# Analyzing the Influence of Anthropogenic Heat on Groundwater Using Remote-Sensing and In Situ Data

## TL;DR

Urban expansion in Bangalore has increased heat, which is affecting groundwater temperatures, highlighting the need for sustainable city planning.

## Contribution

This study demonstrates a strong link between urbanization, surface heat, and groundwater warming using remote sensing and in situ data.

## Key findings

- Built-up areas in Bangalore increased from 7.61% to 28.78% between 1999 and 2017, raising land surface temperatures.
- Groundwater temperature was strongly correlated with anthropogenic heat flux (R2 = 0.83) and land surface temperature (R2 = 0.78).
- Urban expansion led to subsurface warming, with green areas experiencing a ~6 °C temperature rise.

## Abstract

What are the main findings?
Bangalore’s built-up area increased from 7.61% to 28.78% during the period from 1999 to 2017, causing a rise in the land surface temperature (LST) and anthropogenic heat flux (>65 W/m2). There was a rise in temperature (LST) of ~6 °C in green areas and >3 °C in urban areas.Groundwater temperature was strongly correlated with heat flux (R2 = 0.83) and with LST (R2 = 0.78), indicating subsurface warming due to urbanization.
What is the implication of the main finding?
Sustainable urban planning is needed to reduce the heat stress by increasing the extent of green spaces, adopting cool roofing, and improving water resource management.Incorporating urban heat assessment in policies can enhance thermal comfort, reduce heat-related illness and mortality, mitigate groundwater warming, and ensure long-term water and energy sustainability in rapidly urbanizing cities, such as Bangalore.

Bangalore’s built-up area increased from 7.61% to 28.78% during the period from 1999 to 2017, causing a rise in the land surface temperature (LST) and anthropogenic heat flux (>65 W/m2). There was a rise in temperature (LST) of ~6 °C in green areas and >3 °C in urban areas.

Groundwater temperature was strongly correlated with heat flux (R2 = 0.83) and with LST (R2 = 0.78), indicating subsurface warming due to urbanization.

Sustainable urban planning is needed to reduce the heat stress by increasing the extent of green spaces, adopting cool roofing, and improving water resource management.

Incorporating urban heat assessment in policies can enhance thermal comfort, reduce heat-related illness and mortality, mitigate groundwater warming, and ensure long-term water and energy sustainability in rapidly urbanizing cities, such as Bangalore.

The continuous expansion of impervious surfaces replacing the vegetation cover and surface water areas increases urban heating. Such heating leads to downward heat transfer and latent heat flux from the surface to subsurface aquifers. This study used Landsat optical and thermal satellite data for land use/land cover (LULC), land surface temperature (LST), and anthropogenic heat flux (Has) change mapping in Bangalore City, India. The in situ sensor-based land surface temperature (LST) and groundwater temperature (GWT) measurements were used to validate the study outcome. A minor difference was observed between the satellite data and the in situ LST due to the differential data acquisition time. The built-up area increased from 7.61% to 28.78% from 1999 to 2017 at the cost of the green cover and the extent of waterbodies. Therefore, LST change was higher in green cover areas (~6 °C LST) than in urban areas (>3 °C). The anthropogenic heat fluxes increased significantly (above 65 W/m2) during the study period. The in situ GWT was strongly correlated with the Has (R2 = 0.83) and LST (R2 = 0.78). The study highlights the nature of urban expansion in Bangalore City, India, and its impact on LST, Has, and GWT. The observed changes in land use practices with urban heat indicators at 30 m scale can be used for sustainable land use planning to improve the thermal comfort of the city, preserving the urban ecosystems. The high collinearity between satellite-data-derived LST, Has, and GWT can be used for periodic monitoring at seasonal and annual scales using the Landsat data, which can be important inputs for land use planners and policymakers.