Confounding effects of harvesting on urban heat island intensity in a mid-sized city in Brazil

Abstract

Urban heat island (UHI) studies have traditionally focused on the relative difference between air temperatures measured at an urban area and those at a rural location, taken as a reference. Whereas the influence of urban areas on UHI intensity has been abundantly explored, the impact of the choice of an adequate rural reference location, due to the frequent agricultural use of rural areas, still remains understudied. The issue of climate variability of rural areas is a determining factor for assessing UHI intensity. Brazil is the world's largest sugarcane producer, with a 33% share of the global market. Many mid-sized cities in the Brazilian state of São Paulo are located close to sugarcane fields, which all undergo the sugarcane growth cycle with defined pre-harvest and post-harvest stages. The aim of this study is to understand the interference of seasonal harvesting periods in sugarcane plantations on the development of UHI magnitudes in and around (at suburban locations) Piracicaba, located in the state of São Paulo, Brazil, at 22° 42′ 30“ S and 47° 38’ 01” W and characterized by Köppen-Geiger's Cfa, humid subtropical climate. We deployed a fully-equipped weather station at the site of a sugarcane crop at post- and pre-harvest and a small network of three weather stations provided with air temperature and humidity sensors in the city center and in suburban neighborhoods in Piracicaba. Pre-harvest showed the highest UHI intensities, though not confounding the analysis of intra-urban temperature differentiation patterns. Results stress the relevance of the choice of the baseline rural station in terms of temporal variability related to the sugarcane harvesting cycle.