Year	% of land area
1990	29.180908223197648
1991	29.28881957330439
1992	29.396730486627305
1993	29.504640963169038
1994	29.612551002932236
1995	29.720460605919552
1996	29.82934774023796
1997	29.938242331483984
1998	30.047144388611464
1999	30.156053920576447
2000	30.264970170592587
2001	30.363419593364366
2002	30.461875099298126
2003	30.5603374622472
2004	30.65880669032231
2005	30.757282791636204
2006	30.855765774303705
2007	30.954254863087506
2008	31.052257325186233
2009	31.150262753612505
2010	31.24827193933171
2011	31.335755816381322
2012	31.42324155064883
2013	31.51073152810372
2014	31.59822336301777
2015	31.685717850794592
2016	31.7732664163142
2017	31.860333797102125
2018	31.94740117789005
2019	32.03446855867797
2020	32.1215359394659
2021	32.20860332025383