Is "why" implied after "explain" in this context? [closed]

Suppose that we asked to "explain the trend" in the following graph:

Would it be appropriate to just describe the trend (i.e. something along the lines of "it first increases, and then decreases"), or does the question ask for an elaboration on why the trend is so?

In other words, does the verb "explain" in this context imply "explain why" such that "why" is omittable?

Start with the definition of explain.

Cambridge

explain:

to make something clear or easy to understand by describing or giving information about it

You might therefore argue that it is sufficient to describe the trend in the graph (it rises then falls).

However, if the request is part of an exercise or examination question that argument would be a risky strategy to adopt and one likely to earn low marks. You are much better advised to adopt the whole definition. Do not only describe but also give some information about what you have described. The information you give depends on context and your knowledge (it rises because ..., then falls because ...).

This view is reinforced by other definitions, which lay even more emphasis on providing information. For example:

Merriam Webster

explain:

to make something plain or understandable

From this viewpoint it is inadequate merely to describe the trend. You need to make it understandable as suggested above.