Year	% of land area
1990	22.977272727272727
1991	22.827272727272728
1992	22.677272727272726
1993	22.52727272727273
1994	22.377272727272725
1995	22.227272727272727
1996	22.077272727272728
1997	21.92727272727273
1998	21.777272727272727
1999	21.627272727272725
2000	21.477272727272727
2001	21.325
2002	21.172727272727272
2003	21.020454545454545
2004	20.868181818181817
2005	20.715909090909093
2006	20.563636363636366
2007	20.411363636363635
2008	20.25909090909091
2009	20.10681818181818
2010	19.954545454545453
2011	19.804545454545455
2012	19.654545454545456
2013	19.50454545454545
2014	19.354545454545455
2015	19.204545454545453
2016	19.045454545454547
2017	18.90909090909091
2018	18.75
2019	18.59090909090909
2020	18.454545454545453
2021	18.302954545454543