BANGKOK (Thomson Reuters Foundation) - With a booming trade in diamond cutting and textile manufacturing, the port city of Surat in Gujarat is a melting pot for migrants from across the country seeking work and business opportunities. 

Kamlesh Yagnik was one of them. In his early 30s, the Mumbai native moved to the "Diamond City", as Surat is known locally because it handles 90 percent of the world's rough diamond cutting and polishing.

In the two decades since, the engineer has set up a technology consultancy and a clean energy management firm, raised a family, and come to regard Surat as home. 

Now he is the city's first chief resilience officer, tasked with making the industrial hub "cohesive, robust and sustainable". 

It will not be an easy task. 

Surat, home to nearly 6 million people, is one of the world's fastest-growing cities. Up to the 1960s, it occupied 8.2 square kilometres (3.17 square miles) of land on the bank of the Tapi River. By 2009, it had expanded to 326.5 square km. 

It has a limited public transport system and insufficient affordable housing for the throngs of people that continue to arrive, betting their future on the city. 

The Tapi River is the city's main water source but its quality is deteriorating. Surat also faces the threat of sea-level rise, while flooding and saltwater intrusion are already a problem. 

Meanwhile the industries that made Surat's name could lead to its undoing, experts warn. 

"This city is thriving, and it's only because of the growth of diamonds and textiles", Yagnik told the Thomson Reuters Foundation in a phone interview. 

But the raw materials are not produced in India - with much of Surat's diamond supply coming from Africa - and that makes the city highly vulnerable to outside shocks, he emphasised. 

"Economic resilience is a prime pillar for us," said the former head of the Southern Gujarat Chamber of Commerce and Industry. 

Two weeks ago, Surat unveiled a document outlining how to achieve its vision of "healthy, just, economically viable and environmentally sound" communities. 

The strategy explores how the city can diversify its economy, to bolster it against any downturn in diamonds and textiles, by developing policies to support its IT industry, promoting smaller businesses, and providing skills training. 

The strategy was developed under the Rockefeller Foundation's 100 Resilient Cities (100RC) initiative, which helps cities around the world prepare for climate change and other pressures. 

Surat is the first Indian city to publish its strategy, which Yagnik hopes will serve as a model for others, including three - Chennai, Pune and Jaipur - in the 100RC network.