| Since the 20th century,the environmental effects brought about by increased average temperature globally have attracted attention widespread.The climatic conditions determine scope of crop planting and temperature and precipitation are extremely important for crop growth.In 2013,China's National Strategy for Adaptation to Climate Change proposed that it was necessary to make full use of the favorable conditions of warming to develop high-altitude valley agriculture in the ecological barrier area of the Qinghai-Tibet Plateau.The Yarlung Zangbo River,Nyangqu River and Lhasa river(YLN)region in Tibet was sensitive for global climate change and the most important food crop production area in the Qinghai-Tibet Plateau.It was useful to analyze the correlation between the distribution of arable land crops in Tibet and the climatic environmentfor providing references of adaptive climate change for farmers and herdsmen in Tibetan areas and for formulation of government-related agricultural adaptation policies with a view to providing advice for protection of high-quality cultivated land,food security,and adaptation to climate change.In order to reveal the changes of cropping areas in the context of climate change in the Yarlung Zangbo River,Nyangqu River and Lhasa river(YLN)region in Tibe,in this paper we firstly divided the temperature,precipitation,and accumulated temperature data of?10?in growing season from May to September of 39meteorological stations during period from 1989 to 2014 into four stages as from 1989to 1999,1994 to 2004,1999 to 2009,and 2009 to 2014 respectively.During the four periods,the temporal and spatial distribution and change characteristics of the three meteorological elements were analyzed in different stages of the watershed.Then based on multi-temporal Landsat satellite data,maps of crop production areas in the Yarlung Zangbo River,Nyangqu River and Lhasa river(YLN)region in Tibe were generated in2000,2005,2010 and 2015,and changes in the cropping areas were analyzed in terms of changes in total area,rate of change and dynamics,and changes of the center.On this basis,the correlation between the distribution of cultivated land and the temperature,precipitation,and accumulated temperature at or above 10?in the growing season and the correlation between distribution of cultivated cropland and topography and soil types were studied.The main conclusions were listed as following.(1)The Yarlung Zangbo River,Nyangqu River and Lhasa river(YLN)region in Tibet,the annual variation of the temperature in each stage of the growth season from1989 to 2014 is relatively large,showing a growth trend of 0.56?/10a,and the cumulative temperature of 10?or more is increasing at a rate of 108.7?/10a.There was a slow upward trend in fluctuations,and there were significant differences between the interannual changes and the changes at each stage.In terms of spatial distribution,the temperature in the growing season was low in the northwest and high in the southeast.The highest accumulated temperature?10?occured in the Nyingchi region in the southeastern part of the basin,and the least accumulated temperature region appears in the Ali region.Precipitation gradually increases from west to east and slowly from north to south.Incremental,spatial distribution was uneven and regional differences were large.The average temperature in the four growing seasons was11.34?,11.49?,11.71?and 12.10?,showing an upward trend.The accumulated temperature of?10?was 1344.55?,1391.98?,1431.66?and 1489.53?,respectively.It also showed an upward trend.Precipitation was concentrated in 400-600mm.(2)The Yarlung Zangbo River,Nyangqu River and Lhasa river(YLN)region in Tibet showed a growth trend in the recent 15 years.From 2000 to 2015,the crop area increased from 2915.09 km~2 to 2970.04 km~2,and the increase total area is 54.95 km~2,and the area ratio increased from 1.12%to 1.14%.The annual change rate,change amount,and dynamic degree of the crop area also showed an upward trend from 2000 to2015.The annual variation in the first phase was 2.87 km~2,and that in the third phase rose to 4.34 km~2.The annual change rate from the first phase to the third phase was 0.57.The percentage rose to 0.86%and the dynamics of the basin cultivated land were>0 in the period from 2000 to 2015.The centroid latitude of the crop-planting area moved from 29°18'6"N in 2000 to 29°23'38"N in 2015,and the trend of centroid to high-latitude movement was obvious.(3)There were significant correlation between the distribution of crops per unit area of basin and the growing season temperature and?10?accumulative temperature with p values of 0.831 and 0.834,respectively.But there was no significant correlation with precipitation.And there were similar correlation between changes in crop planting areas and the temperature in the growing season and?10?accumulated temperature with p values were 0.991 and 0.997 respectively,and no significant correlation with precipitation changes.(4)More than 90%of the crop growing areas in the river basin were located in areas with low topography;during the study period,the distribution of cultivated land crops continued to higher elevations,and higher slope expansion.There are 25 soil types in the crop cultivation area of the river basin,mainly brown-cold calcareous soil,cold-calcite,fluvo-aquic soil,brown soil and fluvo-aquic soil.The area of brown-cold calcareous soil accounted for 37.69%of the total soil types. |
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