Climate regulating ecosystem services: Introduction to urban microclimates

Transcription

1 Climate regulating ecosystem services: Introduction to urban microclimates Dr Gina Cavan April 2012

2 Outline Climate regulating ecosystem services Fundamentals of urban climatology Urban heat island effect Relevant studies from the literature Modelling impacts of urban microclimate Monitoring the urban microclimate

3 Climate regulating services House et al (2005: Ch13)

4 House et al (2005: Ch 13)

5 Focus on climate regulating services In particular: Today s presentation will focus on climate regulating services relating to temperature regulation; the water balance and related impacts including run-off Precipitation and evapotranspiration are not discussed in any detail Covered in detail by CLUVA hazards, risk and multi-risk assessment course, Naples, 2011; available on CLUVA website at Atmospheric motion (wind parameters) not included

6 Urban climatology Branch of climatology concerned with interactions between urban areas & atmosphere, impacts and processes Concept of scale is fundamental in understanding how urban environment interacts with atmosphere Much focus on urban canopy energy budget modelling

7 Surface radiation balance (Oke, 1987) Amount of reflected SW radiation depends on incident radiation ( ) and albedo (α) Amount of reflected LW radiation depends on atmospheric temperature & emissivity (in absence of clouds) Proportion of ( ) not reflected is absorbed and determine differences in radiation budget between local surfaces (in particular α& T 0 )

8 Surface energy balance (Oke, 1987) = turbulent transport of heat between surface & atmosphere (sensible heat) = heat released or absorbed when water changing state (latent heat; evaporation flux) = heat transferred from or to soil below the surface (Flux = rate of flow of some quantity)

9 Surface energy balance in urban areas (Oke, 1987) Q F energy flow directly controlled by human decisions; depends on average energy use per person and population density In some cities Q F is greater than Q* Reduced evapotranspiration, resulting in energy into sensible forms Q H and Q s Greater urban storage due to greater surface area for absorption due to geometry, reduced latent heat, etc.

10 Radiative properties of natural materials (Oke, 1987)

11 Urban heat island effect Urbanisation alters thermal properties through: Changing albedo (reflectance of solar radiation) Vegetation cover Surface geometry (important for wind moderation) Building mass, and Anthropogenic heat emissions

12 Albedo Most influential property in the formation of UHI Albedo of vegetation much greater than urban structures (US EPA, 1999)

13 Causes of urban heat islands

14 Characteristics of UHI #1 Related to the size of a city strong relationship between population and maximum heat island intensity (Oke, 1987) Strong correlation between geometry of street canyons in city centres & maximum UHI intensity Surface heat islands show similar spatial and temporal pattern to air temperature within urban canopy later. Surface temperatures more strongly related to site characteristics such as sky view factors

15 Characteristics of UHI #2 Average percentage differences between urban and rural areas Annual Cold season Warm season Solar radiation -22% -34% -20% Temperature Humidity Rainfall Thunderstorms (from Briggs and Smithson, 1997)

16 Urban heat island effect & population (Roth, 2007)

17 Water balance On land: In urban areas: Water input into urban system greater due to Fand I(ignoring irrigation), there is no counterpart in rural areas Urban Eand sub-surface storage,, are less than rural areas due to replacement of vegetation by impervious materials with poor infiltration Therefore urban runoff,, is greater in urban areas. (Oke, 1987)

18 Monitoring and modelling evaporation Measuring: Hydrological Water balance pans Atmometers Lysimeters Vegetation (porometer) Meteorological Eddy Correlation Bowen Ratio Modelling: One-step model Penman-Monteith Two-step model Energy (Thornthwaite, Blaney-criddle) (Source: Prof. Clive Agnew, UoM) CLUVA course on Hazard, Risk & Multi-risk assessment, Naples, Module 3.2 Drought

19 Studies on urban microclimate relevant to African cities CLUVA D2.6: A database of international evidence on ecosystem services of urban green infrastructure Evidence from relevant climate zones to African case studies >30 entries for climate regulating services Dropbox: CLUVA WP2/T2.2/Database

20 Urban modification of the surface energy balance in Ouagadougou UHI characteristics in tropical semiarid cities: Strong seasonal differences between wet and dry seasons Maximum intensity reached during dry season, though wet & dry heat islands may exist Seasonal changes caused by seasonal variation in thermal characteristics of rural surfaces Results: Low thermal mass of sheet metal roof used in residential areas reduces heat storage relative to concrete roofs in urban centre Unplanned peri-urban development may have lower impacts on local climate than planned developments in the city If urbanisation leads to more paving, increasing height and density of buildings will lead to higher night-time urban temperatures (Offerle et al. 2005)

21 (Offerle et al. 2005)

22 (Offerle et al. 2005)

23 Urban greening Urban greenspaceoffers potential to help adapt cities for climate change (Gill et al., 2007; Bowler et al. 2010). Urban greenspace can help to mitigate flooding: Reduces rate & volume of surface water runoff as rainfall is intercepted by vegetation Urban greenspace can help to moderate microclimate: Cooling through evapotranspiration Storing & re-radiating less heat than built surfaces Direct shading

24 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Modelling: potential application of land cover analysis Cultivated crops Grasses Palm trees Small trees Large trees Water Sand Bare ground/ soil Land cover types (%) 1.2 Field crops 1.3 Mixed farming 2.2 Mixed forest 2.3 Riverine, 2.4 Mangrove 2.5 Bushland 3.1 Mineral 4.1 Parks 4.2 Stadium 4.3 Beach 4.4 Other open 4.5 Sports ground 5.1 Major road 5.3 Rail 5.4 Port 5.5 Bus stations 6.1 Energy 6.2 Water tanks 6.4 Cemeteries 7.1 Condominium 7.2 Villa & single Mixed 7.5 Scattered 8.1 Education & 8.2 Medical 8.3 Religion 8.4 Institutional 9.1 Malls 9.2 Formal 9.3 Open markets 9.4 Mixed formal 10.1 Manufacturing 10.2 Offices 10.3 Storage & 10.4 Garages 13.1 Marsh/swamp 14.1 Hotels 14.2 Entertainment 15.1 Military

25 Modelling impacts: The STAR Tools

26 Surface temperature tool #1

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28 Surface temperature tool #2

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30 Surface temperature tool #3

31 Presenting outputs: Surface temperature

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34 Runoff tool #2

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36 Runoff tool #3

37 Presenting outputs: Runoff

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39 Monitoring urban microclimates Separate workshop/small group session to discuss monitoring in case study locations (potentially on Thursday afternoon) Including discussion of: Equipment Site selection Sampling techniques Important considerations (e.g. calibration, correcting physical environment effects)

40 References / further reading Bowler et al. (2010). Urban greening to cool towns and cities. A systematic review of the evidence. Landscape and Urban Planning 97(3): Gill (2006). Climate change and urban greenspace. PhD thesis, University of Manchester. House et al (2005). Chapter 13: Climate and air quality. In: Hassan et al. Ecosystems and Human Well-being: Current State and Trends. Volume 1 Millennium Ecosystem Assessment. Oke(1978). Boundary layer climates. Routledge. Roth M. (2007). Review of urban climate research in (sub)tropical regions, Int. J. Climatol., 27, Smith et al (2011). Climate regulating services. In: The UK National Ecosystem Assessment Technical Report. UK National Ecosystem Assessment, UNEP-WCMC, Cambridge US EPA (1999). Heat island, Other resources: Case studies in international evidence database available on dropbox STAR tools