Year	mm per year
1961	836
1962	836
1963	836
1964	836
1965	836
1966	836
1967	836
1968	836
1969	836
1970	836
1971	836
1972	836
1973	836
1974	836
1975	836
1976	836
1977	836
1978	836
1979	836
1980	836
1981	836
1982	836
1983	836
1984	836
1985	836
1986	836
1987	836
1988	836
1989	836
1990	836
1991	836
1992	836
1993	836
1994	836
1995	836
1996	836
1997	836
1998	836
1999	836
2000	836
2001	836
2002	836
2003	836
2004	836
2005	836
2006	836
2007	836
2008	836
2009	836
2010	836
2011	836
2012	836
2013	836
2014	836
2015	836
2016	836
2017	836
2018	836
2019	836
2020	836