As Mumbai struggles to cope with the blistering heat, a first-of-its-kind analysis revealed one of the most harmful effects of the sun is not even visible to the naked eye.
An analysis by the Indian Institute of Tropical Meteorology (IITM), Pune, found Mumbai is exposed to more solar ultraviolet (UV) radiations than cities like Delhi and Pune. In the short term, excess UV rays can cause sun burns, while long-term exposure can lead to skin cancer and cataract.
The researchers said a declining green cover and increasing concretisation has pushed Mumbai’s UV Index (UVI) to average 8.2, which falls under the high-risk category. This category – between 7 to 10 UVI – means everyone is at risk and it is therefore advisable to avoid direct sun exposure. The maximum risk of UV radiations is between 12 and 3pm, with its peak at 1pm.
“Ultraviolet radiation is high near water bodies, sand and barren land because solar radiation gets reflected back because it does not get absorbed. In addition to being closer to the equator, Mumbai is more vulnerable than Delhi and Pune since it is surrounded by the sea and urban heat islands are forming because of dismal greenery,” said Gufran Beig, project director, System of Air Quality and Weather Forecasting and Research (SAFAR), IITM. “Mumbai definitely needs more green cover.”
Work on monitoring of the sun’s UV radiation in Mumbai started on May 15 for a pilot project as part of SAFAR under the Union ministry of earth sciences, with recordings being taken from May 20.
Of the 15 days that the UV rays have been monitored, the highest levels were recorded on May 26 when the UVI was 8.45, followed by June 2 at 8.40. The lowest was on May 28, when the UVI stood at 7.71, which still falls in the high-risk category. During the same period, the UVI in Delhi was between 6 and 8, while it was between 7 and 8 in Pune.
“UV rays form just 1% of the total solar flux, a majority of which is absorbed by the stratosphere, while some of it reaches the surface,” said Beig, adding rising temperature during summer also results in an increase in UV radiation.
Under the SAFAR project, only one or two sensors will be installed in Delhi and Pune. However, 10 UV sensors will be installed across Mumbai given the topography. The current readings are taken at Colaba. “There are variations in Mumbai’s landscape, with some areas close to the sea, some with green spaces and some barren. We want to record UV radiations to assess the situation,” said Beig.