With seven months of drought each year, Indian farmers are rarely far from disaster. Could the answer be as simple as a piece of plastic tubing? In Maharashtra, western India, the temperature is soaring into the forties. The monsoon is over and there are months of relentless baking sunshine ahead. The fertile lands are turning into kilometre after kilometre of scorched brown earth. Farming has become almost impossibly difficult. Solitary figures...

PETTAH, India — As he approaches his first tree of the day, S. Mohan presses his calloused palms together and bows his head. “Oh God, I am climbing the coconut tree,” he whispers. “Protect me from harm.” With no safety gear beyond a strap of palm frond tied around his ankles, he launches himself onto the tree’s arcing trunk, which rises dozens of feet into the air. With a swift...