Period (No. of Years) | Significant Trend of Change | Periodical Average (t/year) | Standard Deviation |
1959-1970 (13) | Stable | 175 | 28 |
1970-1990 (20) | Increase | 248 | 112 |
1990-2010 (20) | Decline | 231 | 154 |
2011-2016 (5) | Increase | 184 | 99 |