A positive trend is found in the first part of the curve (1987–2001, 2.3 × 10 –4 m 2 /s 2 per year, green line in figure), followed by a central decade without statistically significant changes (2001–2010, blue line), and a steep negative trend afterward (2010–2017, – 4.1 10 –4 m 2 /s 2 per year, red line).
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