*2.1. Study Area*

Inner Hanoi was chosen as our study site. It is situated in the capital city of Vietnam, encompassing an area of 160 km2 (yellow polygon in Figure 1c). The studied location mainly comprises built-up areas, vegetation covers, and water bodies. The geographical location of the study area from a global view, to the national scale, to the regional scale is illustrated in Figure 1. The figure also depicts the boundary of Hanoi City before and after 2008, a composited Landsat 8 satellite image acquired on 4 June 2017, and locations of the meteorological stations Lang (yellow) and Ha Dong (orange) were used to acquire air temperature data.

In terms of population, Hanoi is inhabited by more than 7.7 million people (whole Hanoi as shown in Figure 1b) and it has a high population density (12,340 people/km2) in urban districts in 2015. As for climate, it is located in a tropical belt so that its summer lasts from May to August with a hot and humid atmosphere, abundant rainfall, and an average temperature of 29 ◦C. On average, July is the hottest month. Its annual average rainfall is 1680 mm, and the average temperature 23.6 ◦C.

**Figure 1.** Location of the study area: (**a**) Location of the study area in Vietnam; (**b**) detail of the study area with the boundary of Hanoi City before and after 2008; (**c**) inner Hanoi city (yellow polygon) on the composited Landsat 8 satellite image acquired on 4 June 2017, and locations of the meteorological stations Lang (yellow) and Ha Dong (orange) used to acquire air temperature data.
