1961-2010年西北干旱区极端降水指数的时空变化分析

结合绝对阈值和百分位法定义极端降水事件的优点,提出了一种更灵敏的检测极端降水事件的方法. 该方法不仅能检测出常用降水指数无法检测到的降水量稀少地区尤其干旱区的极端降水事件,同时也能过滤掉其检测到的降水量丰富地区的虚假极端降水事件. 此方法首次被应用于统计1961年1月至2010年2月西北干旱区72个气象站点的年和季节的极端降水指数（大降水和强降水指数）,并分析了极端降水指数的时间变化趋势及其空间分布特征. 结果表明：西北干旱区春（3-5月）、秋（9-11月）、冬（12月至次年2月）三季极端降水指数无显著（P>0.05）变化趋势,夏季（6-8月）大降水的频率和降水量以及大降水降水量占总降水量的比重都显著增加;新疆地区极端降水指数为增加趋势的区域基本都分布在海拔较高（约海拔1 000 m以上）的地区;西北干旱区东部极端降水指数变化趋势的空间分布有明显的季节差异,表现为夏、秋季大部分地区为增加趋势,冬、春季大部分地区为减小趋势.     

基于GIMMS NDVI的青藏高原植被指数时空变化及其气温降水响应

青藏高原植被生态系统脆弱, 是研究全球气候变化陆地植被生态系统响应的理想场所。以GIMMS NDVI、 气温和降水及植被类型数据为基础, 利用一元线性回归模型、 相关系数、 偏相关系数及t检验方法, 分析了青藏高原1982 - 2015年NDVI时空变化及其气温降水响应特征, 结果表明： 1982 - 2015年青藏高原NDVI时间变化过程总体表现为不显著的增加过程, 空间变化以显著增加为主, 占总面积的63.26%, 分布在高原北部、 西部和南部; 显著减少集中分布在高原中东部和东南部, 仅占总面积的3.45%。青藏高原主要植被类型NDVI平均值表现为： 阔叶林>针叶林>灌丛>草甸>高山植被>草原>荒漠, 其中草原、 高山植被和荒漠植被NDVI呈显著线性增加过程, 灌丛、 针叶林和阔叶林植被的NDVI呈不显著的减少过程。青藏高原NDVI与气温相关系数空间上呈南北向分布, 具有纬度地带性特征, 显著正相关分布在高原中北部, 显著负相关分布在高原中南部; NDVI与降水的相关系数呈东西向分布, 具有干湿度地带性特征, 显著正相关分布在高原中部, 显著负相关分布在高原东西两侧。研究认为1982 - 2015年青藏高原北部水热条件缺乏区域NDVI出现显著增加趋势, 而高原东南部水热条件充足地区NDVI呈现出显著减少趋势。深入开展植被类型NDVI气候响应的差异性研究, 有助于深入理解全球气候变化影响的区域差异及科学制定植被生态保护政策。     

Eemian and Early Weichselian temperature and precipitation variability in northern Germany

Dramatic changes in European vegetation occurred during the transition from the Eemian interglacial to Weichselian glacial climates, correlative with major changes in global ice core and marine records. Quantitative knowledge of climate change is important for understanding of the climate system and for climate modelling, for which reconstructions of this transitional period are of special interest. However, it has been difficult to quantify the climatic changes involved in the Eemian to Early Weichselian transition from terrestrial archives due to the lack of modern vegetation analogues. To circumvent this problem, we applied a suitable multivariate probabilistic approach to pollen and plant macrofossil assemblages to reconstruct temperature and precipitation for this transition in central Europe. Our reconstructions span the interval from the beginning of the Eemian (Marine Isotope Stage (MIS) 5e) to the Odderade interstadial (MIS 5a). They indicate a relatively stable Eemian, with increasing precipitation reducing the continentality of the climate with time. During the transition from the Eemian to the Herning stadial, mean July and January temperatures decreased by 4 °C and by as much as 20 °C, respectively. Temperatures remained high enough to support forests during the stadials, and we infer that the reconstructed decrease of precipitation below 500 mm per year caused the extirpation of forests during these periods. Thus, we conclude that precipitation, although difficult to reconstruct, is of vital importance for explaining vegetation change during the Eemian and Eemian/Early Weichselian transition.     

Watershed-scale response of groundwater recharge to inter-annual and inter-decadal variability in precipitation (Alberta,Canada)

Groundwater recharge sets a constraint on aquifer water balance in the context of water management. Historical data on groundwater and other relevant hydrological processes can be used to understand the effects of climatic variability on recharge, but such data sets are rare. The climate of the Canadian prairies is characterized by large inter-annual and inter-decadal variability in precipitation, which provides opportunities to examine the response of groundwater recharge to changes in meteorological conditions. A decadal study was conducted in a small (250 km²) prairie watershed in Alberta, Canada. Relative magnitude of annual recharge, indicated by water-level rise, was significantly correlated with a combination of growing-season precipitation and snowmelt runoff, which drives depression-focussed infiltration of meltwater. Annual precipitation was greater than vapour flux at an experimental site in some years and smaller in other years. On average precipitation minus vapour flux was 10 mm y^?1, which was comparable to the magnitude of watershed-scale groundwater recharge estimated from creek baseflow. Average baseflow showed a distinct shift from a low value (4 mm y^?1) in 1982–1995 to a high value (15 mm y^?1) in 2003–2013, indicating the sensitivity of groundwater recharge to a decadal-scale variability of meteorological conditions.     

艾比湖流域1957－2013年潜在蒸散、气温、降水变化特征分析

使用1957－2013年艾比湖流域6个气象站点的平均大气压、平均气温、最高气温、最低气温、平均相对湿度、平均风速、日照百分率以及降水量资料,通过Penman-Monteith方程计算出各个站的月和年潜在蒸散量．利用线性倾向估计、累积距平法和Mann-Kendall法分析了该流域近57年的潜在蒸散量、气温及降水量变化特征．结果表明：近57年来艾比湖流域年潜在蒸散量以－25．05 mm·（10a）－1的速度呈下降趋势．近7年的平均潜在蒸散量与过去50年相比较偏少77．36 mm．年平均气温以0．33℃·（10a）－1的速度上升．近7年的平均气温比过去50年的平均气温增加了1℃．年降水量以7．97 mm·（10a）－1的速度增多．近7年的平均降水量与过去50年的平均降水量相比增多32．45 mm．     

Evaluating the vegetation destruction and recovery of Wenchuan earthquake using MODIS data

The Ms 8.0 Wenchuan earthquake in 2008 has led to huge damage to land surface vegetation in northwest Sichuan, one of the typical ecological fragile regions in China. In this paper, the vegetation degradation by the earthquake and its recovery after the disaster are evaluated from analysis of MODIS Gross Primary Productivity (GPP) time series products and other ancillary GIS data. The results suggest that local vegetation GPP after the earthquake in the heavy afflicted area has decreased by 22%. The local vegetation productivity in the heavy afflicted area had recovered to 84 and 87% after 1 and 2 months later. Since August 2008, the vegetation productivity has increased to a nearly normal level.     

Spatio-temporal variation of groundwater recharge in response to variability in precipitation, land use and soil in Yanqing Basin, Beijing, China

It is important to understand how groundwater recharge responds to precipitation variability in space and time, especially in those areas such as Yanqing Basin (China), where groundwater represents the sole water resource. A simple soil-water balance method is applied for spatio-temporal simulation of groundwater recharge in Yanqing Basin from 1981 to 2000. It was implemented on a monthly time step considering the effects of land use and soil texture. The area-average recharge associated with various land uses and soil textures was then compared with zonal analysis using a geographic information system (GIS). The main findings include: (1) the variation of groundwater recharge follows precipitation changes, either at yearly or seasonal intervals, (2) land use plays a more influential role in groundwater recharge than soil texture in this area, and (3) the water table quickly rises in response to recharge in the shallow parts of the aquifer, while there is a delay of 0.5–1.0?years where the groundwater level is at depth 4–10?m. The application demonstrates how spatio-temporal analysis can be utilized for groundwater-recharge estimation through distributed modeling and GIS.     

The spatio-temporal variability of droughts using the standardized precipitation index in Yunnan,China

As the main greenhouse gas, carbon dioxide (CO₂) has been under intensive studied in the last two decades. This paper addresses the research that whether the environmental Kuznets curve (EKC) for CO₂ emissions exists in G20 group—an international forum for governments and central banks from 19 countries and European Union. To analyze the studied relationship thoroughly, other four explanatory variables—two trade openness terms, the ratio of secondary industry value-added to GDP and population density—are employed to investigate whether they have any influences on the existence and shapes of EKC. In the empirical study, two multinational panel data sets covering the periods between 1960 and 2010 (50 years) and between 1990 and 2010 (20 years) are utilized, and the panel data fixed effects and generalized method of moments estimators are employed. The estimation results indicate that the EKC indeed exists in the G20 members as a whole. To investigate whether the existence of EKC depends on the level of economic growth, the G20 countries are further divided into two subgroups: developed and developing countries. Although the estimation results suggest that there exists EKC in developing countries during both 20- and 50-year period, there is no persuasive evidence to prove the existence of EKC in developed countries during the 20-year period. For the time periods we studied, most developed countries have seen relatively stable or even decreasing CO₂ emissions, while for the majority of the developing countries, the peak of CO₂ emissions could not be reached in the near future.     

Towards an understanding of the response of southern European vegetation to orbital and suborbital climate variability

In recent years, the generation of high-resolution terrestrial and marine long pollen sequences with improved chronological control has provided new insights into the vegetation response in southern Europe to orbital and suborbital climate variability. Here a synthesis of our current understanding of the phase and amplitude relationships between climate forcing and vegetation changes is presented. What emerges is that on orbital frequencies the timing of interglacial forest expansion is closely linked to the summer insolation maximum, but does not have a fixed lag relative to the mid-point of the deglaciation, which may vary from one Termination to another. For the closing phases of interglacials, the available evidence suggests that forest in southern Europe usually extends into the interval of ice growth. However, suborbital variability may override the diachronous relationship between glacial inception and forest decline, leading to a premature ending of forest periods. During glacial intervals, there is a close correspondence between tree-population size and ice volume extent, while during temperate intervals, the extent of forest development is closely related to the amplitude of insolation and associated climate regimes, but may diverge from the extent of residual ice volume. On suborbital frequencies, changes in tree-population size are in phase with climate forcing, while the amplitude of these changes is modulated by geographical position and local factors. Finally, orbital mean state can lead to the modulation of the amplitude of suborbital-scale variability. Examination of additional climatic cycles and increased resolution (better than 200 years) are needed to test further these preliminary conclusions.     

Circulation and representativeness of precipitation and air temperature in the southeast of the Quinghai-Xizang Plateau

Based on time series of 98 stations from the Qinghai-Xizang Plateau, the Indo-Gagnetic Plains, the River Gorge Country and Eastern China, the representativeness of the locally observed interannual variations of temperature and precipitation was analyzed by a statistical method. After an overview, which regards the main circulation patterns as well as the spatial distribution of temperature and precipitation in winter (January) and summer (July), the monthly distribution of the representativeness is discussed in a climato-genetic context. The monthly temperature representativeness is characterized by strong spatial and seasonal contrasts. The values range from less than 200 km in the basins and valley bottoms of NW Sichuan, caused by local summer circulation patterns, and more than 1600 km in the lower areas of E China, affected by the far reaching influence of the winter monsoonal surges of cold continental airmasses. With only a few exceptions mainly occurring in December, the precipitation representativeness does not exceed a 300 km limit. Due to the comparatively modest spatial disparities — except December when a steep rise, greater than 600 km occurs in the upper Tsangpo valley and adjacent areas — it can only be concluded, that a tendency of higher (lower) representativeness is predominantly related to advective (convective) regimes.     

Response of estuarine marsh vegetation to interannual variations in precipitation

The response of deltaic emergent marsh vegetation to increases in precipitation was examined over a 14-mo period at three sites in the lower Nueces Estuary in south Texas. At all three sites, significant changes in plant biomass, percent cover, and allocation of aboveground and belowground tissues were associated with more than double the rainfall in late winter and early spring 1992 compared to the previous year and the 50-yr average for this region. Water column salinities, which ranged from 10‰ to 35‰ at all three sites in 1991, remained below 10‰ through August 1992. Significant changes in marsh vegetative structure included decreases in bare space, increases in the percent cover and aboveground biomass of a relatively less salt tolerant halophytes (Borrichia frutescens), and significant increases in root:shoot ratios inB. frutescens, Batis maritima andSuaeda linearis (inSalicornia virginica root:shoot ratios decreased significantly). Higher precipitation generally led to an overall increase in the biomass of most marsh perennials, but these increases were not statistically significant. For one species,Lycium carolinianum, additional rainfall extended its growing season through August 1992, 2 mo longer than in the previous year. The expansion (+58%) ofB. frutescens at one site was also coincident with the significant loss ofB. maritima, whose cover decreased nearly 20%. In an ecological context, these responses suggest that precipitation events in arid environments may be considered a major physical disturbance that can result in large changes in the composition and relative abundance of emergent vascular plants over a relatively short period. The long-term significance of these changes is unknown and demonstrates the value of ecological studies that are conducted over several years for a more complete understanding of the dynamic processes that regulate marsh productivity.     

Variability of precipitation and temperature in Guanajuato,Mexico

Variability of precipitation and temperature was examined on multiple time scales using data from five surface observing stations in the center of Guanajuato state, Mexico, as well as gridded data from the North American Regional Reanalysis (NARR). Frequency of days with total precipitation exceeding the 90th percentile was not found to have increased from 1979-2011. However, frequency of days with maximum temperature above the 90th percentile more than doubled from 1979-2011, and frequency of days with maximum temperature below the 10th percentile decreased by almost half over the same period, an important result given the scarcity of water resources for the agriculture-based economy. Precipitation within the growing season was found to vary by phase of the Madden-Julian oscillation (MJO), with MJO phases 1-3 associated with above-normal rainfall and MJO phases 4-7 with normal or below normal rainfall. Composite anomalies of precipitation, surface pressure, surface wind, surface temperature, and 700 mbar height showed that days with rainfall in Guanajuato were associated with on-shore, upslope flow, reduced surface temperatures, and reduced potential evaporation. Composites for MJO phases 1-3 and 8 agreed well with these anomalies. Similarly, composite anomalies for days without rainfall in Guanajuato showed warm surface temperatures, broad anticyclonic flow over much of northern Mexico, and enhanced potential evaporation. Composites for MJO phases 4-7 agreed well with these anomalies.     

1953 - 2016年华山积雪变化特征及其与气温和降水的关系

利用华山气象站1953 - 2016年气象观测资料和1989 - 2016年Landsat TM卫星遥感影像数据, 分析华山积雪变化的基本特征及其与气温、 降水和大气环流的关系。结果表明： 1953 - 2016年华山平均积雪日数78.5 d, 积雪主要出现在每年的10月 - 次年5月, 64 a来积雪初日推迟, 终日提前, 初终间日数减少, 年度、 冬半年、 冬季积雪日数分别以8.3 d?（10a）^-1、 7.6 d?（10a）^-1、 4.7 d?（10a）^-1的减少率显著减少。1981 - 2016年华山年度最大积雪深度减少趋势不显著, 年度累积积雪深度以88.2 cm?（10a）^-1的减少率显著减少, 一年中积雪日数、 最大积雪深度和累积积雪深度的减少（小）趋势均以3月最为显著。1989 - 2016年华山区域积雪面积、 浅雪和深雪面积减少趋势不明显。1953 - 2016年华山年度、 冬半年、 冬季平均气温升高, 降水量减少。积雪日数与平均气温存在显著的负相关, 与降水量存在显著的正相关, 气温是影响华山积雪日数的最主要因素。年度、 冬半年和冬季积雪日数突变年份与相应时段平均气温突变年份相近。1953 - 2016年华山冬半年、 冬季平均气温和降水量均与大气环流指数相关显著, 华山冬半年和冬季积雪日数与同期西藏高原指数、 印缅槽强度指数、 南极涛动指数和西太平洋副高西伸脊点指数为明显的负相关, 与850 hPa东太平洋信风指数、 亚洲区极涡面积指数为明显正相关。     

黄河源区气温变化特征及预估分析

利用黄河源区青海段9个代表性站点1961-2017年逐日气温资料和未来RCP4.5排放情景下的预估数据,分析和预估了黄河源区年平均、年平均最高、年平均最低和极端气温变化特征。结果表明：近57年来年平均最高、年平均、年平均最低气温均呈显著上升趋势且倾向率依次增大。年平均气温和年平均最高气温在1997年存在显著突变。通过分析1961-1997年、1998-2007年以及2008-2017年阶段性变化可知,年平均气温持续上升,年平均最高气温先上升后趋于稳定,而年平均最低气温升温速率在1998-2007年最大,2008-2017年升温速率较1998-2007年有所降低。暖昼日数持续增多,霜冻日数和冰封日数持续减少,冷夜日数在1998-2007年减少速率最低,近10年来减少速率增大。未来33年黄河源区年平均、年平均最高、年平均最低气温和极端暖事件均呈明显的增加趋势,极端冷事件呈减少趋势。对黄河源区过去和未来气温变化规律进行了探讨,将为该区域气温变化对策的制定与实施提供理论依据。     

Monitoring of late-season agricultural drought in cotton-growing districts of Andhra Pradesh state,India, using vegetation,water and soil moisture indices

Natural Hazards - Persistent soil moisture deficits during flowering and yield formation stage are referred to as late-season agricultural drought. This study aims to assess late-season...     

基于TRMM降水数据的山区降水垂直分布特征

选择天山和祁连山区为典型区,利用台站降水数据验证以上两区多卫星降水数据(TRMM)精度的基础上,借助TRMM数据分析了所选山区年降水梯度效应,并探讨了天山及祁连山最大降水高度带.结果表明,多卫星降水数据在天山和祁连山区精度较高,天山及祁连山年降水量都明显受到海拔影响,降水随海拔升高而增加,但天山降水与海拔正相关关系最好,南、北和西坡相关系数分别为0.90、0.81和0.58,多年平均降水直减率分别为11.0mm/100 m、6.3 mm/100 m、7.4 mm/100 m,最大降水高度带则分别位于海拔2 200~3 500 m和3 200~3 700 m和3 000m左右;祁连山东、中、西段降水随海拔有增加趋势,但降水梯度效应在祁连山东段明显高于祁连山中西段地区,梯度效应由东向西呈现递减趋势,其最大降水带主要分布在东段4 000~4 500 m的高山带.     

MODIS地表温度产品在青藏高原连续多年冻土区的适用性分析

利用自动气象站观测的长波辐射计算得到的地表温度对MODIS地表温度(LST)产品在青藏高原中部连续多年冻土区的精度进行验证, 并利用具有较高空间分辨率的Landsat 5 TM和Landsat 7 ETM+反演的地表温度与MODIS LST产品进行了对比分析. 结果表明: 白天MODIS LST产品的平均绝对误差(MAE)和均方根误差(RMSE)分别约为3.42~4.41 ℃和4.41~5.29 ℃, 夜晚MODIS产品MAE和RMSE分别为2.15~2.90 ℃和3.05~3.78 ℃, 精度高于白天; MODIS LST与TM、ETM+反演的地表温度一致性较好, 相关系数分别达到0.85和0.95. 说明MODIS LST产品在连续多年冻土区的适用性较高, 是研究多年冻土地表热状况的一个非常好的数据源. 而且, 不同空间尺度的遥感数据之间一致性较好, 可考虑将多源遥感数据应用于多年冻土热状况监测研究.     

Use of objective analysis to estimate winter temperature and precipitation at different stations over western Himalaya

Temperature and fresh snow are essential inputs in an avalanche forecasting model. Without these parameters, prediction of avalanche occurrence for a region would be very difficult. In the complex terrain of Himalaya, nonavailability of snow and meteorological data of the remote locations during snow storms in the winter is a common occurrence. In view of this persistent problem present study estimates maximum temperature, minimum temperature, ambient temperature and precipitation intensity on different regions of Indian western Himalaya by using similar parameters of the neighbouring regions. The location at which parameters are required and its neighbouring locations should all fall in the same snow climatic zone. Initial step to estimate the parameters at a location, is to shift the parameters of neighbouring regions at a reference height corresponding to the altitude of the location at which parameters are to be estimated. The parameters at this reference height are then spatially interpolated by using Barnes objective analysis. The parameters estimated on different locations are compared with the observed one and the Root Mean Square Errors (RMSE) of the observed and estimated values of the parameters are discussed for the winters of 2007–2008.