Holistic approach to assess co-benefits of local climate mitigation in a hot humid region of Australia

Abstract

Overheated outdoor environments adversely impact urban sustainability and livability. Urban areas are particularly affected by heat waves and global climate change, which is a serious threat due to increasing heat stress and thermal risk for residents. The tropical city of Darwin, Australia, for example, is especially susceptible to urban overheating that can kill inhabitants. Here, using a modeling platform supported by detailed measurements of meteorological data, we report the first quantified analysis of the urban microclimate and evaluate the impacts of heat mitigation technologies to decrease the ambient temperature in the city of Darwin. We present a holistic study that quantifies the benefits of city-scale heat mitigation to human health, energy consumption, and peak electricity demand. The best-performing mitigation scenario, which combines cool materials, shading, and greenery, reduces the peak ambient temperature by 2.7 °C and consequently decreases the peak electricity demand and the total annual cooling load by 2% and 7.2%, respectively. Further, the proposed heat mitigation approach can save 9.66 excess deaths per year per 100,000 people within the Darwin urban health district. Our results confirm the technological possibilities for urban heat mitigation, which serves as a strategy for mitigating the severity of cumulative threats to urban sustainability.

Figure 1

Main methodological approaches and framework used in this study.

Figure 2

Cumulative frequency distribution of T_a, relative humidity and hourly ΔT(_{urban-suburban}) over a year (a), box plots of T_a, wind speed and maximum ΔT(_{urban-suburban}) (b).

Figure 3

The range of ambient temperature and air temperature reduction: T_a,MAX (red marker) and T_a,MIN (blue marker) (a), ΔT_a,MAX (°C) (blue marker) and the MAX ΔT_a (red marker) (b). REF (unmitigated), ALB_SH_G (Albedo, greenery and shading), ALB_SH_G_W (albedo, shading, greenery and water), SH (shading), CP (cool pavement), ALB 40% (albedo 0.4), ALB 60% (albedo 0.6), CR (cool roof), G 20% (greenery 20%), G 30% (greenery 30%), W (water), GR (green roof).

Figure 4

Spatial distribution of T_a in each mitigation scenario against that in the reference condition under the prevailing summer condition: ALB_SH_G (a), ALB_SH_G_W (b), SH (c), CP (d), ALB 40% (e), ALB 60% (f), CR (g), G 20% (h), G 30% (i), W (j), GR (k).

Figure 5

∆T_a, _MAX calculated under NW5 = North-Westerly wind of 5 m/s, SE5 = South-Easterly winds of 5 m/s, NW1 = North-Westerly wind of 1 m/s, SE1 = South-Easterly winds of 1 m/s.

Figure 6

Cooling load of the residential (a) and office (b) buildings.

Figure 7

Electricity demand and absolute savings in the green mitigation scenario (a,b), cool materials scenario (c,d) and combined scenario (e,f).

Figure 8

Calculated impact on the annual cumulated anomalies in morbidity and mortality per 100,000 population in the unmitigated and the mitigated scenarios the Darwin Urban Health District, and the Urban and Rural Health Districts.