If you get a question like this one from Cambridge IELTS book 8, you don't need to worry about comparing the two charts. Just describe them separately:
- Introduction: say what each chart shows
- Overview: write one general sentence about the pie chart, and one about the table
- Details: describe the pie chart
- Details: describe the table
Here's an example 'overview'. Notice that I write a separate sentence about each chart, and I paraphrase several of the words from the question.
Overview (paragraph 2):
It is clear from the pie chart that there are three principal reasons why farmland becomes degraded, and over-grazing is the main one. The table shows that Europe had a far higher proportion of unproductive land than Oceania or North America in the 1990s.
Task: Find the examples of paraphrasing in the paragraph above.