*2.4. Urban Planning Strategies*

The impact of the redevelopment and the construction of additional residences was evaluated for two urban districts. One district was a residential area consisting of low- and mid-rise buildings located in the southwestern part of The Hague, referred to as "The Hague Southwest" (Figure 3A). The other district was located near the center of The Hague and mainly consisted of a relatively old business area and newer high-rise commercial buildings. This area is scheduled for redevelopment, and is referred to as the Central Innovation District (CID) (Figure 3B). The densification of this district is much larger than that of The Hague Southwest, because of the larger building assignment.

The building assignments of the districts could either be achieved by building on currently green spaces or by replacing the existing low- and mid-rise buildings with high-rise buildings. This will either reduce the vegetation fraction or raise the SVF, which will consequently increase the UHImax. This choice and the alternative of building residences in surrounding green corridors were examined using five distinct urban planning strategies shown in Table 1.

**Figure 3.** Theoretical building assignment for districts of The Hague Southwest (panel **A**) and the CID (panel **B**). The building assignment is indicated for different neighborhoods within brackets, and the number above the brackets indicates the current number of residences in the neighborhood. The pink areas in panel A indicate green corridors which were built using strategy C. The white numbers label the different neighborhoods.

**Table 1.** Five urban planning strategies that complete the building assignments for The Hague Southwest and the Central Innovation District (CID). The enumeration starts with B, in accordance with the panels in Figures 8 and 10. Panel A in these figures represents the current housing.


In this study, the building assignment was expressed as a change in the SVF and/or vegetation fraction in order to estimate the changes in the UHI (see Equation (1)). Hence, as a first step, we had to determine the numerical relationship among the density of the residences [27], the SVF, and the vegetation fraction (fveg) for the current building volume of the agglomeration of The Hague. This is expressed as

$$\text{Residences per km}^2 = -213(\pm 19)\text{SVF} - 200(\pm 30)\text{f}\_{\text{veg}} + 1.85(\pm 0.04)(\text{SVF} \times \text{f}\_{\text{veg}}) + 22687.\tag{5}$$

Figure 4 shows the empirical relationship among the density of the residences, the SVF, and the fveg in a three-dimensional (3D) plot. Herein, the SVF and the fveg are denoted in percentages. The ranges used for this relationship vary between 52–99% and 11–93% for the SVF and the fveg, respectively. For the CID, it was necessary to extrapolate to a minimum SVF of 22% and a vegetation fraction of 5% to meet the requirements of the high density of residences. Note that the population density does not currently occur in the agglomeration of The Hague. The UHImax equation (Equation (2)), however, was tested for highly urbanized areas [20]; thus, it can deal with the planned densification for the CID. The values used for the SVF, the fveg, and the density of residences for the five urban planning strategies can be found in Tables A1 and A2 in Appendix A.

**Figure 4.** Empirical relationship among the density of the residences [27], the sky-view factor (SVF), and the vegetation fraction for the agglomeration of The Hague presented on a three-dimensional (3D) surface (R<sup>2</sup> = 0.64). Areas with more than one-third non-residential buildings were removed from the analysis. Areas with a population density below 750 per km2 were also removed. The black line and the black dotted line indicate the equilibrium between the slopes of the vegetation fraction and the SVF. The grid resolution used is 500 m.
