Spatial analysis of meteorological and hydrological drought characteristics using Copula model

Drought as a reversible climate phenomenon is an inevitable fact, especially in arid and semiarid areas. Therefore, predicting drought is important to deal with and mitigate its effects. Hydrological drought with its direct effect on water resources is the most important type of drought. It is caused by the lack of surface water flow and river discharge reduction. To measure its characteristics (magnitude and duration), Stream Flow Index (SDI) has been used. However, to predict hydrological drought, it is essential to understand its relationship with meteorological drought, which is described by the Standardized Precipitation Index (SPI). In this study, monthly rainfall and discharge data of Karoon and Maroon Basins in Iran from 1973 to 2014 were collected and used to calculate SDI and SPI indicators. Based on Run theory, drought characteristics, including drought duration and its magnitude, were obtained. In order to have a more reliable analysis of hydrological drought, which is a consequence of meteorological drought, the most suitable relationship between meteorological and hydrological drought characteristics was investigated. A significant relationship between meteorological and hydrological droughts was concluded by regression analysis; on average, the quadratic function showed the best performance. Based on the results, hydrological droughts occur on average at a 7-month interval from meteorological drought. Finally, spatial analysis of drought characteristics (duration and magnitude) was determined and performed by multivariate Copula functions.