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1.
Using the daily maximum and minimum temperature dataset from 128 stations from 1960 to 2004 in Northwest China, daily extreme high temperature （EHT） and extreme low temperature （ELT） thresholds were determined by centesimal method for different stations at first, then yearly EHT and ELT events were counted up in different stations, and the characteristics of their spatio-temporal distribution were diagnosed at last. The study drew following conclusions： 1） The consistent anomaly distribution characteristic was the most important mode of the EHT and ELT events in Northwest China. 2） The spatial distribution of the EHT and ELT events can be divided into five sub-regions, namely, the north of Qinghai and west of Gansu, the north of Xinjiang, the south of Xinjiang, the east of Northwest China and the south of Qinghai. 3） The EHT events showed remarkable increasing trend in all of five sub-regions, but only in the north of Qinghai and west of Gansu area, sudden change phenomenon occurred; the ELT events showed decreasing trend in all of five sub-regions, and sudden change phenomenon occurred in Northwest China except for south of Qinghai. 4） In all of five sub-regions the EHT events showed remarkable 12-14yr period oscillation, and the ELT event showed significant 13-15yr and 7-8yr period oscillation. 5） The EHT and ELT events displayed remarkable positive and negative responses to regional warming of Northwest China respectively.  相似文献   

2.
Xinjiang is located in the core China's ‘Belt and Road’ development, and northern Xinjiang is an important region for economic development. In recent years, due to the strong influence of global climate change and human disturbance, regional climate instability and ecological-economic-social system sensitivity have grown. In this paper, seasonal, interannual, interdecadal, spatial, abrupt, and periodic variations of temperature and precipitation in northern Xinjiang were analyzed using daily surface air temperature and precipitation data from 49 meteorological stations during 1961–2017. At the same time, the driving factors of climate change are discussed. Methods included linear regression, cumulative anomaly, the Mann-Kendall test, and Morlet wavelet analysis. The results indicated that during the study period, annual mean temperature and annual precipitation increased significantly at rates of 0.35℃/10 yr and 13.25 mm/10 yr, respectively, with abrupt changes occurring in 1994 and 1986. Annual mean temperature and annual precipitation in all four seasons showed increasing trends, with the maximum increases in winter of 0.42℃/10 yr and 3.95 mm/10 yr, respectively. The general climate in northern Xinjiang showed a trend towards increasingly warm and humid. In terms of spatial distribution, the temperature and precipitation in high mountainous areas increased the most, while basins areas increased only slightly. Periodic change analysis showed that annual mean temperature and annual precipitation experienced two climatic shifts from cold to warm and dry to wet, respectively. Population change, economic development and land use change are important factors affecting climate change, and more research should be done in this field.  相似文献   

3.
Variations and trends in extreme climate events are more sensitive to climate change than the mean values,and so have received much attention.In this study,twelve indices of temperature extremes and 11 indices of precipitation extremes at 32 meteorological stations in Hengduan Mountains were examined for the period 1961-2008.The results reveal statistically significant increases in the temperature of the warmest and coldest nights and in the frequencies of extreme warm days and nights.Decreases of the diurnal temperature range and the numbers of frost days and ice days are statistically significant.Regional averages of growing season length also display the trends consistent and significant with warming.At a large proportion of the stations,patterns of temperature extremes are consistent with warming since 1961:warming trends in minimum temperature indices are greater than those relating to maximum temperature.As the center of the Shaluli Mountain,the warming magnitudes decrease from inner to outer.Changes in precipitation extremes is low:trends are difficult to detect against the larger inter-annual and decadal-scale variability of precipitation,and only the wet day precipitation and the regional trend in consecutive dry days are significant at the 0.05 level.It can be concluded that the variation of extreme precipitation events is not obvious in the Hengduan Mountains,however,the regional trends generally decrease from the south to the north.Overall,the spatial distribution of temporal changes of all extreme climate indices in the Hengduan Mountains illustrated here reflects the climatic complexity in mountainous regions.  相似文献   

4.
Baseflow, a component of the total streamflow, plays a key role in maintaining aquatic habitats, particularly during extreme drought events. This study investigated baseflow response to a prolonged and extreme meteorological drought event in the Baiyangdian Basin(BYD basin), a temperate water-limited basin in North China. Applying a precipitation series, piecewise regression was used to determine this extreme meteorological drought event, while the Automatic Baseflow Identification Technique(ABIT) was used to estimate a recession parameter(α), which was used to isolate baseflow from total streamflow. Results showed that: 1) annual precipitation exhibited significant decreasing trends(P 0.05) with an average change of –1.81 mm/yr~2. The precipitation deficit revealed that the start and end date of the extreme meteorological drought event was from August 1996 to May 2011, respectively, persisting for a total of 178 months(roughly 15 yr); 2) hydrological drought(including streamflow and baseflow) lagged behind meteorological drought while predictably persisting longer than extreme meteorological drought(i.e., precipitation); and 3) baseflow decreased dramatically under meteorological drought at both seasonal and annual scales, resulting in significantly decreasing trends during drought periods. Findings from this study confirmed that hydrological events caused by extreme meteorological drought can alter the magnitude and duration of baseflow and total streamflow, which will have an inevitable influence on aquatic ecosystems.  相似文献   

5.
The physical decomposition method separates atmospheric variables into four parts, correlating each with solar radiation, land–sea distribution, and inter-annual and seasonal internal forcing, strengthening the anomaly signal and increasing the correlation between variables. This method was applied to the reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR), to study the effects of Arctic factors(Arctic oscillation(AO) and Arctic polar vortex) on wintertime temperatures in the Northern Hemisphere and China. It was found that AO effects on zonal average temperature disturbance could persist for 1 month. In the AO negative phase in wintertime, the temperatures are lower in the mid–high latitudes than in normal years, but higher in low latitudes. When the polar vortex area is bigger, the zonal average temperature is lower at 50°N. Influenced mainly by meridional circulation enhancement, cold air flows from high to low latitudes; thus, the temperatures in Continental Europe and the North American continent exhibit an antiphase seesaw relationship. When the AO is in negative phase and the Arctic polar vortex larger, the temperature is lower in Siberia, but higher in Greenland and the Bering Strait. Influenced by westerly troughs and ridges, the polar air disperses mainly along the tracks of atmospheric activity centers. The AO index can be considered a predictor of wintertime temperature in China. When the AO is in negative phase or the Asian polar vortex is intensified, temperatures in Northeast China and Inner Mongolia are lower, because under the influence of the Siberia High and northeast cold vortex, the cold air flows southwards.  相似文献   

6.
The aim of this study was to better understand the mechanisms of regional climate variation in mountain ranges with contrasting aspects as mediated by changes in global climate. It may help predict trends of vegetation variations in native ecosystems in natural reserves. As measures of climate response, temperature and precipitation data from the north, east, and south-facing mountain ranges of Shennongjia Massif in the coldest and hottest months(January and July), different seasons(spring, summer, autumn, and winter) and each year were analyzed from a long-term dataset(1960 to 2003) to tested variations characteristics, temporal and spatial quantitative relationships of climates. The results showed that the average seasonal temperatures and precipitation in the north, east, and south aspects of the mountain ranges changed at different rates. The average seasonal temperatures change rate ranges in the north, east, and south-facing mountain ranges were from –0.0210℃/yr to 0.0143℃/yr, –0.0166℃/yr to 0.0311℃/yr, and –0.0290 ℃/yr to 0.0084℃/yr, respectively, and seasonal precipitation variation magnitude were from –1.4940 mm/yr to 0.6217 mm/yr, –1.6833 mm/yr to 2.6182 mm/yr, and –0.8567 mm/yr to 1.4077 mm/yr, respectively. The climates variation trend among the three mountain ranges were different in magnitude and direction, showing a complicated change of the climates in mountain ranges and some inconsistency with general trends in global climate change. The climate variations were significantly different and positively correlated cross mountain ranges, revealing that aspects significantly affected on climate variations and these variations resulted from a larger air circulation system, which were sensitive to global climate change. We conclude that location and terrain of aspect are the main factors affecting differences in climate variation among the mountain ranges with contrasting aspects.  相似文献   

7.
Glacier is a common sensitivity indicator of environmental and global climate change.Examining the relationship between glacier area and climate change will help reveal glacier change mechanisms and future trends. Glacier changes are also of great significance to the regulation of regional water resources. This study selected the Hala Lake Basin in the northeastern Qinhai-Tibet Plateau as a study area, and examined the relationships between the temporal and spatial change of glaciers in the northeastern Qinghai-Tibet Plateau and climate change based on remote sensing imagery,climatological data, and topographic data during the past 30 years. Results showed that glacier area in the Hala Lake basin fluctuated and decreased from106.24 km~2 in 1986 to 78.84 km~2 in 2015, with a decreasing rate of 0.94 km~2·yr~(-1). The number of glacier patches, mean patch area, and largest patch index all decreased from 1986 to 2015, while the splitting index increased from 1986 to 2015,indicating that the landscape fragmentation of glacier in the Hala Lake Basin was increasing significantly during the study period. Glacier area change was mainly concentrated in the slopes 25° with an altitude of 4500-5000 m, and the retreating rate of glacier of sunny slope was obviously higher than that of shady slope. Geometric center of glacier in the basin moved from southwest to northeast towards high altitude. Results of the response of glacier extent to climate change showed that temperature was the dominant factor affecting glacier area dynamic change in the Hala Lake Basin. It is predicted that in future several years, the glacier area will decrease and fragment continually as a result of global warming on the Tibetan Plateau.  相似文献   

8.
Variation of Thornthwaite moisture index in Hengduan Mountains,China   总被引：2，自引：1，他引：1  
The Thornthwaite moisture index, an index of the supply of water(precipitation) in an area relative to the climatic demand for water(potential evapotranspiration), was used to examine the spatial and temporal variation of drought and to verify the influence of environmental factors on the drought in the Hengduan Mountains, China. Results indicate that the Thornthwaite moisture index in the Hengduan Mountains had been increasing since 1960 with a rate of 0.1938/yr. Annual Thornthwaite moisture index in Hengduan Mountains was between –97.47 and 67.43 and the spatial heterogeneity was obvious in different seasons. Thornthwaite moisture index was high in the north and low in the south, and the monsoon rainfall had a significant impact on its spatial distribution. The tendency rate of Thornthwaite moisture index variation varied in different seasons, and the increasing trends in spring were greater than that in summer and autumn. However, the Thornthwaite moisture index decreased in winter. Thornthwaite moisture index increased greatly in the north and there was a small growth in the south of Hengduan Mountains. The increase of precipitation and decrease of evaporation lead to the increase of Thornthwaite moisture index. Thornthwaite moisture index has strong correlation with vegetation coverage. It can be seen that the correlation between Normalized Difference Vegetation Index(NDVI) and Thornthwaite moisture index was positive in spring and summer, but negative in autumn and winter. Correlation between Thornthwaite moisture index and relative soil relative moisture content was positive in spring, summer and autumn, but negative in winter. The typical mountainous terrain affect the distribution of temperature, precipitation, wind speed and other meteorological factors in this region, and then affect the spatial distribution of Thornthwaite moisture index. The unique ridge-gorge terrain caused the continuity of water-heat distribution from the north to south, and the water-heat was stronger than that from the east to west part, and thus determined the spatial distribution of Thornthwaite moisture index. The drought in the Hengduan Mountains area is mainly due to the unstable South Asian monsoon rainfall time.  相似文献   

9.
The northeastern China is a sensitive region of climate change, whose detailed trend of climate changes is highly interesting. In this study, this kind of variation trend was analyzed. Potential evapotranspiration (PE) and moisture index (MI) were modeled by using Thornthwaite scheme based on the observation data of 1961-2004 from 94 meteorological stations. To describe the climate fluctuation in the northeastern China in 1961-2004, the linear regression method was used to analyze the variation trends of mean annual temperature, mean annual precipitation, PE and MI. Mann-Kendall method was used to test the significant difference. The results show a general increasing tendency in mean annual temperature, mean annual precipitation, PE and MI. However increasing tendency was more significant in mean annual temperature and PE than in mean annual precipitation and MI. Analysis of seasonal climate variation indicates that there showed positive trends in winter and in spring, while the positive trend was more significant in winter than in spring. Furthermore, the relations between climate changes and geographical factors were analyzed, the results show that both climate factors and their interannual variability were correlated to latitude, longitude and altitude, suggesting that latitude is the most climate factor affecting climate changes, followed by altitude and longitude.  相似文献   

10.
Heat center of the western Pacific warm pool   总被引：1，自引：0，他引：1  
A heat center (HC) of the western Pacific warm pool (WPWP) is defined, its variability is examined, and a possible mechanism is discussed. Analysis and calculation of a temperature dataset from 1945-2006 show that the mean position of the HC during this period was near 0.4°S/169.0°E, at 38.0 m depth. From a time series of the HC, remarkable seasonal variability was found, mainly in the meridional and vertical directions. Interannual variabilities were dominant in the zonal and vertical directions. In addition, semiannual variation in the HC depth was discovered. The longitude of the HC varies with ENSO events, and its latitude is weakly related to ENSO on time scales shorter than a decade. The variation of the HC longitude leads the Nio-3 index by about 3-4 months, and its depth lags the index for approximately 3 months. It is concluded that the HC depth results from a combination of its longitudinal and latitudinal variations. Low-pass-filtered time series reveal that the HC has moved eastward since the mid 1980s.  相似文献   

11.
Multi-temporal series of satellite SPOT-VEGETATION normalized difference vegetation index (NDVI) and normalized difference water index (NDWI) data from 1998 to 2007 were used for analyzing vegetation change of the ecotone in the west of the Northeast China Plain. The yearly and monthly maximal values,anomalies and change rates of NDVI and NDWI were calculated to reveal the interannual and seasonal changes in vegetation cover and vegetation water content. Linear regression method was adopted to characterize the trends in vegetation change. The yearly maximal NDVI decreased from 0.41 in 1998 to 0.37 in 2007,implying the decreasing trend of vegetation activity. There was a significant decrease of maximal NDVI in spring and summer over the study period,while an increase trend was observed in autumn. The vegetation-improved regions and vegetation-degraded regions occupied 17.03% and 20.30% of the study area,respectively. The maximal NDWI over growing season dropped by 0.027 in 1998–2007,and about 15.15% of the study area showed a decreasing trend of water content. Vegetation water stress in autumn was better than that in spring. Vegetation cover and water content variations were sensitive to annual precipitation,autumn precipitation and summer temperature. The vegetation degradation trend in this ecotone might be induced by the warm-drying climate especially continuous spring and summer drought in the recent ten years.  相似文献   

12.
In arid regions, mountains fulfill important ecological and economic functions for the surrounding lowlands. In the scenario of global warming, mountain ecosystems change rapidly, especially in the arid region of northwestern China. This paper provides an assessment of the changes in temperature and precipitation in the historical records of climate on the northern slopes of the eastern Tianshan Mountains. A Mann-Kendall nonparametric trend and Sen＇s tests are employed to analyze the interannual changes and innerannual variability in temperature and precipitatiofi in the regions of low to high altitude. The present study finds that the largest increases in annual temperature are observed at stations in the low altitude regions. The significant increasing trends in temperature tend to occur mainly in late winter and early spring at stations from middle to high altitude, but in summer and autumn at stations of low altitudes. The increasing trends in annual precipitation are found from the middle to high altitude areas, but decreasing trends are found in the low altitude areas. The significant increasing trends in precipitation occur mostly in winter and earlier spring at stations from the middle to high altitudes, while the increasing and decreasing trend coexists at stations of low altitude with most of the significant trend changes occurring in March, June and August.  相似文献   

13.
Based on the authors‘ 1986 to 1994 sporo-pollen assemblage analysis in the southern Yellow Sea area, data from 3 main cores were studied in combination with ^14C, palaeomagnetic and thermoluminescence data. The evolution of the paleoclimate environments in the southern Yellow Sea since 15ka B.P. was revealed that, in deglaciation of the last glacial period, the climate of late glaciation transformed into that of postglaciation, accompanied by a series of violent climate fluctuations. These evolution events happened in a global climate background and related to the geographic changes in eastern China. We distinguished three short-term cooling events and two warming events. Among them, the sporo-pollen assemblage of subzone A1 showed some cold climate features indicating that a cooling event occurred at about 15 - 14ka. B .P. in early deglaciation. This subzone corresponds to the Oldest Dryas. In subzone A3 , many drought-enduring herbal pollens and some few pollens of cold-resistant Picea, Abies, etc. were found, which indicated that a cooling event, with cold and arid climate, occurred at about 12- 11ka. B.P. in late deglaciation. This subzone corresponds to the Younger Dryas. The sporo-pollen assemblage of zone B showed warm and arid climate features in postglaciation. Although the assemblage of subzone B2 indicated a cold and arid climate environment, the development of flora in subzone B2 climate was less cold than that in A3 . Subzone B2 indicated a cooling event which occurred at about 9ka B.P. in early Holocene. Subzone A2, with some distinct differences from subzone A1 and A3 , indicated a warming event which occurred at 14 - 13ka. B.P. and should correspond to a warming fluctuation. The sporo-pollen assemblage of zone C showed features of warm-moist flora and climate, and indicated a warming event which universally occurred along the coast of eastern China at 8 - 3ka B.P. in middle Holocene, and its duration was longer than that of any climate events mentioned above. This period was climatic optimum and belonged to an altithermal period in postglaciation.  相似文献   

14.
Extreme heat events have serious effects on human daily life. Accurately capturing the dynamic variance of extreme high-temperature distributions in a timely manner is the basis for analyzing the potential impacts of extreme heat, thereby informing risk prevention strategies. This paper demonstrates the potential application of multiple source remote sensing data in mapping and monitoring the extreme heat events that occurred on Aug. 8, 2013 in Jiangsu Province, China. In combination with MODIS products, the thermal sharpening(Ts HARP) method and a binary linear model are compared to downscale the original daytime FengY un 2 F(FY-2 F) land surface temperature(LST) imagery, with a temporal resolution of 60 min, from 5 km to 1 km. Using the meteorological measurement data from Nanjing station as the reference, the research then estimates the instantaneous air temperature by using an iterative computation based on the Surface Energy Balance Algorithm for Land(SEBAL), which is used to analyze the spatio-temporal air temperature variance. The results show that the root mean square error(RMSE) of the LST downscaled from the binary linear model is 1.30℃ compared to the synchronous MODIS LST, and on this basis the estimated air temperature has the RMSE of 1.78℃. The spatial and temporal distribution of air temperature variance at each geographical location from 06:30 to 18:30 can be accurately determined, and indicates that the high temperature gradually increases and expands from the city center. For the spatial distribution, the air temperature and the defined scorching temperature proportion index increase from northern to middle, to southern part of Jiangsu, and are slightly lower in the eastern area near the Yellow Sea. In terms of temporal characteristics, the percentage of area with air temperature above 37℃ in each city increase with time after 10:30 and reach the peak value at 14:30 or 15:30. Then, they decrease gradually, and the rising and falling trends become smaller from the southern cities to the northern regions. Moreover, there is a distinct positive relationship between the percentage of area above 37℃ and the population density. The above results show that the spatio-temporal distributions of heat waves and their influencing factors can be determined by combining multiple sources of remotely sensed image data.  相似文献   

15.
The distribution of borehole temperature at four high-altitude alpine glaciers was investigated. The result shows that the temperature ranges from -13.4℃ to -1.84℃, indicating the glaciers are cold throughout the boreholes. The negative gradient （i.e., the temperature decreasing with the increasing of depth） due to the advection of ice and climate warming, and the negative gradient moving downwards relates to climate warming, are probably responsible for the observed minimum temperature moving to lower depth in boreholes of the Gyabrag glacier and Miaoergou glacier compared to the previously investigated continental ice core borehole temperature in West China. The borehole temperature at 10m depth ranges from -8.0℃ in the Gyabrag glacier in the central Himalayas to -12.9℃ in the Tsabagarav glacier in the Altai range. The borehole temperature at 10 m depth is 3-4 degrees higher than the calculated mean annual air temperature on the surface of the glaciers and the higher 10 m depth temperature is mainly caused by the production of latent heat due to melt-water percolation and refreezing. The basal temperature is far below the melting point, indicating that the glaciers are frozen to bedrock. The very low temperature gradients near the bedrock suggest that the influence of geothermal flux and ice flow on basal temperature is very weak. The low temperature and small velocity of ice flow of glaciers are beneficial for preservation of the chemical and isotopic information in ice cores.  相似文献   

16.
Drought, as a recurring extreme climate event, affects the structure, function, and process of terrestrial ecosystems. Despite the increasing occurrence and intensity of the drought in the past decade in Southwestern China, the impacts of continuous drought events on vegetation in this region remain unclear. During 2001–2012, Southwestern China experienced the severe drought events from 2009 to 2011. Our aim is to characterize drought conditions in the Southwestern China and explore the impacts on the vegetation condition and terrestrial ecosystem productivity. The Standardized Precipitation Index(SPI) was used to characterize drought area and intensity and a light-use efficiency model was used to explore the effect of drought on the terrestrial ecosystem productivity with Moderate Resolution Imaging Spectrometer(MODIS) data. The SPI captured the major drought events in Southwestern China during the study period, indicated that the 12-year period of this study included both ‘normal' precipitation years and two severe drought events in 2009–2010 and 2011. Results showed that vegetation greenness(Normalized Difference Vegetation Index, NDVI and Enhanced Vegetation Index, EVI) both declined in 2009/2010 drought, but the 2011 drought resulted in less declines of vegetation greenness and productivity due to shorten drought duration and rising temperature. Meanwhile, it was about 5 months lapse between drought events and maximum declines in vegetation greenness for 2009/2010 drought events. In addition, forest, grassland and cropland revealed significant different ecosystem responses to drought. It indicated that grassland showed an early sensitivity to drought, while cropland was the most sensitive to water deficit and forest was more resilient to drought. This study suggests that it is necessary to detect the difference responses of ecosystem to drought in a regional area with satellite data and ecosystem model.  相似文献   

17.
Understanding the net primary productivity(NPP) of grassland is crucial to evaluate the terrestrial carbon cycle. In this study, we investigated the spatial distribution and the area of global grassland across the globe. Then, we used the Carnegie-Ames-Stanford Approach(CASA) model to estimate global grassland NPP and explore the spatio-temporal variations of grassland NPP in response to climate change from 1982 to 2008. Results showed that the largest area of grassland distribution during the study period was in Asia(1737.23 × 104 km~2), while the grassland area in Europe was relatively small(202.83 × 10~4 km~2). Temporally, the total NPP increased with fluctuations from 1982 to 2008, with an annual increase rate of 0.03 Pg C/yr. The total NPP experienced a significant increasing trend from 1982 to 1995, while a decreasing trend was observed from 1996 to 2008. Spatially, the grassland NPP in South America and Africa were higher than the other regions, largely as a result of these regions are under warm and wet climatic conditions. The highest mean NPP was recorded for savannas(560.10 g C/(m~2·yr)), whereas the lowest was observed in open shrublands with an average NPP of 162.53 g C/(m~2·yr). The relationship between grassland NPP and annual mean temperature and annual precipitation(AMT, AP, respectively) varies with changes in AP, which indicates that, grassland NPP is more sensitive to precipitation than temperature.  相似文献   

18.
According to loess and palaeosol climatic record, field observation, analysis data and 14C dating, we discuss the climatic changes and the water level fluctuations of Qinghai Lake. It is pointed out that there were four relatively warm and moist stages in Qinghai Lake basin during the Holocene. They formed in the periods from 10,300 yr.B.P. to 8,500 yr.B.P., 7,000 yr.B.P. to 3,500 yr.B.P., 2,800 yr.B.P. to 2,000 yr.B.P. and from 1,300 yr.B.P. up to now. The climate in the Holocene optimum period, from 7,000 yr.B.P. to 3,500 yr.B.P., was much warmer and moister than that today. Polypodium plant grew luxuriantly around Qinghai Lake. The annual temperature was 2.5℃ higher than that today, but there was no forest at Qinghai Lake shore. It is found that there was a good relationship between precipitation and water level fluctuation. In warm and moist period water level was high and in the cold and dry period it was low in the Holocene. There were four high water level periods for Qinghai Lake in the Holocen  相似文献   

19.
The characteristics of seasonal variation in phytoplankton biomass and dominant species in the Changjiang River Estuary and adjacent seas were discussed based on field investigation data from 1959 to 2009. The field data from 1981 to 2004 showed that the Chlorophyll-a concentration in surface seawater was between 0.4 and 8.5 μg dm-3. The seasonal changes generally presented a bimodal trend, with the biomass peaks occurring in May and August, and Chlorophyll-a concentration was the lowest in winter. Seasonal biomass changes were mainly controlled by temperature and nutrient levels. From the end of autumn to the next early spring, phytoplankton biomass was mainly influenced by temperature, and in other seasons, nutrient level(including the nutrient supply from the terrestrial runoffs) was the major influence factor. Field investigation data from 1959 to 2009 demonstrated that diatoms were the main phytoplankton in this area, and Skeletonema costatum, Pseudo-nitzschia pungens, Coscinodiscus oculus-iridis, Thalassinoema nitzschioides, Paralia sulcata, Chaetoceros lorenzianus, Chaetoceros curvisetus, and Prorocentrum donghaiense Lu were common dominant species. The seasonal variations in major dominant phytoplankton species presented the following trends: 1) Skeletonema(mainly S. costatum) was dominant throughout the year; and 2) seasonal succession trends were Coscinodiscus(spring) →Chaetoceros(summer and autumn) → Coscinodiscus(winter). The annual dominance of S. costatum was attributed to its environmental eurytopicity and long standing time in surface waters. The seasonal succession of Coscinodiscus and Chaetoceros was associated with the seasonal variation in water stability and nutrient level in this area. On the other hand, long-term field data also indicated obvious interannual variation of phytoplankton biomass and community structure in the Changjiang River Estuary and adjacent seas: average annual phytoplankton biomass and dinoflagellate proportion both presented increased trends during the 1950 s-2000 s.  相似文献   

20.
The views of local people on climate change along different ecological regions are relatively unexplored in Nepal. This study was conducted in 13 villages in central Nepal at different altitudes to document the views of small holder farmers and compare their perception with trends of climatic variables, finger millet yield, natural disasters, plant phenology(flowering and fruiting), status of forest and wild life, as well as the spread of diseases and pests. Analysis on the climatic data of stations for 36-41 years between 1975 and 2016 showed significant increases in the minimum temperature in lower tropical climatic region(500 m), upper tropical to subtropical climatic region(500-2000 m) and temperate climatic region(2000-3000 m) by 0.01, 0.026 and 0.054℃/year, respectively, and an increase of maximum temperature by 0.008, 0.018, and 0.019℃/year, respectively. Rainfall showed a strongly significant decreasing trend in all elevation regions. This result matches with the views of respondents except 38% respondent from temperate climatic region. People from the temperate climatic region also mentioned that current onset of snowfall is delayed but amount of snowfall remained the same. From the documented records, except events of wild fire, frequency of natural disasters events have increased in the recent years, which was in harmony with the views of local people. Multi-linear regression analysis showed that contribution of climatic variables on finger millet yield in lower tropical climatic region and upper tropical to subtropical regions was 23% and 57.3%, respectively, which was supported by increasing trend on average growing degree day(GDD) temperature at the rate of 0.01℃ in upper tropical to subtropical region and 0.007℃ in lower tropical climatic region yearly. Finger millet yield has been increasing at the rate of 7.39 and 36.9 kg/ha yearly in lower tropical climatic region and upper tropical to subtropical climatic region, respectively. This result provides deeper understanding of people's perception of causes and effects of climate change on diverse variables along different elevation and related magnitude which can contribute to policy making in Nepal.  相似文献   

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