Natural Environment

• • Hotter, drier summers and a growing population will put increasing pressure upon already limited water resources, potentially leading to more frequent drought management measures and negative impacts on the water environment.
  • Increasing London’s green space can help to cool the urban environment, improve air quality and help reduce surface water flood risk.
  • London’s habitats and biodiversity are expected to change as a result of climate impacts.

Green infrastructure

Whilst containing a densely populated urban area, London enjoys a remarkable amount of space for nature with two-thirds of its area occupied by green spaces or water. Of this about a third is made up of private gardens, a third parks or sports grounds and the remaining third a variety of habitats, including grassland, woodland and rivers.

As discussed in the Built Environment section, London is more vulnerable to heat than its surrounding areas due to the Urban Heat Island effect. There is evidence that green space reduces the urban heat island impacts as evaporation and transpiration from plants, and their shading effects, can cool the atmosphere.

In London monitoring of the urban heat island suggests that large parkland areas are typically 1˚C cooler than surrounding built up areas. This issue is already being tackled through the Mayor’s plans to enhance 1,000ha of green space in London by 2012, and to increase green cover in central London by five per cent by 2030 and a further five per cent by 2050.

Climate change is recognised as a serious threat to the presence of trees in urban areas in London. Not only would some species be vulnerable to changing weather conditions but also the potential increase in pests and diseases.

Drought is likely to influence the health, growth and productivity of London’s tree stock, and can ultimately cause tree mortality, often when in combination with other stresses such as pests and pathogens. This may have an adverse affect on the cooling effect of urban tree-planting programmes if the drought resistant types of tree are not used.

Trees in the right place, like other vegetation, intercept rainwater and reduce the rate and scale of eventual run-off. As a consequence, this reduces the risk of localised storm water flooding. The sponginess of leaf litter beneath broadleaved woodland can also improve water retention and infiltration. Conversely, inappropriate trees alongside rivers and watercourses can hinder river and stream flows and so cause flooding (although identified wet woodland habitats should be managed and conserved). The role of trees in soil shrinkage and subsidence, and the adequacy or otherwise of building foundations, needs to be understood and addressed, particularly given the shrinkable nature of London Clay soils.

London’s green space could become suitable for different tree species to those that are currently grown. The Mayor of London produced the Right Trees in a Changing Climate tool, which was designed to aid decision-making in planting regimes by incorporating projected climate change. This tool has now been transferred to the Forestry Commission’s Forest Research website.

Further information:

LCCP in collaboration with Victoria BID has produced a study to analyse and quantify the benefits that urban greening and in particular trees bring to Victoria. Read ‘Green benefits in Victoria Business Improvement District.’

Biodiversity

Climate change in London could affect biodiversity in two distinct ways: direct effects, such as changes in species composition due to higher temperatures; and ‘knock-on’ effects resulting from climate change adaptation actions.

• These changes are likely to include:
  • Lack of water to irrigate sites of nature conservation importance and other green spaces
  • Change in species composition in river, wetland and other habitats due to more frequent drought conditions
  • Change in species composition due to higher temperatures
  • Increased pressures on biodiversity from people using open spaces for recreation in hot weather
  • Increase in the area of natural or vegetated surfaces in the urban environment, with considerable flexibility to deliver biodiverse ‘greenery’, due to climate change adaptation actions that increase green cover
  • Increased pollution of watercourses due to flooding of sewers during intense rainfall events
  • Increased pollution of watercourses from wastewater discharges due to low river flows during drought
  • Change in habitats due to managed retreat and restoration of functional floodplains
  • Increased in algal blooms, some of which may be harmful to either biodiversity or humans if the food chain is affected.
  • Colonisation by new species from southern England and continental Europe. However, London’s habitats are highly fragmented;

It may be the case that otherwise suitable habitats cannot be colonised by new species owing to the inability of species to disperse to or through London.

Further information

LCCP’s report ‘Adapting to Climate Change: Creating Natural Resilience’ looks at how adaptation actions can respect and benefit London’s biodiversity.

Water supply

London is already in an area of Serious Water Stress. The large population in the South East of England combined with the relatively low level of rainfall means that the amount of water available per person is strikingly low in comparison to many hotter, drier countries.

Whilst supply is short, demand is also disproportionately high in London. Londoners now consume an average of 167 litres per day, compared to the national average of less than 150 litres per person per day. This increased consumption is primarily linked to affluence (more water consuming devices per home) and lower occupancy rates (smaller household units, such as flats, each with water consuming devices). An additional factor is that only one in four households in London has a water meter, and thus the majority have no incentive to save water and no opportunity to save money on their water bills.

Another factor in London’s increasing shortage of water is that nearly 600 million litres a day, a quarter of all the water distributed to London customers, is lost in leakage. This is the equivalent to an additional person’s demand in every home in London. This is because: much of London’s mains water network dates back to the Victorian era; subsidence and heave cause the pipes and joints to break (discussed further in the Built Environment section); and London clay is particularly corrosive and weakens the pipes.

• Climate change is expected to affect water availability by:
  • reducing river flows
  • reducing groundwater replenishment (‘recharge’)
  • increasing evaporation
  • increasing loss from broken water mains due to increasing subsidence
  • increasing demand for water from people and wildlife.

In the long term (2080s), estimates of the supply-demand deficit are very large (several times the total supply of the UK’s largest water company), indicating that major demand and supply-side measures could be required to maintain supplies in London at today’s level of risk.

Further information

The Mayor has developed a Water Strategy to tackle the issues that London faces with managing water