Survey of drought process in Kermanshah province of Iran by Z and SPI indexes

Precipitation is the most important factor of weather and also it has an important role in peopleʹs life and economy and its shortage affects on agriculture, animal and industrial production. Precipitation shortage have different effects on groundwater, soil moisture and river flow as well. To show drought affects an index has to be defined. One of these indexes is SPI (standard precipitation index) which is a climatology index. For determination of precipitation shortage in different time scale, SPI index has been used. Time scales shows drought effects on ability of water resources. Precipitation shortage affects on soil moisture in short time and on groundwater in long time. Drought study and its evaluation are based on different indexes that can show intensity and its frequency in a region. In this study precipitation and drought analysis was studied in Kermanshah province with SPI index estimation for different 3, 6, 12, 24 and 48 monthly period, percent difference and precipitation standard indexes. Due to drought study in this region, 39 years rainfall data (1972-2011) by using of decade index by Excel software were analyzed and high droughts locations for this region were found. The results investigations showed that the average annual precipitation to west and north-west of this province increased. Also in years 1990, 1999, 2000 and 2001 years Kermanshah province has been more affected by drought. In short-time droughts the maximum intensity was -1.14 for 3-month SPI and -1.43 for 6-month SPI which occurred in most of drought years and in long-time droughts with -2.05 index happened in year of 2000.