Year	mm per year
1961	1904
1962	1904
1963	1904
1964	1904
1965	1904
1966	1904
1967	1904
1968	1904
1969	1904
1970	1904
1971	1904
1972	1904
1973	1904
1974	1904
1975	1904
1976	1904
1977	1904
1978	1904
1979	1904
1980	1904
1981	1904
1982	1904
1983	1904
1984	1904
1985	1904
1986	1904
1987	1904
1988	1904
1989	1904
1990	1904
1991	1904
1992	1904
1993	1904
1994	1904
1995	1904
1996	1904
1997	1904
1998	1904
1999	1904
2000	1904
2001	1904
2002	1904
2003	1904
2004	1904
2005	1904
2006	1904
2007	1904
2008	1904
2009	1904
2010	1904
2011	1904
2012	1904
2013	1904
2014	1904
2015	1904
2016	1904
2017	1904
2018	1904
2019	1904
2020	1904