Quantifying Spatiotemporal Dynamics of Solar Radiation over the Northeast China Based on ACO-BPNN Model and Intensity Analysis

Table 5

Area statistics of vegetation coverage levels in each period.

Periods	Area & ratio	I	II	III	IV
1982–1990	Area (km^2)	18923	275287	222010	725953
	Ratio (%)	1.52%	22.16%	17.87%	58.44%
1991–2000	Area (km^2)	65289	256145	270977	649762
	Ratio (%)	5.26%	20.62%	21.81%	52.31%
2001–2010	Area (km^2)	155302	256224	327766	502881
	Ratio (%)	12.5%	20.63%	26.39%	40.48%
Variable area (km^2)	1980s–1990s	46366	−19142	48967	−76191
	1990s–2000s	90013	79	56789	−146881