What did christians believe they had to do to be saved

Salvation in Christianity, or deliverance, redemption is the "saving [of] human beings from death and separation from God" by Christ's death and resurrection,[1][note 1] and the justification following this salvation. Christians partake in this redemption by baptism, repentance, and participating in Jesus' death and resurrection.

the causes of the dust bowls were severe droughts,   lands became dry and hard, temperature was higher than usual, hot and dry conditions killed crops, high winds. because of those factors, the winds kicked up dry soil and created clouds of dust.