Rainfall data collected at the Meshref station for year 2003 (a wet year) and year 2010 (a dry year) as obtained from the Lebanese National Meteorological Service at Beirut airport we used for the calculations, and the projections for the future precipitation were obtained from El-Samra et al. (2017) (DOI 10.1007/s00382-017-3542-z) as shown in the following table:
Past & Future Precipitation (mm)
So under the worst future conditions in 2050, the yearly rainfall will be 475mm.
The roof of Block E has a surface of 1600 m2, so we can harvest under the worst condition 760 m3 of rainwater.