Summer Microclimates and Thermal Perception in Japanese Gardens and Small Urban Parks: Hints for Climate-Adaptive Green Space Designs

概要

Abstract
Title: Summer Microclimates and Thermal Perception in Japanese Gardens
and Small Urban Parks: Hints for Climate-Adaptive Green Space Designs
Lihua CUI
In the face of escalating global warming, the intensity and frequency of extreme
weather events, including heat waves, have been increasing in various cities in
Japan. This environmental context has prompted a growing demand for urban
green spaces, as they have been demonstrated to offer microclimate regulation
services. However, a significant barrier to climate-adaptive green space
implementation lies in the limited understanding of the optimal strategies for
leveraging green spaces. To fill this gap, this study was undertaken with the
primary objective of exploring optimal green space designs that are adaptable to
the current and projected future climates in Kyoto, Japan.
In Chapter 1, I introduce the strategic framework of this thesis, along with the
presentation of key findings from existing studies and the emphatic identification
of the knowledge gap. A novel facet of this thesis lies in its pursuit of climateadaptive design strategies sourced from historical green spaces, namely
Japanese gardens in Kyoto. This exploration is predicated on the hypothesis that
the evolutionary trajectory of these historical gardens was intrinsically intertwined
with the local climate, resulting in the provision of thermally comfortable
microclimates that catered to the year-round enjoyment of the gardens. I also
investigated the microclimates and thermal perception within urban parks, as we
have little understanding of the current conditions of urban parks. This
investigation not only seeks to comprehend the efficacy of existing urban parks
in heat mitigation but also endeavors to provide recommendations for redesigning
these spaces to optimally shield inhabitants from summer heat.
Chapter 2 covers the introduction of the study sites and methodology. I selected
three distinct types of study sites including historic pond gardens, dry gardens,
and small urban parks. Given the prevalent small size of urban parks in Kyoto, I
opted to investigate historic gardens with sedentary-style characteristics that
possess a small-scale design aspect. To focus on the impact of garden and park
designs on individuals' thermal experiences within these sites, my investigation
exclusively delved into the microclimates and thermal perceptions within the
resting areas situated within the gardens and parks. Meteorological
measurements were conducted during the summer period from morning to

afternoon. I used the physiological equivalent temperature (PET) to assess the
thermal perception within the resting areas. Subsequently, I measured the areas
of various landscape elements around the resting areas to understand their
spatial configurations. Finally, I analyzed how spatial configurations affected
thermal perception within the resting areas.
Chapter 3 covers the findings of the study, which focused on six resting areas in
three historic pond gardens. The thermal perception within the resting areas was
assessed as "slightly warm" conditions, while the nearby open areas were under
"very hot" conditions. Within the pond gardens, the dominant approach for
mitigating heat was demonstrated to be shade provision. The roof to pavement
area ratios, which were 7:3 within a 5 m radius and 6:2 within a 10 m radius of
the resting areas, played a substantial role in effectively reducing heat in the
resting areas. In addition to shade provision, the large area of green ground in
the pond gardens further improved thermal perception in the resting areas,
whereas trees and ponds did not significantly affect the thermal perception.
Chapter 4 covers the findings of the study on nine resting areas within four dry
gardens. Despite the extreme conditions observed in the garden surroundings,
the resting areas exhibited significantly improved thermal perception, categorized
as "warm". Similar to pond gardens, the high ratio of roofs around the resting
areas ameliorated thermal perception within the resting areas from “very hot” to
“warm” conditions. The ratios of the roof to the pavement in the dry gardens were
8:2 in a 5 m radius and 7:2 in a 10 m radius. This study also revealed several
new insights into the association between thermal perception and surrounding
spatial configurations. For example, the increase in roof area in a 20 m radius no
longer improved thermal perception, whereas green ground and tree canopies
improved thermal perception only in a 20 m radius from the resting areas.
Chapter 5 introduces the study of the thermal perception and design features of
small urban parks. Among the 11 resting areas investigated within three urban
parks, half were found to be “hot” during the noon hours. The thermal discomfort
in those resting areas was due to the lack of shade. The study suggests that it is
crucial to place shade elements, particularly in the west and south of the resting
areas. Moreover, shade elements must be concentrated close to the resting
areas. The recommended proportions for shade elements in the west and south
were at least 61% and 65%, respectively. However, most resting areas did not
have this condition, resulting in ineffective heat mitigation in the resting areas.
Overall, the spatial design of urban parks needs to be revised to provide cool
shelters for people in Kyoto.

Chapter 6 concludes the findings of Chapters 3-5 and provides climate-adaptive
design strategies. The “slightly warm” and “warm” conditions in the pond and dry
gardens successfully validated the hypothesis that historic green spaces can
adapt to the local climate. Both pond gardens and dry gardens exhibited a
common strategy of incorporating substantial shade elements around their
resting areas, specifically encompassing approximately 70-80% within a 5 m
radius and 60-70% within a 10 m radius from the resting areas, resulting in
improved thermal comfort. Shade elements in the west and south from resting
areas exhibited the most effective in heat mitigation, particularly when situated
close (within 5 m) to the resting areas and covering areas exceeding 60%. Broadranging green coverage emerged as another pivotal heat alleviation measure,
although its cooling effects were comparatively inferior to those of shade
provision. Last, but not least, green spaces in the past were designed strategically
in Japan, however from the investigation of thermal conditions and spatial design
of urban parks, the wisdom for adapting to the local climate seems not fully
embraced in the modern urban green spaces. As global warming persists, an
urgent and essential task involves a comprehensive evaluation of thermal
conditions in urban parks across Kyoto and other Japanese cities, coupled with
the implementation of climate-adaptive design strategies to safeguard urban
residents from escalating heat. ...