Year	% of land area
1961	0.20288979999935075
1962	0.20559499733267542
1963	0.21154643146598973
1964	0.2158747471993092
1965	0.2191209839992988
1966	0.22074410239929362
1967	0.22561345759927803
1968	0.2310238522659274
1969	0.23372904959925206
1970	0.24076256266589624
1971	0.2450908783992157
1972	0.24617295733254557
1973	0.25309826250585676
1974	0.24996023359920014
1975	0.2514210401591955
1976	0.2567232269325118
1977	0.26159258213249625
1978	0.270175234850831
1979	0.27125055916864527
1980	0.27544432400812086
1981	0.2814661401878807
1982	0.2817349712673342
1983	0.28334795774405563
1984	0.297864836034548
1985	0.2967895117167338
1986	0.30324145762361926
1987	0.31076872784831905
1988	0.3123817143250404
1989	0.32582326829771857
1990	0.32313495750318294
1991	0.32101595043025166
1992	0.32173561693778324
1993	0.3206969224521084
1994	0.3213329087117443
1995	0.32816090725857944
1996	0.3396277750471575
1997	0.36568883820301673
1998	0.37090105083418856
1999	0.38914379504329005
2000	0.40003210722980803
2001	0.40153843668021666
2002	0.3981452862573238
2003	0.39876346112048433
2004	0.3985324282646846
2005	0.39612544720222775
2006	0.3974527136794642
2007	0.3948553081313608
2008	0.3904448224916442
2009	0.38997341467104024
2010	0.38562673863830627
2011	0.38805053145472196
2012	0.3886156245062462
2013	0.37988656161578505
2014	0.3815616835272761
2015	0.3823742759759407
2016	0.3813073379651562
2017	0.38436019644668107
2018	0.38655215528493353
2019	0.38830391910076045
2020	0.3862940079338977
2021	0.3867980036339001