Study On The Change Characteristics Of Surface Dryness/Wetness And The Responses Of Terrestrial Ecosystems In China

Based on the surface meteorological database and the Chinese Digital Elevation Model(DEM),using spatial spline interpolation and temporal series method, we analyzed the spatio-temporal change characteristics of the surface Dryness/Wetness in china during 1954 to 2002.Further more,by using remote sensing imagery database,we preliminarily studied the responses of terrestrial ecosystems to climate change in china. The main conclusions of this study are:There was an obviously increasing trend of the temperature from 1954 to 2002 in china, about 0.26℃/10a.It increased most obviously in winter about 0.38℃/10a, and then autumn,spring and summer. When investigated in spatial patterns and seasonal differences, it increased much more obviously in northern than southern of china;and there was obviously increasing trend of spring and winter in Northeast China and North China;however,there was a little decreasing trend of summer in the south of Yangtze River,while significantly increasing trend of winter. On the whole, the total increasing trend of temperature in China ws comparable with that of global in the analyzed period, and the difference was presented on the little declining trend in part of Southwest China.There was an obviously decreasing trend of precipitation from 1960s to 1990s in china, and a recovery occurred in the late of 1990s, while in summer and winter precipitation were comparable with that in 1950s and 1960s. Furthermore, results also showed that precipitation presented clear regional spatial differences in the analyzed period: In North China, Central China, and southern of Northeast China, precipitation reduced persistently in the period we studies, while sharp increases occurred in the south of Yangtze River and in northern of Xinjiang, northern of Northeast China, and west of Tibetan Plateau, precipitation decreased from 1960s to 1970s, and had a relatively recovery in the 1980s. In the whole, the total declining trend of precipitation in China were comparable with that of global in the analyzed period, but regional variation patterns were opposite from global that precipitation increased obviously in the middle and high latitude regions, and decreased in the tropical and semi-tropical regions.We also calculated the spatio-temporal variations of surface Dryness/Wetness Index from 1954-2002 in china, by using the Penman-Monteith potential evapotranspiration model. Results showed that: the mean surface Dryness/Wetness Index distribution increased from southeast to northwest. The spatial patterns of variabilities were comparable with the precipitation from 1954-2002, Southeast China and Northwest China became wetter,North China and Northeast China significantly became droughter. When investigated in seasonal variations, southern of china became wetter in january and july, while North China became droughter in april, but it significantly became wetter in july and October in xinjiang province. When investigated in physical geographic regionalizations,the Dryness/Wetness Index reduced a little,that is it became wetter, in South China , Central China and SouthWest China,where the precipitation was much more than else regions in china;and the Dryness/Wetness Index increased a little, that is it became droughter, in Northeast China,North China,Neimeng and Tibetan Plateau,where the precipitation was relatively less in china.Northwest of china experienced a little warm/wet trend after1980s.Meanwhile,we analyzed the dry/wet shift variations during the analyzed period of the four typical warm/wet and warm/dry regions.After analyses of climate change and the surface Dryness/Wetness Index, based on the NOAA/AVHRR imagery database, we studied the responses of Terrestrial Ecosystems to climate change.According to our study, following conclusions are reached:Dryness/Wetness Index can acturally presented the surface vegetation cover.NDVI(Normalized Difference Vegetation Index) declined by forest-shrubland-grassland-desert steppe in the recent 20 years. There existed a logarithmic relationship between NDVI and Dryness/Wetness Index and precipitation.Under the climate base state, thermal conditions impacted the vegetation much more than water conditions in the regions where precipitation was surficient(Dryness/Wetness Index<5); while water conditions influenced vegetation much more than thermal conditions in the regions where precipitation was deficient(Dryness/Wetness Index>5). When investigated in seasons, water conditions affected the seasonal variations of vegetation NDVI much more than thermal conditions. Terrestrial vegetation activity were totally increasing for the last 20 years in china, and showed remarkale biological differences:forests NDVI decreased,while grasslands and desert steppes NDVI increased.It indicted that the vegetation activity in northern of china increased.For the last one, we investigated the changing trend of growing season duration of our contury, the results showed that over the study period, the green-up of vegetation has advanced in spring by 0.5 day/a, and the dormancy delayed in autumn by 0.05/a.The datas of onset are most significantly related with the mean temperature during the preceding 1.5 months, while the relation with precipitation was unremarkable.