What might cause the peaks in river discharge between november and march answer?

The period between the month of November and March is the rainy season in the mountain regions. The precipitation levels reach its highest levels of the year, causing a great amount of water discharge to the rivers that end pouring water to the ocean.

Although it is known as a regular annual weather phenomenon, many communities that live near the river banks are negatively affected during this period, as floods produced by the risen water levels cause destruction along the river's path.

i would go with the last one

it affected it because the kingdoms (with trade) slowly got richer and richer.