Year	% of land area
1990	17.27974936406761
1991	17.346739571430632
1992	17.413729778793655
1993	17.48071998615669
1994	17.573166117662836
1995	17.640253505661864
1996	17.707340914615237
1997	17.774428302614265
1998	17.841515690613292
1999	17.90860307861232
2000	17.97437222244339
2001	18.009431382696754
2002	18.044490542950115
2003	18.079549703203472
2004	18.12099897567506
2005	18.156070503403203
2006	18.191142031131346
2007	18.226213558859488
2008	18.26128508658763
2009	18.296356593355572
2010	18.33142812108372
2011	18.38177527438473
2012	18.43212242768574
2013	18.482469580986752
2014	18.532816734287763
2015	18.586346703339323
2016	18.628349129808516
2017	18.68010843248975
2018	18.72717145298529
2019	18.77410339357455
2020	18.821054816231037
2021	18.867988645987943