| Year | Area (km2) | Northern part (km2) | Southern part (km2) |
| 1972 | 986.21 | 986.21 | |
| 1975 | 926.01 | 926.01 | |
| 1984 | 968.37 | 697.94 | 270.43 |
| 1986 | 911.65 | 672.08 | 239.57 |
| 1988 | 898.30 | 667.70 | 230.60 |
| 1990 | 892.10 | 661.50 | 230.60 |
| 1992 | 904.62 | 642.87 | 261.75 |
| 1998 | 887.99 | 639.35 | 248.63 |
| 2000 | 901.82 | 642.04 | 259.78 |
| 2002 | 859.80 | 639.57 | 220.23 |
| 2004 | 865.80 | 637.43 | 228.37 |
| 2006 | 837.99 | 624.69 | 213.30 |
| 2008 | 832.89 | 618.34 | 214.55 |
| 2010 | 844.47 | 631.27 | 213.21 |
| 2013 | 812.18 | 611.32 | 200.86 |