Year	% of land area
1990	31.628694607231466
1991	31.646718209758443
1992	31.460489526360853
1993	31.486887178322696
1994	31.50686485168907
1995	31.526838535019422
1996	31.546847800063286
1997	31.56690249110703
1998	31.586984551836256
1999	31.606973914071165
2000	31.613867591261606
2001	31.63808015309066
2002	31.66438980894128
2003	31.687871959636517
2004	31.71220309570307
2005	31.736315126958964
2006	31.76085493095986
2007	31.784754845597604
2008	31.823922556219724
2009	31.847012290014447
2010	31.869510058024456
2011	31.90907361231173
2012	31.948692681441166
2013	31.990679853630702
2014	32.02994841512806
2015	32.070233090796776
2016	32.09868457419038
2017	32.094319722540384
2018	32.098942165634085
2019	32.104262189077225
2020	32.110874564169755
2021	32.29850259132561