Year	% of land area
1990	30.765626659369406
1991	30.625493087031227
1992	30.485359514693048
1993	30.249808198857334
1994	30.11021974979795
1995	29.970631300738567
1996	29.831042851679186
1997	29.691454402619804
1998	29.551865953560423
1999	29.41227750450105
2000	29.272689055441663
2001	29.12315569692856
2002	28.973622338415456
2003	28.824088979902346
2004	28.646171318397073
2005	28.496725701179628
2006	28.347370581651077
2007	28.19794548663763
2008	28.048525937486627
2009	27.903340263635677
2010	27.75296291862982
2011	27.576769975471592
2012	27.233762284606758
2013	27.059318478747098
2014	26.884597199292887
2015	26.70978930879879
2016	26.5274001430678
2017	26.349098187952862
2018	26.172624567340744
2019	25.991142317190775
2020	25.81166596813751
2021	25.630837601600557