In the Shuo Wen Chieh Tzu, an ancient Chinese dictionary, lung is defined as "jade used for prayer during droughts." Dragons have been associated with religious practices connected with praying for rain.
就是說，在依賴雨水灌溉維生的古代農業社會中，萬一久旱不雨，便以玉雕龍，祭天求雨。