Year	% of land area
1961	36.02523659305994
1962	36.92834610184768
1963	37.39792699414151
1964	37.85038305543038
1965	38.76340694006309
1966	38.77422262280306
1967	38.77692654348805
1968	38.77872915727805
1969	38.78323569175304
1970	38.78323569175304
1971	40.60748084722848
1972	40.620099143758445
1973	40.634520054078415
1974	40.64803965750338
1975	40.662460567823345
1976	40.67598017124831
1977	40.84272194682289
1978	40.79405137449301
1979	40.80847228481298
1980	40.821991888237946
1981	40.83641279855791
1982	40.849932401982876
1983	40.86435331230284
1984	40.8796755295178
1985	40.896800360522754
1986	40.91482649842271
1987	40.9202343397927
1988	40.813880126182966
1989	40.72374943668319
1990	40.63361874718341
1991	40.45425867507886
1992	40.54348805768364
1993	40.47138350608382
1994	40.437133844073905
1995	40.1198738170347
1996	40.48670572329878
1997	40.63271744028842
1998	41.04821991888238
1999	41.1608832807571
2000	40.43172600270392
2001	37.62505633168094
2002	37.50067598017125
2003	37.900856241550244
2004	38.20730058584948
2005	38.35691753041911
2006	38.01171698963497
2007	38.247859396124376
2008	38.40829202343398
2009	38.341595313204145
2010	38.30824695808923
2011	37.60342496620099
2012	38.411536728255975
2013	40.39260928346102
2014	40.37854889589905
2015	40.36448850833709
2016	40.35042812077512
2017	39.19513294276701
2018	39.70076611086075
2019	39.97656602073006
2020	39.70462190175755
2021	38.50202794051374