| 年份 | 覆盖度/% | ||||
|---|---|---|---|---|---|
| 低覆盖度 | 中低覆盖度 | 中等覆盖度 | 中高覆盖度 | 高覆盖度 | |
| 2000 | 3.33 | 5.61 | 55.48 | 32.89 | 2.69 |
| 2001 | 3.54 | 5.48 | 61.57 | 26.80 | 2.61 |
| 2002 | 3.93 | 6.45 | 59.84 | 27.15 | 2.63 |
| 2003 | 4.05 | 6.51 | 51.88 | 34.99 | 2.57 |
| 2004 | 4.23 | 6.41 | 49.01 | 37.40 | 2.94 |
| 2005 | 4.42 | 6.02 | 45.02 | 40.98 | 3.56 |
| 2006 | 3.87 | 5.34 | 38.63 | 48.77 | 3.39 |
| 2007 | 3.60 | 6.00 | 44.68 | 42.35 | 3.37 |
| 2008 | 3.93 | 5.93 | 42.72 | 44.25 | 3.17 |
| 2009 | 4.40 | 6.49 | 34.21 | 51.32 | 3.58 |
| 2010 | 3.57 | 5.13 | 21.55 | 64.63 | 5.13 |
| 2011 | 4.30 | 5.98 | 26.66 | 57.78 | 5.28 |
| 2012 | 3.57 | 5.13 | 21.55 | 64.63 | 5.13 |
| 2013 | 2.58 | 4.71 | 19.75 | 68.18 | 4.78 |
| 2014 | 2.16 | 4.68 | 23.16 | 65.38 | 4.61 |
| 2015 | 2.18 | 4.61 | 26.77 | 61.39 | 5.05 |
| 2016 | 2.09 | 4.37 | 25.66 | 63.36 | 4.53 |
| 2017 | 2.28 | 5.10 | 27.18 | 60.86 | 4.59 |
| 2018 | 2.20 | 5.07 | 33.99 | 53.68 | 5.06 |
| 2019 | 2.58 | 5.57 | 32.69 | 53.94 | 5.22 |
| 2020 | 1.97 | 4.43 | 23.64 | 63.84 | 6.13 |
