与研究区面积之比（最大/最小积雪覆盖率）显示,中天山和东天山的最大积雪覆盖率的年递减率较大,分别为-0.32%、 -0.28%,而西天山的最大/最小积雪覆盖面积略呈增加趋势,近12年分别增加了0.01%、1.02%（表2）。
Tab. 2
表2
表22002-2013年中亚天山山区积雪变化①
Tab. 2Snow cover changes of the Tianshan Mountains in Central Asia during 2002-2013
| 最大积雪② | 最小积雪③ | ||||||
|---|---|---|---|---|---|---|---|
| 覆盖率(%) | 面积变化(km2/a) | 变化率(%/a) | 覆盖率(%) | 面积变化(km2/a) | 变化率(%/a) | ||
| 西天山 | 87 | 2.3 | 0.001 | 1.4 | 16 | 0.085 | |
| 中天山 | 79 | -672 | -0.32 | 4.7 | -60 | -0.029 | |
| 北天山 | 90 | -78 | -0.28 | 0.51 | -20 | 0.02 | |
| 东天山 | 54 | -240 | -0.09 | 2.1 | 17.6 | 0.08 | |
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2.2.3 水储量减少 气候变暖及持续高位震荡加速了天山山区的冰川退缩,加剧了山区冰川积雪等固态水体的消融[23-24],导致山区水储量减少。本文利用GRACE重力卫星的时变重力位资料,对天山山区2003-2014年的陆地水储量变化做了计算,得出天山山区的陆地水储量呈明显减少趋势,减小幅度约为-3.72 mm/a（图3）。同时详尽分析还发现,不同地区的水储量变化不尽一致。由图3a可见,天山山区水储量减少最为强烈的区域主要分布在中天山一带,达-5.5 mm/a,而西天山一带水储量减少幅度较小,约为-0.12 mm/a。天山山区的冰川积雪退缩及水储量减少与气候因子变化有着密切的关系。由图3b可见,中天山一带在2003-2014年间升温速率达到0.4~0.8℃/10a,而西天山的温度升高不甚明显,个别地区甚至出现下降趋势;从降水变化分析,在2003-2014年,天山山区的降水量变化非常平稳,略有降低,降低速率为-0.7 mm/a,因此,温度的快速升高加速了冰川积雪消融,是导致天山山区水储量减少的重要因素。
显示原图|下载原图ZIP|生成PPT图32003-2013年中亚天山水储量变化分析
-->Fig. 3Terrestrial water storage variation and temperature trend in the Tianshan Mountains during 2003-2013
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2.3 气候变暖加大了水资源时空分布的不确定性
2.3.1 干旱区水循环各环节受陆表格局和气候变化影响显著 伴随着气温升高和高位震荡,水循环要素发生了改变,山区的降水、冰川、积雪等因气候变化而对河流水文过程的影响也变得更为复杂,水资源系统更为脆弱。中国境内天山过去50年气候变化对水文过程包括径流、潜在蒸散发、冰川积雪影响的研究结果显示,气候变暖引起的冰川、积雪变化的区域差异性和对气候变化响应的复杂性加大了应用水文模型开展融冰、融雪径流研究的不确定性[5, 25]。2.3.2 气候变暖加大了以冰川融水补给为主的河川径流量 由冰雪融水补给为主的河流,其水文过程受冰川积雪融水变化影响显著[2]。由于气温持续的高位态波动引起冰川和积雪退缩,固态水资源转化为液态水资源,中亚以冰川融水补给为主的河流普遍呈现出径流量增加趋势,而且冰川比例越高,径流量增加水平越大[26-28]。如发源于中天山的阿克苏河,其两大支流—库玛拉克河和托什干河（冰川面积比例分别为16.2%、4.2%）的径流量,在1998年之后相比之前分别增加了26.2%和14.9%,其中分别有35%~48%和9%~24%的径流量增加来自冰川融水[29];在Karatal河流域,冰川面积比例在5%以上的子流域的径流普遍呈上升趋势,而冰川面积在2%以下的子流域,径流增加不显著甚至呈现减少趋势[27];位于天山西部的伊塞克湖流域,几乎所有小河流的径流量都呈增加趋势,增加幅度在3.2%~36%之间[30]。但是,对于天山东段的一些流域,由于冰川面积较小,冰川水资源补给量较低,径流量增加不明显,甚至出现了减少趋势,部分地区已经出现冰川消融拐点。如发源于东天山的哈密头道沟和二道沟流域,冰川面积比例不足1%,径流量在1998年后分别减少了12.5%和增加6.6%,这也证明了冰川比例越高,径流量增加水平越大。同样的规律在阿尔卑斯山也存在,如冰川覆盖度在10%以上的流域,径流量存在增加趋势,而冰川覆盖度在10%以下的流域,径流量呈明显减少趋势[31]。
2.3.3 气候变暖改变了径流的年内分配规律 气候变化不仅引起径流补给方式和水资源数量的改变,而且改变了径流年内分配规律。由于气候变暖,天山山区冰川积雪融水补给河流的最大径流出现时间已经出现了季节性变化,表现为冰川和积雪消融期提前、径流峰值提前等一系列水文响应[19]。以积雪融水为主要补给源的河流,水文过程对气候变暖的响应表现为最大径流峰值前移,夏季径流减少明显;以冰川融水补给为主的河流,一般表现为6-9月汛期径流量明显增大,汛期洪水增多,年径流量增加[32]。例如,位于西天山锡尔河的支流Naryn河,由于冬季气温上升和日最高气温高于融化基温的天数增加,流域内冰川由20世纪90年代末的1019 km2退缩到2000年代中期的926 km2,冬季和早春的径流明显增加[33];对于以冰川融水补给为主的库玛拉克河,在1998年以后冬季、春季和夏季的径流增加量分别为13%、15%和15%,而以融雪径流补给为主的托什干河流域,3个季节的径流增加分别为65%、56%和11%,也证明了以融冰水和以融雪水补给为主的河流对气候变暖响应的差异性。同样,在世界其他山区流域也发现了由于气候变暖导致的由冰川/积雪融水补给河流的水文过程的改变。如美国山区典型流域,融雪日期提前使得径流峰值提前,积雪减少明显削弱了洪峰流量[34];在兴都库什—喜马拉雅山脉由于气候变暖导致的冰川积雪融水径流提前约30天,冰雪融水径流在过去30年增加了33%~38%[35]。
2.3.4 气候变暖改变了水资源构成 天山山区的水资源主要由高山冰川积雪融水、中山森林带降水以及低山带基岩裂隙水构成,产汇流机制复杂,在世界干旱区都具有很强的代表性。长期以来,天山山区的水资源依靠自然界独特的水循环过程维持着相对脆弱的平衡关系。气候变暖及高位持续波动,不仅对河流上源冰川积雪储量造成影响,同时导致水资源补给和径流组分发生变化,这对变化环境下的水资源未来趋势预估带来了新的挑战。
基于分布式VIC模型,对气候变化影响下的阿克苏河两大支流径流组分的未来变化进行了分析,结果显示,冰川融水、积雪融水和降雨分别占库玛拉克河和托什干河径流补给量的43.8%、27.7%、28.5%和23.0%、26.1%、50.9%[36]。再如,发源于东天山的乌鲁木齐河,在1950-2009年间径流量增加了10%[28],其中1994年以后69.7%的径流增加是由于冰川融水导致的,冰川融水所占比例从62.8%增加到72.1%[37-38];位于天山西段的伊犁河流域,其主要支流特克斯河的冰川退缩尤为突出,引起了河流的补给类型的改变,降雨径流所占比例减少,自20世纪70年代以来,特克斯河流域冰川退缩了22%,降雨径流由1966-1975年的9.8%减少到2000-2008年的7.8%[39]。
2.3.5 气候变化加剧了水文波动性 气候变暖影响区域水循环和水系统的稳定性,加剧了河流水文波动和水资源不确定性。天山山区的河川径流对冰川、积雪的依赖性较强,随着冰川退缩、冰川调节功能的下降以及因降水异常等极端气候水文事件的影响而变率增大[2],河流水文过程将会变得更为复杂,极端气候水文事件的频度和强度增大。如中国西北干旱区的极端水文事件的发生频率由20世纪80年代以前的40次/10a,增加到20世纪80年代后期以来的78次/10a[40];中国最大的内陆河—塔里木河,2009年和2010年上游的来水量分别为14.02×108 m3、72×108 m3,是塔里木河流域有水文记录以来径流量最少和最多年份,二者比值相差5倍多。研究结果显示,随着气候变暖,冰川面积比例降低,径流的变异系数（径流不稳定性）呈幂函数形式增长[26]。预估到2070-2099年,塔里木河流域的冰川将退缩32%~90%,导致径流量减少,水资源危机加重,不确定性将进一步加剧[30]。
3 结语
自1998年以来全球出现了升温滞缓现象,中亚地区与全球气候变化大趋势一致,但是,值得一提的是,1998年以来这一地区的气温却一直处于高位态波动状态,较其之前的30年平均温度升高了1.0 ℃。中亚天山深居欧亚大陆腹地,是世界上距海洋最远的山系,在过去的15年,气温为何会出现高位态波动,值得特别关注。因为在中亚干旱区,气温升高及持续高位态波动导致降雪率降低,加速天山山区冰川积雪融化,加快了以冰川、积雪为主体的“固体水库”的消融和萎缩,加重了中亚干旱区水资源危机,对未来中亚地区的发展和丝绸之路经济带建设产生重要影响。全球变暖加速了山区冰川积雪消融,加大了冰川积雪融水量,天山山区在近期或一定时段内会因为冰雪融水增多,径流量增加现象。但是,就长远来看,由于冰川萎缩,冰川储量减少,在未来气候持续变暖、降水条件维持不变的条件下,河川径流量总体上会出现减少趋势,尤其是夏季径流量。届时,中亚干旱区生产与生态用水的矛盾会进一步加剧。
全球变暖导致降水的时空分布、降水形式发生变化,加大了水文波动性,改变了水资源构成和径流组分,给变化环境下的水资源未来趋势预估带来了新的挑战。为此,需要进一步加强山区水资源储量变化趋势、速率及影响机制研究,加强山区径流组分变化及其对气候变化响应的研究,为准确掌握水资源数量变化、科学管理水资源提供科学基础,服务于国家一带一路建设。
The authors have declared that no competing interests exist.
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| [1] | More than 1.4 billion people depend on water from the Indus, Ganges, Brahmaputra, Yangtze, and Yellow rivers. Upstream snow and ice reserves of these basins, important in sustaining seasonal water availability, are likely to be affected substantially by climate change, but to what extent is yet unclear. Here, we show that meltwater is extremely important in the Indus basin and important for the Brahmaputra basin, but plays only a modest role for the Ganges, Yangtze, and Yellow rivers. A huge difference also exists between basins in the extent to which climate change is predicted to affect water availability and food security. The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60 million people. |
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| [4] | The coupled atmosphere–ocean Climate Model of the Centre National de Recherches Météorologiques (CNRM) has been used to run a time-dependent climate change experiment to study the impact of increasing amounts of greenhouse gases and aerosols on the simulated water cycle. This simulation has been initialised with the oceanic temperature and salinity profiles and the atmospheric trace gas concentrations observed in the 1950s, and has been carried out for 150 years after a 20-year spin-up. The simulated climate change has been analysed as the difference between two 30-year time slices: 1970–2000 and 2070–2100 respectively. The model achieves a reasonable simulation of present-day climate and simulates a general increase in precipitation throughout the twenty first century. The main exceptions are the subtropics, where the enhanced Hadley circulation has a drying impact, and the mid-latitude continents, where the increased evaporation in spring and decreased moisture convergence in summer lead to a relative summer drying. Global and regional analyses suggest that the precipitation increase is generally limited by a decrease in the water vapour cycling rate and in the precipitation efficiency, which appear as key parameters of the simulated water cycle. In order to reduce the spread between climate scenarios, more efforts should be devoted to estimate these parameters from satellite observations and meteorological analyses, and their possible evolution over recent decades. In the present study, the impacts of global warming on the surface hydrology have been also investigated. The main findings are the amplification of the annual cycle of soil moisture in the mid-and-high latitudes, and the decrease in the Northern Hemisphere snow cover, at a rate that is consistent with recent satellite estimations and should increase during the twenty first century. The runoff simulated over the 1950–2100 period has been converted into river flow using a linear river routeing model. The trends simulated over recent decades are surprisingly consistent with the river flow measurements available from the Global Runoff Data Centre. These trends can differ from those estimated over the whole 150-year integration, thereby indicating that it is not safe to predict hydrological impacts just by extrapolating the trends found in the available observations. Our climate model seems likely to provide qualitative hydrological scenarios over large river basins, but it still shows serious biases in the simulation of present-day river flows. Regional hydrological projections remain a challenge for the global climate modelling community and downscaling techniques are still necessary for this purpose. |
| [5] | Climate-driven changes in glacier-fed streamflow regimes have direct implications on freshwater supply, irrigation and hydropower potential. Reliable information about current and future glaciation and runoff is crucial for water allocation and, hence, for social and ecological stability. Although the impacts of climate change on glaciation and runoff have been addressed in previous work undertaken in the Tien Shan (known as the 'water tower of Central Asia'), a coherent, regional perspective of these findings has not been presented until now. In our study, we explore the range of changes in glaciation in different climatic regions of the Tien Shan based on existing data. We show that the majority of Tien Shan glaciers experienced accelerated glacier wasting since the mid-1970s and that glacier shrinkage is most pronounced in peripheral, lower-elevation ranges near the densely populated forelands, where summers are dry and where snow and glacial meltwater is essential for water availability. The annual glacier area shrinkage rates since the middle of the twentieth century are 0.38-0.76% per year in the outer ranges, 0.15-0.40% per year in the inner ranges and 0.05-0.31% per year in the eastern ranges. This regionally non-uniform response to climate change implies that glacier shrinkage is less severe in the continental inner ranges than in the more humid outer ranges. Glaciers in the inner ranges react with larger time lags to climate change, because accumulation and thus mass turnover of the mainly cold glaciers are relatively small. Moreover, shrinkage is especially pronounced on small or fragmented glaciers, which are widely represented in the outer regions. The relative insensitivity of glaciers in the inner ranges is further accentuated by the higher average altitude, as the equilibrium line altitude ranges from 3'500 to 3'600 masl in the outer ranges to 4'400 masl in the inner ranges. For our study, we used glacier change assessments based both on direct data (mass balance measurements) and on indirect data (aerial and satellite imagery, topographic maps). Latter can be plagued with high uncertainties and considerable errors. For instance, glaciated area has been partly overestimated in the Soviet Glacier catalogue (published in 1973, with data from the 1940s and 1950s), probably as a result of misinterpreted seasonal snowcover on aerial photographs. Studies using the Soviet Glacier catalogue as a reference are thus prone to over-emphasize glacier shrinkage. A valuable alternative is the use of continued in situ mass balance and ice thickness measurements, but they are currently conducted for only a few glaciers in the Tien Shan mountains. Efforts should therefore be encouraged to ensure the continuation and re-establishment of mass balance measurements on reference glaciers, as is currently the case at Karabatkak, Abramov and Golubin glaciers. Only on the basis of sound data, past glacier changes can be assessed with high precision and future glacier shrinkage can be estimated according to different climate scenarios. Moreover, the impact of snowcover changes, black carbon and debris cover on glacier degradation needs to be studied in more detail. Only with such model approaches, reflecting transient changes in climate, snowcover, glaciation and runoff, can appropriate adaptation and mitigation strategies be developed within a realistic time horizon. |
| [6] | 西北干旱区是对全球变化响应最敏感地区之一,研究分析全球变暖背景下的西北干旱区水资源问题,对应对和适应未来气候变化带来的影响具有重要意义。本文通过对西北干旱区气候变暖影响下的水资源形成、转化与水循环等关键问题最新研究成果的总结分析,得出如下结论:(1)西北干旱区温度、降水在过去的50年出现过"突变型"升高,但进入21世纪,温度和降水均处于高位震荡,升高趋势减弱;(2)西北干旱区冬季温度的大幅升高是拉动年均温度抬升的重要原因,而西伯利亚高压活动和二氧化碳排放是引起冬季升温的重要影响因素;(3)西北干旱区蒸发潜力在1993年出现了一个明显的转折变化,由显著下降逆转为显著上升的趋势。气候变暖、蒸发水平增大对西北干旱区生态效应的负作用已经凸显;(4)西北干旱区冰川变化对水资源量及年内分配产生了重要影响,部分河流已经出现冰川消融拐点。在塔里木河流域,冰川融水份额较大(50%),可能在未来一段时期,河川径流还将处在高位状态波动。全球气候变暖在加大极端气候水文事件发生频率和强度的同时,加剧了西北干旱区内陆河流域的水文波动和水资源的不确定性。 西北干旱区是对全球变化响应最敏感地区之一,研究分析全球变暖背景下的西北干旱区水资源问题,对应对和适应未来气候变化带来的影响具有重要意义。本文通过对西北干旱区气候变暖影响下的水资源形成、转化与水循环等关键问题最新研究成果的总结分析,得出如下结论:(1)西北干旱区温度、降水在过去的50年出现过"突变型"升高,但进入21世纪,温度和降水均处于高位震荡,升高趋势减弱;(2)西北干旱区冬季温度的大幅升高是拉动年均温度抬升的重要原因,而西伯利亚高压活动和二氧化碳排放是引起冬季升温的重要影响因素;(3)西北干旱区蒸发潜力在1993年出现了一个明显的转折变化,由显著下降逆转为显著上升的趋势。气候变暖、蒸发水平增大对西北干旱区生态效应的负作用已经凸显;(4)西北干旱区冰川变化对水资源量及年内分配产生了重要影响,部分河流已经出现冰川消融拐点。在塔里木河流域,冰川融水份额较大(50%),可能在未来一段时期,河川径流还将处在高位状态波动。全球气候变暖在加大极端气候水文事件发生频率和强度的同时,加剧了西北干旱区内陆河流域的水文波动和水资源的不确定性。 |
| [7] | Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970-2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Ni帽a-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase. |
| [8] | Numerous websites, blogs and articles in the media have claimed that the climate is no longer warming, and is now cooling. Here we show that periods of no trend or even cooling of the globally averaged surface air temperature are found in the last 34 years of the observed record, and in climate model simulations of the 20th and 21st century forced with increasing greenhouse gases. We show that ... |
| [9] | Observations indicate that although average temperatures in Central Asia showed almost no increases from 1997 to 2013, they have been in a state of high variability. Despite the lack of a clear increasing trend, this 15 year period is still the hottest in nearly half a century. Precipitation in Central Asia remained relatively stable from 1960 to 1986 and then showed a sharp increase in 1987. Since the beginning of the 21st century, however, the increasing rate of precipitation has diminished. Dramatic changes in meteorological conditions could potentially have a strong impact on the region's natural ecosystems, as some significant changes have already occurred. Specifically, the normalized difference vegetation index (NDVI) of natural vegetation in Central Asia during 1982-2013 exhibited an increasing trend at a rate of 0.004 per decade prior to 1998, after which the trends reversed, and the NDVI decreased at a rate of 0.003 per decade. Moreover, our results indicate that shrub cover and patch size exhibited a significant increase in 2000-2013 compared to the 1980s-1990s, including shrub encroachment on grasslands. Over the past 10 years, 8% of grassland has converted to shrubland. Precipitation increased in the 1990s, providing favorable conditions for vegetation growth, but precipitation slightly reduced at the end of the 2000s. Meanwhile, warming intensified 0.93掳C since 1997 compared to the average value in 1960-1997, causing less moisture to be available for vegetation growth in Central Asia. |
| [10] | This paper describes the construction of an updated gridded climate dataset (referred to as CRU TS3.10) from monthly observations at meteorological stations across the world's land areas. Station anomalies (from 1961 to 1990 means) were interpolated into 0.5掳 latitude/longitude grid cells covering the global land surface (excluding Antarctica), and combined with an existing climatology to obtain absolute monthly values. The dataset includes six mostly independent climate variables (mean temperature, diurnal temperature range, precipitation, wet-day frequency, vapour pressure and cloud cover). Maximum and minimum temperatures have been arithmetically derived from these. Secondary variables (frost day frequency and potential evapotranspiration) have been estimated from the six primary variables using well-known formulae. Time series for hemispheric averages and 20 large sub-continental scale regions were calculated (for mean, maximum and minimum temperature and precipitation totals) and compared to a number of similar gridded products. The new dataset compares very favourably, with the major deviations mostly in regions and/or time periods with sparser observational data. CRU TS3.10 includes diagnostics associated with each interpolated value that indicates the number of stations used in the interpolation, allowing determination of the reliability of values in an objective way. This gridded product will be publicly available, including the input station series (http://www.cru.uea.ac.uk/ and http://badc.nerc.ac.uk/data/cru/). 漏 2013 Royal Meteorological Society |
| [11] | Abstract The arid and semiarid region in central Asia is sensitive and vulnerable to climate variations. However, the sparse and highly unevenly distributed meteorological stations in the region provide limited data for understanding of the region's climate variations. In this study, the near-surface air temperature change in central Asia from 1979 to 2011 was examined using observations from 81 meteorological stations, three local observation validated reanalysis datasets of relatively high spatial resolutions, and the Climate Research Unit (CRU) dataset. Major results suggested that the three reanalysis datasets match well with most of the local climate records, especially in the low-lying plain areas. The consensus of the multiple datasets showed significant regional surface air temperature increases of 0.36 degrees-0.42 degrees C decade(-1) in the past 33 years. No significant contributions from declining irrigation and urbanization to temperature change were found. The rate is larger in recent years than in the early years in the study period. Additionally, unlike in many regions in the world, the temperature in winter showed no increase in central Asia in the last three decades, a noticeable departure from the global trend in the twentieth century. The largest increase in surface temperature was occurring in the spring season. Analyses further showed a warming center in the middle of the central Asian states and weakened temperature variability along the northwest-southeast temperature gradient from the northern Kazakhstan to southern Xinjiang. The reanalysis datasets also showed significant negative correlations between temperature increase rate and elevation in this complex terrain region. |
| [12] | ABSTRACT This study is an extensive revision of the Climatic Research Unit (CRU) land station temperature database that has been used to produce a grid-box data set of 5° latitude × 5° longitude temperature anomalies. The new database (CRUTEM4) comprises 5583 station records of which 4842 have enough data for the 1961-1990 period to calculate or estimate the average temperatures for this period. Many station records have had their data replaced by newly homogenized series that have been produced by a number of studies, particularly from National Meteorological Services (NMSs). Hemispheric temperature averages for land areas developed with the new CRUTEM4 data set differ slightly from their CRUTEM3 equivalent. The inclusion of much additional data from the Arctic (particularly the Russian Arctic) has led to estimates for the Northern Hemisphere (NH) being warmer by about 0.1°C for the years since 2001. The NH/Southern Hemisphere (SH) warms by 1.12°C/0.84°C over the period 1901-2010. The robustness of the hemispheric averages is assessed by producing five different analyses, each including a different subset of 20% of the station time series and by omitting some large countries. CRUTEM4 is also compared with hemispheric averages produced by reanalyses undertaken by the European Centre for Medium-Range Weather Forecasts (ECMWF): ERA-40 (1958-2001) and ERA-Interim (1979-2010) data sets. For the NH, agreement is good back to 1958 and excellent from 1979 at monthly, annual, and decadal time scales. For the SH, agreement is poorer, but if the area is restricted to the SH north of 60°S, the agreement is dramatically improved from the mid-1970s. |
| [13] | |
| [14] | |
| [15] | ABSTRACT The precipitation falling as rain or snow has different impact on regional water resources and their annual distribution. Shift from solid to liquid form of precipitation following the increase of the surface air temperatures could be quite important because such change could influence the timing of spring runoff and cause water shortage in summer. In this study, the ratio of snowfall to precipitation (S/P) for November鈥揗arch in the contiguous United States is analyzed and temperature effects on the changes of S/P are examined for 1949鈥2005. Major results show that the S/P ratio has been decreasing strongly in the Pacific Northwest and the central United States. The S/P decreased slightly in the eastern United States. In the Pacific Northwest, the changes of S/P are attributed to decrease of both snowfall and precipitation with snowfall decreasing at a greater rate. In the central United States, decrease of the S/P ratio resulted primarily from the decrease of snowfall and increase of the winter precipitation. Averaged over the contiguous United States, the changes of S/P are mainly related to the changes of the snowfall and with little effect from changes of winter precipitation. Decreases of the S/P ratio are largest in March and least in January. The significant decreases of the S/P ratio are associated with large increase in mean winter wet-day temperatures in the western and central United States. Weak warming in the eastern United States concurred with weak and no change of S/P. |
| [16] | ABSTRACT 1] This paper analyzes the proportion of snowfall days relative to precipitation days, in order to assess the impact of changing temperatures on snowfall, while minimizing the impact of variations in precipitation frequency and intensity. We analyzed the ratio of snowfall days to precipitation days for up to 100 years at 76 meteorological stations, spanning elevations from 200 to 2700 m asl in Switzerland. Our re-sults show clear decreasing trends in snowfall days relative to precipitation days. These decreases are connected to increasing temperatures. The decrease in snowfall days was stronger at lower elevations, i.e., at locations with tem-peratures closer to the melting point. We observed a baseline seasonal temperature threshold of 612.7°C ± 0.8°C in winter and 613.8°C ± 0.6°C in spring, above which the decrease in snowfall days grew rapidly. From these observations, we developed an empirical model that can be used to evaluate the impact of future temperature increases on snowfall, inde-pendent of changes in the frequency and intensity of precip-itation events. |
| [17] | Snowfall is an important element of the climate system, and one that is expected to change in a warming climate. Both mean snowfall and the intensity distribution of snowfall are important, with heavy snowfall events having particularly large economic and human impacts. Simulations with climate models indicate that annual mean snowfall declines with warming in most regions but increases in regions with very low surface temperatures. The response of heavy snowfall events to a changing climate, however, is unclear. Here I show that in simulations with climate models under a scenario of high emissions of greenhouse gases, by the late twenty-first century there are smaller fractional changes in the intensities of daily snowfall extremes than in mean snowfall over many Northern Hemisphere land regions. For example, for monthly climatological temperatures just below freezing and surface elevations below 1,000metres, the 99.99th percentile of daily snowfall decreases by 8% in the multimodel median, compared to a 65% reduction in mean snowfall. Both mean and extreme snowfall must decrease for a sufficiently large warming, but the climatological temperature above which snowfall extremes decrease with warming in the simulations is as high as -9掳C, compared to -14掳C for mean snowfall. These results are supported by a physically based theory that is consistent with the observed rain-snow transition. According to the theory, snowfall extremes occur near an optimal temperature that is insensitive to climate warming, and this results in smaller fractional changes for higher percentiles of daily snowfall. The simulated changes in snowfall that I find would influence surface snow and its hazards; these changes also suggest that it may be difficult to detect a regional climate-change signal in snowfall extremes. |
| [18] | |
| [19] | In a warming climate, precipitation is less likely to occur as snowfall. A shift from a snow- towards a rain-dominated regime is currently assumed not to influence the mean streamflow significantly. Contradicting the current paradigm, we argue that mean streamflow is likely to reduce for catchments that experience significant reductions in the fraction of precipitation falling as snow. With more than one-sixth of the Earth population depending on meltwater for their water supply and ecosystems that can be sensitive to streamflow alterations, the socio-economic consequences of a reduction in streamflow can be substantial. By applying the Budyko water balance framework to catchments located throughout the contiguous United States we demonstrate that a higher fraction of precipitation falling as snow is associated with higher mean streamflow, compared to catchments with marginal or no snowfall. Furthermore, we show that the fraction of each year precipitation falling as snowfall has a significant influence on the annual streamflow within individual catchments. This study is limited to introducing these observations; process-based understanding at the catchment scale is not yet provided. Given the importance of streamflow for society, further studies are required to respond to the consequences of a temperature-induced precipitation shift from snow to rain. |
| [20] | Long term (1921-2011) yearly and seasonal hydrological regime of 23 Alpine rivers in Northern Italy (ca. 10-10km) was investigated here. First, for regulated catchment, the potential effect of flow storage was investigated using an index of potential flow regulation, and pre and post reservoirs' installation flow analysis. For catchments displaying little regulation effect, non stationarity was studied using linear regression, including variable (segmented) slope analysis, and Mann Kendall test, traditional and progressive. The link of the observed trends against descriptive physiographic variables was then investigated, to highlight geographic and topographic patterns of changes of the hydrological cycle. Dependence upon global thermal and North Atlantic Oscillation NAO anomalies were analysed to highlight potential impact of large scale climate drivers against regional hydrological regimes. Also, the correlation between stream flows and climatic drivers of precipitation and temperatures in nearby stations was investigated, to highlight climate trends potentially driving hydrological changes, and potential changes in the nexus between climate and hydrology given by reservoirs' operation. |
| [21] | Populations in Central Asia are heavily dependent on snow and glacier melt for their water supplies. Changes to the glaciers in the main mountain range in this region, the Tien Shan, have been reported over the past decade. However, reconstructions over longer, multi-decadal timescales and the mechanisms underlying these variations--both required for reliable future projections--are not well constrained. Here we use three ensembles of independent approaches based on satellite gravimetry, laser altimetry, and glaciological modelling to estimate the total glacier mass change in the Tien Shan. Results from the three approaches agree well, and allow us to reconstruct a consistent time series of annual mass changes for the past 50 years at the resolution of individual glaciers. We detect marked spatial and temporal variability in mass changes. We estimate the overall decrease in total glacier area and mass from 1961 to 2012 to be 18 +/- 6% and 27 +/- 15%, respectively. These values correspond to a total area loss of 2,960 +/- 1,030 km, and an average glacier mass-change rate of -5.4 +/- 2.8 Gt yr. We suggest that the decline is driven primarily by summer melt and, possibly, linked to the combined effects of general climatic warming and circulation variability over the north Atlantic and north Pacific. |
| [22] | Abstract The fresh water lack in Central Asian countries with fast-growing population is one of the most critical problems in this region, where runoff of most rivers closely depends on supply of glaciers melting water. However, the impact of glacier shrinkage on the river runoff remains poorly understood. In this paper, we took the Karatal river basin, Tien Shan, as a model for investigation interrelation between dramatic decreasing of glaciers (1 % annually) and river runoff. We investigated long-term observed climatic and runoff data for different sub-basins of the river, having various glaciated area and used non-parametric Mann-Kendall test for our analyses. Analyzing weather station climatic data, we found a significant increase in temperature and quite stable trends for precipitation during study period. Positive trends in annual discharge were detected in almost all glacierized tributaries of Karatal river. This obvious upward trend in river runoff is likely connected with a general trend of increasing temperatures and intensive melting of glaciers in Tien Shan. |
| [23] | Terminus fluctuation and area change in mountain glaciers in the middle Chinese Tien Shan over the past four decades are examined, based on Landsat multispectral scanner (MSS), Enhanced Thematic Mapper Plus (ETM+), Système Probatoire pour l'Observation de la Terre (SPOT) high-resolution visible (HRV) imagery, topographical maps and China Glacier Inventory data using Geographical Information System (GIS) and remote-sensing techniques. This study shows that the glaciers in the study area have undergone continuous recession between 1963 and 2000. Over the past 37 years the total glacier area decreased from 55 × 106 m2 to 48 × 106 m2 (a 13% decrease). The glaciers at low elevations decreased more rapidly than those at high elevations. Seven of the ten large valley glaciers in the study area retreated by at least 150 ± 49 m during this period. The average rate of recession for these glaciers was 4-8 m a-1. The recession rate between 1986 and 2000 was larger than between 1963 and 1986. The glacier changes in the study area were similar to those in the 05rümqi river basin in the northern Chinese Tien Shan. It is apparent that temperature rise over the past four decades has had a profound impact on these glaciers. |
| [24] | RTK-GPS data, aerial photographs and Aster images were used to quantify volume, surface elevation, terminus position and area changes of Glacier No. 4 of Sigong River over Mt. Bogda, Tianshan during the period from 1962 to 2009. Glacier surface elevation of the tongue area decreased by 1502±02802m (0.3202±020.1702m02a 611 ) and ice volume loss reached 0.01402±020.00802km 3 (0.01302±020.00702km 3 02w.02e.). The glacier terminus retreated at a rate of 8.002m02a 611 and the area decreased by about 0.5302km 2 , accounting for 15.8% of the glacier area in 1962 (3.3302km 2 ). The changes can be primarily attributed to the significant increase in temperature in this region. A comparison with glacier changes by field measurements in other regions of eastern Tianshan showed obvious spatial differences in the magnitude of the changes, owing to a combination of regional climate change and topographical factors. |
| [25] | This book examines the possible impacts of climate change on hydrology and water resources in the vast arid region of Northwest China, which is one of the world's largest arid places. The first chapter offers an introductory discussion of the physical geography and socioeconomic conditions in the region. Chapters 2 through 7 discuss the climate system and hydrologic system changes in the region, and assess some implications of these changes in relation to potential evapotranspiration, the hydrological cycle and spatiotemporal variations of the snow cover and glaciers as measured via remote sensing, geographic information systems, and statistical analysis. Chapters 8 and 9 focus on model description and experimental design for interpreting the hydro-climatic process, emphasizing the integration of water, climate, and land ecosystems through field observations and computer-based simulations. Chapter 10 examines some extreme hydrological events and presents a study using the historical trend method to investigate the spatial and temporal variability of changing temperature and precipitation extremes in the hyper-arid region of Northwest China. A concluding chapter discusses possible strategies for sustainable watershed management. The contributors are acknowledged experts who bring broad, relevant experience on water resources research in China's cold and arid regions. The lessons of this volume will prove useful for understanding arid areas elsewhere in the world. 2014 Springer Science+Business Media Dordrecht. All rights are reserved. |
| [26] | Twenty-four headwater catchments with varying glacier area ratios (GARs) in the Eastern and Central Tian Shan Mountains were simulated by the glacier-enhanced Soil and Water Assessment Tool (SWAT) model from 1961 to 2007. The mean catchment GAR ranges between 0.7% and 44.8% with a mean of 8.6%. Through synthetic analysis of the glacio-hydrological processes simulation results of the catchments, it was found that the GAR is an effective index that can be used to interpret quantitatively the varying influences of glaciers on runoff across catchments. Among the twenty-four catchments, the ratio of glacier melt contribution (RGMC) to runoff varies between 3.5% and 67.5% with a mean of 24.0%; the ratio of ice melt contribution (RIMC) between 1.4% and 35.8% with a mean of 10.5%; the ratio of ice melt in glacier melt between 33.4% and 59.1% with a mean of 43.4%; the runoff coefficient (RC) between 0.24 and 0.90 with a mean of 0.52; and the coefficient of variation (CV) of runoff between 0.10 and 0.29 with a mean of 0.18. Based on synthetic analysis, it was found that (1) power functions fit the relations between RGMC, RIMC, RC, and CV and GAR with high certainty; (2) the CV decreases with increasing GAR while others increase; and (3) these power functions change sensitively with GAR when GAR is less than 10%, implicating that a small change in GAR may cause remarkable changes in RGMC, RIMC, RC, and CV in the less glacierized catchments. |
| [27] | Abstract The fresh water lack in Central Asian countries with fast-growing population is one of the most critical problems in this region, where runoff of most rivers closely depends on supply of glaciers melting water. However, the impact of glacier shrinkage on the river runoff remains poorly understood. In this paper, we took the Karatal river basin, Tien Shan, as a model for investigation interrelation between dramatic decreasing of glaciers (1 % annually) and river runoff. We investigated long-term observed climatic and runoff data for different sub-basins of the river, having various glaciated area and used non-parametric Mann-Kendall test for our analyses. Analyzing weather station climatic data, we found a significant increase in temperature and quite stable trends for precipitation during study period. Positive trends in annual discharge were detected in almost all glacierized tributaries of Karatal river. This obvious upward trend in river runoff is likely connected with a general trend of increasing temperatures and intensive melting of glaciers in Tien Shan. |
| [28] | The magnitude and variability of water system’s response to climate change impacts have been assessed through a detailed analysis of discharge composition of two selected typical glacier rivers originated from Tianshan Mountains, Xinjiang Uygur Autonomous Region in West China, which is considered as the water tower of Central Asia. Here we demonstrate climate change in the last 6002years using meteorological data (1951–2009) in the region. Both of the temperature and precipitation show a remarkable rise before and after year 1990 and these changes are much more significant in North Xinjiang than it is in South Xinjiang. Response of water systems towards climate change is then assessed by comparing annual discharge change of Urumqi River (10.0%) in the North and Kumalak River (38.7%) in South Xinjiang. We found significant inconsistency of the climate change impact on water resources. Furthermore, we quantitatively determine the ratio of ice-melt water using isotope hydrograph separation as well as other conservative tracers. Results show that Urumqi River is recharged by less than 9% of ice-melt water, while Kumalak River contains more than 57% of ice-melt water in their discharges. The extent of glacier input to a water system governs its sensitivity towards climate change. The method has overwhelming potential for un-gauged watersheds and may offer ways of adaptation to climate change in terms of water resources management for flood control and sustainable agriculture. |
| [29] | Observed streamflow of headwater catchments of the Tarim River (Central Asia) increased by about 30% over the period 1957-2004. This study aims at assessing to which extent these streamflow trends can be attributed to changes in air temperature or precipitation. The analysis includes a data-based approach using multiple linear regression and a simulation-based approach using a hydrological model. The hydrological model considers changes in both glacier area and surface elevation. It was calibrated using a multiobjective optimization algorithm with calibration criteria based on glacier mass balance and daily and interannual variations of discharge. The individual contributions to the overall streamflow trends from changes in glacier geometry, temperature, and precipitation were assessed using simulation experiments with a constant glacier geometry and with detrended temperature and precipitation time series. The results showed that the observed changes in streamflow were consistent with the changes in temperature and precipitation. In the Sari-Djaz catchment, increasing temperatures and related increase of glacier melt were identified as the dominant driver, while in the Kakshaal catchment, both increasing temperatures and increasing precipitation played a major role. Comparing the two approaches, an advantage of the simulation-based approach is the fact that it is based on process-based relationships implemented in the hydrological model instead of statistical links in the regression model. However, data-based approaches are less affected by model parameter and structural uncertainties and typically fast to apply. A complementary application of both approaches is recommended. |
| [30] | |
| [31] | Mean daily streamflow records from 48 watersheds in Switzerland with an undisturbed runoff regime are analysed for trends with the Mann–Kendall nonparametric test in three study periods (1931–2000, 1961–2000, 1971–2000). The statistical significance of trends is tested for each station on an annual and seasonal basis and for different streamflow quantiles. The field significance of trends is tested by a bootstrap procedure. Identified trends in streamflow are examined together with changes in precipitation and air temperature, and correlated with watershed attributes. Complex changes in the streamflow regime in Switzerland especially in the more recent periods are demonstrated. The main identified trends are an increase in annual runoff due to increases in the winter, spring and autumn season runoff, an increase in winter maximum streamflow (at more than 60% of the stations) and an increase in spring and autumn moderate and low flows. The behaviour in the summer period is different, with both upward and downward trends present in moderate and low flow quantiles. Many of the trends are field significant. Changes in precipitation are not sufficient to explain the observed trends in streamflow. Air temperature, most notably a substantial increase in the number of days with minimum daily temperature above 002°C, may explain some of the observed increases in winter and spring season runoff. Correlation analyses reveal a strong relationship between streamflow trends and mean basin elevation, glacier and rock coverage (positive), and basin mean soil depth (negative). These relationships suggest that the most vulnerable environments from the point of view of streamflow change are mountain basins. |
| [32] | 新疆是我国冰川、积雪资源最为丰富的地区,冰川和积雪融水在水资源构成中占有重要的地位,其 对气候变化的响应使得河流水文过程发生明显的变化,对新疆干旱区的水资源利用和管理产生重大影响.新疆高山流域产流占地表径流的80%以上,其中冰川和积 雪融水径流在总径流中的比例可达45%以上,积雪和冰川融水是河流的主要补给来源.在新疆北部的阿尔泰山和天山北坡河流主要以融雪径流补给为主,而在天山 南坡、昆仑山、喀喇昆仑山和天山北坡的伊犁河流域的河流以冰川融水补给为主;以融雪径流为主要的河流主汛期在春季到夏初,而冰川融水补给的河流夏季是主汛 期.随着新疆气候向暖湿转变,高山流域的水文过程对气候变暖和积雪增加产生明显的响应：以积雪为主补给的河流,水文过程对气候变暖的响应表现为最大径流前 移,夏季径流减少明显;以冰川融水补给的河流,径流响应表现为6-9月汛期径流量明显增大,汛期洪水增多,年流量增加.由于不同补给类型河流的水文过程发 生变化,其相应对下游的水资源供给和洪水安全管理产生了重大影响,在水资源管理方面需要适应气候变化对水文过程的调整,减缓气候变化对水资源安全的影响. . 新疆是我国冰川、积雪资源最为丰富的地区,冰川和积雪融水在水资源构成中占有重要的地位,其 对气候变化的响应使得河流水文过程发生明显的变化,对新疆干旱区的水资源利用和管理产生重大影响.新疆高山流域产流占地表径流的80%以上,其中冰川和积 雪融水径流在总径流中的比例可达45%以上,积雪和冰川融水是河流的主要补给来源.在新疆北部的阿尔泰山和天山北坡河流主要以融雪径流补给为主,而在天山 南坡、昆仑山、喀喇昆仑山和天山北坡的伊犁河流域的河流以冰川融水补给为主;以融雪径流为主要的河流主汛期在春季到夏初,而冰川融水补给的河流夏季是主汛 期.随着新疆气候向暖湿转变,高山流域的水文过程对气候变暖和积雪增加产生明显的响应：以积雪为主补给的河流,水文过程对气候变暖的响应表现为最大径流前 移,夏季径流减少明显;以冰川融水补给的河流,径流响应表现为6-9月汛期径流量明显增大,汛期洪水增多,年流量增加.由于不同补给类型河流的水文过程发 生变化,其相应对下游的水资源供给和洪水安全管理产生了重大影响,在水资源管理方面需要适应气候变化对水文过程的调整,减缓气候变化对水资源安全的影响. |
| [33] | Glaciers are significant fresh water storages in Central Asian high mountains and are considered to substantially contribute to the summer runoff of Central Asian Rivers. We present a comprehensive study of the glacier area changes in the Naryn catchment located in the Tien Shan Mountains. The catchment with a size of 55,944 kmis a major tributary of the Syrdarya River which is heavily used for water supply and irrigation. We analysed the glacier retreat based on Landsat MSS, TM and ETM + imagery for the mid-1970s, late 1990s and mid-2000s and based on a SPOT scene for 2007. Our results show a decreasing glacierisation within the catchment, shrinking from 1210 卤 30 km(2.2% glacierisation) in the 1970s to 1019 卤 25 km(1.8% glacierisation) in the late 1990s and further down to 926 卤 23 km(1.7% glacierisation) in the mid-2000s, corresponding to an area loss of 23% in total. The analysis reveals spatially heterogeneous area loss within the catchment. This can be associated with different hypsometries, size distributions, aspects and presences of debris cover. Small glaciers (with an area < 1 km) suffered from a strong area loss within the 30-years investigation period. |
| [34] | ABSTRACT Climate change has the potential to alter streamflow regimes, having ecological, economic, and societal implications. In the northeastern United States, it is unclear how climate change may affect surface water supply, which is of critical importance in this densely populated region. The objective of this study was to evaluate the impact of climate change on the timing and quantity of streamflow at small watersheds at the Hubbard Brook Experimental Forest in New Hampshire. The site is ideal for this analysis because of the availability of long-term hydroclimatological records for analyzing past trends and ample data to parameterize and test hydrological models used to predict future trends. In this study, future streamflow projections were developed with the forest watershed model PnET-BGC, driven by climate change scenarios from statistically downscaled outputs of atmospheric-ocean general circulation models. Results indicated that earlier snowmelt and the diminishing snowpack is advancing the timing and reducing the magnitude of peak discharge associated with snowmelt. Past increases in precipitation have caused annual water yield to increase significantly, a trend that is expected to continue under future climate change. Significant declines in evapotranspiration have been observed over the long-term record, although the cause has not been identified. In the future, evapotranspiration is expected to increase in response to a warmer and wetter environment. These increases in evapotranspiration largely offset increases in precipitation, resulting in relatively little change in streamflow. Future work should aim to decrease uncertainty in the climate projections, particularly for precipitation, obtain a better understanding of the effect of CO2 on vegetation, determine if climate-induced changes in tree species composition will influence discharge, and assess the impacts of changing hydrology on downstream water supplies. |
| [35] | ABSTRACT The impact of warmer climate on melt and evaporation was studied for rainfed, snowfed and glacierfed basins located in the western Himalayan region. Hydrological processes were simulated under current climatic conditions using a conceptual hydrological model, which accounts for the rainfall鈥搑unoff, evaporation losses, snow and glacier melt. After simulations of daily observed streamflow (R2=0.90) for 6 years, the model was used to study the impact of warmer climate on melt and evaporation. Based on the future projected climatic scenarios in the study region, three temperature scenarios (T+1, T+2 and ) were adopted for quantifying the effect of warmer climate. The comparison of the effect of warmer climate on different types of basins indicated that the increase in evaporation was the maximum for snowfed basins. For a T+2 掳C scenario, the annual evaporation for the rainfed basins increased by about 12%, whereas for the snowfed basins it increased by about 24%. The high increase of the evaporation losses would reduce the runoff. It was found that under a warmer climate, melt was reduced from snowfed basins, but increased from glacierfed basins. For a T+2 掳C scenario, annual melt was reduced by about 18% for the studied snowfed basin, while it increased by about 33% for the glacierfed basin. Thus, impact of warmer climate on the melt from the snowfed and glacierfed basins was opposite to each other. The study suggests that out of three types of basins, snowfed basins are more sensitive in terms of reduction in water availability due to a compound effect of increase in evaporation and decrease in melt. For a complex type of basin, the decrease in melt from seasonal snow may be counterbalanced by increase in melt from glaciers. However, on long-term basis, when the areal extent of glaciers will decrease due to higher melt rate, the water availability from the complex basins will be reduced. |
| [36] | ABSTRACT Arid and semiarid lowland areas of central Asia are largely dependent on fluvial water originating from the Tian Shan. Mountain glaciers contribute significantly to runoff, particularly in summer. With global warming, the total glacier area in the Kunma Like River catchment declined by 13.2% during 1990-2007. For future water resources, it is essential to quantify the responses of hydrologic processes to both climate change and shrinking glaciers in glacierized catchments, such as the headwaters of the Tarim River. Thus, a degree-day glacier melt algorithm was integrated into the macroscale hydrologic Variable Infiltration Capacity model (VIC). Good results were obtained for monthly runoff simulations in the Kunma Like River catchment, which suggest that the extended VIC has acceptable performance. Because of increased precipitation and air temperature, annual runoff in the catchment has increased by about 4.07 x 10(8) m(3) decade(-1) during 1984/85-2006/07. Under the assumption of the same climatic conditions, sensitivity analyses indicated that annual and summer river runoff volumes would decrease by 9.3% and 10.4%, respectively, for reductions in glacier area of 13.2%. The variation coefficient of annual runoff also increased because of shrinking glaciers. Runoff scenarios for warmer future climate and various deglaciation situations suggest that reductions in glacier area by >30% will likely produce less meltwater in summer and river runoff will decline. Consequently, the annual total discharge of the Kunma Like River is projected to decrease by 2.8%-19.4% in the 2050s scenario because of glacier shrinking. |
| [37] | Small glaciers are more sensitive to climate change and can drive remarkable runoff variation in local catchments. Here, the recent shrinkage and hydrological response of Urumqi Glacier No.1, a typical continental glacier, situated in the arid region of northwest China, were investigated using glacier data, hydrological and meteorological data collected near the glacier during the past 5065years. The results showed that annual air temperature and precipitation increased by 0·965°C and 9165mm (17.5%), respectively. Glacier length shortened by about 215·265m (9·7%) and its area diminished by 0·30465km(15·6%). The cumulative mass balance of the glacier was 61136569365mm, equivalent to 15·265m of glacier ice. Annual glacier runoff calculated by using a water balance model and the runoff measured at the outflow gauging station increased remarkably. The percentage of the increased river flow being derived from the increased glacier runoff reached 69·7% especially after 1994. Temperature and precipitation during the ablation season were the governing factors affecting the runoff at the glacierized (Glacier No.1) and non‐glacierized (Empty Cirque) catchments, respectively. Temperature rise and precipitation increase between 1959 and 2008 have had a combined effect on glacier mass loss and runoff change. Copyright 08 2012 John Wiley & Sons, Ltd. |
| [38] | ABSTRACT The impact of climate change on the variability of local discharge was investigated in a glacierized high mountain catchment located in the source area of the 05rümqi river, northwest China. We used past climate records to drive a hydrological model to simulate the discharge from 2000 to 2008. The model was then used to project future discharge variations for the period 2041–60, based on a regionally downscaled climate-change scenario combined with three stages of glacier coverage (i.e. compared to the glacier coverage in 2008): unchanged glacier size (100% glacierized), recession of half the glacier area (50% glacierized) and complete disappearance of glaciers (0% glacierized). In each scenario, snowmelt will begin half a month earlier and the discharge will increase in May. For the 100% glacierized scenario, the discharge will increase by 66 ± 35% in a smaller (3.34 km2) and more glaciated (50%) catchment and 33 ± 20% in a larger (28.90 km2) and proportionally less glaciated (18%) catchment. If the glacier area reduces by half, the discharge will decrease by 8 ± 5% and 9 ± 6%, respectively. Once the glacier disappears, the discharge will decrease by 58 ± 20% and 40 ± 13%, respectively. Together, the results indicate that a warming climate and the resulting glacier shrinkage will cause significant changes in the volume and timing of runoff. |
| [39] | ABSTRACT The glacier is an important and stable water supply in Central Asia. Monitoring the change of glacier and understanding the impacts of glacier change on river discharge are critical to predict the downstream water availability change in future. Glacier changes were discussed and their impacts on river discharge were evaluated by hydrological modeling with a distributed hydrological model SWAT under two land use and land cover scenarios (1970 and 2007) in Tekes watershed, the most important source of water discharge to the Ili River. Compared to the glacier area of 1511 km2 in 1970s it decreased by 332 km2 in 2007, which resulted in the contribution the discharge from precipitation in the glacier area to the average annual discharge of the watershed changing from 9.8% in the period 1966-1975 to 7.8% in the period 2000-2008. In the month scale, with the decrease of glacier area, the distribution of the contribution of monthly discharge from precipitation in the glacier area to the total of the watershed changed from bimodal pattern to unimodal pattern. By linking a hydrological model to remote sensing image analysis and Chinese glacier inventories to determine glacier area change our approach in quantifying the impacts of glacier changes on hydrology at different scales, will provide quantitative information for stakeholders in making decisions for water resource management. |
| [40] | We analyzed the characteristics of streamflow changes in the Tarim River Basin using daily data collected at 7 hydrological stations. We ran the nonparametric Mann鈥揔endall test to detect trends in hydrological extremes. We also applied the Indicators of Hydrological Alteration (IHA), to assess flow regime variations. The results indicate that: (1) the hydrological extremes in headwater experienced increases in magnitude, duration, and high flow frequency; the mainstream exhibited increases in low flow duration and low flow frequency, and adecrease in high percentile flow and high flow frequency; (2) The trends of extremes related to minimum flow is greater than maximum flow; the date of maximum flow in both the headwater and mainstream has advanced; the most drastic changes in extreme streamflow occurred during winter; (3) Climate change has considerably altered flow regime in the headwater. Although climate change has profoundly affected the water supply upstream, human activities are dominant in determining flow regime. |
