Takehiro Morimoto

Quantifying Surface Urban Heat Island Formation in the World Heritage Tropical Mountain City of Sri Lanka

Presently, the urban heat island (UHI) phenomenon, and its adverse impacts, are becoming major research foci in various interrelated fields due to rapid changes in urban ecological environments. Various cities have been investigated in previous studies, and most of the findings have facilitated the introduction of proper mitigation measures to overcome the negative impact of UHI. At present, most of the mountain cities of the world have undergone rapid urban development, and this has resulted in the increasing surface UHI (SUHI) phenomenon. Hence, this study focuses on quantifying SUHI in Kandy City, the world heritage tropical mountain city of Sri Lanka, using Landsat data (1996 and 2017) based on the mean land surface temperature (LST), the difference between the fraction of impervious surfaces (IS), and the fraction of green space (GS). Additionally, we examined the relationship of LST to the green space/impervious surface fraction ratio (GS/IS fraction ratio) and the magnitude of the GS/IS fraction ratio. The SUHI intensity (SUHII) was calculated based on the temperature difference between main land use/cover categories and the temperature difference between urban-rural zones. We demarcated the rural zone based on the fraction of IS recorded, <10%, along with the urban-rural gradient zone. The result shows a SUHII increase from 3.9 °C in 1996 to 6.2 °C in 2017 along the urban-rural gradient between the urban and rural zones (10 < IS). These results relate to the rapid urban expansion of the study areas from 1996 to 2017. Most of the natural surfaces have changed to impervious surfaces, causing an increase of SUHI in Kandy City. The mean LST has a positive relationship with the fraction of IS and a negative relationship with the fraction of GS. Additionally, the GS/IS fraction ratio shows a rapid decline. Thus, the findings of this study can be considered as a proxy indicator for introducing proper landscape and urban planning for the World Heritage tropical mountain city of Kandy in Sri Lanka.

Accessing the soil erosion rate based on RUSLE model for sustainable land use management: a case study of the Kotmale watershed, Sri Lanka

Water based soil erosion is a serious socio-economic and environmental problem across the world especially in the tropical region. Assessing the soil erosion quantitatively and spatially provides information to prioritize the soil conservation area in sustainable land management view point. Among the other soil erosion approaches, erosion modeling has been playing a significant role and provides an accurate result in a cost-effective manner. In this study, revised universal soil loss equation (RUSLE) was integrated with remote sensing (RS) and geographic information system (GIS) to analyse the quantitative and spatial distribution of soil erosion across the entire Kotmale watershed which is located in the western part of the central mountain region in Sri Lanka. In the methodology, the parameters of the RUSLE model were estimated using pixel overlay method in ArcGIS software, both spatial data and remote sensing data facilitated with appropriate calibration. From the analysis, the annual soil erosion ranges from 0 to 472 t ha− 1 year− 1 with the mean and standard deviation 9.8 t ha− 1 year− 1 and 15.7 t ha− 1 year− 1 respectively. The mean erosion rate of the model was correlated with ground based data. After the final model was established, conservation priority area was identified by using hot and cold spot analysis. Here “hot spots” shows the area with high soil erosion clustering value, while “cold spot” refers to area with low soil erosion clustering. The soil conservation priority map has been produced and the result shows that approximately 25% represents hot sport. The result would be an aid and sources for soil and water conservation in the Kotmale watershed.