Year	% of land area
1990	19.162011173184357
1991	19.513035381750466
1992	19.864059590316575
1993	20.21508379888268
1994	20.56610800744879
1995	20.917132216014895
1996	21.268156424581004
1997	21.619180633147113
1998	21.970204841713223
1999	22.321229050279328
2000	22.672253258845437
2001	23.135009310986966
2002	23.821787762007705
2003	24.286654135338345
2004	24.75143313598346
2005	25.211386696730553
2006	25.68072911772996
2007	26.145246148064636
2008	26.61217587373168
2009	27.079105599398723
2010	27.546035325065766
2011	27.908630676660774
2012	28.437209912891824
2013	29.583573210516217
2014	30.124975966160356
2015	30.585975024015372
2016	31.151480199923103
2017	31.233140655105974
2018	31.233140655105974
2019	31.233140655105974
2020	31.233140655105974
2021	31.233140655105974