WASET
    Mosaad Khadr and  Gerd Morgenschweis and  Andreas Schlenkhoff,  Analysis of Meteorological Drought in the Ruhr Basin by Using the Standardized Precipitation Index.   journal   = {International Journal of Environmental and Ecological Engineering}, [online]. World Academy of Science, Engineering and Technology.
    September 2009, vol. 33(9). 291 - 300
    [viewed 07 May 2024]. Available from: https://publications.waset.org/pdf/12783.