The diurnal variation and inter-annual variation of urban heat island in Beibu Gulf Economic Zone were quantitatively analyzed, based on 2005-2014 MOD11A2 land surface temperature dataset, by the method of land surface temperature departure. Furthermore, the relationship between vegetation NDVI and urban heat island intensity were studied. Results showed: (1) Spatial distribution and extent of urban heat island in Beibu Gulf Economic Zone had a certain difference between daytime and nighttime in summer, the temperature departure decrease with distance from the city center increasing, and the decreasing trend of daytime was significant compared with nighttime. The temperature difference was about 4 to °C between the city and suburb in the daytime, and was about 2-6°C at night (2) The inter-annual variation intensity of urban heat island was not obvious in summer daytime during 2005-2014, while the difference of spatial distribution was significant. The urban heat island intensity increased in Nanning city during 2005-2011, and slowed in 2014. The heat island variation intensity was not obvious in Beihai city before 2011, but increased significantly in 2014. (3) The correlation coefficient between NDVI and land surface temperature in summer is -0.29, which showed high vegetation coverage plays an important role in reducing the urban heat island.
MOD17A3 NPP datasets from 2000-2010 and meteorological data were used to quantitatively analyze the spatial and temporal variations of vegetation NPP and its correlation with meteorological factors by using linear regression and correlation analysis methods in Guangxi. Results show: (1) the annual NPP ranged from 626 to 715 g C·m-2·a-1, with an average of 663 g C·m-2·a-1. The average annual vegetation NPP was higher in the west and east while lower in the middle and north part of the study area. The highest NPP (> 900 g C·m-2·a-1) mainly distributed in Baise, Chongzuo, Fangchenggang and Wuzhou. While the lowest NPP (<450 g C·m-2·a-1) mainly located in cities of Guigang and Hezhou. (2) In recent 11 years, the linear changing trend of NPP in Guangxi was decreased slowly. The regions of NPP with no significant difference (P>0.05), increased significantly (P<0.05) and decreased significantly (P<0.05) were respectively about 93.15%, 0.80% and 6.05% of the total study area. The area with an annual NPP decreased rate lower than -10% occupied 26.96% of the total study area, and the area with more than 10% NPP increment was 8.37%, and an unchanged area (NPP variation from -10% to 10%) accounted for 64.68%. (3) At the annual time scale, the correlations between vegetation NPP and temperature/precipitation were spatially various in Guangxi. The correlation of vegetation NPP with temperature was positive in 58.41% of the total area, and negative in the rest 41.59%, while its correlation with precipitation was positive in 38.16% of the study area, and negative for the other 61.84%. The above analysis indicated that temperature affecting vegetation growth more remarkable than precipitation.
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