Conditional Copula-Based Spatial-Temporal Drought Characteristics Analysis-A Case Study over Turkey

In this study, commonly used copula functions belonging to Archimedean and Elliptical families are fitted to the univariate cumulative distribution functions (CDF) of the drought characteristics duration (LD), average severity (S), and average areal extent (A) of droughts obtained using standardized precipitation index (SPI) between 1960 and 2013 over Ankara, Turkey. Probabilistic modeling of drought characteristics with seven different fitted copula functions and their comparisons with independently estimated empirical joint distributions show normal copula links drought characteristics better than other copula functions. On average, droughts occur with an average LD of 6.9 months, S of 0.94, and A of 73%, while such a drought event happens on average once in every 6.65 years. Results also show a very strong and statistically significant relation between S and A, and drought return periods are more sensitive to the unconditioned drought characteristic, while return periods decrease by adding additional variables to the analysis (i.e., trivariate drought analysis compared to bivariate).