Year mm per year 1961 416 1962 416 1963 416 1964 416 1965 416 1966 416 1967 416 1968 416 1969 416 1970 416 1971 416 1972 416 1973 416 1974 416 1975 416 1976 416 1977 416 1978 416 1979 416 1980 416 1981 416 1982 416 1983 416 1984 416 1985 416 1986 416 1987 416 1988 416 1989 416 1990 416 1991 416 1992 416 1993 416 1994 416 1995 416 1996 416 1997 416 1998 416 1999 416 2000 416 2001 416 2002 416 2003 416 2004 416 2005 416 2006 416 2007 416 2008 416 2009 416 2010 416 2011 416 2012 416 2013 416 2014 416 2015 416 2016 416 2017 416 2018 416 2019 416 2020 416