Changes Of Ground Temperature In Sichuan And Evaluation Model

As an indicator of climate changes,ground temperature plays an important role in the process of soil biology and microorganism.Air temperature,precipitation and land cover affect ground temperature.In contrary,ground temperature can influence climate changes by the reflectivity of the underlying surface,soil humidity,soil thermal storage and so on.Located in the eastern part of Qinghai Tibet Plateau,Sichuan Province has unique climate characteristics owing to the influence of the plateau monsoon climate,the southwest monsoon and plateau leeward slope.Furthermore,with the typical geographic location and complex topography,the different regions in Sichuan Province display various climatic characteristics and atmospheric circulation patterns.Therefore,the study of ground temperature in Sichuan Province can further understand the reason of climate changes.Based on the data of monthly mean ground temperature,air temperature,precipitation,sunshine duration and wind velocity from 34 stations from 1961 to 2014,the characteristics of ground temperature and the difference between ground soil and air temperature,response to climate change and future trends are analyzed.Evaluation model based on GIS in Sichuan are also discussed.The main results are as follows:(1)Inter-decade anomaly of annual,seasonal and monthly mean ground temperatures in Sichuan are lower from the 1960 s to the 1990 s,and higher from 2001 to 2014.Annual,seasonal and monthly mean ground temperatures display significant increasing trends at the 0.05 level.Changes of mean ground temperatures are larger and more unstable in winter,and more stable in summer.Spatial distribution of annual,seasonal and monthly trends and significance are not the same in the study area.The abrupt change of mean ground temperatures occurs in 2004 in autumn and 1999 in winter,and are not obvious in the other seasons.More anomalous years appear in spring.The periodic variations of annual,seasonal and monthly mean ground temperatures in Sichuan are significant,and the structure characteristics in different time scales exist differences.Annual,seasonal and monthly mean ground temperatures in Sichuan have stronger negative correlations with the longitude and the latitude,and significant positive ones with elevation.(2)The range of the difference between ground and air temperature(Ts-Ta)is smaller than that of ground temperature and air temperature,and there is an obvious peak near the 2.5 ?.It is the strongest in February and the weakest in May.The spatial distribution pattern of Ts-Ta in cool season,warm season and annual is banded from the west to the east.Analyzing the characteristics of cool season,warm season and annual mean Ts-Ta during the period from 1961 to 2014 through principal component analysis,the convergence is faster in cold season considering the comparison.For the first loading vector space(LV1)in cool season,warm season and annual,Sichuan Province is all positive value regions.For the second loading vector space(LV2)and the third loading vector space(LV3)of them,positive and negative regions are contrary from the northwest to the southeast,and they form multi-center regions.There is an decreasing pattern of time evolution that PC of Ts-Ta in year has on the first loading vector space,and monotonous increasing trend on the second and third loading vector space.Changes in cool and warm seasons are consistent with those in year.There is a negative correlation between Ts-Ta and the area of subtropical high in the western Pacific in Sichuan Province.Negative correlations between Ts-Ta and longitude(latitude)of subtropical high ridge in the western Pacific are displayed in most parts of the north and the edge of the south in Sichuan Province.The rest are positive correlations.(3)Annual and seasonal spatial distributions in ground temperature as well as air temperature have a great similarity.Significant positive correlations between ground temperature and air temperature at the 0.01 level are the largest in winter and the lowest in summer.Ground temperature and precipitation have contrary trends.The trend of precipitation is significant at the 0.01 level in autumn alone.The more precipitation is,the lower ground temperature is.There are positive correlations between seasonal sunshine duration and ground temperature and negative correlations between annual sunshine duration and ground temperature in Sichuan Province,but they are significant at the 0.01 level in spring and summer alone.The spatial distribution patterns of correlation coefficients and significance are not the same.There are positive correlations between wind velocity and ground temperature in summer and negative correlations in spring,autumn,winter and year.They are significant at the 0.05 level in autumn and year.Temperature extreme indices chosen in this study have better indicative functions concerning the changes of ground temperature.The negative correlations between ground temperature and precipitation indices,including annual precipitation,wet day precipitation and very wet precipitation indicate that the decrease of rainfall causes the reduction of soil moisture.Therefore,the energy using evaporation decreases,which causes soil temperature increasing.Consecutive dry days have also positive correlations with ground temperature and they are significant at the 0.01 level,indicating that the degree of drought is gradually strengthening with ground temperature increasing.(4)The trends of annual,seasonal and monthly mean ground temperatures in future will generally be the same as the past using R/S method and are likely to develop towards the extreme.The results of Hurst Index experiment show that annual,summer and winter ground temperature are no transitions,and that spring and autumn ground temperatures exhibit transitions.Similarly,Hurst Index experiment shows that there are abrupt points for ground temperature in February,March,July and November.(5)Integrated relevant research data on the basic of establishing the comprehensive evaluation model,the analysis prototype system of spatial and temporal variation in ground temperatures is exploited in Sichuan.Realize automation,intelligentialize and visualization of the ground temperature analysis based on GIS to provide the support for the model analysis of ground temperature in other regions.