Khan's announcement comes after a huge number of fires raged across the capital last week caused by the record high temperatures, prompting London Fire Brigade (LFB) to declare a major incident.
"The extreme temperatures and fires that raged across the capital last week laid bare how vulnerable London is to the effects of climate change, which is why today I've pledged a further £3.1m for a mass tree-planting package to help limit the affects of the climate emergency and the ecological crisis," Khan said.
He added: "These additional street trees and improvements to green spaces are targeted in areas where they're most needed and will improve resilience of neighbourhoods in our city."
London remains at immediate risk of wildfires because of tinder dry grass, with the LFB warning that any small sparks can start a serious fire.
Meanwhile, the Environment Agency has warned that more prolonged dry weather in the coming weeks could push London and the southeast into a drought as soon as August.
Since 2016, the Mayor has funded the planting of over 430,000 trees across London, including two major woodland creation projects, creating an additional 85 hectares of new accessible green space in the Green Belt, a policy for controlling urban growth.
Khan has also invested over £20m in green infrastructure programmes that have supported green space projects in all 32 boroughs and the City of London, improving or creating over 500 hectares of green space. This includes over 250 community green space projects, over 80 community tree-planting projects and six major capital projects.
The 'urban heat island' effect intensifies heat in cities, a result of the sun's rays being absorbed by hard surfaces - which warm up and radiate the heat back out - instead of being handled more efficiently by trees, plants and grass, experts have said. Increasing the number of trees in London will help tackle this, cooling the city, providing shade to Londoners and making London more resilient to flooding.
London's existing trees are estimated to provide at least £133m of benefits to Londoners every year. They help improve air quality by removing 2,241 tonnes of pollution annually, including harmful PM10 particulates and NO2 roadside emissions and making our streets more beautiful and encouraging walking and cycling.
Trees also create a vital habitat for London's wildlife, reduce flood risk and help to tackle climate change through absorbing and storing carbon.
The Mayor's funding package will be targeted in areas where there are low numbers of existing trees and where Londoners are most vulnerable to the effects of climate change.
Kham said: "The climate emergency is the biggest global threat we face today and we know it doesn't affect all Londoners equally, with communities suffering poverty, deprivation and health inequalities more likely to experience the worst effects of flooding, overheating and poor quality air.
"As Mayor, I will continue my bold action to preserve and increase tree coverage across the capital as we build a better, greener and more sustainable London for everyone."
Mayor Philip Glanville, London Councils' Climate Change, Transport and Environment Lead, said: "London is already experiencing the serious affects of climate change. The severe heatwave and fires last week and the devastating flash flooding last year are just two examples that prove the time for action is now.
"London boroughs are collaborating with partners, like the Mayor of London, on initiatives such as this that work for every resident across London's diverse communities and crucially, have a long-lasting impact.
"More trees in London will contribute to our capital's climate resilience, especially in areas more vulnerable to climate risk, and will take steps to ensure that London can continue to thrive as a resilient and green city."
"London's trees and green spaces play a critical role in the fightback against climate change," said David Elliot, chief executive of Trees for Cities. "This new tree programme from the Mayor of London and the Greater London Authority to further enhance our 'urban forest' will ensure that our city remains a leader in setting the bar high for others to follow."
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