"The greatest reward comes with the greatest trial. When Allah loves a people He tests them. Whoever accepts that win His pleasure but whoever is discontent with that earns His wrath." Narrated by al-Tirmidhi (2396) and Ibn Majah (4031).
Calamities and disasters are a test, and they are a sign of Allah's love for a person, because they are like medicine: even though it is bitter, despite its bitterness you give it to the on whom you love - and for Allah is the highest description.
Calamities are good for the believer in the sense that reward is stored up for him in the hereafter, he is raised in status and his bad deeds are expiated.
Sheikh al Islam Ibn Taymiyyah (may Allah have mercy on him) said; A calamity that make you turn to Allah is better for you than a blessing which makes you forget the remembrance of Allah.