"Decadal changes" refers to changes or shifts that occur over a period of 10 years. It means that something is gradually evolving or transforming over the course of a decade. Full definition
Here, we show that, during the recent global warming of about 0.4 °C since the late 1970s, a coherent decadal change of precipitation and circulation emerges in the entirety of the NHSM system. (dotearth.blogs.nytimes.com)
With this final correction, the ERBS Nonscanner - observed decadal changes in tropical mean LW, SW, and net radiation between the 1980s and the 1990s now stand at -0.7, +2.1, and +1.4 W / m2, respectively.» (watertechbyrie.com)
April 23, 2018 - A new earth modeling system unveiled today will have weather - scale resolution and use advanced computers to simulate aspects of Earth's variability and anticipate decadal changes that will critically impact the U.S. energy sector in coming years. (llnl.gov)