(TheGuardian) - On a day when the skies were ashen from the smoke of distant wildfires, Chase Hurley kept his eyes trained on the slower-moving disaster at ground level: collapsing levees, buckling irrigation canals, water rising up over bridges and sloshing over roads.

This is the hidden disaster of California’s drought. So much water has been pumped out of the ground that vast areas of the Central Valley are sinking, destroying millions of dollars in infrastructure in the gradual collapse.

Four years of drought – and the last two years of record-smashing heat – have put water in extremely short supply.

Such climate-charged scenarios form the backdrop to the United Nations negotiations starting in Paris on 30 November, which are seeking to agree on collective action to reduce greenhouse gas emissions.

But the real-time evidence of climate change and the other effects of human interference in natural systems are already changing the contours of California’s landscape.

The strongest El Niño in 18 years is expected to bring some drought improvementto the Central Valley this winter, but the weather system won’t end it, according to the National Oceanic and Atmospheric Administration.

The Central Valley is the world’s largest patch of class one soil, considered to be the best for crops, and produces about 40% of the country’s fruits, nuts and vegetables.

In some parts of the valley, however, the land is sinking at a rate of 2in (5cm) a month. About 1,200 square miles, roughly bounded by interstate 5 and state route 99, is collapsing into what scientists describe as a “cone of depression”.