“…Copulas are widely used to investigate multivariate distribution in hydrology. However, most research focuses on rainfall and floods (De Michele and Salvadori, 2003;Favre et al, 2004;de Michele, 2004a, 2004b;De Michele et al, 2005;Shiau et al, 2006;Grimaldi and Serinaldi, 2006;Salvadori and de Michele, 2006;Zhang and Singh, 2006;Kao and Govindaraju, 2007;Renard and Lang, 2007;Zhang and Singh, 2007;Evin and Favre, 2008;Kao and Govindaraju, 2008). To our knowledge, Shiau (2006) is the first use the copula method to investigate the drought problem.…”