Study On Spatio-temporal Variations Of Crop Planting Areas In The Valley Of Brahmaputra And Lhasa River And Nian-Chu River,Tibet,China

The Qinghai-Tibet Plateau is a sensitive region responding to global changes,and the global changes have brought significant impact on Qinghai-Tibet Plateau.The effect of global changes on the Qinghai-Tibet plateau is complicated which is becoming a popular research in recent years.A warm and humid climate would benefit to the crop production.The warming and wetting of the climate in the platea Qinghai-Tibet Plateau has greatly influenced its agriculture which resulted in the increasing of climateproductivity.Remote sensing(RS)technology which provided a new technology to analyze the spatial distrubiton of crop makes it possible to monitor the temporal-spatial change of the distribution of the crop.Crop-growing areas discrimination using RS is the basis of agricultural monitoring which is an important application for argriculture.The research on the distribution of the crop-growing areas can provide scientific basis for the regional crop production and the agricultural development planning,while it has great significance to the formulating policies of local governments and the sustainable development of the agriculture.This study is aimed to analyse space distribution characteristics of study area in 2000,2005,and 2010,and to research the correlationships in space between distribution characteristics,changes of crop-growing area and terrain & temperature,based on crops phenology information characteristics of Valley of Brahmaputra and Lhasa River and Nian-chu River extracted by MODIS-NDVI time series data and phenology characteristics information.The conclusions of study were deduced as following.The MODIS-NDVI based on time sequence can extract the phenological characteristics parameters of the crop in reseach region including the start time of growing season,the ending time of growing season,amplitude of the NDVI,NDVI curve left derivative,NDVI right derivative,NDVI growing season threshold of integral.With those phenological characteristics parameters,the distubution of the crop growing areas in 2000,2005 and 2010 was deduced by the decision tree method.The crop-growing areas extracted from the NDVI based on the phenological characteristics of crop showed great agreement to the validating data which all reached 92% above.The distribution area of crop-growing region in Valley of Brahmaputra and Lhasa River and Nian-chu River is approximately 3100 square kilometers,which is relatively less in the valley,and cover 1.2% of drainage area.Crops region is distributed dendritically and mostly focus on the mid-tail valley of Brahmaputra River and river valley of its main tributary(Lhasa River and Nian-chu River).And there are major differences in the distribution of space with the growing regions in the basin among every administractive district,and mainly distribute river valley in Nyingtri Prefecture 29%,Shigatse Prefecture 33%,Lhasa Prefecture 22%,Lhoka Prefecture 15%,other area are covered by rare rate.From 2000 to 2010,the area of stable crop-growing region in Basin of Brahmaputra and Lhasa River and Nian-chu River is about 3095 km2.There are both increasing and decending area of crop-growing region which scattered in the sptial distribution.The total area of crop-growing is declining but with a minor trend about 0.47%.The main crop-growing region distributed in the Lhasa、Nian-chu River and Shigatse Prefecture.The increasing and decending area in Nyingtri is relatively larger with a frequent change;Chamdo Prefecture is a new increasing crop-growing region.The increasing region is mainly in the north of Nyingtri which continuing increasing,while the decending region is mainly in the southwest of Nyingtri.Terrain factors decided the re-distribution of the water and heat on the surface of the earth largely,so it influenced the distrubiton and area of the crop-growing significantly.Crop-growing superior region are the region with lower altitude,gentler slope and sunny or half sunny slope.The crop-growing region distribute in the region with warm and sunny or half sunny slope,flat slope.Although the total area of the crop-growing areas in the Basin of Brahmaputra and Lhasa River and Nian-chu River from 2000 to 2010 is decending,the warming region show great agreement to the new crop-growing region which is ablout 37.58 km2 located in the south and north of Nyingtri.Above all,the areas of crop-growing region are increasing with the temperatures rising that make the climate warming and wetting.