The mean annual rainfall in  nepal ranges fro below 500 mm to above 5,000 mm. this variation is the pattern of  annual rainfall mainly results from the direction of mountain, aspect if slop, distance from the sea and altitude.because of the monsoon, the rain fall decreases from east to west. the south facing slope receives higher amount of rainfall out of the total rainfall, about 805 rainfall occurs in the monsoon period in the months of June, July and august.
the higher amount of rainfall is converted in the Annapurna region,particularly in pokhara. besides, eastern nepal and langtang area also receive nigh amount of rainfall. the tarai region 1,000 to 25,00 mm annual rainfall in general. the hill region receives 1,700 to 3,000 mm average annual rainfall. however, there are certain pocket areas which receive 2,500 to 3,000 mm average annual rainfall in the hill. the least amount of rainfall occurs in the north western part of WDR, MWDR, FWDR.