So far, we have only used verbs to describe these line graphs but we can also use nouns. We change the adverbs into adjectives.

The population rose slowly. There was a slow rise in the population.
The population rose steadily. There was a steady rise in the population.
The population rose slightly. There was a slight rise in the population.
The population rose gently. There was a gentle rise in the population.
The population rose gradually. There was a gradual rise in the population.

From 1996 to 1998, the population increased dramatically. From 1996 to 1998 there was a dramatic increase in the population.
From 1996 to 1998, the population increased significantly. From 1996 to 1998 there was a significant increase in the population.
From 1996 to 1998, the population increased considerably. From 1996 to 1998 there was a considerable increase in the population.
From 1996 to 1998, the population increased rapidly. From 1996 to 1998 there was a rapid increase in the population.
From 1996 to 1998, the population increased substantially. From 1996 to 1998 there was a substantial increase in the population.
From 1996 to 1998, the population increased markedly. From 1996 to 1998 there was a dramatic increase in the population.
From 1996 to 1998, the population increased greatly. From 1996 to 1998 there was a great increase in the population.
After 1998, the population grew more slowly. After 1998, the population growth was slower.

From 1996 to 1998, the population rose from 9.9 million to 10.25 million. From 1996 to 1998, there was a rise in population from 9.9 million to 10.25 million.
From 1996 to 1998, the population rose by 0.35 million. From 1996 to 1998, there was a rise in population of 0.35 million.
From 1996 to 1998, the population rose by 350,000. From 1996 to 1998, there was a rise in population of 350,000.
From 1996 to 1998, the population rose by 3.535%. From 1996 to 1998, there was a rise in population of 3.535 per cent.

From 1998 to 2007, the population grew from 10.25 million to 10.30 million. From 1998 to 2007, there was a growth in population from 10.25 million to 10.30 million.
From 1998 to 2007, the population grew by 0.05 million. From 1998 to 2007, there was a growth in population of 0.05 million.
From 1998 to 2007, the population grew by 50,000. From 1998 to 2007, there was a growth in population of 50,000.
From 1998 to 2007, the population grew by 0.488%. From 1998 to 2007, there was a growth in population of 0.488 per cent.

Overall, the population went up from 9.9 million to 10.3 million. Overall, there was a growth in population from 9.9 million to 10.3 million.
Overall, the population went up by 0.4 million. Overall, there was an increase in population of 0.4 million.
Overall, the population went up by 400,000. Overall, there was a rise in population of 400,000.
Overall, the population went up by 4.04%. Overall, there was a growth in population of 4.04 per cent .

Instead of "growth in population" you can also say "population growth".

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