Project 3: Green Cities and Micro‐Climate Rationale The urban atmospheric environment is a unique three‐dimensional adjustment to massive anthropogenic alterations of the natural surface and atmosphere that transform the natural aerodynamic, radiative, thermal and moisture regimes of the local area. Because of enhanced sensible and reduced evaporative turbulent heat fluxes, urban climates are generally characterised by a warmer and drier atmosphere, although magnitudes and directions of change vary spatially and temporally (Sturman and Tapper, 2005). In other words, the Urban Heat Island (UHI) (Figure 3.1). Figure 3.1: Melbourne’s Urban Heat Island (UHI) – ‘The AGE’ Nov 15, 2004. It is interesting to note that the magnitude of urban warmth (i.e., maximum urban heat island) imposed on the environment is of the same order as some of the most pessimistic predictions of global warming through the 21st century (e.g. Melbourne’s maximum observed heat‐island intensity is 7.0ºC (Torok et al., 1996), so are effectively superimposed on global warming. With rapidly increasing levels of urbanisation in Australia and around the world, there are important implications of such trends for human thermal stress, and health in particular (see for example Nicholls et al, 2007). Moreover, this situation will be exacerbated by the likely increase in thermal extremes under projected climate change (Meehl et al., 2007) including hot days and heat waves. WSUD and Project 3: Green Cities and Micro‐Climate Page 1 stormwater reuse provide a potential mitigation tool for the UHI and global climate change. In addition, this will influence water runoff, infiltration, drainage and soil moisture that interacts with urban stream water regimes, vegetation growth (carbon sequestration) and resilience (P4). Aim and Key Questions The aim of this project is to identify the climatic advantages of stormwater harvesting/reuse and water sensitive urban design at building to neighbourhood scales. The objectives of Project 3 are to: (1) determine the micro‐climate processes and impacts of decentralised stormwater harvesting solutions and technologies (link to Project 1) at both household and neighbourhood scales; (2) assess the impacts of these solutions on human thermal comfort and heat related stress and mortality (link to Project 5); (3) establish the impacts of the solutions on urban hydrology feedback to stream ecology (link to Project 4); (4) provide stormwater harvesting strategies to improve the urban climate and benefit the carbon balance of cities; and (5) project the likely impact of climate change on local urban climate, with and without stormwater reuse as a mitigation strategy (link to Project 2). Proposed Approaches and Methods We will use a combination of observational and modelling approaches at different scales to address these questions. Figure 3.2 maps the activities of this project and illustrates the inter‐relationships between this project and the activities of several other projects. In the early stages of the project, we will identify existing urban environments with expected differences in micro‐climate human thermal comfort levels as empirical templates for calibrating a micro‐climate model. Sites in major Australian cities will be selected to capture the different climatic regions in Australia. These templates will encompass block and neighbourhood scales and will include examples of conventional urban designs in high and medium density environments (e.g. CBD and suburban areas). Monitoring of micro‐climate human thermal levels will be undertaken for each of these templates. Project 3: Green Cities and Micro‐Climate Page 2 Large scale impact of WSUD and/or urban
planning
Forcing.
Supply, risk,
scenerios
Large scale climate, climate change and variability (link to P2)
Scenarios/
Technology
options
Water Sensitive Urban
Design
STORMWATER (link to P1)
Impact on human
thermal comfort
and health (Bot
simulation)
Link to P5
Bot
simulations
Microclimate response
Building scale using
micromet model (Temp,
Humidity, etc.) (Beringer)
Microclimate response at
Neighbourhood scale using
TEB (or similar)
Response at City
scale using
ACCESS (or
similar)
Observations:
Validate building scale model using microclimate sensor and radiation
equip. Neighbourhood scale use EC flux towers. Water balance of urban
landscapes including profiles (Beringer & Tapper)
OUTP
UTS
WATER BALANCE
Evapotranspiration (water
losses)
Soil moisture, infiltration,
runoff
(Links to P3)
VEGETATION
Microclimate
(feedback to plant
growth)
Plant growth –
Carbon
sequestration
Increasing Scale
Figure 3.2: Conceptual design and integration of microclimate aspects and WSUD Household scale At the household scale, the emphasis will be on measuring response variables above active surfaces (e.g., temperature, humidity, and surface radiative temperature using microsensors). A microscale 3D turbulence model (ENVIMET) (Bruse, 1999) will be validated using this observed data (e.g. Figure 3.3, left). We will then use the model to assess the impacts of various WSUD strategies and the influence of stormwater reuse (irrigation) on urban climate for household to neighbourhood scale. In addition, the calibrated micro‐climate models will be used to inform the design of demonstration projects (Project 8) in collaboration with other project researchers. Monitoring of the performance of these demonstration projects will be undertaken to verify the micro‐climate performance of the modelling. Project 3: Green Cities and Micro‐Climate Page 3 Figure 3.3: Left: An example of the microscale urban climate model applied in Brunswick, Melbourne, showing expected temperatures of people Right: Typical Flux tower instrumentation over an urban area in Preston, Melbourne Neighbourhood scale At the neighbourhood scale, micrometerological flux towers will be established (Figure 3.3, right). These towers will measure the surface energy balance (radiation, sensible heat flux, evaporation from the ground and transpiration from vegetation) along with the exchange of carbon dioxide. A suite of environmental and climate measurements will be made concurrently with the flux measurements and will include full solar and terrestrial radiation balance, air temperature, vapour pressure, atmospheric pressure, wind speed (at various heights to define roughness lengths), and wind direction (to determine fetch). These measurement systems will be implemented at the demonstration sites (link to Project 8). The ENVIMET model (Bruse, 1999) will give outputs up to the neighbourhood scale and for neighbourhood scale to suburban/regional we will use the Town Energy Balance (TEB) model (Masson et. al., 2002) which can be implemented in a regional climate model (link to Project 2). Remote sensing of surface temperature and other parameters (NDVI/fluxes) will also be undertaken. Catchment scale We will use a powerful integrating framework (Catchment Modelling Framework, CMF) developed as part of a $14 million EcoTender program at the Victorian State Department of Sustainability and Environment. This framework accesses the unique state geospatial datasets that provide all the inputs (soil type, vegetation type, groundwater, river flow, climate, etc.) for modelling in the urban Project 3: Green Cities and Micro‐Climate Page 4 environment at 20m spatial resolution. The CMF consists of a range of sub models that are effectively plug and play. The CMF also provides a unique toolbox for analysis and production of policy relevant outputs. We will use the extensive research program (above) to improve and validate the underlying datasets and models. Integration of Research Efforts with Other Projects As illustrated in Figure 3.2, Project 3 interacts actively with Project 1 in iteratively defining systems that are effective in improving stormwater quality while having characteristics that positively influence micro‐climates. Technologies such as impervious pavements will be measured and modelled. Various WSUD strategies will also be simulated to assess the effectiveness. Outputs from this project will inform the further design of technologies in Project 1. The influences of micro‐climate on regional‐scale weather conditions are captured through interaction of the activities of this project with those of Project 2. Project 2 will supply the meteorological forcing (rainfall, temperature, humidity, wind speeds and solar radiation) for the current period as well as for projected climates in 2050 and 2100. The micro‐climate model developed, calibrated and verified in this project will also form an important module in the Water Sensitive City Simulation Model developed jointly in Project 8. An important output from the microscale model and flux tower observation will be a full energy balance that includes evapotranspiration. This is a critical parameter for the surface water balance (infiltration, runoff, drainage, soil moisture storage). The runoff and drainage will supply the streams, which links explicitly to Project 4. The soil moisture store is important for increasing evaporative cooling and mitigating excess urban heat. It is also important in sustaining vegetative growth and production that is crucial in sequestering carbon dioxide. Spaces in the public domain are essential features of public amenities. However, these urban landscapes must be functional beyond providing spatial amenities. Our knowledge of the traditional ‘values’ of open spaces and landscape features needs to be bolstered with an understanding of the ‘ecological functioning’ of the urban landscapes that capture the essences of sustainable water management and micro‐climate influences. This project adds a further dimension to the traditional design considerations of WSUD and is an important water sensitive prelude into building sustainable cities. Project 3 will directly input to the activities of Project 8. Project 3: Green Cities and Micro‐Climate Page 5 References Bruse, M. (1999) Modelling and Strategies for improved urban climates. Invited Paper, In: Proceedings International Conference on Urban Climatology & International Congress of Biometeorology, Sydney, 8‐12. Nov, Australia, 6 pages. Masson, V., Grimmond C.S.B., and Oke T.R. (2002) Evaluation of the Town Energy Balance (TEB) Scheme with Direct Measurements from Dry Districts in Two Cities. J. Appl. Meteor., 41, 1011–
1026. Meehl, G.A., Stocker T.F., Collins W.D., et al. (2007): Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Nicholls N., Skinner C., Loughnan M. and Tapper N. (2007) A simple heat alert system for Melbourne, Australia. International Journal of Biometeorology (accepted October 2007) Sturman, A. and Tapper N. (2005) The Weather and Climate of Australia and New Zealand, 2nd edition, Oxford University Press, Melbourne, 541 pp. (ISBN 9 78019558 4660, ISBN 0 19 558466 X). Torok S., Gallo K., Morris, C. et al. (1996) The effect of the urban heat island on the climate of southeast Australia. International Journal of Climatology. (ref. to be supplied) Project 3: Green Cities and Micro‐Climate Page 6