Year	% of land area
1961	31.03222898929495
1962	31.102205636374105
1963	31.158717389263103
1964	31.19380771957685
1965	31.222777643440523
1966	31.23751762230778
1967	31.27148587810568
1968	31.34804196211866
1969	31.423781991938302
1970	31.422047876777448
1971	31.475805446763914
1972	31.562970235290354
1973	31.58577894999429
1974	31.58780557581423
1975	31.61619701086534
1976	31.683202894499118
1977	31.70936869970893
1978	31.743287336092013
1979	31.804544903454556
1980	31.87860484334665
1981	31.87518747697422
1982	31.90400556653278
1983	31.949145405929823
1984	31.955776116801704
1985	32.0973672966505
1986	32.30317436102007
1987	32.395545264012206
1988	32.58814191210625
1989	32.66500715275184
1990	32.7914497085318
1991	32.919820809511236
1992	34.209820771069175
1993	33.554563711599506
1994	33.76435444200331
1995	34.0044988521979
1996	34.15854112244588
1997	34.256827090458025
1998	34.31191531484911
1999	34.39447004060394
2000	34.49966975083834
2001	34.644375536851804
2002	34.73651143485316
2003	34.99451221853255
2004	34.82193356388949
2005	35.18407023814741
2006	35.325990172792615
2007	35.49058864815149
2008	35.49181845263425
2009	35.628072782318974
2010	35.827128660568974
2011	36.006308377447546
2012	36.052973209191116
2013	36.22320404031728
2014	36.33705858348544
2015	36.41183391697265
2016	36.52683468502915
2017	36.644995187944915
2018	36.72262437416343
2019	36.75640112359432
2020	36.81510886827078
2021	36.847182912799134