Dominant control of agriculture and irrigation on urban heat island in India

Abstract

As is true in many regions, India experiences surface Urban Heat Island (UHI) effect that is well understood, but the causes of the more recently discovered Urban Cool Island (UCI) effect remain poorly constrained. This raises questions about our fundamental understanding of the drivers of rural-urban environmental gradients and hinders development of effective strategies for mitigation and adaptation to projected heat stress increases in rapidly urbanizing India. Here we show that more than 60% of Indian urban areas are observed to experience a day-time UCI. We use satellite observations and the Community Land Model (CLM) to identify the impact of irrigation and prove for the first time that UCI is caused by lack of vegetation and moisture in non-urban areas relative to cities. In contrast, urban areas in extensively irrigated landscapes generally experience the expected positive UHI effect. At night, UHI warming intensifies, occurring across a majority (90%) of India’s urban areas. The magnitude of rural-urban temperature contrasts is largely controlled by agriculture and moisture availability from irrigation, but further analysis of model results indicate an important role for atmospheric aerosols. Thus both land-use decisions and aerosols are important factors governing, modulating, and even reversing the expected urban-rural temperature gradients.

The impact of climate change and urban growth on urban climate and heat stress in a subtropical city

“…The decrease in the average UHI was driven by increased warming in rural areas as compared to urban areas, which reduced the urban-rural contrast in temperature at night and increased the difference between urban and rural temperatures during the day. This rural control on the intensity of the urban heat island has also been found for many Indian cities, where irrigation of agriculture is a large factor in the surface UHI (Kumar et al, 2017). The change in UHI intensity found in this study with climate change was most pronounced during the daytime, when the urban cool island strengthened.…”

Characterization of Extreme Wet‐Bulb Temperature Events in Southern Pakistan

“…Our results also point to the role that land use change could play in changing these extremes. In particular, our results point to the role of irrigation in enhancing heat stress, a concern that has been explored for the South Asian region (Kumar et al, ). If the amount of land under irrigation increases, the area of enhanced latent heat fluxes also increases.…”

Decline in surface urban heat island intensity in India during heatwaves

“…We used 56 m resolution Land Use Land Cover (LULC) from National Remote Sensing Center (NRSC) for the year 2011 and urban extent map derived from Moderate Resolution Imaging Spectroradiometer (MODIS) 500 m land cover data (Schneider et al 2010). The urban core or densely built-up areas were extracted by overlapping the MODIS urban extent maps and NRSA LULC for 89 major urban areas in India as described in Kumar et al (2017). The intersecting built-up area from both the datasets were considered as urban core area.…”

“…The MODIS products also provide quality control flags, which were used to improve the reliability of LST (Wan et al 2015). More details on data quality and selection of urban areas can be obtained from Kumar et al (2017).…”