Rich with promise and potential, the grapes that create the Russian River Valley’s famed wines are ripening in the intense midday heat.

But soon they’ll face the fight of their lives, deprived of water as the state diverts scarce supplies from agriculture to the region’s thirsty cities and subdivisions.

“Whatever water we have on the ground is all we’re going to get,” said Mendocino County supervisor and plant scientist Glenn McGourty, whose district spans the rural upper reaches of the river’s watershed, where the dance of cool nights and hot days, combined with alluvial soil, produces unique growing conditions.