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