Why are some rivers still able to flow during times of

"Due to the increased temperature the snow starts melting and more water gets deposited in the upstream that flows downwards" as a result of which rivers flow in drought condition.

Explanation:

During hotter days, snows begins to melt hence the river gets more water when compared to the other seasons of the year. But in some case the rivers only rely on the rainfall which often gets dry due to lack of proper rainfall. In some cases it has also been seen that, in spite of low rainfall the river still continue to flow because of the presence of more water in the upstream that begins to flow towards the downward stream having larger basins.

a physical change is being made.