Urban Heat Island or UHI is a well-known phenomenon which refers to the trapping of heat by extensively paved and built-up urban centres and megacities. These places are usually warmer than surrounding rural areas which typically boast of a higher vegetation cover. The cooler temperatures in the rural areas are largely related to the evapotranspiration by the vegetation, while the buildings in cities heat up during the day and tend to bounce the thermal radiation into each other and down to the ground instead of losing it to space, especially during nighttime. UHI has been documented all over the world, but India is an exception.
For nearly all cities in India, the surrounding rural areas are measurably warmer during the day than the cities themselves during the pre-monsoon (and warmest) months...
In other words, for nearly all cities in India, the surrounding rural areas are measurably warmer during the day than the cities themselves during the pre-monsoon (and warmest) months of March-April-May. Employing high-resolution satellite data for land temperatures and vegetation cover along with estimates of evapotranspiration, a study found that the land temperatures in India, in fact, drop as we traverse from rural areas to urban centres! Satellite data indicates that the parched post-harvest agricultural land is in fact more denuded than the urban areas with their gardens and lawns. An additional cooling effect in urban India may come from the extensive water use for various purposes; this water evaporates and tempers the warming during the day. The vast agricultural landscape of India has been established by essentially removing all the trees—most of rural India, in effect, is barren land waiting for the monsoons to arrive.
This is of course bad news on multiple fronts. The Indian monsoon is experiencing a downward trend in the seasonal amounts of rain. And the rain that does fall comes in bursts, leading to an increase in the so-called extreme events that typically lead to flash floods and landslides or devastating droughts that have hammered the farmers repeatedly in the last 15 years. Pre-monsoon heatwaves are a part of this phenomenon, leading to heart-wrenching reports of hundreds of deaths in rural India nearly every year. City-dwellers tend to have more amenities such as air-conditioning or access to offices and movie theatres to escape the hottest parts of the day. On the other hand, the pre-monsoon months are days of peak outdoor activity for the farmers in preparation of their land for the planting season. They are thus particularly vulnerable to heatwaves, which are expected to get worse with continued warming due to increasing greenhouse gas emissions.
Students at IIT-Bombay are now performing modelling experiments to show that increasing vegetation cover over rural India will help mitigate heatwaves and save precious lives.
However, this bad news for rural India in fact offers a golden opportunity to solve not only the exacerbated daytime warming during the pre-monsoon months but also the alarming groundwater depletion in the face of a decreasing monsoon. Tree-based farming or agroforestry is a time-tested and well-proven approach to sustainable watershed management and food production. Combining forestry with agriculture retains the soil moisture from the post-monsoon months through to the following monsoon season year after year since trees harvest groundwater sustainably while moistening and nourishing the soil. They also offer post-monsoon income when the trees are chosen wisely, and extensive data exists to show that retaining the farmers in the villages after the agricultural season has numerous other benefits for the entire community. Large scale post-monsoon migration of farmers to cities as labourers brings many social problems such as alcoholism and break-up of family units, poor health among women and illiteracy among children, etc. Exemplary work in tree-based farming is being performed with community participation by organisations such as SCOPE. Agroforestry not only recharges groundwater but also sequesters carbon due to the multiyear vegetation cover and renders the tract of land more resilient to drought and extreme rainfall. Indeed, Prime Minister Modi has declared that soil health is a matter of importance. Expanding agroforestry over all of India is the best way to accomplish a reduction in soil erosion while enhancing its health.
The bright students at IIT-Bombay are now performing modelling experiments to show that increasing vegetation cover over rural India will indeed help mitigate heatwaves and save precious lives. Combined with weather and climate prediction efforts under the Ministry of Earth Science, these studies offer a beacon of hope for climate action in India that will enhance food security while also reducing the ill-effects of global warming. UHI is still a major concern for India since nearly 40 crore people live in cities at present and the country is projected to have the largest growth in urban population in the coming decades. Urban policies will need attention soon enough but it is time to move post-haste on mitigating heatwaves for farmers, our annadaatas.