Year	% of land area
1961	19.929753002492635
1962	20.01472920915477
1963	20.06571493315205
1964	20.365964196691593
1965	20.547246770904145
1966	20.547246770904145
1967	20.558576931792434
1968	20.26399274869703
1969	19.6974847042828
1970	19.368910038522547
1971	13.879447088148652
1972	13.879447088148652
1973	13.879447088148652
1974	14.162701110355766
1975	14.162701110355766
1976	14.445955132562883
1977	14.445955132562883
1978	14.729209154769999
1979	14.729209154769999
1980	15.012463176977114
1981	15.012463176977114
1982	15.182415590301382
1983	15.239066394742807
1984	15.24473147518695
1985	16.938590527985497
1986	18.63811466122819
1987	20.960797643326533
1988	23.510083843190575
1989	25.124631769771135
1990	25.237933378653977
1991	25.549512803081804
1992	25.577838205302516
1993	25.668479492408792
1994	25.889417629730342
1995	25.889417629730342
1996	25.946068434171764
1997	25.946068434171764
1998	26.229322456378878
1999	26.285973260820306
2000	27.0224337185588
2001	27.70224337185588
2002	28.32540222071153
2003	28.891910265125766
2004	29.62837072286427
2005	30.342170858826194
2006	30.336505778382055
2007	30.336505778382055
2008	30.336505778382055
2009	30.336505778382055
2010	30.608429639700883
2011	30.878618853387717
2012	31.34133355993655
2013	31.5665318377521
2014	31.73507874461817
2015	31.994266938590528
2016	32.29311126217993
2017	32.767572513029684
2018	33.17405279854974
2019	33.71083050079311
2020	34.247607636528436
2021	34.552117040561974