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1.
Recent trends in observed temperature and precipitation extremes in the Yangtze River basin,China 总被引：14，自引：1，他引：14
Summary The present study is an analysis of the observed extreme temperature and precipitation trends over Yangtze from 1960 to 2002
on the basis of the daily data from 108 meteorological stations. The intention is to identify whether or not the frequency
or intensity of extreme events has increased with climate warming over Yangtze River basin in the last 40 years. Both the
Mann-Kendall (MK) trend test and simple linear regression were utilized to detect monotonic trends in annual and seasonal
extremes.
Trend tests reveal that the annual and seasonal mean maximum and minimum temperature trend is characterized by a positive
trend and that the strongest trend is found in the winter mean minimum in the Yangtze. However, the observed significant trend
on the upper Yangtze reaches is less than that found on the middle and lower Yangtze reaches and for the mean maximum is much
less than that of the mean minimum. From the basin-wide point of view, significant increasing trends are observed in 1-day
extreme temperature in summer and winter minimum, but there is no significant trend for 1-day maximum temperature. Moreover,
the number of cold days ≤0 °C and ≤10 °C shows significant decrease, while the number of hot days (daily value ≥35 °C) shows
only a minor decrease. The upward trends found in the winter minimum temperature in both the mean and the extreme value provide
evidence of the warming-up of winter and of the weakening of temperature extremes in the Yangtze in last few decades.
The monsoon climate implies that precipitation amount peaks in summer as does the occurrence of heavy rainfall events. While
the trend test has revealed a significant trend in summer rainfall, no statistically significant change was observed in heavy
rain intensity. The 1-day, 3-day and 7-day extremes show only a minor increase from a basin-wide point of view. However, a
significant positive trend was found for the number of rainstorm days (daily rainfall ≥50 mm). The increase of rainstorm frequency,
rather than intensity, on the middle and lower reaches contributes most to the positive trend in summer precipitation in the
Yangtze. 相似文献
2.
Summary ?The variability of the winter mean precipitation observed at 40 rainfall stations in Emilia-Romagna (a region in northern
Italy) from 1960 to 1995 is examined. The results are compared with those obtained for the whole of Italy using records from
32 stations. Temporal variability of the time series is investigated by means of Mann-Kendall and Pettitt tests, in order
to estimate the presence of trends and “change points”. Before analysis the original precipitation data set have been tested
to detect the inhomogeneity points, using the Standard Normal Homogeneity Test (SNHT). Almost all stations situated in Emilia
Romagna exhibit a significant decreasing trend in winter precipitation during the 1960–1995 period. The same characteristics
are revealed, more significant in the northern and central part of the region, when the stations for all Italy are analysed.
A significant downward shift in the winter precipitation is detected through the Pettitt test in Emilia Romagna, around 1980 at some stations, while the rest of the stations reveal the shift point occurrence around 1985. A significant downward shift in the winter precipitation is detected around 1985, when analysing the time series for all Italy. Spatial variability of winter precipitation is studied using the Empirical
Orthogonal Function. The first pattern indicates that a common large-scale process could be responsible for the winter precipitation
variability. The second EOF pattern shows an opposite sign of climate variability, which highlights the influence of relief
on the precipitation regime. The time series associated with the first precipitation pattern (PC1) at both scales emphasises
a significant decreasing trend and a downward shift point around 1985. The internal structure analysis of the North Atlantic
Oscillation (NAO) index during the 1960–1995 period reveals a significant increasing trend and an upward shift around 1980.
Strong correlation is also detected between PC1 (Emilia Romagna and at the scale of all Italy) and the NAO index. Thus, the
changes detected in the winter precipitation around 1985 could be due to an intensification of the positive phase of the [NAO],
especially after 1980.
Received March 23, 2001; revised February 20, 2002; accepted March 3, 2002 相似文献
3.
The high variability of the Mediterranean climate from year to year and within each year makes it difficult to assess changes
that could be associated with a climate change. In this paper some indices, such as changes in the precipitation concentration
during the year, maximum 1-day and 5-day precipitation, number of wet days (total and those with precipitation higher than
the 75th and 95th percentile), magnitude and frequency of extreme events (considered as the rainfall higher than that corresponding
to the 99th percentile), fraction of annual total precipitation due to events exceeding the 95th and 99th percentile, strength
of the events, and length and frequency of dry period (days between consecutive rains) are evaluated for the Penedès-Anoia
region (NE Spain). A 80-year daily dataset (1923–2002) and two 40-year series were used to assess possible trends. The indices
indicate an increase in precipitation in winter and summer and a positive trend of concentration in autumn, with a higher
number of extreme events separated by longer dry periods. The total number of wet days per year increased, although it was
irregularly distributed over the year, with an increase in the extremes and in the fraction of total rainfall that these events
represent in autumn and winter, and with an increase of the strength of the events in autumn. These changes in rainfall distribution
have negative effects on water availability for crops and contribute to accelerate erosion processes in the area. 相似文献
4.
H. Feidas Ch. Noulopoulou T. Makrogiannis E. Bora-Senta 《Theoretical and Applied Climatology》2007,87(1-4):155-177
Summary In this study, the trends of annual and seasonal precipitation time series were examined on the basis of measurements of 22
surface stations in Greece for the period 1955–2001, and satellite data during the period 1980–2001. For this purpose, two
statistical tests based on the least square method and one based on the Mann-Kendall test, which is also capable of detecting
the starting year of possible climatic discontinuities or changes, are applied. Greece, in general, presents a clear significant
downward trend in annual precipitation for the period 1955–2001, which is determined by the respective decreasing trend in
winter precipitation. Both winter and annual series exhibit a downward trend with a starting year being 1984. Satellite-derived
precipitation time series could be an alternative means for diagnosing the variability of precipitation in Greece and detecting
trends provided that they have been adjusted by surface measurements in the wider area of interest. The relationship between
precipitation variability in Greece and atmospheric circulation was also examined using correlation analysis with three circulation
indices: the well-known North Atlantic Oscillation Index (NAOI), a Mediterranean Oscillation Index (MOI) and a new Mediterranean
Circulation Index (MCI). NAOI is the index that presented the most interesting correlation with winter, summer and annual
precipitation in Greece, whereas the MOI and MCI were found to explain a significant proportion of annual and summer precipitation
variability, respectively. The observed downward trend in winter and annual precipitation in Greece is linked mainly to a
rising trend in the hemispheric circulation modes of the NAO, which are connected with the Mediterranean Oscillation Index. 相似文献
5.
Z. Yan S. Bate R. E. Chandler V. Isham H. Wheater 《Theoretical and Applied Climatology》2006,83(1-4):121-137
Summary We investigate the capability of generalized linear models (GLMs) to simulate sequences of daily maximum wind speed (DMWS),
at a selection of locations in NW Europe. Models involving both the gamma and Weibull distributions have been fitted to the
NCEP reanalysis data for the period 1958–1998. In simulations, these models successfully reproduce the observed increasing
trends up to 0.3 m/s per decade in coastal or oceanic locations for the wintertime and the decreasing trends down to –0.2 m/s
per decade in inland Europe for the summertime. Annually extreme winds exhibit an increasing tendency (with median estimates
up to 0.6 m/s per decade) at the studied locations. The gamma model slightly overestimates the upper percentiles of the wind
speed distribution, but reproduces trends better than the Weibull model. In both the NCEP data and GLM simulations, local
extreme DMWS events (defined in terms of threshold exceedances) have increased dramatically in frequency during winter; decreasing
trends are more common in summer. The NCEP data indicate similar trends in the frequencies of large-scale windy events (defined
via simultaneous exceedances at 2 or more locations). Overall, these events have increased in number; at the scale of the
North Sea basin, their number may have changed from 3–5 days per year during the earlier decades, to 5–7 days per year during
later decades based on observational estimates. An increase in the frequency of large-scale extreme winter storms is implied.
The GLMs underestimate these large-scale event frequencies, and provide imprecise estimates of the corresponding secular trends.
These problems could be rectified by using a better representation of spatial dependence. The present results suggest that
GLMs offer a useful tool to study local climate extremes in the context of changing climate distributions; they also provide
some pointers towards improving the representation of extremes at a regional scale. 相似文献
6.
Summary Spatial-temporal characteristics of temperature variations were analyzed from China daily temperature based on 486 stations
during the period 1960–2000. The method of hierarchical cluster analysis was used to divide the territory into sub-regional
areas with a coherent evolution, both annually and seasonally. Areas numbering 7–9 are chosen to describe the regional features
of air temperature in mainland China.
All regions in mainland China experienced increasing trends of annual mean temperature. The trend of increasing temperature
was about 0.2–0.3 °C/10 yr in northern China and less than 0.1 °C/10 yr in southern China. In the winter season, the increasing
trend of temperature was about 0.5–0.7 °C/10 yr in northern China and about 0.2–0.3 °C/10 yr in southern China. The increasing
trend of autumn temperature was mainly located in northwestern China and southwestern China including the Tibetan Plateau.
In spring, the rising trend of temperature was concentrated in Northeast China and North China while there was a declining
temperature trend of −0.13 °C/10 yr in the upper Yangtze River. In summer, the declining trend of temperature was only concentrated
in the mid-low valley of the Yangtze and Yellow Rivers while surrounding this valley there were increasing trends in South
China, Southwest China, Northwest China, and Northeast China.
Rapid changes in temperature in various regions were detected by the multiple timescale t-test method. The year 1969 was a rapid change point from a high temperature to a low temperature along the Yangtze River
and South China. In the years 1977–1979, temperature significantly increased from a lower level to a higher level in many
places except for regions in North China and the Yangtze River. Another rapid increasing temperature trend was observed in
1987. In the years 1976–1979, a positive rapid change of summer temperature occurred in northwestern China and southwestern
China while a decreasing temperature was found between the Yellow River and the Yangtze River. A rapid increase of winter
temperature was found for 1977–1979 and 1985–1986 in many places.
There were increasing events of extreme temperature in broad areas except in the north part of Northeast China and the north
part of the Xinjiang region. In winter, increasing temperature of the climate state and weakening temperature extremes are
observed in northern China. In summer, both increasing temperature of the climate state and enhancing temperature extremes
were commonly exhibited in northern China.
Present address: Linfen Meteorological Office, Linfen 041000, Shanxi Province, China. 相似文献
7.
J. Jaagus 《Theoretical and Applied Climatology》2006,83(1-4):77-88
Summary Trends in the time series of air temperature, precipitation, snow cover duration and onset of climatic seasons at ten stations
in Estonia during 1951–2000 are analysed. Using the conditional Mann-Kendall test, these trends are compared with trends in
the characteristics of large-scale atmospheric circulation: the NAO and AO indices, frequency of circulation forms according
to the Vangengeim-Girs’ classification, and the northern hemisphere teleconnection indices. The objective of the study is
to estimate the influence of trends in circulation on climate changes in Estonia. Statistically significant increasing trends
in air temperature are detected in January, February, March, April and May, in winter (DJF), spring (MAM) and in the cold
period (NDJFM). The trends in precipitation, as a rule, differ from station to station. Increasing trends are present during
the cold half-year – from October until March – and also in June. Snow cover duration has decreased in Estonia by 17–20 days
inland and by 21–36 days on the coast. The onsets of early spring and spring have shifted to an earlier date. Some important
changes have occurred in the parameters of atmospheric circulation during 1951–2000. Intensity of zonal circulation, i.e.
westerlies, has increased during the cold period, especially in February and March. Results of the conditional Mann-Kendall
test indicate that the intensification of westerlies in winter is significantly related to climate changes in winter and also
in spring. A negative trend in the East Atlantic Jet (EJ) index, i.e. the weakening of the westerlies in May has caused warming
during that month. Decrease in northerly circulation, i.e. in frequency of circulation form C and in East Atlantic/West Russia
teleconnection index (EW) is related to an increase in precipitation in October. 相似文献
8.
Summary This paper assesses recent changes in extremes of seasonal rainfall in Ethiopia based on daily rainfall data for 11 key stations
over the period 1965–2002. The seasons considered are Kiremt (‘main rains’, June–September) and Belg (‘small rains’, February/March–May). The Mann-Kendall and linear regression trend tests show decreasing trends in the Kiremt and the Belg extreme intensity and maximum consecutive 5-day rains over eastern, southwestern and southern parts of Ethiopia whereas no
trends are found in the remaining part of Ethiopia. In general, no trends are found in the yearly maximum length of Kiremt and Belg dry spells (days with rainfall below 1 mm) over Ethiopia. 相似文献
9.
中国降水极值变化趋势检测 总被引：215，自引：9，他引：206
利用中国２９６个分布均匀的测站的逐日降水资料,研究了中国过去４５ａ中降水量、降水频率、降水强度等方面的极值变化趋势。结果表明,总体上讲,中国年降水量、１日和３日最大降水量以及不同级别的强降水总量没有发现明显的极端化倾向,但伴随着降水日数极端偏多的区域范围越来越小的变化趋势,平均降水强度极端偏高的区域范围表现为扩大的趋势。中国降水极值变化还反映出明显的区域性特点。在中国东部,平均降水强度极值出现的范围趋于扩大。如华北地区在年降水量明显趋于减少的同时,年降水量极端偏多的范围减少,１日和３日最大降水量、日降水≥５０ｍｍ和１００ｍｍ的暴雨日数极端偏多的情况也趋于减少,而平均降水强度极值显著增加。在年降水明显趋于增多的西北西部地区,降水日数的极值变化趋势不明显,但年降水量、１日和３日最大降水量以及日降水≥１０ｍｍ的降水总量极端偏多的区域范围均反映出趋于增加的变化趋势。 相似文献
10.
研究大陆或次大陆尺度日降水长期趋势变化规律,对于检测、理解区域气候和陆地水循环对全球气候变暖的响应特征十分重要。利用美国国家气候资料中心(NCDC)和中国基准气候站、基本气象站网降水观测资料,在对该站点资料进行基本质量控制基础上,选取东亚地区619个站1951～2009年日降水数据,按照百分位阈值对降水进行分级,共分为弱、中、强、极强4个级别,用经纬度网格面积加权平均方法构建区域平均的时间序列,分析了各类降水事件长期变化趋势的时空特征。结果表明:东亚地区近59年平均总降水量表现出不显著下降趋势,降水日数没有出现趋势性变化,平均日降水强度略有减小;区域平均的年降水量、降水日数和日降水强度在中国北方大部、蒙古东部、俄罗斯远东地区南部和日本列岛多呈减少趋势,而在俄罗斯中西伯利亚南部、朝鲜半岛南部和中国长江中下游流域一般表现为增加。从季节上看,近59年东亚区域平均的冬、春季降水量、降水日数和日降水强度均呈增加趋势,而夏、秋季一般呈减少趋势,仅夏季日降水强度略有增加。降水的年内分配出现均匀化趋势。从不同级别降水事件看,近59年来东亚区域平均的各级别降水量均为下降趋势,中降水、强降水和极强降水日数也呈现下降趋势,弱降水日数表现出较明显增加;仅有全区秋季强降水量、日数减少趋势和冬季中降水量、日数增加趋势通过了显著性水平检验。分析还发现,近30年(1980～2009年)东亚地区日降水趋势变化出现了新的特征,主要表现为大部分地区降水日数呈现增加,日降水强度减少,45°N以南多数台站降水量也增加,全区降水有向非极端化方向发展趋势。 相似文献
11.
Summary We use the regional climate model RegCM nested within time-slice atmospheric general circulation model experiments to investigate
the possible changes of intense and extreme precipitation over the French Maritime Alps in response to global climate change.
This is a region with complex orography where heavy and/or extended precipitation episodes induced catastrophic floods during
the last decades. Output from a 30-year simulation of present-day climate (1961–1990) is first analysed and compared with
NCEP reanalysed 700 hPa geopotential heights (Z700) and daily precipitation observations from the Alpine Precipitation Climatology
(1966–1999). Two simulations under forcing from the A2 and B2 IPCC emission scenarios for the period 2071–2100 are used to
investigate projected changes in extreme precipitation for our region of interest. In general, the model overestimates the
annual cycle of precipitation. The climate change projections show some increase of precipitation, mostly outside the warm
period for the B2 scenario, and some increase in the variability of the annual precipitation totals for the A2 scenario. The
model reproduces the main observed patterns of the spatial leading EOFs in the Z700 field over the Atlantic-European domain.
The simulated large scale circulation (LSC) variability does not differ significantly from that of the reanalysis data provided
the EOFs are computed on the same domain. Two similar clusters of LSC corresponding to heavy precipitation days were identified
for both simulated and observed data and their patterns do not change significantly in the climate change scenarios. The analysis
of frequency histograms of extreme indices shows that the control simulation systematically underestimates the observed heavy
precipitation expressed as the 90th percentile of rainday amounts in all seasons except summer and better reproduces the greatest 5-day precipitation accumulation.
The main hydrological changes projected for the Maritime Alps consist of an increase of most intense wet spell precipitation
during winters for both scenarios and during autumn for the B2 scenario. Case studies of heavy precipitation events show that
the RegCM is capable to reproduce the physical mechanisms responsible for heavy precipitation over our region of interest. 相似文献
12.
South Asian summer monsoon precipitation variability: Coupled climate model simulations and projections under IPCC AR4 总被引：6，自引：2，他引：6
R. H. Kripalani J. H. Oh A. Kulkarni S. S. Sabade H. S. Chaudhari 《Theoretical and Applied Climatology》2007,90(3-4):133-159
Summary South Asian summer monsoon precipitation and its variability are examined from the outputs of the coupled climate models assessed
as part of the Intergovernmental Panel on Climate Change Fourth Assessment. Out of the 22 models examined, 19 are able to
capture the maximum rainfall during the summer monsoon period (June through September) with varying amplitude. While two models
are unable to reproduce the annual cycle well, one model is unable to simulate the summer monsoon season. The simulated inter-annual
variability from the 19 models is examined with respect to the mean precipitation, coefficient of variation, long-term trends
and the biennial tendency. The model simulated mean precipitation varies from 500 mm to 900 mm and coefficient of variation
from 3 to 13%. While seven models exhibit long-term trends, eight are able to simulate the biennial nature of the monsoon
rainfall. Six models, which generate the most realistic 20th century monsoon climate over south Asia, are selected to examine
future projections under the doubling CO2 scenario.
Projections reveal a significant increase in mean monsoon precipitation of 8% and a possible extension of the monsoon period
based on the multi-model ensemble technique. Extreme excess and deficient monsoons are projected to intensify. The projected
increase in precipitation could be attributed to the projected intensification of the heat low over northwest India, the trough
of low pressure over the Indo-Gangetic plains, and the land–ocean pressure gradient during the establishment phase of the
monsoon. The intensification of these pressure systems could be attributed to the decline in winter/spring snowfall. Furthermore,
a decrease of winter snowfall over western Eurasia is also projected along with an increase of winter snowfall over Siberia/eastern
Eurasia. This projected dipole snow configuration during winter could imply changes in mid-latitude circulation conducive
to subsequent summer monsoon precipitation activity. An increase in precipitable water of 12–16% is projected over major parts
of India. A maximum increase of about 20–24% is found over the Arabian Peninsula, adjoining regions of Pakistan, northwest
India and Nepal. Although the projected summer monsoon circulation appears to weaken, the projected anomalous flow over the
Bay of Bengal (Arabian Sea) will support oceanic moisture convergence towards the southern parts of India and Sri Lanka (northwest
India and adjoining regions). The ENSO-Monsoon relationship is also projected to weaken. 相似文献
13.
中国近50a极端降水事件变化特征的季节性差异 总被引：14，自引：2，他引：12
利用中国419个测站1958-2007年逐日降水资料集,分析了近50a中国不同区域年和季节极端降水事件的基本变化特征。结果表明,多年平均极端降水事件的空间分布具有明显的纬向分布特征,并表现出显著的季节性差异。长江以南地区是春、冬季极端降水事件发生频次较高的区域;而年、夏季以及秋季极端降水事件发生频次在西南地区较高,在西北东部较低。年极端降水事件频次的长期变化趋势与夏季相似,华北和东北有增加趋势,其他地区为弱的减少趋势;其他季节的长期变化趋势存在明显的区域和季节性差异。年和季节极端降水事件的发生频次具有显著的年际和年代际变化特征。年极端降水事件时间序列的多项式拟合曲线的变化情况与夏季基本一致;而其他季节的变化则存在较大差异,表现出显著的季节性差异。 相似文献
14.
北方农牧交错带中部区域气候变化特征 总被引：12，自引：0，他引：12
分析北方农牧交错带中部区域1951-2005年温度、降水的变化特征,结果表明,研究区近55 a的气温和降水具有如下特征：1）增温明显,气温变率为0.4℃/10 a,不同季节增温幅度以冬、春、夏、秋依次递减;2）降水变化可分为3个阶段：20世纪50-60年代降水量呈减少趋势,70-80年代处于较平稳的过渡期,90年代以来降水量又呈现增加趋势。夏季降水与年降水变化趋势类似,秋季与冬季降水波动较小,基本保持平稳。研究区高温、干旱有所加强,暴雨、低温事件减少。 相似文献
15.
根据武汉市1951—2007年逐日气温、降水量计算分析了10个极端天气气候指数的变化特征。结果表明:1)4个气温指数中,年及四季高、低温阈值均为上升趋势,并造成最长热浪天数的延长和霜冻日数的减少;低温阈值升速明显快于高温阈值,高温阈值仅在春季变化显著,最长热浪天数仅在冬季变化显著;低温阈值则为极显著上升趋势,尤其是年和冬季,造成"热春"、"暖冬"频繁;暖夜、闷热、傍晚至夜间的强对流等显著增多,暖日、高温热浪增加,霜冻日大幅减少。2)6个极端降水指数以增趋势为主,其中强降水阈值、比例、日数以及最大5日降水量在冬季增趋势最明显,仅夏季强降水阈值、比例略有减小,冬季日降水强度的增大趋势、夏季持续干期的缩短趋势显著性水平分别可达0.1、0.01。3)一些气温指数在1980—1990年代发生突变,而降水指数未现突变。 相似文献
16.
SST and circulation trend biases cause an underestimation of European precipitation trends 总被引：2，自引：0，他引：2
Ronald van Haren Geert Jan van Oldenborgh Geert Lenderink Matthew Collins Wilco Hazeleger 《Climate Dynamics》2013,40(1-2):1-20
Clear precipitation trends have been observed in Europe over the past century. In winter, precipitation has increased in north-western Europe. In summer, there has been an increase along many coasts in the same area. Over the second half of the past century precipitation also decreased in southern Europe in winter. An investigation of precipitation trends in two multi-model ensembles including both global and regional climate models shows that these models fail to reproduce the observed trends. In many regions the model spread does not cover the trend in the observations. In contrast, regional climate model (RCM) experiments with observed boundary conditions reproduce the observed precipitation trends much better. The observed trends are largely compatible with the range of uncertainties spanned by the ensemble, indicating that the boundary conditions of RCMs are responsible for large parts of the trend biases. We find that the main factor in setting the trend in winter is atmospheric circulation, for summer sea surface temperature (SST) is important in setting precipitation trends along the North Sea and Atlantic coasts. The causes of the large trends in atmospheric circulation and summer SST are not known. For SST there may be a connection with the well-known ocean circulation biases in low-resolution ocean models. A quantitative understanding of the causes of these trends is needed so that climate model based projections of future climate can be corrected for these precipitation trend biases. 相似文献
17.
The trends and features of China’s climatic change in the past and future are analysed by applying station obser-vations and GCM simulation results. Nationally, the country has warmed by 0.3oC in annual mean air temperature and decreased by 5% in annual precipitation over 1951-1990. Regionally, temperature change has varied from a cooling of 0.3oC in Southwest China to a warming of 1.0oC in Northeast China. With the exception of South China, all regions of China have shown a declination in precipitation. Climatic change has the features of increasing remark-ably in winter temperature and decreasing obviously in summer precipitation. Under doubled CO2 concentration, climatic change in China will tend to be warmer and moister, with increases of 4.5oC in annual mean air temperature and 11% in annual precipitation on the national scale. Future climatic change will reduce the temporal and spatial differences of climatic factors. 相似文献
18.
利用G分布函数对中国1951-2004年地面台站逐日降水观测资料进行雨日降水量概率分布拟合并定义极端降水事件,在此基础上对极端降水日数与ENSO的关系进行分析研究。结果表明,ENSO对同期的极端降水发生频率在不同地区和不同季节表现出不同的影响作用。总体而言,中国极端降水事件更易发生在厄尔尼诺年的冬春季和拉尼娜年的夏秋季。极端降水在对ENSO强信号的滞后响应上,其发生频率在时空上发生了变化,主要表现为,多数地方更易在ENSO暖位相出现后的半年左右发生极端降水事件。研究表明,ENSO冷暖信号对我国极端降水事件多寡的影响具有不对称性。 相似文献
19.
Spatial patterns and temporal trends of precipitation in Iran 总被引：3，自引：0，他引：3
Tayeb Raziei Jamal Daryabari Isabella Bordi Luis S. Pereira 《Theoretical and Applied Climatology》2014,115(3-4):531-540
Spatial patterns of monthly, seasonal and annual precipitation over Iran and the corresponding long-term trends for the period 1951–2009 are investigated using the Global Precipitation Climatology Centre gridded dataset. Results suggest that the spatial patterns of annual, winter and spring precipitation and the associated coefficients of variation reflect the role of orography and latitudinal extent between central-southern arid and semi-arid regions and northern and western mountainous areas. It is also shown that precipitation occurrence is almost regularly distributed within the year in northern areas while it is more concentrated in a few months in southern Iran. The spatial distribution of Mann–Kendal trend test (Z statistics) for annual precipitation showed downward trend in north-western and south-eastern Iran, whereas western, central and north-eastern exhibited upward trend, though not statistically significant in most regions. Results for winter and autumn revealed upward trend in most parts of the country, with the exception of north-western and south-eastern where a downward trend is observed; in spring and summer, a downward trend seems to prevail in most of Iran. However, for all seasons the areas where the detected trend is statistically significant are limited to a few spot regions. The overall results suggest that the precipitation is decreasing in spring and summer and increasing in autumn and winter in most of Iran, i.e. less precipitation during the warm season with a consequent intensification of seasonality and dryness of the country. However, since the detected trends are often not statistically significant, any stringent conclusion cannot be done on the future tendencies. 相似文献
20.
Changes of Climate Extremes in China 总被引：89，自引：0，他引：89
Changes in China's temperature and precipitation extremes have been studied by using observational data after 1950. The results reveal that mean minimum temperature has increased significantly in China during the past 40 years, especially in the winter in northern China. Meanwhile, nation-wide cold wave activity has weakened and the frequency of cold days in northern China has been reduced significantly. Mean maximum temperatures display no statistically significant trend for China as a whole. However, decreasing summer mean maximum temperatures are obvious in eastern China, where the number of hot days has been reduced. Seasonal 1-day extreme maximum temperatures mainly reflect decreasing trends, while seasonal 1-day extreme minimum temperatures are increasing.A statistically significant reduction of much above normal rain days in China has been detected. Contrarily, an increasing trend was detected in much above normal of precipitation intensity (precipitation/number of precipitation days) during the past 45 years. 相似文献