近47年哈密地区气候变化

利用新疆哈密地区5个气象台站1961~2007年气候资料,采用线性回归、Morlet小波和Mann-Kendall突变检测等方法,对哈密地区近47年的年平均气温、降水量、日照时数、年平均风速和相对湿度等气候要素以及年潜在蒸散量和地表干燥度的变化趋势和变化特征进行了研究。结果表明：①近47年哈密地区年平均气温、降水量和相对湿度呈升高趋势,日照时数和年平均风速呈减小趋势;②潜在蒸散量与年平均气温、日照时数和平均风速呈极显著的正相关关系,而与年降水量和相对湿度呈极显著的负相关关系。受上述各气候要素变化的综合影响,近47年,哈密地区潜在蒸散量和地表干燥度呈极显著的减小趋势;③突变检测表明,哈密地区年平均气温、降水量分别在1973年、1965年发生了突变性的升高,而风速、潜在蒸散量和地表干燥度分别于1980年、1980年和1975年发生了极显著的突变性减小,综合气温和地表干燥度的突变特征,可以认为,哈密地区气候在1973~1975年发生了＂暖湿化＂的突变;④各气候要素和潜在蒸散量、地表干燥度分别存在不同时间尺度的周期性变化。     

近45年来河北省极端降水事件的变化研究

利用河北省1961-2005年逐日降水资料,采用通用的极端气候指数,分析了近45年河北省极端降水事件频率变化的时空特征.结果表明,全省平均年最大日降水量呈下降趋势,1980年为由多向少的转折点;强降水日数和暴雨日数变化不大,但南部平原地区一般减少,北部山地区域多有增加,暴雨日数和强度在1990年代中后期显著增加;降水日数有较明显减少,南部和东南部平原减少更显著;降水日数的减少主要是中、小雨(雪)日数减少造成的.这些结果说明,河北省强降水日数和暴雨日数在降水日数中的比重有增大趋势,强降水量和暴雨降水量在总降水量中的比重可能增加了.这种相对增加趋势主要发生在1990年代中期以后.     

西藏近35年地表湿润指数变化特征及其影响因素

利用1971-2005年西藏25个气象站月平均最高气温、最低气温、风速、相对湿度、日照时数、降水量等资料,应用Penman-Monteith模犁计算了最大潜在蒸散、地表湿润指数,分析了其空间分布、年际变化特征及季节差异,并讨论了影响地表湿润指数变化的气象因子.研究表明:近35年,西藏年降水量表现为显著的增加趋势,增幅为15.0 mm/(10 a);年最大潜在蒸散呈不同程度的减小趋势,为-4.6--71.6 mm/(10 a).阿里地区西南部、聂拉木年地表湿润指数为不显著的减小趋势,其他各地均呈增大趋势,增幅为0.02-0.09.就西藏平均而言,年地表湿润指数以0.04/10 a的速率显著增大,尤其足近25年增幅更为明显.各季节地表湿润指数也表现为增大趋势,以夏季增幅最明显.20世纪70年代剑80年代主要表现为以低温低湿为主的年际变化特征,进入90年代后,气温持续升高,地表湿润指数明显增加,呈现山暖湿型的气候特征.降水量和相对湿度的明显增加,以及平均气温日较差的显著减小是地表湿润指数显著增加的主要原因,平均风速和日照时数的明显减少,在湿润指数增加趋势中也起着重要作用.     

滕州市近50年气候干湿变化

利用滕州市1956~2005年降水量、平均气温资料,用Holdridge干燥度指数来分析近50年气候干湿变化趋势和特征。滕州市近50年来在年生物温度、年可能蒸散量极显著上升背景下,年降水量不显著的减小趋势,造成年水分盈亏量显著亏损及年干燥度指数显著增大,总体呈现暖干化趋势。年干燥度指数变化有明显的阶段性,干湿期交替变化,大体经历了3个湿期和2个干期。1976年年干燥度指数发生由偏湿向偏干的突变,突变后气候类型分布发生显著变化。通过对近50年年干燥度指数滑动平均值和标准差分析发现:随着干燥度指数平均值的增大,异常湿事件明显减少,而异常干事件明显增多,同时,随着标准差的增大,异常干湿事件频率明显增大。     

阿尔山市地表干湿分布特征与生态环境的关系

利用阿尔山市的气象资料,分析了1971—2007年地表潜在蒸散量和湿润指数的变化特征。结果表明:(1)从20世纪80年代以来,阿尔山市地表潜在蒸散量一直呈增大的趋势。(2)从对湿润指数(K)、潜在蒸散量(Eti)、年降水量(R)、年平均气温(T)的趋势分析看,阿尔山市干旱化有加重的趋势,降水有集中的趋势,阶段性干旱有增多加重的发展趋势,从而导致阿尔山市生态环境趋于恶化。     

1965-2007年沙澧河流域潜在蒸散量变化趋势

利用1965-2007年沙澧河流域12个气象站的逐月气候资料,采用FAO推荐的彭曼-孟蒂斯公式计算潜在蒸散量,分析了沙澧河流域43 a潜在蒸散量的变化趋势,并在ArcGIS环境下通过Spline插值法分析了该流域潜在蒸散量空间分布特征,此外还对造成潜在蒸散量变化的主要气候影响因子进行了探讨。结果表明:从空间分布来看,潜在蒸散量年和四季从西北到东南基本呈下降趋势。从时间变化来看,年潜在蒸散量略呈下降趋势,但变化不明显;冬、春季呈增加趋势,年际变化率分别为0.189 mm.a-1和0.540 mm.a-1,夏、秋季呈减小趋势,其中夏季减少尤其明显,年际变化率为-1.354 mm.a-1。日照是影响年和夏、秋季潜在蒸散量变化的主导因素,而气温是影响冬、春季潜在蒸散量变化的主导因素。     

黑龙江省地表湿润状况及趋势分析

利用1958～2003年黑龙江省均匀分布的16站月降水和平均气温资料,通过计算地表最大潜在蒸发、地表干燥度指数、地表水分盈亏量,对比分析了黑龙江省各不同干湿气候区域地表干湿状况的分布规律及其变化趋势,并讨论了它与降水和气温的关系。给出了地表干燥度指数的地理分布和变化趋势。研究表明:全省及各区地表干燥度均存在变干的趋势,特别在进入21世纪以后,变干的趋势更加明显。但各地变干的特征差别较大,其中西部地区地表变干的程度最为严重,北部地区最轻,甚至个别地区还有变湿的倾向。     

1961-2009年三江源地区气候变化特征分析

利用三江源地区18个气象台站1961—2009年气温、年最高气温、年最低气温、降水量、降水日数等资料,分析了该地区年最高气温、年最低气温、降水量、降水日数等气候要素的变化趋势。研究表明:近49年来三江源年平均气温、年平均最高气温、年平均最低气温均在升高,升高速率平均最低气温明显大于平均气温和平均最高气温,年平均气温的升高主要是由最低平均气温升高引起的;三江源年和四季降水量均呈增多趋势,冬、春季降水量增幅最明显,年降水量变化的空间分布北部增多而东南部减少,年降水量除20世纪70年代—21世纪初均呈增加趋势;年和冬、春季≥0.1mm降水日数增加,而夏秋季降水日数减少;年和冬、夏、秋季潜在蒸散量呈显著性增加趋势,春季变化则不明显;年和四季平均风速均呈显著下降趋势;年和四季日照时数变化不显著。     

气候变化和人类活动对太子河流域径流变化的贡献

为揭示气候变化与人类活动对太子河流域径流量变化的影响,基于1961—2018年气温、降水量等常规观测资料以及水文站径流量资料,采用线性回归分析、累积距平等方法,对该流域径流量、面降水量及潜在蒸散量趋势特征、突变点进行统计分析。在此基础上,采用累积量斜率变化率比较法定量估算不同时期气候变化和人类活动对径流量变化的贡献。结果表明:1961—2018年,太子河流域径流量与面降水量、潜在蒸散量均呈现微弱减少趋势,径流量和面降水量分别在1975、1984、1996、2009年发生显著突变,而面潜在蒸散量仅在1983年发生显著突变。径流量与面降水量、潜在蒸散量存在极显著的相关关系,径流量随着降水量增加、潜在蒸散量减少而增大。根据径流量的突变点将研究时段划分为5个时期,与基准期1961—1975年相比,1976—1984年、1985—1996年、1997—2009年及2010—2018年气候因子对径流量变化的贡献率分别为23.24%、-0.08%、18.57%及28.45%,而人类活动的贡献率分别为76.76%、100.08%、81.43%及71.55%,表明人类活动是太子河流域径流量减少的主要影响因素。     

近53a来祁连山南北坡潜在蒸散量及地表湿润度变化趋势分析

利用祁连山地区15个气象台站1961~2013年月气象资料,计算和分析该地区潜在蒸散量和湿润指数的变化趋势。研究表明:(1)祁连山南北坡潜在蒸散量的年变化表现为单峰型,较大值出现在5~8月,较小值出现在12月至翌年2月。湿润指数从5月开始逐渐增大,南坡7月最大,北坡9月最大,10月开始逐步减小。湿润指数与潜在蒸散量在祁连山地区存在明显的位相差。季节表现均为夏季最大、春秋季次之、冬季最小,潜在蒸散量相邻季节间的波动北坡明显大于南坡,湿润指数则相反;(2)祁连山地区南北坡潜在蒸散量均在波动中呈显著增加趋势,而湿润指数波动中缓慢增加,但变化趋势不明显。潜在蒸散量和湿润指数增加速率均是北坡大于南坡。南北坡潜在蒸散量和湿润指数未来变化趋势总体上将同过去保持一致,且北坡年潜在蒸散量变化趋势强度强于南坡;(3)通过与各气候因子的多元回归分析表明,影响祁连山南北坡湿润指数(潜在蒸散量)的主要因子是降水量(气温),其他气候因子的变化对地表干湿状况起增强或削弱作用。     

Sensitivity analysis of climate on streamflow in north China

The economics and crowded cities of north China play important roles in China’s overall economic development. Streamflow is a hot issue in ecohydrological studies, and research into changes in streamflow in north China is of great significance. In this study, the sensitivities of streamflow to the aridity index, precipitation, and potential evapotranspiration are evaluated to assess the impact of climatic variation in streamflow in north China. The results show that the average coefficient of sensitivity of streamflow to aridity index is ?2.24, and streamflow would decrease by 22.4 % with a 10 % increase in the aridity index. The average coefficients of sensitivity of streamflow to precipitation and potential evapotranspiration are 3.21 and ?2.21, respectively. A 10 % increase in precipitation or potential evapotranspiration would induce a 32.1 % increase or a 22.1 % decrease of streamflow, respectively. Basins with low streamflows would be more sensitive to climatic variation than basins with high streamflows.     

Comparison of the streamflow sensitivity to aridity index between the Danjiangkou Reservoir basin and Miyun Reservoir basin, China

The central route of China’s South-to-North Water Diversion Project would divert water from the Danjiangkou Reservoir basin (DRB) to Beijing beginning in the year 2014. The current main surface water source for Beijing is the Miyun Reservoir basin (MRB). The observed streamflows into the DRB and the MRB decreased significantly due to climatic variation and human activities from 1960 to 2005. The climate elasticity method is widely used to quantitatively separate the impacts of climatic variation and human activities on streamflow. One of the uncertainties of the method is that the impacts of changes in precipitation and potential evapotranspiration on streamflow are separated with the assumption that they are independent. However, precipitation and potential evapotranspiration are not totally independent. Aridity index, as the ratio between potential evapotranspiration and precipitation, could be considered as the representative indicator of climatic variation. In this study, the sensitivity of streamflow to aridity index is evaluated to assess the impact of climatic variation on streamflow in the DRB and the MRB. The result shows that streamflow in the MRB is more sensitive to climatic variation than that in the DRB. However, the effective impact of aridity index on streamflow is the product of the sensitivity and the change rate of aridity index. The attribution results show that change in aridity index contributed 68.8 % of the decrease in streamflow in the DRB while it contributed 31.5 % of the decrease in streamflow in the MRB. This indicated that the impact of climatic variation was the main reason of decrease in streamflow in the DRB while human activities such as increasing water consumption and land use change were the main reasons of decreasing streamflow in the MRB.     

近30年安徽省地表干湿时空变化及对农业影响

采用FAO Penman-Monteith模型, 并利用安徽省辐射观测资料对其净辐射项进行修正, 计算近30年安徽省的参考作物蒸散量。用此计算值和相应时段的降水量计算干燥度 (I_a), 并进行了基于干燥度指标不同时间尺度的区域地表干湿状况变化分析。分析表明:1971—2000年安徽省年干燥度平均值I_a=1的等值线为湿润区和半湿润区的分界线, 该分界线与1000 mm的年雨量线有很好的一致性, 同时也具有清晰的农业意义。20世纪70—90年代I_a=1的等值线南北波动, 其波动区域正是安徽省江淮分水岭易旱区。在此基础上分析了半湿润区、波动区域和湿润区降水量、参考作物蒸散量和干燥度年代际、年际和半年际的变化趋势及变异率以及逐月干旱频率及其对农业的影响。     

Dryland expansion in northern China from 1948 to 2008

This study examines the expansion of drylands and regional climate change in northern China by analyzing the variations in aridity index(AI), surface air temperature(SAT), precipitation and potential evapotranspiration(PET) from 1948 to 2008.It is found that the drylands of northern China have expanded remarkably in the last 61 years. The area of drylands of the last 15 years(1994–2008) is 0.65 × 106km2(12%) larger than that in the period 1948–62. The boundary of drylands has extended eastward over Northeast China by about 2° of longitude and by about 1° of latitude to the south along the middleto-lower reaches of the Yellow River. A zonal band of expansion of semi-arid regions has occurred, stretching from western Heilongjiang Province to southern Gansu Province, while shifts to the east of semi-arid regions in dry subhumid regions have also occurred. Results show that the aridity trend of drylands in northern China is highly correlated with the long-term trend of precipitation and PET, and the expansion of semi-arid regions plays a dominant role in the areal extent of drylands, which is nearly 10 times larger than that in arid and subhumid regions.     

The potential of vegetation feedback to alleviate climate aridity over the United States associated with a 2×CO2 climate condition

This study examines the potential impact of vegetation feedback on changes in summer climate aridity over the contiguous United States (US) due to the doubling of atmospheric CO₂ concentration using a set of 100-year-long climate simulations made by a global climate model interactively coupled with a dynamic vegetation model. The Thornthwaite moisture index (I _m ), which quantifies climate aridity on the basis of atmospheric water supply (i.e., precipitation) and atmospheric water demand (i.e., potential evapotranspiration, PET), is used to measure climate aridity. Warmer atmosphere and drier surface resulting from increased CO₂ concentration increase climate aridity over most of the contiguous US. This phenomenon is due to larger increments in PET than in precipitation, regardless of the presence or absence of vegetation feedback. Compared to simulations without active dynamic vegetation feedback, the presence of vegetation feedback significantly alleviates the increase in aridity. This vegetation-feedback effect is most noticeable in the subhumid regions such as southern, midwestern and northwestern US, primarily by the increasing vegetation greenness. In these regions, the greening in response to warmer temperatures enhances moisture transfer from soil to atmosphere by evapotranspiration (ET). The increased ET and subsequent moistening over land areas result in weaker surface warming (1–2?K) and PET (3–10?mm?month^?1), and greater precipitation (4–10?mm?month^?1). Collectively, they result in moderate increases in I _m . Our results suggest that moistening by enhanced vegetation feedback may prevent aridification under climatic warming especially in areas vulnerable to climate change, with consequent implications for mitigation strategies.     

Spatial and temporal changes in aridity index in northwest China: 1960 to 2010

Northwest China is the driest region in China and the regional climate fluctuated dramatically during the last century. Aridity index, as the ratio between potential evapotranspiration and precipitation, is a good indicator to represent regional climate character. In this study, the change and attribution of the aridity index was investigated in northwest China using the observed climate data from 80 national meteorological stations during 1960–2010. The spatial and temporal variabilities of the aridity index shows that the annual aridity index decreased significantly (P?<?0.05) by 0.048 year^?1, indicating that northwest China became wetter from 1960 to 2010. A differentiation equation method was used to attribute the change in aridity index to climate variables. The results indicate that the aridity index was most sensitive to the change in precipitation, followed by vapor pressure, solar radiation, wind speed, and air temperature. Increase in air temperature should have led to an increase in aridity index, but this effect had been offset by the increase in precipitation and vapor pressure and the decrease in wind speed. Increasing precipitation, which contributed 91.7 % of the decrease in the aridity index, was the dominant factor to the decrease in the aridity index in northwest China from 1960 to 2010.     

Using aridity indices to describe some climate and soil features in Eastern Europe: a Romanian case study

Summary As a result of climatic change associated with global warming, aridity is an increasing problem in many parts of the world, including south-eastern and southern regions of Romania. This paper clarifies the concept of aridity, and discusses related concepts including indices of aridity, and their influence on some landscape and soil features including climatic water deficit (WD) and the depth to soil carbonates (DC). As used here, WD is calculated as the difference between precipitation sum (P) and the Penman-Monteith reference evapotranspiration sum (ET_o-PM) over certain periods. Another three well-known aridity indices are also considered: De Martonne’s index (I_ar-DM), Thornthwaite’s index (I_ar-TH), the UNESCO (1979) P/ET_o-PM ratio index (I_ar-P/ETo-PM). WD is as high as −450 mm during the growing season in the most arid, south-eastern and southern regions of Romania, especially in the Dobrogea and Baragan areas. In other regions of Romania, including most of the plains and plateaus where agriculture is an important branch of the economy, WD reaches −100 to −300 mm during the growing season. The above aridity indices were spatially interpolated for specific periods by kriging, to generate relatively homogeneous areas. WD can also be seen as an aridity index which has the advantage of a more accurate quantification of the water supply needed for a reference crop, e.g. grass under standardised conditions, for various geographical regions. WD is significantly correlated with the other aridity indexes and with DC. This paper also examines the risk of aridity spreading, and suggests improvements to the water management system for agriculture in Romania.     

Influence of climate variability on land degradation (desertification) in the watershed of the upper Paraíba River

The study aimed to evaluate the influence of the rainfall and aridity index variability on the process of land degradation (desertification) in order to establish the current degree of increase or decrease in dryness in the watershed of the upper Paraíba River. It included all or part of 18 municipalities, distributed in the western and eastern Cariri regions of Paraíba state. The monthly average values of reference evapotranspiration according to Penman-Monteith method were applied in the annual hydrological balance for obtaining the annual time series of the aridity index for the period from 1950 to 2013. The Mann-Kendall test (MK) was used for trend identification in the annual time series of rainfall and aridity index, at a significance level of α = 0.05. The slope of the trends was obtained by Sen’s method, and the values of rainfall, aridity index, and statistics MK were spatially kriging, to generate thematic maps. The results indicate an increase in rainfall and reduced dryness in the watershed of the upper Paraíba River, conditions that do not contribute to trigger the process of land degradation (desertification), indicating that the cause of this environmental problem is not climatic. Thus, it can be suggested that the observed manifestations of land degradation (desertification) derive much of human than climatic actions. However, there is a trend of increasing dryness and reducing rainfall in the central portion of the watershed, with stronger core in the location of Camalaú. The spatial distribution of rainfall and aridity index shows that minimum values of rainfall coincide with maximum values of the aridity index. Higher values of rainfall were observed in the northwestern portion of the watershed, while the northeast and southeast portions had the lower rainfall values, with the strongest core in the locality of Cabaceiras. The eastern sector of the watershed has high dryness, unlike the western sector, rainier, with minimum values of dryness. In the western portion of the watershed, the aridity index was in the range considered semiarid, with moderate susceptibility to land degradation process. Similarly, in the eastern portion, the dryness stood in the range considered arid, with high susceptibility. The cores with more pronounced dryness correspond to the municipalities of Cabaceiras, Caraúbas, and São João do Cariri.