Spatial-Temporal Evolution Of Reference Crop Evapotranspiration And Its Climatic Factors In Liaodong Peninsula

Reference crop evapotranspiration?ET₀?is an important index to measure moisture loss and surface energy balance in the atmosphere.Due to the change of ET₀ only depends on the climate factors,thus clear the change rule of ET₀ itself response factors and its effect on climate change will help to evaluate regional drought degree and distribution of water resources.At present,global climate change has become an indisputable fact that extreme weather frequency has occurred.The Liaodong peninsula is located in the subtropical monsoon region with the largest change rate of the earth environment,and its ecological environment is sensitive to the response of the external climate change.The climatic characteristics of coastal areas are also different from that of most inland regions in China.Therefore,it is of great significance to study the climatic influence factors and ET₀ of the Liaodong peninsula.The results will be of great significance to the hydrological cycle and ecological balance in coastal region.According to the meteorological data of 10 weather stations in the Liaodong peninsula from 1960 to 2015,the thesis analyzes the temporal and spatial changes and trends of the climatic factors.Based on the temporal and spatial evolution of climatic factors,the thesis analyzes the temporal and spatial evolution of ET₀ in the region,including the annual variation,inter-annual variation,interdecadal variation,spatial variation trend and distribution,persistent characteristics and periodicity characteristics.Finally comprehensive climatic factors and the changes of ET₀,analyzes the reason for the changes of ET₀ and builds a statistical decision model for evaluating the regional ET₀ climatic factors.The main conclusions are as follows:?1?Clear the characteristics of temporal and spatial variations of the main climatic factors in Liaodong peninsula.The yearly variation of ET₀ is unimodal distribution and the seasonal precipitation is obvious,the annual distribution of the average temperature,relative humidity and precipitation shows the pattern of parabola,the seasonal distribution pattern is higher in summer and lower in winter.The annual distribution of sunshine duration and wind speed shows the pattern of bimodal,the seasonal distribution of sunshine hours is decreasing from spring to winter,and the wind speed is high in winter,the second in spring and autumn,the lowest in summer.The average temperature is consistent with the global temperature annual change trend and shows a significant increase,the relative humidity,sunshine hours,wind speed,precipitation and temperature range are not significantly decreased.The spatial distribution characteristics of various climatic factors are different,the annual average temperature decreases gradually from the south to north,and temperature range is on the opposite;relative humidity and precipitation decreases gradually from the east to west;sunshine hours decreases gradually from the west to east;the wind speed shows the coastal areas higher than the inland areas.?2?Clear the spatial-temporal evolution rules of ET₀ in Liaodong peninsula.The ET₀ shows no significant downward trend;The yearly variation of ET₀ was unimodal distribution and the seasonal precipitation was obvious,crop growth season accounts for a high proportion of the whole year;Spatially,the annual average ET₀ decreased gradually from the west to east,the spatial distribution of ET₀ in four seasons is different.There is a marked geographical difference in the tendency of ET₀ change which decreases from“west-north-east-south”,there is a clear trend of the spring ET₀ which decreases from“west-north-east-south”.The R/S analysis found that the strength sustainability of annual average ET₀ showed a zonal distribution which decreased from the south to north,and the Hurst indices in four seasons are also found to be greater than 0.5,which indicate that the long-term characteristics of the meteorological series are all persistent.The average annual and seasonal ET₀ in the Liaodong peninsula are characterized by periodical oscillating changes on different time scales,all experiencing different cycles which are from high to low,and the main cycles are different,the turbulence centers are all in the early 21st century.?3?Clear the reason for the changes of ET₀ and build a statistical decision model for evaluating the regional ET₀ climatic factors.Taking into account the direct impact of various climatic factors on ET₀ changes and their indirect effects on ET₀ through other factors,the impact degree is sunshine hours>relative humidity>temperature range>wind speed>precipitation>temperature.Considering that future climates are prone to sudden changes in a single climatic factor,such as a sudden increase in temperature,using partial correlation analysis and contribution rate analysis to clarify the impact of single factors on ET₀,the results shows that the average temperature and wind speed are the most relevant factors for ET0 which also have the most contribution rate.The conclusion drawn from these several statistical methods complemented each other,the partial correlation analysis and the contribution analysis qualitatively and quantitatively analyzed the influence of meteorological factors on ET₀.Path analysis considered the interaction among the factors,which comprehensively analyzed the cause of ET₀ changes in Liaodong Peninsula.Therefore,the three methods are combined to build a statistical decision model for evaluating the regional ET₀ climatic factors.