What Defines a Drought?
Specifically, a drought is a period to time when there is less than normal precipitation resulting in hydrologic imbalance, such as water shortages. Geographic regions vary in both short-term and long-term precipitation patterns and normal precipitation varies among these regions. What constitutes normal precipitation in one part of the world would constitute a severe drought in another. Scientists have developed several standardized indices to measure drought. The Palmer drought indices are water balance indices that include factors for water supply, water demand, and water runoff. The standardized precipitation index only considers precipitation. According to the National climactic data center (NCDC) the forests of southern California have experienced moderately dry conditions for the past 24 months.
