Analysis of urban microclimates (UMCs) in Thrissur corporation using micro meteorological measurements and remote sensing data

Abstract

Global urban population is increasing at an alarming rate. Unplanned and inadequately managed urbanization has profound effects on microclimate. The unplanned urbanization could transform cities and townships into urban heat islands (UHI) one of the most evident climatic modifications in urbanized areas. The increased heat in the cities affect the environment and the thermal comfort of organisms. Understanding the urban climate is very necessary to make the cities sustainable. The objective of this study is to investigate and analyse the urban microclimates in Thrissur Corporation limits and to understand their linkages with urban greenery. This study will also examine and analyse the perceptions of urban residents in the study locations about different aspects of climate change. The LULC map of Thrissur Corporation was prepared based on NRC guidelines in ArcGIS using Landsat 8 satellite data acquired from Earth Explorer. Three urban LULC class were selected to take the in-situ temperature measurement. Ambient air temperature and relative humidity were measured during the study period in morning 7.30 am and afternoon 2.30pm, the data is further used to assessing urban heat island intensity. Highest temperature was recorded from LULC urban compact, that constitute the commercial center of the city, where the region occupied by highly dense buildings, dense population, heavy traffic, pavement and other impervious structures. The temperature recorded from other urban LULC classes such as urban_sparse and urban- _vegetation is comparatively low. The least temperature was recorded from urban_vegetation. It was noted that temperature difference between LULC classes such as urban_compact, urban_sparse and urban_vegetation is prominent during afternoon compared to morning air temperature. The urban heat island intensity ranging between 0ºC -5.53ºC was observed in LULC class urban_compact. Land surface temperature (LST) and normalized difference vegetation index (NDVI) of various LULC classes in Thrissur corporation was estimated and it was found that the LST is maximum in the LULC urban_compact, where the NDVI values are minimum. Whereas the LST is minimum in the LULC cropland_paddy where the NDVI is maximum. Among the three urban classes, viz. the urban_compact, urban_sparse and urban_vegetated the minimum LST was estimated in the LULC urban_vegetated. To understand the linkage between microclimate and urban greenery correlation test was done between the LST and NDVI values estimated in various urban LULC classes. A strong negative correlation was observed in LULC urban_vegetated (-0.35). The correlation coefficient estimated in urban_sparse and urban_compact is - 0.46 and -0.41 respectively. A perception study was done among 30 people residing in urban area. The way people think about climate change is crucial to developing strategies to address the problem. Among the respondents, majority (80%) have the opinion that the human interventions, predominantly deforestation are the major cause of climate change. On the other hand, 20 % of the respondents are not sure whether human interventions only causes climate change or any natural causes are also there. Chi-square test was done to find the association of respondent’s age and gender with their perception on various aspects of climate change, and no association was found between the respondents age and gender with their perception on climate change. From the study it was understood that the UHI has been developed in the core of Thrissur muncipal corporation belongs to LULC class urban_compact that includes places like East fort, High road and North bus stand. The study also observed the role of urban vegetation in mitigating the urbanization induced climatic modification. However a more focused study considering extra parameter such as air quality , wind speed and wind direction etc will give a better understanding of UMC. In the wake of rapid urbanization UMC study would be helpful in modelling cities for sustainable development.