Analysis of Meteorological Drought Using Standard Precipitation Index for Some regions in Jafara Plain, Libya During 1962-1999

Abstract

Meteorological drought based on the Standard Precipitation Index (SPI) was estimated for some regions in the Jafara plain, North west Libya. The study considered the annual rainfall during the years 1962 to 1999 for the meteorological stations of Abukmash, Aassah, Zawia, Bir Al-Ghanam, Tripoli Airport and Gaser Al-Akhaiar, which are spread over different geographic features. The amount of the missing precipitation data was estimated using the inverse distance weighting (IDW) method. The statistical characteristics of precipitation as arithmetic mean, median, standard deviation, skewness, kurtosis and coefficient of variation were determined. The drought and humid years, drought duration, drought accumulated magnitude and drought intensity were also estimated. The results showed high rainfall in the stations which are located in the east compared with the west ones. According to kurtosis coefficient, the frequency of low precipitation values was found to be bigger than the frequency of extreme values. The annual rainfall fluctuated in varying degrees throughout the study area. It was noted that the values of the coefficient of variation (CV) ranged between 33.01% for Gaser Al-Akhiar station and 46.5% for Asah station. The results revealed that cases of moderate drought and moderate humidity were predominant compared to extreme and severe drought. The maximum drought duration was seven consecutive years between 1988 and 1994 in Tripoli airport station. The cumulative drought magnitude reached its maximum with 690 mm in Zawia station during the five years between 1965 and 1969. Zawia station had a maximum value of drought intensity with 147mm / year in 1971.

Keywords: Drought, Gamma distribution, Standard Precipitation Index, Jafara plain