India's climate and environment

The southwest monsoon normally reaches Kerala around 1 June and advances northwest over roughly six weeks, covering the whole country by mid-July. It withdraws from late September through October. A separate northeast monsoon brings the main rainy season to Tamil Nadu and coastal Andhra Pradesh from October to December — which is why Chennai's rain calendar is opposite to Mumbai's.

Most of India receives the large majority of its annual rainfall in these months. That concentration is what makes the monsoon economically decisive: reservoir levels, groundwater recharge, hydropower, the kharif sowing season, food prices and rural incomes all move with it.

The IMD's seasonal forecast is national news for exactly that reason, and the language matters — 'normal' means within a band around the long-period average, not that the rain will be evenly distributed. A normal-total monsoon delivered in fewer, heavier events is a flood and a drought in the same season.

That is increasingly what happens. The observed trend across the region is towards fewer rainy days with more intense rainfall on each, which is worse for agriculture and much worse for urban drainage than the same total spread evenly.

Mumbai, Chennai, Bengaluru, Hyderabad and Delhi have all had severe urban flooding in recent years, driven as much by construction over natural drainage and encroached water bodies as by rainfall intensity.

The Himalayan states have their own calendar entirely: passes close in winter, the high-altitude travel season is roughly June to September, and the monsoon brings landslide risk to hill roads across Himachal Pradesh, Uttarakhand and the northeast.

The southern peninsula has a much flatter temperature range through the year and a second rainy season, so 'Indian seasons' described generically usually describe the north.

October to March is the conventional travel window for most of the country — but it coincides exactly with the worst air quality in the northern plains, which is a real trade-off rather than a footnote.

Air pollution in the Indo-Gangetic plain is among the most severe in the world, and it is strongly seasonal. From November to January, cool air and low wind speeds create temperature inversions that trap pollutants close to the ground across a plain hundreds of kilometres wide.

The sources are multiple and disputed in proportion but not in kind: vehicle emissions, industry, construction dust, waste burning, domestic fuel use, and post-harvest stubble burning in Punjab and Haryana. The airshed is regional, so no single city can solve it alone — which is the reason for the Commission for Air Quality Management covering the whole National Capital Region and adjoining areas.

The practical tools are public and free: the National Air Quality Index publishes real-time AQI for hundreds of cities with health advisories attached to each band, and the SAMEER app carries the same data.

For residents during high-pollution months, the standard advice is to check the AQI before outdoor exercise, use an N95-grade mask rather than a cloth one when levels are severe, and use indoor filtration where possible. This matters most for children, older adults and anyone with respiratory or cardiac conditions.

The Graded Response Action Plan triggers escalating restrictions in the NCR as AQI worsens — construction bans, restrictions on certain vehicles, school closures — so checking what stage is in force is worth doing during winter.

Heat. Heatwaves in the pre-monsoon period are the most lethal recurring weather hazard in India. The IMD issues colour-coded heat alerts, and a number of cities and states operate Heat Action Plans with cooling centres and adjusted working hours. The advice is unglamorous and effective: avoid outdoor exertion in the afternoon, drink more than you feel you need, and treat confusion or absent sweating in hot conditions as a medical emergency.

Cyclones. The Bay of Bengal is substantially more cyclone-prone than the Arabian Sea, with peak seasons around April–June and October–December. India's cyclone warning and mass evacuation system has improved dramatically over the past two decades and is regarded internationally as a success — deaths from major cyclones have fallen by orders of magnitude since 1999.

Floods. River flooding is annual in the Ganges and Brahmaputra basins, with Assam and Bihar particularly affected. Urban flash flooding is a separate and growing problem driven by drainage capacity.

Earthquakes. Large parts of the Himalayan belt, the northeast, and Gujarat's Kutch region sit in the highest seismic zones. The Bureau of Indian Standards zone map is the reference used in building codes.

Water stress is severe and structural. Groundwater depletion in the northwest is among the fastest anywhere in the world, driven by irrigation for water-intensive crops in water-poor states — a policy problem rather than a climatic one.

The National Disaster Management Authority coordinates preparedness and response, and the NDRF is the specialist response force. IMD warnings, NDMA advisories and state disaster management authority alerts are the systems to follow, and all are free and public.