Year mm per year 1961 536 1962 536 1963 536 1964 536 1965 536 1966 536 1967 536 1968 536 1969 536 1970 536 1971 536 1972 536 1973 536 1974 536 1975 536 1976 536 1977 536 1978 536 1979 536 1980 536 1981 536 1982 536 1983 536 1984 536 1985 536 1986 536 1987 536 1988 536 1989 536 1990 536 1991 536 1992 536 1993 536 1994 536 1995 536 1996 536 1997 536 1998 536 1999 536 2000 536 2001 536 2002 536 2003 536 2004 536 2005 536 2006 536 2007 536 2008 536 2009 536 2010 536 2011 536 2012 536 2013 536 2014 536 2015 536 2016 536 2017 536 2018 536 2019 536 2020 536