Continuous heatwaves and droughts in the northern hemisphere are drying up rivers in many countries. In the western U.S., officials say the once-mighty Colorado River's water levels are at a "tipping point." The waterway and its tributaries are a vital source of water for 40 million people. In Europe, the Rhine is also thinning out, with water levels dropping considerably. Italy's main grain-producing area, the Po River basin, is also facing the worst drought in seven decades.