Year	% of land area
1990	28.902708383381853
1991	28.89516425207105
1992	28.88303873815428
1993	28.870913217909646
1994	28.858787697665015
1995	28.846680431175326
1996	28.83457315569087
1997	28.822447620100515
1998	28.81032208451017
1999	28.79819654891982
2000	28.692550009825382
2001	28.81369561023719
2002	28.935871956494687
2003	29.044669127529932
2004	29.166477072013592
2005	29.28262500301364
2006	29.39803619207133
2007	29.519485616028724
2008	29.640531405896212
2009	29.761707569150737
2010	29.882208128481846
2011	29.918836363908415
2012	29.95536374380869
2013	29.99293360759227
2014	30.028836360417753
2015	30.065398886359727
2016	30.19550187641993
2017	30.197766192014477
2018	30.247480086724234
2019	30.297160090120173
2020	30.346427943161135
2021	30.36733345129391