The death toll from floods in four provinces of Indonesia's Sumatra Island has risen to 20 people.The Indonesian National Disaster Management Agency reported Tuesday that flash floods and landslides have affected four provinces on Sumatra Island, including Karo, Deli Serdang, South Tapanuli and Padang Lawas.The death toll from the floods has so far reached 20, with two people still missing.Indonesia has faced a series of extreme weather conditions during the rainy season, which climate scientists believe are becoming more frequent due to climate change.