How did climatic conditions help Haitians defeat the French?

Facing both slave rebellion and the possibility of attack
by British troops, Napoleon Bonaparte sent an army of 40,000 European troops to Haiti in
1802. Led by Napoleon's brother-in-law, Charles Leclerc, the French regained control
of eastern Hispaniola and won several victories against the Haitian rebels led by
Toussaint Louverture. After Louverture was captured during a supposed peace negotiation,
he was deported to France, where he died in custody. Louverture's one-time allies,
Jean-Jacque Dessalines and Henri Christophe, reunited and fought back against Leclerc's
troops. Fighting was bloody, but it was actually the rainy season which eventually
defeated the French army. A yellow fever and malaria epidemic virtually wiped out the
Napoleon's troops. More than 24,000 French soldiers died, including their leader,
Leclerc, while another 8,000 were hospitalized, effectively reducing the French force by
more than 75%.