Year	% of land area
1990	17.436147186147185
1991	17.549783549783548
1992	17.66341991341991
1993	17.77705627705628
1994	17.89069264069264
1995	18.004329004329005
1996	18.117965367965365
1997	18.231601731601728
1998	18.345238095238095
1999	18.458874458874458
2000	18.57251082251082
2001	18.58582251082251
2002	18.5991341991342
2003	18.612445887445887
2004	18.625757575757575
2005	18.639069264069263
2006	18.652380952380952
2007	18.66569264069264
2008	18.67900432900433
2009	18.692316017316017
2010	18.705627705627705
2011	18.702813852813854
2012	18.7
2013	18.697186147186144
2014	18.694372294372293
2015	18.69155844155844
2016	18.68073593073593
2017	18.67857142857143
2018	18.676406926406926
2019	18.674242424242422
2020	18.67207792207792
2021	18.66991341991342