Evaluation of drought in South Khorasan province (Iran) using normal precipitation index (PNPI) and standardized method index (Z)

Drought is among the natural disasters which happens in a long period of time and intermittently makes problems for human societies and consequently the economy through negative effects on water resources and agriculture compared to other natural phenomena. Thus, the basic step in drought studies is to select appropriate indicators for each area based on severity, duration and magnitude of drought in the study area. The aim of this study is to select appropriate indicators to classify and determine the degree of severity of the drought and wet and to identify the drought prone regions in South Khorasan province for planning and better management of drought. The values of drought severity were calculated by the desired index for each station using Matlab software. Then, based on the tables for each index, the drought and wet intensities were determined. In this study, the situation of drought in South Khorasan province was evaluated using the drought index, weather percent of normal precipitation (PNPI) and standard methods of index (Z). Since most stations do not cover the long-term (30 years) statistics of precipitation data, the available stations with the precipitation data for period of 24 years (2014- 1990) were used. PNPI index results showed that among the studied stations, Khor Birjand stations with 5 months, Boshrooyeh, Ghain and Ferdous stations with 4 months and Birjand and Nehbandan stations with 3 months has the longest wet period. Drought is in the range of moderate drought to moderate humidity in most stations. The highest Z (wet 1/84) belongs to Nehbandan station in March and most of the stations experience moderate drought in June, July, August, September and October. The two methods show that the drought is in the range of moderate drought to moderate humidity in most of the stations. According to the results of hypothesis evaluation, the drought has been very severe and has led to occurrence of minimum annual precipitation. In this study, PNPI index was found to be a more appropriate index for the region.