Year	% of land area
1990	28.998661399327435
1991	29.05644976982598
1992	29.114238140324527
1993	29.172026510823073
1994	29.229814881321627
1995	29.287603251820173
1996	29.34539162231872
1997	29.403179992817265
1998	29.46096836331581
1999	29.51875673381436
2000	29.576545104312906
2001	29.66469685592086
2002	29.752848607528815
2003	29.84587251828631
2004	29.925244017889202
2005	30.013384258805864
2006	30.10250718203186
2007	30.190650300339517
2008	30.280770486451193
2009	30.37090244220974
2010	30.4590570719603
2011	30.523462756751464
2012	30.583893932466854
2013	30.64432905522354
2014	30.705770926548876
2015	30.76521114340769
2016	30.81420033312649
2017	30.85339168490153
2018	30.894601038638665
2019	30.939858220900984
2020	30.977035899781143
2021	31.01927474681477