Year	% of land area
1990	30.073217029738768
1991	30.116604899213595
1992	30.159992768688422
1993	30.203380638163246
1994	30.246768507638073
1995	30.290156377112897
1996	30.333544246587724
1997	30.376932116062548
1998	30.420319985537375
1999	30.463707855012203
2000	30.507095724487026
2001	30.834312573443007
2002	31.68566176470588
2003	32.02721338604395
2004	32.36300110334682
2005	32.7319587628866
2006	33.068213200773265
2007	33.407605192892
2008	33.74090783537427
2009	34.08990420044215
2010	34.42336035372144
2011	34.600221075902724
2012	34.77708179808401
2013	34.953942520265294
2014	35.130803242446575
2015	35.30766396462786
2016	35.38135593220339
2017	35.50110537951363
2018	35.62085482682388
2019	35.74060427413412
2020	35.86035372144436
2021	35.98010316875461