(CNN) -- Colombia's president called for national unity Monday night as the country struggles to dig out of the devastation wrought by the torrential rains and massive floods that have so far claimed 91 lives this year.
It is the longest rainy season the country has had in the past 40 years, according to the Colombian Red Cross, which released new casualty figures Monday.
So far this year, 91 people have been killed in the floods, 79 have been hurt, and 15 people remain missing, according to the Red Cross figures. Most of those are from the month of April.
"This is the worst natural tragedy in memory," Colombian President Juan Manuel Santos said about the rains, calling on his countrymen to work together. "Colombia is bigger than the adversity it faces."
He said humanitarian assistance would be the government's first priority, securing people's homes and health.
According to the Red Cross, more than 1,000 municipalities in 28 of Colombia's 32 provinces have been affected, in addition to the district around the capital, Bogota.
The aid agency said the extreme weather is a result of La Nina, the weather phenomenon known to bring heavy rainfall to northern South America. La Nina typically happens every few years, though Colombia also has an annual rainy season.
It is the second straight year that Colombia has been devastated by torrential rain and massive flooding. Last year, 408 people died in the nation and more than 2.8 million people were left homeless or affected in some way by the rain.
CNN's Helena deMoura, Rafael Romo, and Taylor Ward contributed to this report.