Browsing by Author "Rathnayaka, W. R. A. J. W."

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Assessing urban heat island dynamics: A comparative study of Colombo district in 2015 and 2022
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Perera, A. A. I. U.; Dickowita, D. K. R. R.; Rathnayaka, W. R. A. J. W.; Weerasinghe, V. P. A.
Widespread industrialization and migration of the rural population to urban areas have led to rapid urbanization. This phenomenon transforms permeable surfaces into impermeable surfaces, leading to an increase in land surface temperature. This accelerates the formation of urban heat islands. Colombo city can be considered as the commercial capital of Sri Lanka. It is a densely populated and highly urbanized city. Over the past few years, residents have experienced discomfort due to elevated temperatures in the Colombo district. Hence, it is necessary to implement mitigation measures to reduce the impact of urban heat islands. Therefore, this study aims to identify urban heat islands in the Colombo district to facilitate the implementation of mitigation measures. To compare the urban heat island effect in Colombo district between 2015 and 2022, two Landsat 8 images with a cloud cover less than 10% were obtained from USGS Earth Explorer. Land surface temperature (LST) for both years was calculated using ArcGIS 10.8 software, utilizing bands 4, 5, and 10. Various equations were applied to determine Top of Atmosphere Radiance, Brightness Temperature, NDVI, Land Surface Emissivity, and finally LST. The LST data was then extracted for Colombo district, and another equation was used to generate a spatial distribution layer of urban heat islands for both years. When comparing the results obtained from the map of 2015 and 2022, an increase in the critically high urban heat island areas was observed, along with a relative decrease in the critically low urban heat islands. In conclusion, the comparative analysis of Urban Heat Islands (UHI) in the Colombo District for 2015 and 2022 shows significant temporal variations in thermal patterns. There is an increase in UHI intensity, which relates to the higher Land Surface Temperatures obtained according to the methodology, highlighting the dynamic nature of urban heat in rapidly developing regions. The spatial distribution of UHI effects proves considerable changes, with previously cooler areas showing intensified warming trends. The reasons for these could be land cover changes, such as increased impervious surfaces and reduced green spaces, playing a crucial role in UHI formation.
Soil erosion and sediment yield estimation using GIS-based RUSLE model in Attanagalu Oya watershed, Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Rathnayaka, W. R. A. J. W.; Weerasinghe, V. P. A.
Soil erosion is considered a significant cause of land degradation that negatively impacts natural resources and socioeconomic activities across the globe. Hence, estimating the spatial distribution of soil erosion is essential for making successful policies and implementing proper land conservation and management practices. The present study was designed to estimate the soil erosion and sediment yield in the Attanagalu Oya Watershed, one of the major watersheds located in the low-country wet zone in Sri Lanka, which acts as an important natural ecological zone and a source of surface water for the area. The Revised Universal Soil Loss Equation (RUSLE) model integrated with the Geographic Information System and Remote Sensing was used to quantify soil erosion and map the spatial variation of the soil erosion hazard over a 20-year period. The Sediment Delivery Ratio (SDR) was utilized to estimate the sediment yield generated in the Attanagalu Oya watershed. Land use land cover derived from Landsat 7 ETM and Landsat 8 OLI imagery and Digital Elevation Model (DEM) were integrated into the model. The results indicated that the average annual soil erosion in the Attanagalu Oya watershed has substantially increased from 1.58 t ha-1 yr-1 in 2001 to 2.3 t ha-1 yr-1 in 2020, an increment of about 45.6%. The spatial distribution of soil erosion reflected that the moderate to extremely high erosion levels increased from 2001 to 2020, and the extremely erosion-prone areas (>60 t ha-1 yr-1) were distributed in the eastern part of the watershed. Furthermore, the average annual sediment yield in the Attanagalu Oya watershed was estimated as 0.39 t ha-1 yr-1 with a range of 0 to 124.4 t ha-1 yr-1 in 2001 and 0.57 t ha-1 yr-1 with a range of 0 to 87.4 t ha-1 yr-1 in 2020. The spatial distribution of sediment yield revealed that the high sediment yield was also generated in the eastern part of the watershed as soil erosion. The spatial analysis further revealed that steep slopes (>10.41%), high mean annual rainfall levels (>2500mm), erosion-prone soil types and land use land cover changes, contributed to the high soil erosion and sediment yield in the Attanagalu Oya watershed. The soil erosion hazard information obtained through this study on the Attanagalu Oya watershed can be utilized to design proper erosion conservation and land management practices for improving the sustainability of the watershed.