## 3 Results and Discussion
### Response of Urban Heat Island Effect to Land Use/Land Cover Change  
#### 3.3.1 Spatial Correlation between LULC Types and NLST Levels  
Table 8 presents the minimum (MIN), maximum (MAX), average (MEAN) and standard deviation (STDEV) of NLST values for different LULC categories. Similar patterns were detected in all study years. Construction land was covered by the highest average NLST values, ranging from 0.43 to 0.65, followed by farmland (0.28-0.52), greening land (0.27-0.46) and water bodies (0.10-0.13). The significant difference in average NLST values between different LULC categories means that the UHI effect exists in all cases, which could be supported by the spatial consistence between the NLST patterns (Figure 2) and LULC distribution (Figure 4). Due to the impervious surface and associated materials, construction land is characterized by higher radiation absorption and greater thermal capacity [14,24]. Thus, extreme hot spots and heat islands were detected in construction land in all cases. In comparison, the other three natural land covers expressed relatively lower NLST values [26,27]. Among them, water bodies were covered by the lowest NLST values and defined as cool islands. There was an ongoing increase in the STDEV values for almost all the LULC categories from 1987 to 2016, indicating an increasing temperature difference within a certain LULC type. This is partly attributed to closer and closer interaction and interpenetration among different land covers [15,30]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Period** & **LULC Category** & **Farmland** & **Greening Land** & **Water Bodies** & **Construction Land** & **Total** \\ \hline \multirow{4}{*}{1987–1996} & Farmland & - & 5.8 & 28.6 & 90.4 & 124.8 \\  & Greening land & 7.2 & - & 1.3 & 11.0 & 19.5 \\  & Water bodies & 17.5 & 1.1 & - & 14.3 & 32.9 \\  & Construction land & 7.5 & 2.2 & 2.4 & - & 12.1 \\  & Total & 32.2 & 9.1 & 32.3 & 115.7 & - \\ \hline \multirow{4}{*}{1996–2007} & Farmland & - & 5.6 & 4.5 & 92.4 & 102.5 \\  & Greening land & 3.8 & - & 0.2 & 7.7 & 11.7 \\  & Water bodies & 34.3 & 7.5 & - & 48.5 & 90.3 \\  & Construction land & 19.1 & 2.0 & 0.5 & - & 21.5 \\  & Total & 57.2 & 15.1 & 5.2 & 148.5 & - \\ \hline \multirow{4}{*}{2007–2016} & Farmland & - & 3.8 & 2.1 & 88.1 & 94.0 \\  & Greening land & 2.8 & - & 0.7 & 10.8 & 14.3 \\ \cline{1-1}  & Water bodies & 0.5 & 0.3 & - & 6.1 & 6.9 \\ \cline{1-1}  & Construction land & 15.3 & 4.8 & 7.6 & - & 27.8 \\ \cline{1-1}  & Total & 18.5 & 9.0 & 10.5 & 105.1 & - \\ \hline \multirow{4}{*}{1987–2016} & Farmland & - & 4.9 & 5.7 & 218.3 & 228.9 \\ \cline{1-1}  & Greening land & 3.5 & - & 0.1 & 18.4 & 22.0 \\ \cline{1-1}  & Water bodies & 7.9 & 1.6 & - & 78.9 & 88.5 \\ \cline{1-1}  & Construction land & 4.1 & 3.2 & 0.4 & - & 7.7 \\ \cline{1-1}  & Total & 15.5 & 9.7 & 6.3 & 315.6 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Transfer matrix among different LULC categories during 1987–2016 in Wuhan (km\({}^{2}\)). To make the relationship between the NLST and LULC clearer, the area proportion of different LULC types was counted for each NLST level in the four observed years. Figure 6 shows that 74.5-98.1% of low temperature (level I) and 11.5-40.2% of sub-low temperature (level II) were distributed in water bodies. In other words, the Yangtze River, Han River and other large urban lakes were the main contributors to mitigating the UHI effect. However, 85.8-99.2% of high temperature (levels V) and 50.8-96.3% of sub-high temperature (level IV) were concentrated in construction land. The developed areas with dense buildings and interconnected road networks contributed the most to the UHI effect.