Effects of urbanization on the relationship between greenspace patterns and evolution of regional heat island in cities of Ethiopia

Dynamics of green spaces- Land surface temperature intensity nexus in cities of Ethiopia

“…First, the digital numbers were converted into absolute radiance using Eq (2) [ 53 ]. Accordingly, the TOA radiance of the thermal band was transformed into at-sensor brightness temperature using Eq (3) [ 9 , 11 , 39 ]. where L λ is the spectral radiance, L min and L max (mW/(cm 2 .sr.μm)) are spectral radiances for each band at digital numbers 0 and 255, respectively.…”

“…The generated brightness temperature values (Eq (2) ) were then converted to emissivity-corrected LST in Kelvin using Eq (3) . Furthermore, study areas are heterogeneous areas; thus, to avoid the emissivity effect (ε) in estimating LST, the NDVI threshold method was applied using Equations ( Eq 4 , Eq 5 , Eq 6 , Eq 7 ) [ 9 , 13 ]. Where λ is the wavelength of emitted radiance equals 11.5 μm; α = hc/b (1.438 × 10^-2 mk); b refers to Boltzman constant as 1.38 × 10^-23 J/K; h is the Planck's constant 6.626 × 10^-34 JS; C refers to the velocity of light 2.998 × 10^8 m/s, and ε is the surface emissivity.…”

“…Extreme heat is a growing threat to the health of urban ecosystems, particularly in densely populated and industrialized cities [ 1 ]. Urbanization can greatly influence the urban thermal environment by increasing land surface temperature [ 9 , 22 , 61 ], the composition, structure, and function of the urban ecosystem services [ 8 ], the energy flow between the land surface and the atmosphere [ 34 ], and overall urban ecosystem sustainability [ 8 ]. The most common phenomenon that increases the surface temperature of a city relative to its fringe is called the “urban heat island (UHI)" [ 34 ]; Oke, 1995).…”

“…Conversely, urban green spaces (UGSs) are significant, nature-based solutions to climate change and have immense potential to reduce vulnerability to heat waves (the UHI effect) while enhancing the resilience of climate change [ 9 ]. However, the decline of green spaces is often induced by a human-related factor, such as accelerated urban expansion [ 58 ] which creates pressure on the existing resources and leads to the fragmentation of green spaces [ 8 , 58 ].…”

“…Even though some studies have been conducted, the results focused on the linear relationship between LST and single influencing factors, such as biophysical factors [ 67 ]. Specifically in Ethiopia, there are a few studies that are spatially limited and focused on single-factor analysis [ 9 , 11 , 20 , 63 ] and failed to disclose the comprehensive characterization of the LST-green space nexus [ 9 , 10 ]. In addition, a couple of issues of great importance serve to justify our research: 1) The analyzed cities do not have enough UGS-LST interlinks studies for responses with spatial and temporal variability.…”