Year	% of land area
1961	21.07609371760315
1962	20.71324901513581
1963	20.83765291312461
1964	21.677379224549036
1965	22.423802612481857
1966	22.672610408459466
1967	22.76591333195107
1968	22.537839518971595
1969	22.35123367198839
1970	22.32013269749119
1971	22.123159859008915
1972	21.812150114036907
1973	21.718847190545304
1974	21.511507360563964
1975	21.366369479577028
1976	21.35600248807796
1977	21.428571428571427
1978	21.55297532656023
1979	21.449305411569565
1980	21.35600248807796
1981	21.262699564586356
1982	21.241965581588225
1983	21.065726726104085
1984	20.91022185361808
1985	20.827285921625542
1986	20.77545096413021
1987	20.80655193862741
1988	20.70288202363674
1989	20.50590918515447
1990	20.246734397677795
1991	19.977192618702052
1992	19.67654986522911
1993	19.43810906075057
1994	19.127099315778562
1995	18.484345842836408
1996	18.090400165871863
1997	17.851959361393323
1998	17.706821480406386
1999	17.613518556914784
2000	17.810491395397055
2001	17.459168906346907
2002	17.295175121396838
2003	17.138429752066113
2004	17.072918818425943
2005	16.96437790397522
2006	16.71139554087531
2007	16.477507222451507
2008	16.135684091143418
2009	15.825262724088192
2010	15.504115226337447
2011	15.310217100524746
2012	15.642791080053437
2013	15.35319113994211
2014	15.149337986246536
2015	15.028990712709733
2016	14.576003446542687
2017	14.323659111885961
2018	14.089417555373258
2019	13.975409836065575
2020	13.852459016393443
2021	13.760245901639346