Temporal and spatial changes of temperature and precipitation in Hexi Corridor during 1955–2011

This study is focused on the northwestern part of Gansu Province, namely the Hexi Corridor. The aim is to address the question of whether any trend in the annual and monthly series of temperature and precipitation during the period 1955-2011 appears at the scale of this region. The temperature and precipitation variation and abrupt change were examined by means of linear regression, five-year moving average, non-parameter Mann-Kendall test, accumulated variance analysis and Pettitt test method. Conclusions provide evidence of warming and wetting across the Hexi Corridor. The mean annual temperature in Hexi Corridor increased significantly in recent 57 years, and the increasing rate was 0.27℃/10a. The abrupt change phenomenon of the annual temperature was detected mainly in 1986. The seasonal average temperature in this region exhibited an evident upward trend and the uptrend rate for the standard value of winter temperature indicated the largerst of four seasons. The annual precipitation in the Hexi Corridor area displayed an obviously increasing trend and the uptrend rate was 3.95 mm/10a. However, the annual precipitation in each basin of the Hexi Corridor area did not passed the significance test. The rainy season precipitation fluctuating as same as the annual one presented insignificant uptrend. No consistent abrupt change was detected in precipitation in this study area, but the rainy season precipitation abrupt change was mainly observed in 1968.     

青藏高原植被覆盖变化与降水关系

The temporal and spatial changes of NDVI on the Tibetan Plateau, as well as the relationship between NDVI and precipitation, were discussed in this paper, by using 8-km resolution multi-temporal NOAA AVHRR-NDVI data from 1982 to 1999. Monthly maximum NDVI and monthly rainfall were used to analyze the seasonal changes, and annual maximum NDVI, annual effective precipitation and growing season precipitation (from April to August) were used to discuss the interannual changes. The dynamic change of NDVI and the corre- lation coefficients between NDVI and rainfall were computed for each pixel. The results are as follows: (1) The NDVI reached the peak in growing season (from July to September) on the Tibetan Plateau. In the northern and western parts of the plateau, the growing season was very short (about two or three months); but in the southern, vegetation grew almost all the year round. The correlation of monthly maximum NDVI and monthly rainfall varied in different areas. It was weak in the western, northern and southern parts, but strong in the central and eastern parts. (2) The spatial distribution of NDVI interannual dynamic change was different too. The increase areas were mainly distributed in southern Tibet montane shrub-steppe zone, western part of western Sichuan-eastern Tibet montane coniferous forest zone, western part of northern slopes of Kunlun montane desert zone and southeastern part of southern slopes of Himalaya montane evergreen broad-leaved forest zone; the decrease areas were mainly distributed in the Qaidam montane desert zone, the western and northern parts of eastern Qinghai-Qilian montane steppe zone, southern Qinghai high cold meadow steppe zone and Ngari montane desert-steppe and desert zone. The spatial distribution of correlation coeffi- cient between annual effective rainfall and annual maximum NDVI was similar to the growing season rainfall and annual maximum NDVI, and there was good relationship between NDVI and rainfall in the meadow and grassland with medium vegetation cover, and the effect of rainfall on vegetation was small in the forest and desert area.     

Changes in daily climate extremes in Xinjiang, northwestern China

Based on daily maximum and minimum surface air temperature and precipitation records at 48 meteorological stations in Xinjiang, the spatial and temporal distributions of climate extreme indices have been analyzed during 1961-2008. Twelve temperature extreme indices and six precipitation extreme indices are studied. Temperature extremes are highly correlated to annual mean temperature, which appears to be significantly increasing by 0.08 °C per year, indicating that changes in temperature extremes reflect consistent warming. The warming tendency is clearer at stations in northern Xinjiang as reflected by mean temperature. The frequencies of cold days and nights have both decreased, respectively by 0.86 and 2.45 d/decade, but the frequencies of warm days and nights have both increased, respectively by +1.62 and +4.85 d/decade. Over the same period, the number of frost days shows a statistically significant decreasing trend of 2.54 d/decade. The growing season length and the number of summer days exhibit significant increasing trends at rates of +2.62 and +2.86 d/decade, respectively. The diurnal temperature range has decreased by 0.28 °C/decade. Both annual extreme low and high temperatures exhibit significant increasing trend, with the former clearly larger than the latter. For precipitation indices, regional annual total precipitation shows an increasing trend and most other precipitation indices are strongly correlated with annual total precipitation. Average wet day precipitation, maximum 1-day and 5-day precipitation, and heavy precipitation days show increasing trends, but only the last is statistically significant. A decreasing trend is found for consecutive dry days. For all precipitation indices, stations in northwestern Xinjiang have the largest positive trend magnitudes, while stations in northern Xinjiang have the largest negative magnitudes.     

Hydroclimatological changes in the Bagmati River Basin, Nepal

Study on hydroclimatological changes in the mountainous river basins has attracted great interest in recent years. Changes in temperature, precipitation and river discharge pattern could be considered as indicators of hydroclimatological changes of the river basins. In this study, the temperatures （maximum and minimum）, precipitation, and discharge data from 1980 to 2009 were used to detect the hydroclimatological changes in the Bagmati River Basin, Nepal. Simple linear regression and Mann-Kendall test statistic were used to examine the significant trend of temperature, precipitation, and discharge. Increasing trend of temperature was found in all seasons, although the change rate was different in different seasons for both minimum and maximum temperatures. However, stronger warming trend was found in maximum temperature in comparison to the minimum in the whole basin. Both precipitation and discharge trend were increasing in the pre-monsoon season, but decreasing in the post-monsoon season. The significant trend of precipitation could not be observed in winter, although discharge trend was decreasing. Furthermore, the intensity of peak discharge was increasing, though there was not an obvious change in the intensity of maximum precipitation events. It is expected that all these changes have effects on agriculture, hydropower plant, and natural biodiversity in the mountainous river basin of Nepal.     

雅鲁藏布江流域1961-2005年气候变化趋势

The Yarlung Zangbo River (YR) is the highest great river in the world, and its basin is one of the centers of human economic activity in Tibet. Using 10 meteorological stations over the YR basin in 1961–2005, the spatial and temporal characteristics of temperature and precipitation as well as potential evapotranspiration are analyzed. The results are as follows. (1) The annual and four seasonal mean air temperature shows statistically significant increasing trend, the tendency is more significant in winter and fall. The warming in Lhasa river basin is most significant. (2) The precipitation is decreasing from the 1960s to the 1980s and increasing since the 1980s. From 1961 to 2005, the annual and four seasonal mean precipitation is increasing but not statistically significant, especially in fall and spring. The increasing precipitation rates are more pronounced in Niyangqu and Palong Zangbo river basins, the closer to the upper YR is, the less precipitation increasing rate would be. (3) The annual and four seasonal mean potential evapotranspiration has decreased, especially after the 1980s, and most of it happens in winter and spring. The decreasing trend is most significant in the middle YR and Nianchu river basin. (4) Compared with the Mt. Qomolangma region, Tibetan Plateau, China and global average, the magnitudes of warming trend over the YR basin since the 1970s exceed those areas in the same period, and compared with the Tibetan Plateau, the magnitudes of precipitation increasing and potential evapotranspiration decreasing are larger, suggesting that the YR basin is one of the most sensitive areas to global warming.     

Distribution of winter-spring snow over the Tibetan Plateau and its relationship with summer precipitation in Yangtze River

The distribution of winter-spring snow cover over the Tibetan Plateau(TP) and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley(MLYRV) during 2003–2013 have been investigated with the moderate-resolution imaging spectrometer(MODIS) Terra data(MOD10A2) and precipitation observations. Results show that snow cover percentage(SCP) remains approximately 20% in winter and spring then tails off to below 5% with warmer temperature and snow melt in summer. The lower and highest percentages present a declining tendency while the middle SCP exhibits an opposite variation. The maximum value appears from the middle of October to March and the minimum emerges from July to August. The annual and winter-spring SCPs present a decreasing tendency. Snow cover is mainly situated in the periphery of the plateau and mountainous regions, and less snow in the interior of the plateau, basin and valley areas in view of snow cover frequency(SCF) over the TP. Whatever annual or winter-spring snow cover, they all have remarkable declining tendency during 2003–2013, and annual snow cover presents a decreasing trend in the interior of the TP and increasing trend in the periphery of the TP. The multi-year averaged eight-day SCP is negatively related to mean precipitation in the MLYRV. Spring SCP is negatively related to summer precipitation while winter SCP is positively related to summer precipitation in most parts of the MLYRV. Hence, the influence of winter snow cover on precipitation is much more significant than that in spring on the basis of correlation analysis. The oscillation of SCF from southeast to northwest over the TP corresponds well to the beginning, development and cessation of the rain belt in eastern China.     

Assessing changes in extreme precipitation over Xinjiang using regional climate model of PRECIS

In this paper, an analysis, with the simulation of PRECIS(Providing Regional Climate for Impact Studies), was made for future precipitation extremes, under SRES(Special Report on Emission Scenarios) A2 and B2 in IPCC(Intergovernmental Panel on Climate Change) AR4. The precipitation extremes were calculated and analyzed by ETCCDI(Climate Change Detection and Indices). The results show that:(1) In Present Scenario(1961–1900), PRECIS could capture the spatial pattern of precipitation in Xinjiang.(2) The simulated annual precipitation and seasonal precipitation in Xinjiang had a significantly positive trend and its variability had been deeply impacted by terrain. There was a strong association between increasing trend and the extreme precipitation's increase in frequency and intensity during 1961–2008. Under SRES A2 and B2, extreme precipitation indicated an increasing tendency at the end of the 21 st century. The extreme summer precipitation increased prominently in a year.(3) PRECIS's simulation under SRES A2 and B2 indicated increased frequency of heavy precipitation events and also enhancement in their intensity towards the end of the 21 st century. Both A2 and B2 scenarios show similar patterns of projected changes in precipitation extremes towards the end of the 21 st century. However, the magnitude of changes in B2 scenario was on the lower side. In case of extreme precipitation, variation between models can exceed both internal variability and variability of different SRES.     

三江源地区1961-2010年降水时空变化(英文)

Based on a monthly dataset of precipitation time series (1961-2010) from 12 meteorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province, China, the spatio-temporal variation and abrupt change analysis of precipitation were examined by using moving average, linear regression, spline interpolation, the Mann-Kendall test and so on. Major conclusions were as follows. (1) The long-term annual and seasonal precipitation in the study area indicated an increasing trend with some oscillations during 1961-2010; however, the summer precipitation in the Lantsang (Lancang) River Headwater Region (LARHR), and the autumn precipitation in the Yangtze River Headwater Region (YERHR) of the THRHR decreased in the same period. (2) The amount of annual precipitation in the THRHR and its three sub-headwater regions was greater in the 1980s and 2000s. The springs were fairly wet after the 1970s, while the summers were relatively wet in the 1960s, 1980s and 2000s. In addition, the amount of precipitation in the autumn was greater in the 1970s and 1980s, but it was relatively less for the winter precipitation, except in the 1990s. (3) The normal values of spring, summer, winter and annual precipitation in the THRHR and its three sub-headwater regions all increased, but the normal value of summer precipitation in the LARHR had a negative trend and the normal value of winter precipitation declined in general. (4) The spring and winter precipitation increased in most of the THRHR. The summer, autumn and annual precipitation increased mainly in the marginal area of the west and north and decreased in the regions of Yushu, Zaduo, Jiuzhi and Banma. (5) The spring and winter precipitation in the THRHR and its three sub-headwater regions showed an abrupt change, except for the spring precipitation in the YARHR. The abrupt changes of spring precipitation were mainly in the late 1980s and early 1990s, while the abrupt changes of winter precipitation were primary in the mid-to late 1970s. This research would be helpful for further understanding the trends and periodicity of precipitation and for watershed-based water resource management in the THRHR.     

中国近代北方极端干湿事件的演变规律

Using monthly precipitation and monthly mean temperature, a surface humid index was proposed. According to the index, the distributed characteristics of extreme dryness has been fully analyzed. The results indicated that there is an obvious increasing trend of extreme dryness in the central part of northern China and northeastern China in the last 10 years, which shows a high frequency period of extreme dryness; while a low frequency period in the regions during the last 100 years. Compared with variation trend of the temperature in these regions, the region of high frequent extreme dryness is consistent with the warming trend in the same region.     

Spatial and temporal distribution of precipitation based on corrected TRMM data around the Hexi Corridor, China

Accurate rainfall distribution is difficult to acquire based on limited meteorological stations, especially in remote areas like high mountains and deserts. The Hexi Corridor and its adjacent regions （including the Qilian Mountains and the Alxa Plateau） are typical districts where there are only 30 available rain gauges. Tropical Rainfall Measuring Mission （TRMM） data provide a possible solution. After precision analysis of monthly 0.25 degree resolution TRMM 3B43 data from 1998 to 2012, we find that the correlations between TRMM 3B43 estimates and rain gauge precipitation are significant overall and in each station around the Hexi Corridor; however, the biases of annual precipitation differ in different stations and are seriously overestimated in most of the sites. Thus, Inverse Distance Weighting （IDW） interpolation method was used to rectify TRMM data based on the difference between TRMM 3B43 estimates and rain gauge observations. The results show that rectified TRMM data present more details than rain gauges in remote areas where there are few stations, alt- hough they show high coherence of distribution. Precipitation decreases from southeast to northwest on an annual and seasonal scale. There are three rainfall centers （〉500 mm） including Menyuan, Qilian and Toson Lake, and two low rain- fall centers （〈50 mm） including Dunhuang and Ejin Banner. Meanwhile, precipitation in most of the study area presents an increasing trend; especially in northern Qilian Mountains （〉5 mm/a）, Badain Jaran Desert （〉2 mm/a）, Toson Lake （〉20 mm/a） and Qingtu Lake （〉20 ram/a） which shows a significant increasing trend, while precipitation in Hala Lake （〈-2 mm/a） and Tengger Desert （〈-3 mm/a） demonstrates a decreasing trend.     

近35 年青藏高原雨量和雨日的变化特征

利用青藏高原1971-2005 年49 个气象台站逐日雨量和雨日资料, 分析了青藏高原年、 季雨量和雨日变化趋势。结果表明, 近35 年西藏大部分地区年雨量、雨日呈现显著增加趋 势, 而青海省大部分地区雨量、雨日却呈减少趋势。夏半年, 高原上雨日减少, 雨量增加, 说明降水越来越集中, 降水强度在增加。冬半年, 高原上雨日、雨量均在增加。高原夏半年小雨(0.1~4.9 mm) 雨日减少, 雨量增加; 小雨(5.0~9.9 mm) 和中雨的雨日和雨量均呈增加趋 势, 大雨以上的雨日和雨量均减少。冬半年, 青藏高原小雪、中雪、大雪不同量级日数和雪 日的平均雪量均呈增加趋势; 暴雪日和雪量变化均不明显。     

青海高原近40 a降水变化特征及其对生态环境的影响

 利用青海省1961-2002年26个代表站逐日雨量资料和高原东部地区10个站的降水自记资料,分析了近40 a来降水量、雨日、雨强的气候变化特征。结果表明:青海高原近40 a来年降水量无明显的变化,但夏半年降水量呈减少趋势,冬半年降水量呈明显的增多趋势；夏半年降水量和雨日虽在减少,但降水强度在增大；夏半年降水量的减少主要是降水日数的减少造成的,而冬半年降水量的增加是由于雨日增多和每个降水日平均雨量的增大所造成；随着气候变暖,夏、秋季降水明显偏少,出现暖干化的气候趋势。     

祁连山讨赖河流域1957—2012年极端气候变化

全球气候变化背景下,极端气候事件发生的频率逐年增大,由此引发的气象灾害事件也随之增加。鉴此,本文利用祁连山讨赖河流域1957—2012年的气象观测资料,对该流域23个极端气候指数的时空变化特征做了研究。结果表明：（1）极端气温升高趋势明显,夜间和白天极端低温日数显著减少,极端气温昼指数显著增大;气温日较差变化幅度很小,霜冻日数显著减少,生长季长度明显加长,冰冻日数2000年后增加;夜指数增大幅度大于昼指数,秋、冬季极端气温升高幅度大于春、夏季。（2）极端降水指数增大趋势明显,雨日降水总量、连续五日降水总量和中雨天数均展现出增大态势,反映出连续降水事件的增加;极端降水量事件增大显著,但雨日降水强度变化不大;除最多连续无降水日数外,极端降水日数指数展现出增大趋势;降水日数夏、秋季节分配趋向均匀化;降水量的增加主要是单次降水时间持续加长和中雨日数增加的贡献;高海拔区极端降水事件发生的频次较大。     

西藏高原降水变化趋势的气候分析

利用西藏1971~2000年月降水量、降水日数资料,分析了近30年高原降水的变化趋势。结果发现,西藏大部分地区年降水量变化为正趋势,降水倾向率为1.4~66.6 mm/10a,而阿里地区呈较为明显的减少趋势。年降水日数变化阿里地区、林芝地区东部为负趋势,正趋势以那曲地区中西部、昌都地区北部最为明显。20世纪70年代高原西部为正距平、东部为负距平,20世纪80年代大部分地区为负距平,20世纪90年代高原西部为负距平,东部为正距平。近30年来西藏高原平均年、四季降水量均呈增加趋势,年降水量以19.9 mm/10a的速率增加,尤其是20世纪90年代增幅较大,1992年以来春、夏季降水明显增加。阿里地区出现了暖干化趋势。年降水异常偏涝年主要出现在20世纪80和90年代。     

1960—2017年太湖流域不同等级降水时空特征

基于太湖流域1960—2017年逐日降水数据，运用Mann-Kendall非参数检验法、R/S分析等方法，分析太湖流域不同等级降水的时空变化特征，并探讨了不同等级降水对年降水的影响。结果表明：1）近60年来，流域小雨发生率最高，为73.55%；年总降水量中，中雨量所占比例最大，为32.05%。小雨发生率呈显著减少趋势，暴雨贡献率呈显著增加趋势。2）太湖流域大雨、暴雨的降水量和降水日数都呈显著增加，小雨日数显著减少，小雨强度、年总降水强度显著增强。3）不同等级降水变化趋势的空间分布存在明显差异。小雨日数与年总降水日数，以及小雨强度与年总降水强度的变化趋势空间格局相一致。中雨日数、大雨日数、暴雨日数变化趋势的空间分布与其对应的降水量变化趋势的空间格局相似。4）R/S分析结果显示，小雨、暴雨、年总降水相关指标（小雨量除外）都表现出较强的持续性，未来变化趋势与过去相一致。5）近60年来，太湖流域年总降水量、降水日数、年总降水强度的变化，分别受中雨量、小雨日数、暴雨量的影响较大。在旱年流域年降水量偏少受大雨量减少的影响较大，而涝年年降水量偏多受暴雨增加的影响较大。     

昆明市不同等级降水日数的时空分布特征

采用线性趋势法,Mann-Kendall检验的方法,分析了近42年（1971-2012年）昆明市12个测站逐日降水资料的时空分布特征和变化规律。昆明市的小雨日数占总雨日数的比重最大,总雨日数的减少主要是由于小雨日数的减少所致。2001年后降水的减少趋势更加明显,且在2009年后出现极端化发展的趋势。全市年总雨日数及不同等级降水日数分布不均匀,存在两个多雨日中心。各站年总降水日数和小雨日数均呈减少趋势,但是东川不显著;中雨、大雨和暴雨日数大部以缓慢减少为主,部分有所增加,但变化趋势并不明显。     

1961—2015年中国降水面积变化特征研究

基于中国0.5°×0.5°逐月与逐日降水量网格数据集，采用线性趋势、克里金插值（Kriging）、森斜率等方法，分析1961—2015年中国3个自然区的降水量和降水面积的变化特征。结果表明：（1） 中国1961—2015年年均和季节平均降水量呈现由东南沿海向西北内陆递减的空间分布特征，中国一半以上的地区年均和四季降水量呈增加趋势。（2） 日变化特征上，东部季风区、西北干旱区和青藏高寒区均以小雨和中雨为主，其日降水面积多年平均值分别为：1 112.75×10³ km²、52.65×10³ km²，1 380.57×10³ km²、92.83×10³ km²，1 253.9×10³ km²、34.3×10³ km²，暴雨和大暴雨占的面积较小；三个区域不同等级日降水面积年内变化均符合二次函数曲线，三个区小雨日平均降水面积年际变化均呈略微减少趋势，青藏高寒区和西北干旱区大雨、暴雨和大暴雨均呈略微增加趋势，大暴雨整体波动较大。（3） 季节变化特征上，三个区四季均以小雨为主，暴雨和大暴雨所占面积较少。春季和秋季三个区小雨降水面积均呈减少趋势，春季和夏季三个区暴雨降水面积均呈增加趋势，冬季三个区中雨和大雨降水面积呈增加趋势。（4） 东部季风区春季和秋季，西北干旱区年均和四季，青藏高寒区春季、秋季和冬季不同等级降水量对应的降水面积均符合负指数分布规律。km²     

西沙群岛和涠洲岛气候变化特征 及其与近岸陆地的对比

采用1959―2014年中国西沙站和涠洲岛站及其临近陆地台站的基本气象观测资料,分析了2个海岛的气候变化特征及其与近岸陆地的差异。结果表明：1）近56年西沙和涠洲岛及近岸陆地气温变化均呈上升趋势,西沙增暖速率（0.19℃/10 a）大于涠洲岛（0.104℃/10 a）。显著的差异出现在近10年,西沙持续增暖（0.38℃/10 a）,而涠洲岛气温却呈下降趋势（-0.48℃/10 a）。从季节变化上,2个海岛都有春季越来越暖、冬季越来越冷的趋势。与周围陆地的气温相比,2个海岛的气温均高于近海陆地,但增温速率却小于近岸陆地。2）分析近56年降水量的变化,发现海岛降水量、降水强度和降水天数均小于陆地。受冬、夏季风转换的控制,海岛及近岸陆地有旱季、雨季的划分,且近半个世纪以来降水量波动大、变化趋势不显著,但伴随降水天数的减少,降水强度呈显著增长趋势。对比2个海岛近10年的降水变化特征,发现西沙站的旱季有越来越旱的趋势,涠洲岛及近岸陆地无论旱季、雨季降水量都有增加的趋势,表现为湿润化的趋势。     

西藏高原汛期降水日数和强度的时空演变特征

利用西藏高原38个气象站自建站以来至2007年的逐日降水资料,分析了西藏高原汛期不同等级降水日数和降水强度的时空演变特征及其对旱涝的影响。结果表明：西藏降水日数和小雨日数呈现北增南减的趋势,中雨日数在雅鲁藏布江中下游、昌都地区东南部一线增加。1961-2007年总降水日数的减少主要体现在小雨日数下降和贡献率减少,而中雨的日数和贡献率增加;降水强度表现出一定的增加趋势,体现为小雨和大雨强度的增加。20世纪80年代前多小雨,80年代至90年代多中雨以上强度的降水,21世纪前7年多小雨,而大雨主要在90年代对降水量的贡献率较大。西藏高原降水有向不均衡、极端化发展的趋势,这对西藏高原旱涝灾害的发生具有重要的影响。