Temporal And Spatial Variations Of Water Vapor Over China

As one of the most important components in the lower atmosphere,water vapor is indispensable for the formation and evolution of precipitation and other weather and climate phenomena,while it is also an important factor affecting the generation and development of extreme weather.Meanwhile,as the only component in the atmosphere that may undergo phase change,water vapor will continuously release and absorb heat during its change,affecting the temperature of the atmosphere and the ground,which makes water vapor one of the main greenhouse gases.In addition,water vapor can directly or indirectly affect the movement and change of the atmosphere,while diffusion and transport of water vapor are important part of the hydrosphere.In summary,under the background of global climate change,the study of the spatiotemporal changes of water vapor is of great significance for further understanding the working mechanism of the entire climate and weather system.Water vppor is not only influenced by the seasons,temperature,and radiation,but also affected by other regional climate conditions such as atmospheric circulation,sea-land distribution,and topography.With complex spatiotemporal distributions and rapid changes,water vapor is one of the meteorological parameters which are mostly difficultly monitored and described.With a vast area,large span from north to south,significant temperature difference,large span from the coast to the inland,and diverse step-like topography in China,there is diverse warm-cold and dry-wet areas where types of climate is various,while China is the country with the most significant monsoon climate in the world.Various climate types,especially the monsoon climate,result in inverse spatiotemporal distribution of water vapor in China.Also,Chinese production and life are also strongly affected by global climate phenomena such as El Nino and La Nina,as well as droughts,torrential rains,typhoons and other disasters which are often related to spatiotemporal changes of water vapor.Therefore,comprehensive monitoring and analysis of the spatiotemporal distribution of water vapor in China is of great significance for the study of complex climate features,short-term weather forecast and disaster warning there.ECMWF's(European Centre for Medium Range Weather Forecast)reanalysis products,as an important data source in atmospheric science research today,are calculated with considering the atmospheric background field,measured meteorological data,and the hydrodynamic and thermodynamic principles of the weather evolution process.ECMWF's water vapor data have higher spatiotemporal resolution and so is more sufficient for study on medium and long-term climate than that obtained by traditional techniques such as radiosondes,very long baseline interferometers(VLBI),infrared detectors,and microwave radiometers,while it is therefore more and more widely used in the current research of water vapor.In this paper,based on the entire water vapor data provided by ECMWF's ERA-Interim dataset,we systematically analyze the spatiotemporal distribution of water vapor in China for the past 39 years by the methods of spectrum analysis,linear fitting,and singular spectral decomposition,while the meteorological parameters such as temperature,precipitation,soil moisture,vegetation index and other ecological indices are used to study the influence mechanism of the spatiotemporal distribution of water vapor and its impact on the ecological environment.The main research contents and results are:(1)In China,the distribution pattern of water vapor is generally related to latitude,while the regional difference is also significant.The factors affecting water vapor 's spatial distribution are complex,while its spatial distribution is mainly affected by temperature and topography,regional climatic conditions such as distance from the sea and monsoon.(2)In terms of long-term changes,water vapor in most parts of China has increased in recent decades.The larger increase trends appear in the southern Tibet Plateau(TP),the Qilian Mountains,the Alashan and Hexizoulang in the northeastern TP,the southwest of Yunnan,the Shandong Peninsula and the Taiwan.In addition,there are also decreasing trends in the long term change of water vapor in some areas,while the larger decreasing trends appear in the eastern part of the Inner Mongolia Plateau and the western Liaohe Plain,the Yanshan region,the Fenwei Plain,parts of the upper and middle reaches of the Yangtze River,the Minyuegui hills,and parts of central and eastern Xinjiang.(3)The characteristics of long-term changes in water vapor and precipitation in southern TP have been studied.It is statistically show that there is an increasing trend of water vapor and precipitation in May in southern TP.Meanwhile,it's confirmed that there is a lag correlation between precipitation and precipitation with soil moisture and vegetation cover.The increase of precipitation in May promoted the increase of soil moisture and vegetation cover in June.By in-depth study,it's confirmed that the advance of the South Asian summer monsoon,which was rooted in the long-term oscillation of the Pacific Ocean resulting from the phase transition in the 1990s,is the main driving factor to promote the increase of precipitation in May in southern TP.(4)Singular spectral decomposition method is used to analyze the seasonal variation of water vapor in China.There are significant annual and semi-annual variations in water vapor over several major climate regions in China.In the terms of annual variations,peaks appear in July,while there is significant east-west distribution difference in annual amplitude,with larger amplitudes in the eastern part of North China,the downstream areas,the Yuegui area and smaller amplitudes in the central and eastern parts of TP.The regional distribution of annual variations is mainly affected by monsoon,and the annual variations in water vapor in regions affected by stronger monsoonal effects are stronger.For the semiannual variations of water vapor,the larger semiannual amplitudes appear in the Northeast China and the North China,while the smaller semiannual amplitudes appear in the eastern part of Yunnan.In terms of semiannual phase,the peak values of the semiannual variations appear in January and July,the valley values appear in April and October in the most region of the Northeast China,the North China,and the Western China,and the peak values appear in April and October,and the valley values appear in January and July in the Yuegui region,Taiwan and Hainan,while in other region,the peak values appear in February and August,and the valley values appear in May and November.The spatial distribution of the semiannual variations is closely related from the seasonal difference and monsoon.