TITLE:
Variability of In-Situ Plant Species Effects on Microclimatic Modification in Urban Open Spaces of Nairobi, Kenya
AUTHORS:
Sharon Anyango Onyango, John Bosco Mukundi, Aggrey Ochieng’ Adimo, John Mwaibanda Wesonga, Sahar Sodoudi
KEYWORDS:
Local Climate Zones (LCZ), Physiological Equivalent Temperature (PET), Tree Architecture, Leaf Area Index (LAI), Thermal Comfort (TC), Urban Heat Island (UHI)
JOURNAL NAME:
Current Urban Studies,
Vol.9 No.1,
March
25,
2021
ABSTRACT: Plant species play a key role in microclimate regulation especially in
cities where Urban Heat Island (UHI) effects are mostly felt. This study aimed
at determining the impact that different tree species have on microclimatic
parameters in urban open spaces of Nairobi and the degree to which they reduce
UHI implications and improve Thermal Comfort (TC) of inhabitants. Two sites
representing two Local Climate Zones (LCZ) were selected for sampling namely;
LCZ B: Central Park (Site 1),
and LCZ 4: Taifa road (Site 2).
Four mature and isolated in-situ plant species with varied tree
architecture were chosen for measurements of climatic variables done at 1.1 m
above the ground, at the trunk base, 5 m horizontally away from the plant and
open in the sun with no trees (control). Leaf area index (LAI) and Physiological
Equivalent Temperature (PET) were measured under the trees. In both sites, Terminalia mantaly species with a
spreading canopy form provided the best cooling effect with a PET reduction of
9.6°C and 9.3°C in Site 1 and Site 2, respectively. Tipuana tipu (round canopy form) was
the second best with 9.2°C and 8.2°C, followed by Cassia spectabilis (vase canopy form) with 8.5°C and 7.6°C, and lastly Podocarpus falcatus (pyramidal canopy
form) with 7.9°C and 6.4°C. Air temperatures in Site 1 (Park) were 2.3°C, 1.3°C
and 1.0°C lower compared to those in Site 2 (Street) at 1 pm, 6 pm and 8
am, respectively. A strong negative correlation (S1; r = -0.96, S2; r = -0.8) was obtained between LAI and
PET for both sites. This showed that plants with higher canopy densities
reduced temperature more, which in turn helps improve human TC.