The search strategy will be based on that conducted for the original review but with improvements to include learning gained from the original review and to reflect developments in availability of potential sources and/or of searching technology.
A sensitive search of both published and unpublished sources will be conducted in order to capture as comprehensive and unbiased a sample of the relevant literature as possible. A three-step search strategy will be used in this review. An initial limited search of two key databases: Scopus and Medline will be undertaken followed by analysis of the text-words in relevant titles and abstracts, and of the index terms used to describe the papers.
A second search using all identified keywords and index terms will then be undertaken across all included databases. The third step will be reference list follow-up. The comprehensiveness of the search will be checked by examination of reference lists for any reviews found.
Papers published since December 2007 i.e. those published since the conclusion of the search for the original review, will be considered for inclusion in the review. No language limit will be applied. No document type or study type limits will be applied. No country limits will be applied.
Authors will be contacted for provision of any unpublished material, where suggested in an article, or missing data that may be relevant to the review.
The databases of different disciplines (environmental, ecological, public health) to be searched include:
Web of science
PROQUEST database: Environmental sciences and pollution management sub-files (Bangor University)
CAB (Commonwealth Agricultural Bureau)
Directory of open access journals
Copac: joint catalogue of of academic libraries
Index to theses online
Geo ref preview database
The searches will use free-text, keywords and subject indexing and combine the Greening and Climate change sets of terms. Search strings will be adapted for the different databases to allow for differing wild cards (*, $), word truncation (*) and proximity operators (“–”, adj, (-)).
Initial search terms to be used:
Street* or Cities or City or Town* or “Built environment”
‘Urban green*’ ‘Urban vegetat*
‘Urban open space*’
‘Urban park*’‘Urban ‘wood*’
A second phase of the search will use additional search terms e.g. built environment, city, cities, towns, street trees, plants, planting.
Google and Google Scholar search engines will be used. Websites of relevant organisations will be searched (Appendix).
Hand searching of electronic table of contents will be carried out for the following journals:
Social Sciences in Forestry
Urban Forestry and Urban Greening
Landscape and Urban Planning
Building and Environment
Article screening and study inclusion criteria
Citations captured from computerised databases will be imported into Endnote. In the first instance, the inclusion criteria will be applied to title only in order to remove spurious citations. Articles remaining after this filter will be screened by viewing abstracts and then full texts.
Hits from website searches will be filtered initially with the inclusion criteria on the title and abstract of articles (or introduction section if an abstract is not available). URLs for hits deemed relevant at title and abstract will be maintained within an Excel spreadsheet, and subsequently viewed at full text.
To assess and limit the effects of between-reviewer differences in determining relevance, at title, abstract and full-text stages, two reviewers will screen the same randomly selected sample of articles (sample size will depend on number of articles located by the search—a minimum of 10 % sample will be screened). The kappa statistic will be calculated, which measures the level of agreement between reviewers. If kappa is less than 0.6, the reviewers will discuss the discrepancies and clarify the interpretation of the inclusion criteria. Agreement will be reached through discussion. If necessary disagreements will be referred to a third reviewer. This may entail a modification in the criteria specification. Following this process one reviewer will then screen all items, applying the agreed new interpretation of, or modified, criteria. This process will be followed for both articles retrieved through the database and journal searches and those located through web-based searching.
Each article must satisfy each of the following criteria in order to be included after each filter. However, in cases of uncertainty, the reviewer will tend towards inclusion.
Urban temperatures, ground-level ozone or its main precursor concentrations (NOx and VOCs) and UV levels in any geographic location.
Human exposures to these variables or health-related outcomes in an environmental context of changes in these variables.
Types of intervention
Creation, enhancement or presence of green spaces in urban areas
Creation or enhancement of different types of urban greening
Enhancement of green spaces refers to any interventions that have changed the management of existing green spaces to increase the abundance of vegetation or area covered (e.g. additional planting). Green spaces would include any form of semi-natural environment (e.g. parks; green roofs) or plant species (e.g. trees) in urban areas. Urban areas would include any town or city including suburbs.
Types of outcome
Changes in quantitative measurements of the relevant subjects: temperature, ultraviolet (UV) and ground-level ozone or it’s precursors.
Changes in human exposures to these variables or recorded health outcomes in the context of these variables.
Types of study design
Only studies which include a relevant comparator will be included.
Examples of comparators
Relevant comparisons that would be investigated by a study would include:
The presence of green space versus the absence of green space
Creation versus no creation of green spaces
Enhancement versus no enhancement of green spaces
Changes in recorded outcomes after creation or enhancement of green space
One type of urban greening versus a different type of urban greening
A list of articles excluded at full-text, with reasons for exclusion, will be compiled.
Study quality assessment
The methodology for this review will follow that of Bowler et al. . The purpose of this process is to assess the risk of bias arising from study design or conduct and to identify confounding issues. The process will cover assessment and recording of details of the presence of a comparator (before/after intervention or control/intervention site), randomisation, identification and management of confounding factors, and replication. Studies which do not meet the minimum standard required in relation to unbiased sampling (e.g., random) and replication (e.g., sampling different sites at different times of day), will be excluded. One reviewer will appraise all included studies and a second reviewer will appraise a random sample of studies (size of sample will depend upon the number of included studies—a minimum of 10 % will be checked). The kappa statistic will be calculated and if less than 0.6, the reviewers will discuss the discrepancies. Agreement will be reached through discussion. If necessary disagreements will be referred to a third reviewer. All appraised studies will then be re-assessed by one reviewer in the light of the agreements reached. A summary of the findings of the study quality assessment will be compiled.
Data extraction strategy
Where possible, data will be extracted from each article and recorded in a spreadsheet. Data to be extracted will include the data on the outcomes, methodology and other factors that have been identified as reasons for heterogeneity. Data extraction forms will be the same as for the original review. Missing data (e.g. sample size or variance) will be calculated or inferred where possible from the summary statistics presented, or the authors contacted. Data will be extracted by one reviewer. A second reviewer will extract data from a random sample of articles (size of sample will depend upon the number of included studies—a minimum of 10 % will be checked). The consistency of data extraction will be examined and any reasons for variation identified. If necessary data extraction will be repeated to correct errors or inconsistencies. Extracted data files will be made available as additional files.
Potential effect modifiers or reasons for heterogeneity
Type of urban ‘greening’ and vegetation (low/high emitting vegetation)
Geographic location (latitude/altitude/longitude)
Degree of urbanisation (town or city, population density)
Extremity of the event (e.g. duration and intensity of a heatwave).
Empirical/modelling/different types of modelling approaches
This list was compiled for the original systematic review following consultation with the stakeholder group set up for the review. The findings of the review do not suggest that it needs altering for this update.
Random effects meta-analysis with calculation of Hedges g will be carried out on subsets of data, following the methodology of Bowler et al.  in order to update the meta-analysis conducted in the previous review. Sensitivity analysis will be run to explore the effects of including studies with different designs and methodological quality. Variation in effect sizes between studies will be explored using a priori reasons for heterogeneity. Specific attention will be given to the type of greening. The transferability of findings from studies under different climates will be considered.
In the previous review, quantitative synthesis was performed on only studies with comparators. Studies that were not suitable for meta-analysis were listed in appendices. We will follow the same procedure in the update.