Regional Wet and Dry Spell Analysis with Heterogeneous Probability Occurrences

Wet and dry spells are among the most significant natural phenomena because they affect the water resources, crop yield, and food demand, causing surpluses and deficits within a region. Wet- and dry-induced natural disasters have increased due to climate change effects with their temporal and spatial coverage during the last two decades because of anthropogenic and naturally unexpected developments such as the global warming implying greenhouse effect and precipitation deficiency. Many countries have set up national drought and flood preparedness plans in the expectation of reducing societal vulnerability to such effects by the adaptation of preventive anticipatory policies and programs. Although wet- or dry-prone countries may have different causal effects, the drought and flood evaluation methodologies are common irrespective of geographical locations. It is therefore necessary to elaborate on different wet and dry hazard assessment methodologies on a scientific basis so as to be useful to all concerned parties whether hydrologist, agriculturalist, meteorologist, researcher, or administrator. This paper provides regional probabilistic wet and dry period areal coverage modeling, which is useful for temporal and spatial wet or dry risk predictions and parameter assessments. The basis of the methodology is mutually exclusive and has independent subareal (site) dry and wet spell heterogeneous probabilities. Derived expressions are general and reduce to a simple Bernoulli (homogeneous) trial case as available in the literature. The application of the proposed methodology is presented for six precipitation sites in the northwestern part of Turkey.