Copper prices buckled under a stronger dollar on Tuesday ahead of key U.S. payroll data later this week and on lingering concerns over the fate of China Evergrande. The U.S. dollar edged toward a one-year high against major peers, making greenback-priced metals more expensive to holders of other currencies, in anticipation of Friday's non-farm payrolls data which is expected to give the Federal Reserve ammunition to start unwinding its easy monetary policy soon. Worries over defaults at Chinese property developers and the potential impact on metals demand grew on Tuesday, amid fresh credit rating downgrades and uncertainty about the fate of China Evergrande 3333.HK. On-warrant copper stocks in LME-registered warehouses that are available to the market have more than halved since mid-August to 100,250 tonnes. Meanwhile, in warehouses monitored by the Shanghai Futures Exchange, copper stocks are at their lowest since 2009 at 43,525 tonnes CU-STX-SGH. Three-month copper on the London Metal Exchange CMCU3 shed 1.7% to $9,090 a tonne. The metal is seen as a sensitive gauge of global economic growth.