Dynamic Variation Characteristics of NDVI in Dianchi Lake Basin and Its Response to Climate

Normalized Difference Vegetation Index（NDVI）is an important parameter to reflect change of forest vegetation.It is of great significance to analyze change trend and influencing factors of NDVI in Dianchi Lake Basin for accurately evaluating vegetation coverage and changes in recent years and analyzing driving factors of climate.Two data sets were used： monthly NDVI data of computer network information center geospatial data cloud platform from 2000 to 2015，and MOD13A2 products of NASA in 2020—2021.Trend analysis was used to analyze interannual and intra annual changes of NDVI in Dianchi Lake Basin.The data of precipitation and average temperature in Dianchi Lake Basin from 1999 to 2015 were downloaded from China Meteorological Data Network.Combined with NDVI data，correlation between NDVI and precipitation and temperature was analyzed respectively.Results showed that，during 2000—2015，the annual NDVI in Dianchi Lake Basin and in spring，autumn and winter showed an increasing trend，while annual summer NDVI showed a decreasing trend.However，the NDVI of Dianchi Lake Basin was small in 2020，and it showed a seasonal change trend during the year.On the whole，spatial distribution of vegetation in different areas of Dianchi Lake Basin was obviously different，showed a trend of increasing gradually from south to north and from west to east.The areas with high NDVI were concentrated in the upper reaches of river basin，while vegetation coverage in water body and its surrounding areas was low，and the NDVI in water body and its surrounding areas was decreasing.Precipitation and average temperature in Dianchi Lake basin were fluctuating，and precipitation in 2000—2015 was obviously declining.Through corresponding partial correlation analysis，it was found that precipitation and average temperature had a positive correlation with NDVI，and the strongest correlation was the average temperature and NDVI in the early stage （meteorological factors were one quarter ahead of NDVI）.On the whole，NDVI of Dianchi Lake Basin increased in time and space from 2000 to 2015，but it was smaller in 2020.In terms of climate response，change of average temperature three months ago played a major role in change of NDVI.