Year	% of land area
1961	39.517624739941056
1962	39.516301719967146
1963	39.555519440958086
1964	39.56913653629014
1965	39.625309845119716
1966	39.637402647972365
1967	39.68997734632257
1968	40.36672993819007
1969	40.29715748626497
1970	39.69993153241586
1971	39.823267156059636
1972	39.818686188211174
1973	39.73101513456596
1974	39.759940959964
1975	39.73808161516616
1976	39.77910054271418
1977	39.509296656145935
1978	39.585936046983555
1979	39.49701912577764
1980	39.542749866265495
1981	39.535098926908034
1982	39.42459234132887
1983	39.251223769850014
1984	39.34560917255099
1985	39.35340543802462
1986	38.832580193075465
1987	38.81746083669175
1988	38.83494289172573
1989	38.7280989782256
1990	38.63757072236213
1991	38.5549098376755
1992	38.574722411879854
1993	38.35348021441875
1994	38.53687085837524
1995	38.25792870530052
1996	38.202848299681214
1997	38.051391976444854
1998	38.110505559058026
1999	37.792175500654025
2000	37.79948071601023
2001	37.69010805966118
2002	37.358451621486246
2003	37.07661367299245
2004	35.844759368809505
2005	36.26197572849953
2006	36.142419178980475
2007	35.74866086830428
2008	35.34382661220535
2009	35.05751053476459
2010	34.66261231454327
2011	35.05280235145901
2012	34.71727506644151
2013	34.303971506374225
2014	34.32357207446293
2015	33.56371698815653
2016	33.37280794850895
2017	34.11918908140496
2018	33.71932557691729
2019	33.82313490735642
2020	33.58749316977391
2021	33.92086978348014