Critical drought severity/intensity-duration-frequency curves based on precipitation deficit

Drought is one of the most disastrous natural phenomena that causes scarcity and lack of water in hydrological basins and affects seriously the majority of the population in many ways such as economical, social and environmental. Therefore, drought plays a significant role in the risk management of water resources systems. The purpose of this study is to develop the severity/intensity–duration-frequency curves based on precipitation deficit and provide a comprehensive characterization of droughts by using Standardized Precipitation Index (SPI) which considers precipitation data only. Instead of using SPI directly, the severity and intensity were calculated in the duration-frequency curves. On the other hand, SPI is a technical tool and thus difficult to understand at first glance by end-users and decision-makers. Precipitation deficit is therefore more useful and physically meaningful to the users. In this study, drought with the largest severity in each year is defined as the critical drought of the year. Frequency analysis is applied on the critical drought severity to determine the best-fit probability distribution function by using the total probability theorem. Results show that the 2 year-return period drought severity/intensity–duration-frequency curve is well lower than and separated clearly from the curves at higher return periods of 5–100 years although it has the same tendency with the longer return period curves, and also that almost no difference is observed between the precipitation deficit of the droughts of 25 years or longer return periods. With the precipitation deficit and such newly introduced concepts as critical drought severity, singular drought and within-period drought, the proposed methodology gains a novelty. It is expected that the destructive and irreversible effects of meteorological, agricultural and hydrological droughts can be realized in a more physical sense with the use of precipitation deficit.