Standing where her family home once was, Ruth Deidree Boelan closed her eyes and prayed for relatives missing in devastating flash floods that swept resort island Bali this year.

The deluge that killed at least 18 people and left four missing was the island's worst in a decade, according to the Meteorology, Climatology and Geophysics Agency (BMKG).

It was caused partly by record rain, but was also a reckoning for years of rampant overdevelopment and a waste management system under enormous strain.

The island's formerly verdant south has been transformed by a tourism boom that brought jobs and economic benefits, but also paved over and built on paddy fields and coconut groves that once provided drainage.

The changes are made starkly clear in comparisons by conservation start-up The TreeMap's Nusantara Atlas project, which paired declassified Cold War-era US spy images of the island with recent satellite photos.

"All this land is now turned into roads or buildings, the soil doesn't have the same capability to absorb the water," The TreeMap founder David Gaveau explained.

More than 4.6 million foreign tourists........

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