Year	mm per year
1961	2666
1962	2666
1963	2666
1964	2666
1965	2666
1966	2666
1967	2666
1968	2666
1969	2666
1970	2666
1971	2666
1972	2666
1973	2666
1974	2666
1975	2666
1976	2666
1977	2666
1978	2666
1979	2666
1980	2666
1981	2666
1982	2666
1983	2666
1984	2666
1985	2666
1986	2666
1987	2666
1988	2666
1989	2666
1990	2666
1991	2666
1992	2666
1993	2666
1994	2666
1995	2666
1996	2666
1997	2666
1998	2666
1999	2666
2000	2666
2001	2666
2002	2666
2003	2666
2004	2666
2005	2666
2006	2666
2007	2666
2008	2666
2009	2666
2010	2666
2011	2666
2012	2666
2013	2666
2014	2666
2015	2666
2016	2666
2017	2666
2018	2666
2019	2666
2020	2666