Spatial analysis of vegetation cover response to climate trends in Khakassia(South Siberia)

An analysis of the changes in vegetation cover on the territory of the Republic of Khakassia in 2000–2021 due to climatic trends was carried out based on the MODIS data.The changes in vegetation cover were estimated based on trends in Normalized Difference Vegetation Index(NDVI)and Enhanced Vegetation Index(EVI).In general,in the 21st century,an increase in the biomass of vegetation cover is observed.Positive trends were observed in 16%–22%of the territory,and negative only in 1%–3%.For about 20%of the analyzed territory,a significant influence of climate on the changes in vegetation cover was revealed.The most pronounced negative impact on vegetation cover was caused by summer air and soil temperatures,spring temperature,and summer winds,and the positive impact was caused by summer precipitation and soil moisture.The response of the vegetation cover to climate was non-uniform concerning the topography.Thus,a significant correlation with the amount of precipitation was observed for~20%–35%of vegetation growing below 600 m above sea level and for less than 5%above this elevation.The negative effect of summer temperatures on plants prevailed mainly at an elevation below~1400 m above sea level.Projected climate change is likely to lead to significant degradation of vegetation in the steppe and foreststeppe in Khakassia in the coming decades.

Discovery of the Significant Impacts of Swell Propagation on Global Wave Climate Change

This study compared the differences in the wave climate in the South China Sea and North Indian Ocean under these two datasets:ERA-40 wave reanalysis and Mei’s hindcast wave data.In the numerical calculation of regional ocean waves,the wave climate characteristics exhibited significant bias if the influence of external swells(swells from afar)was not fully considered,which may provide an incorrect basis for global climate change analysis.1)The trends of the significant wave height(SWH)obtained from the two datasets showed significant differences,such as those of the Bay of Bengal and the Java Sea in June-July-August.For the past 45 years,SWH from ERA-40(SWH-ERA)exhibited a significant annual increase in low-latitude waters of the North Indian Ocean(0.2-0.6 cm yr^(-1))and South China Sea(0.2-0.8 cm yr^(-1)).2)In the Bay of Bengal,the SWH-ERA in each month was generally 0.5 m higher than the SWH from Mei’s hindcast wave data(SWH-Mei)and can reach 1.0 m higher in some months.3)In the Bay of Bengal,SWH-ERA and SWH-Mei increased significantly at annual rates of 0.13 and 0.27 cm yr^(-1),respectively.This increasing trend was mainly reflected after 1978.SWH-ERA showed a trough in 1975(1.33 m)and a crest in 1992(1.83 m),which were not reflected in SWH-Mei.

A positive trend in the stability of global offshore wind energy

The recognition on the trend of wind energy stability is still extremely rare,although it is closely related to acquisition efficiency,grid connection,equipment lifetime,and costs of wind energy utilization.Using the 40-year(1979–2018)ERA-Interim data from the European Center for Medium-Range Weather Forecasts,this study presented the spatial-temporal distribution and climatic trend of the stability of global offshore wind energy as well as the abrupt phenomenon of wind energy stability in key regions over the past 40 years with the climatic analysis method and Mann-Kendall(M-K)test.The results show the following 5 points.(1)According to the coefficient of variation(C_(v))of the wind power density,there are six permanent stable zones of global offshore wind energy:the southeast and northeast trade wind zones in the Indian,Pacific and Atlantic oceans,the Southern Hemisphere westerly,and a semi-permanent stable zone(North Indian Ocean).(2)There are six lowvalue zones for both seasonal variability index(S_(v))and monthly variability index(M_(v))globally,with a similar spatial distribution as that of the six permanent stable zones.M_(v) and S_(v) in the Arabian Sea are the highest in the world.(3)After C_(v),M_(v) and S_(v) are comprehensively considered,the six permanent stable zones have an obvious advantage in the stability of wind energy over other sea areas,with C_(v) below 0.8,M_(v) within 1.0,and S_(v) within 0.7 all the year round.(4)The global stability of offshore wind energy shows a positive climatic trend for the past four decades.C_(v),M_(v) and S_(v) have not changed significantly or decreased in most of the global ocean during 1979 to2018.That is,wind energy is flat or more stable,while the monthly and seasonal variabilities tend to shrink/smooth,which is beneficial for wind energy utilization.(5)C_(v) in the low-latitude Pacific and M_(v) and S_(v) in both the North Indian Ocean and the low-latitude Pacific have an obvious abrupt phenomenon at the end of the20th century.

Climate trends in tropical cyclone-induced precipitation and wind over Shanghai

The trends in annual precipitation and wind induced by tropical cyclones(TCs)over Shanghai during the last 40 years are estimated.Results indicate that there is a significant increasing trend in the annual total precipitation induced by TCs,which is related to the significant positive trends in daily precipitation and annual torrential rain days.Meanwhile,a significant decreasing trend shows in maximum sustained wind,which seems to be related to the downward trend in the intensity of TCs when affecting Shanghai.The annual frequencies of affected TCs,TC translation speed and distance from Shanghai when affecting Shanghai have no obvious tendency.The different trends in precipitation and wind suggested that a more comprehensive metric for assessing TCs'influence on society is necessary.

Changes in Climate Regionalization Indices in China during 1961–2010

The regionalization of climate in China is based on a three-level classification in terms of lasting days for accumulated temperature （AT）,aridity index,and July mean temperature.Based on daily meteorological observational data from 756 stations,trends and interdecadal variation in indices for classifying temperature zones,moisture regions and climatic subregions in the period 1961-2010 are discussed.Results reveal that the nationwide AT ≥ 10℃C （AT10） and its lasting days are basically increasing,while aridity in northern Xinjiang is decreasing.The increasing trend of July mean temperature in North China is found to be notably larger than in South China.In terms of their national averages,a marked step increase of AT10 and its lasting period,as well as July mean temperature occurred around 1997,while the aridity index presents no such clear change.By comparing regionalization areas for 1998-2010 with those for 1961-97,it is found that the semi-humid,semi-dry and dry regions in the sub-temperate zone,as well as the humid region in the middle subtropical zone,have experienced substantial shrinkage in terms of area.In contrast,the areas of semi-dry and dry regions in the warm temperate zone,as well as the humid region in the south subtropical zone,present drastically increasing trends.Owing to the influence of such step changes that took place in 1997,that particular point in time should be given close attention in future studies regarding the regionalization of climate in China.

Climatic trends over the Tibetan Plateau during 1971-2000

Trends of annual and monthly temperature, precipitation, potential evapotranspiration and aridity index were analyzed to understand climate change during the period 1971-2000 over the Tibetan Plateau which is one of the most special regions sensitive to global climate change. FAO56-Penmen-Monteith model was modified to calculate potential evapotranspiration which integrated many climatic elements including maximum and minimum temperatures, solar radiation, relative humidity and wind speed. Results indicate generally warming trends of the annual averaged and monthly temperatures, increasing trends of precipitation except in April and September, decreasing trends of annual and monthly potential evapotranspiration, and increasing aridity index except in September. It is not the isolated climatic elements that are important to moisture conditions, but their integrated and simultaneous effect. Moreover, potential evapotranspiration often changes the effect of precipitation on moisture conditions. The climate trends suggest an important warm and humid tendency averaged over the southern plateau in annual period and in August. Moisture conditions would probably get drier at large area in the headwater region of the three rivers in annual average and months from April to November, and the northeast of the plateau from July to September. Complicated climatic trends over the Tibetan Plateau reveal that climatic factors have nonlinear relationships, and resulte in much uncertainty together with the scarcity of observation data. The results would enhance our understanding of the potential impact of climate change on environment in the Tibetan Plateau. Further research of the sensitivity and attribution of climate change to moisture conditions on the plateau is necessary.

Climatic trends of different intensity heavy precipitation events concentration in China

Based on 740 stations of daily precipitation datasets in China, the precipitationconcentration degree （PCD） and precipitation-concentration period （PCP） of different intensity durative precipitation events were calculated to analyze their statistical characteristics, mainly including spatial and temporal distributions, variations and climatic trends of the two parameters of the durative heavy precipitation events in China. It is proved that these two parameters of heavy rainfall can display the temporal inhomogeneity in the precipitation field. And it is also found that there is a good positive relationship between the precipitation-concentration degree and annual rainfall amount in the Eastern and Central China. This method can be anolied in flood assessment and climate change fields.

A Statistical Model for Investigating Climatic Trend Turning Points

A two-phase trend model is presented to investigate the turning-point signals of evolution trend in long-term series of a climatic element. Based on nonlinear fitting, the revised model brings out more evident improvement of the linear model proposed by Solow et al. (1987). Both theoretical deduction and case calculation show that our version can search the turning point and period accurately and objectively. In particular it is fit for computer exploring the turning points in long-range records from stations covering a large area, thus avoiding subjective judgement by a usual drawing method.

Analysis on the Climate Variation Characteristics of Frost in Shandong Province

[Objective] The research aimed to study the climate variation characteristics of frost in Shandong Province. [Method] The daily minimum surface temperature ≤ 0 ℃ in autumn or spring was as the frost index. Based on the daily minimum surface temperature data in 67 meteorological observatories of Shandong Province during 1961-2008, the variation characteristics of first, last frost dates and frost-free period in Shandong Province were analyzed by using the climate diagnosis analysis method. [Result] The climate characteristics of first, last frost dates and frost-free period had the obvious geographical differences in Shandong Province in recent 48 years. The extreme differences of first, last frost dates and frost-free period were all above the three times of their standard deviations. It illustrated that the dispersion degrees of first, last dates and frost-free period were all very big. The average first frost date postponed with 1.99 d/10 a velocity in Shandong Province in recent 48 years, and the last frost date advanced with 1.46 d/10 a velocity. The postponing range of first frost date was bigger than the advancing range of last frost date, and the frost-free period prolonged with 3.42 d/10 a velocity. Seen from the interdecadal variations, the first frost date started to obviously postpone, and the last frost date obviously advanced since the 1990s. The frost-free period also started to obviously prolong since the 1990s. [Conclusion] The research provided the certain reference for the predication, prevention of frost disaster and the structure adjustment of crops.

Spatial / Temporal Features of Antarctic Climate Change

Bused on January 1962-October 1993 mean value series of monthly mean temperature anomalies of 16 Antarctic stations on 10 standard isobanc surfaces from the surface to the 30 hPa,long term trends and periodic features of climate changes from the troposphere to the lower stratosphere over the Antarctic region are investigated by maximum entropy power spectrum analysis,and the relation between climate change of the stratosphere (troposphere) and tolal ozone (southern 500 hPa circulation) is discussed.

The Impact of Current Climate Changes on Morphodynamic Regimes of Steppes and Forest Steppes in Southern Siberia

Predictive assessments of the geomorphological systems’ behavior under climate warming in southern Siberia have been performed based on time-series data, using theoretical and empirical models of processes. High sensitivity and fast response of erosional, aeolian, and cryogenic processes to current climatic changes are presented. The current trends under changing functioning conditions of geomorphological systems while maintaining climatic trends have been determined. Areas with different targeting of morpholithogenesis are identified.

Study on Ann-Based Multi-Step Prediction Model of Short-Term Climatic Variation

In the context of 1905–1995 series from Nanjing and Hangzhou, study is undertaken of estab-lishing a predictive model of annual mean temperature in 1996–2005 to come over the Changjiang (Yangtze River) delta region through mean generating function and artificial neural network in combination. Results show that the established model yields mean error of 0.45°C for their abso-lute values of annual mean temperature from 10 yearly independent samples (1986–1995) and the difference between the mean predictions and related measurements is 0.156°C. The developed model is found superior to a mean generating function regression model both in historical data fit-ting and independent sample prediction. Key words Climate trend prediction. Mean generating function (MGF) - Artificial neural network (ANN) - Annual mean temperature (AMT)

Research for length change of four seasons over China in recent 47 years

Using daily temperature data from 599 Chinese weather stations during 1961-2007, the length change trends of four seasons dur- ing the past 47 years were analyzed. Results show that throughout the region, four seasons＇ lengths are： spring becomes shorter （-0.8 d/10yrs）, summer becomes longer （3.2 d/10yrs）, autumn （-0.5 d/10yrs） and winter （-1.6 d/10yrs） becomes shorter. This trend is different in spatial distribution, namely it is very obvious in northern than southern China, and also remarkable in eastern than western China. Summer change is most obvious, but autumn has little change comparatively. This trend is highly obvious in North, East, Central and South China. In the Southwest starting in the 21st century, summer becomes longer and winter shortens. The trend in the Plateau region since the 1980s is that spring becomes longer and winter shortens. The average annual temperature increased during the past 47 years, and the change of the average annual temperature precedes seasons＇ length. Thus, the average annual temperature has a certain influence on the length change of seasons.

Dryland agriculture and rangeland restoration priorities in Afghanistan

Afghanistan is threatened by rangeland degradation.A quantitative visual analysis of Google Earth Imagery was used to systematically locate,characterize and quantify the current extent of rangelands in Afghanistan degraded as a consequence of dryland agriculture.Climate data were used in conjunction with dryland agriculture locations to establish a climate envelope comprised by temperature and mean annual precipitation to create a geographical mask known to contain dryland agriculture.Within this mask we created a grid of 100 km2 cells that we analyzed individually to access dryland agriculture extent.Climatic limits to sustainable dryland agriculture and areas of high restoration priority were also assessed as was the distribution of rain-fed agriculture with respect to the location of traditional migration routes for extensive livestock producers.The extents of agriculture in Afghanistan,at both upper and lower elevations,correlated most closely with mean annual temperature（MAT） at the upper elevation limits,and with mean annual precipitation（MAP） at the lower elevation limits.In total,dryland agriculture comprised 38,980 km2 of former native rangeland.Conversion was highest in the northwestern,northern and northeastern provinces of Herat,Badghis,Faryab,Jawzjan,Sar-e-Pul,Samangan,Balkh,Baghlan,Kunduz,Takhar and Badakhshan,with the highest percentage of conversion occurring in Takhar.An MAP value of 〈400 mm is perceived by farmers as the current climatic limit to sustainable dryland agriculture across the northern regions of the country.Uder this MAP value,approximately 27,677 km2 of converted rangeland met the need for restoration priority.Climate projections indicate that Afghanistan will become warmer and drier in the coming decades.One consequence of this trend is that the MAP threshold of 〈400 mm to sustainable dryland agriculture will become obsolete in the coming decades.Restoration of currently converted rangelands is needed to restore critical grazing areas as is the adoption of prudent range management policies to prevent further land degradation and support a vital livestock industry.Food security is at stake as the conversion of rangelands to unsustainable rain-fed agriculture may leave large tracks of land unusable for either agriculture or livestock production.

Climatic Trend of Cloud Amount Related to the Aerosol Characteristics in Beijing During 1950-2005

This paper analyzes the correlation between variations of total and low cloud amounts and the varying features of aerosols related to urban development of Beijing by using the cubic spline fitting method based on the monthly meteorological data of temperature,humidity,precipitation,clouds,and aerosol optical depth （AOD） during 1950-2005.The statistics on the development of the city of Beijing in this period,including the total industrial output,population,residential housing development,highway construction,charcoal production,etc.,is revealed.Accompanying the rapid urban development of Beijing over the past 55 years or so,the urban aerosol concentration and composition have changed.The results indicate that：1） there is a general trend of climate warming and drying in Beijing;2） the total cloud amount in all seasons declines drastically,but lower cloud amount climbs up slightly;3） the high correlations between cloud amount and the indices of Beijing urban development such as the housing area,charcoal production,and road construction show that the variation of cloud amount is closely related to the urban development;4） the changing trend of AOD coincides more closely with the variation of low cloud amount.The evident drop of total cloud amount is in agreement with the trend of climate warming and drying,while the slight growth of low cloud amount is likely caused by more haze and fog occurrences in the lower troposphere in association with the pollution responsible for the＂darkening＂of Beijing and the surrounding areas.

ANNUAL DISTRIBUTION FEATURES OF PRECIPITATION IN CHINA AND THEIR INTERANNUAL VARIATIONS

The hierarchy and definition of the precipitation-concentration degree and precipitation- concentration period of annual precipitation have been proposed by using the so-called vector method of annual distribution of precipitation,so that the two relevant parameters can represent the annual distribution of total precipitation correctly and indeed accurately.The relationship between the spatial and temporal distribution patterns and variations of the two parameters and the annual precipitation amount in China has been further investigated.Results demonstrate that the precipitation-concentration degree and the precipitation-concentration period increase from southeast to northwest gradually.Moreover there obviously exists a belt pattern:the largest variability of the precipitation-concentration degree and the precipitation-concentration period occurs in the Yellow River Valley and the middle and lower reaches of the Yangtze River, corresponding to the significant zones in which flood and drought take place frequently.It is found that there exist high correlations between the precipitation-concentration degree and precipitation- concentration period and the annual precipitation amount in Northeast China,North China,the middle and lower reaches of the Yangtze River. Furthermore,8-year and 22-year periodic oscillations in the precipitation-concentration degree and 6-year and 12-year cycles in the precipitation-concentration period are identified by use of their Morlet wavelet analysis.

TEMPERATURE,RAINFALL VARIATIONS AND THEIR ANOMALIES OVER CHINA UNDER THE COLD-WARM BACKGROUND IN THE 20TH CENTURY

In this study,the climate trend of the annual average air temperature and total annual rainfall in China in the present century has been examined.It is noted that in the Northwest,the Northeast and North China the climate has become notably warmer this century but the rainfall trend has not been evident,mainly negative.In the 1980s China's rainfall and temperature showed noticeable regional features: warm and dry in North China,cold and dry in the Southwest,warm and wet in the Northeast,cold and wet in the middle-lower reaches of the Changjiang River.Besides,the four interdecadal climate change features and ranges of this century have been studied.It is found that on the scale of several decades there was considerably less rainfall in the most part of China in the warm background than in the cold background.The increase of temperature which started from the 1970s mainly happened in the Northwest and Northeast,while to the south of the Huanghe River the temperature increase did not even as great as in 1940s.The corresponding rainfall feature is that most areas experienced much less rainfall except the area to the south of the Huanghe River and over the Changjiang and Huaihe River basin.

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

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