# Spatiotemporal Dynamics of Net Primary Productivity in China's Urban Lands during 1982-2015
## 3 Results
### Changes in Multiple Variables Affecting NPP in Three Urban Agglomerations in China  
In addition, we analyzed changes in multiple variables including the annual cumulative precipitation, the annual average air temperature, the annual cumulative sunshine duration, and the proportion of vegetation in the urban lands, 5 km buffer zone, 10 km buffer zone, and 20 km buffer zone of the BTHUA, the YRDUA, and the PRDUA (Figure 10).  
Figure 9: The NPP trends in the buffer zones ( 5-20 km) based on urban lands in 2015 between 1982 and 2015 in **(a)** the BTHUA, **(b)** the YRDUA, and **(c)** the PRDUA. The mark (***) indicates a relative level of significance where \(p<0.001\), and the mark (**) indicates a relative level of significance where \(p<0.01\).  
In the BTHUA, precipitation, sunshine duration, and proportion of vegetation all showed a decreasing trend, while temperature showed an increasing trend. Specifically, the average annual cumulative precipitation in the BTHUA was less than in other urban agglomerations. From urban lands to the 20 km buffer zone, the decreasing trend of precipitation was accelerated from \(-1.75\) mm/yr to \(-4.51\) mm/yr. In addition, the increasing trend of temperature slowed down, from 0.050 \({}^{\circ}\)C/yr to 0.047 \({}^{\circ}\)C/yr. The sunshine duration decreased significantly, and the decreasing trend was the fastest in the 5 km buffer zone, which was \(-12.23\) h/yr. In the BTHUA and its buffer zones, cropland accounted for the vast majority of vegetation. With urban expansion, the proportion of vegetation in urban lands was rapidly decreasing at a rate of \(-1.27\%\)/yr. From the 5 km to 20 km buffer zone, although the proportion of vegetation still showed a decreasing trend, the rate of decrease was relatively low, which was only \(-0.27\%\)/yr in the 20 km buffer zone.  
Figure 10: The annual cumulative precipitation, the annual average air temperature, the annual cumulative sunshine duration, and the proportion of vegetation in the BTHUA, the YRDUA, and the PRDUA.  
In the YRDUA, the precipitation showed a decreasing trend. Although the decreasing trend of precipitation was faster than that in the BTHUA, the average annual cumulative precipitation was higher than that in the BTHUA. The temperature showed an increasing trend. From urban lands to the 20 km buffer zone, the increasing trend of temperature was slowed down, from 0.061 \({}^{\circ}\)C/yr to 0.056 \({}^{\circ}\)C/yr. The sunshine duration in urban lands and buffer zones had a similar decreasing trend, and the rate decrease was slower than that in the BTHUA. For the proportion of vegetation, it decreased at a rate of \(-\)1.78%/yr in urban lands. Although the rate of vegetation reduction slowed down from \(-\)0.81%/yr in the 5 km buffer zone to \(-\)0.48%/yr in the 20 km buffer zone, it was still faster than that in the BTHUA.  
In the PRDUA, the precipitation showed an increasing trend in urban lands, but it showed a decreasing trend in the buffer zones. The temperature in urban lands was higher than that in the buffer zones, and they increased at almost the same rate (around 0.04 \({}^{\circ}\)C/yr). The sunshine duration showed a decreasing trend, and its decreasing rate was the slowest among the three urban agglomerations. Moreover, forest and cropland were the main vegetation types in the PRDUA, and the proportion of forest was higher than that in other urban agglomerations. It was obvious that urban expansion had a great impact on the vegetation in the PRDUA. Whether in urban land or its buffer zones, the proportion of vegetation decreased rapidly. Even in the 20 km buffer zone, the proportion of vegetation was still decreasing at a rate of \(-\)0.54%/yr, which was higher than that in other two urban agglomerations.