The words "sparse" and "scarce" are often used interchangeably, but they have slightly different meanings. "Sparse" refers to something that is thinly scattered or spread out over a large area.
For example, you might say that a forest is "sparse" if there are few trees.

"Scarce" refers to something that is in short supply or difficult to obtain.
For example, you might say that water is "scarce" in a desert.

In some cases, something can be both sparse and scarce.
For example, diamonds are both sparse and scarce. There are very few diamonds in the world, and they are difficult to find.

However, not all sparse things are scarce. For example, a desert might be sparse, but there is no shortage of sand. Here are some examples of how to use the words "sparse" and "scarce" in a sentence:
The population of the town is sparse.
The rainfall in the region is scarce.
The forest is sparsely populated.
Water is scarce in the desert.
The diamonds are both sparse and scarce.