Year	sq. km
1961	22969
1962	22873
1963	22769
1964	22578
1965	22473
1966	22481
1967	22417
1968	22347
1969	22182
1970	22013
1971	21364
1972	21217
1973	21080
1974	20991
1975	20871
1976	20799
1977	20658
1978	20503
1979	20368
1980	20372
1981	20305
1982	20274
1983	20088
1984	20149
1985	20198
1986	20180
1987	20143
1988	20154
1989	20059
1990	20180
1991	19695
1992	19638
1993	19669
1994	19504
1995	19647
1996	19506
1997	19633
1998	19158
1999	19726
2000	19596
2001	19227
2002	19401
2003	19137
2004	19494
2005	19377
2006	19196
2007	19144
2008	19293
2009	19174
2010	18723
2011	18584
2012	18417
2013	18476
2014	18391
2015	18460
2016	18150
2017	18190
2018	18230
2019	18168
2020	18144.5
2021	18120