Ecological connectivity in the three-dimensional urban green volume using waveform airborne lidar

This is the final version. Available on open access from Nature Research via the DOI in this record.The movements of organisms and the resultant flows of ecosystem services are strongly shaped by landscape connectivity. Studies of urban ecosystems have relied on two-dimensional (2D) measures of greenspace structure to calculate connectivity. It is now possible to explore three-dimensional (3D) connectivity in urban vegetation using waveform lidar technology that measures the full 3D structure of the canopy. Making use of this technology, here we evaluate urban greenspace 3D connectivity, taking into account the full vertical stratification of the vegetation. Using three towns in southern England, UK, all with varying greenspace structures, we describe and compare the structural and functional connectivity using both traditional 2D greenspace models and waveform lidar-generated vegetation strata (namely, grass, shrubs and trees). Measures of connectivity derived from 3D greenspace are lower than those derived from 2D models, as the latter assumes that all vertical vegetation strata are connected, which is rarely true. Fragmented landscapes that have more complex 3D vegetation showed greater functional connectivity and we found highest 2D to 3D functional connectivity biases for short dispersal capacities of organisms (6 m to 16 m). These findings are particularly pertinent in urban systems where the distribution of greenspace is critical for delivery of ecosystem services.This work was funded under the NERC Biodiversity and Ecosystem Services Sustainability (BESS) thematic programme for the ‘Fragments Functions and Flows in Urban Ecosystems’ project (Reference: NE/J015237/1; http://bess-urban.group.shef.ac.uk/). The waveform ALS data were acquired by the NERC Airborne Research and Survey Facility (ARSF) and the team from the ARSF Data Analysis Node at Plymouth Marine Laboratory is acknowledged for undertaking initial ALS processing

Seasonal differences in thermal sensation in the outdoor urban environment of Mediterranean climates – The example of Athens, Greece

Outdoor urban areas are very important for cities and microclimate is a critical parameter in the design process, contributing to thermal comfort which is important for urban developments. The research presented in this paper is part of extensive field surveys conducted in Athens aimed at investigating people’s thermal sensation in a Mediterranean city. Based on 2313 questionnaires and microclimatic data the current work focuses on the relative frequencies of people’s evaluation of the thermal along with the sun and wind sensations between two seasons trying to identify the seasonal differences in thermal sensation. The impact of basic meteorological factors on thermal discomfort with respect to season are also examined, as well as the use of the outdoor environment. Results show that psychological adaptation is an important contributing factor influencing perception of the thermal environment between seasons. In addition, the thermal sensation votes during the cool months show that individuals are satisfied to a great extend with the thermal environment whereas the combination of high air temperature, strong solar radiation and weak wind lead to thermal discomfort during summertime. As far as the appropriate urban design in the Mediterranean climate is concerned, priority should be given to the warm months of the year

The Impact of Urban Forest Structure and its Spatial Location on Urban Cool Island Intensity

Urban forest can help decrease land surface temperature (LST) and create urban cooling effect (UCI) to mitigate urban heat island (UHI). However, it is still unclear how urban forest structure and its location affect UCI, particularly under different seasons. In this study, with plot-based urban forest structure and UCI intensity extracted from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) thermal data, we first conducted correlation analyses between UCI and different forest structures (crown closure, tree height, leaf area index, basal area, stem density and diameter at breast height, etc.) and spatial location (distances from buildings and from water bodies and elevation) attributes, and we then carried out quantitative regression analyses between them. Our results indicate that (1) Urban forest could create “urban cool islands”, which were higher in summer than those in autumn.(2) UCI could be significantly affected by urban forest structural attributes, especially by crown closure and LAI. All urban forest structural attributes had positive linear relationships with UCI except for LAI and basal area which had positive non-linear relationships with UCI.; (3) UCI in urban forest could also be affected by its spatial location but not by its elevation. The UCI non-linearly decreased with decreasing distance from buildings and with increasing distance from water bodies. The threshold values of DB for significantly affecting UCI variation is approximately between 100 m and 300 m in summer and autumn, respectively; and (4) the relationships between UCI and urban forest structure and its location attributes were complex and seasonal dependent. Urban forest attributes had greater effects on increasing UCI in summer than those in autumn. These findings would deepen our understanding of interactions between UCI and urban forest attributes and provide urban planners with useful information about how to design urban forest to effectively mitigate UHI effects