Precipitation is the first important parameter in studying dry and wet years. It has a direct relation with precipitation systems entering Iran and the sources of humidity which inject humidity into those systems.
Studies performed on Sudanese system indicate that precipitation in southern parts of the country have a close relation with the activities of this system in cold days of the year and it plays the most important role in heavy rainfalls. Reviewing synoptic maps of high and low precipitation reveals that two different dominating patterns exist in the area. In the high precipitation pattern, Sudanese low pressure is located on the South West of the Red Sea and continues toward North East and influences South and South West of Iran.
This pattern dominates South East of the Arabian Peninsula. It inject heat and humidity from the Oman Sea and the Arabian Sea on one hand and the Adan Gulf and the Red Sea on the other hand to the mentioned systems. Then, this heat and humidity enters Iran Southern area with the Sudanese system. Due to the deepening of east Mediterranean trough, and the falling of cold weather from eastern latitudes in the Sudanese system, the system becomes extremely powerful and changes into dynamic status, creating a heavy rainfall on the area. In the weak precipitation pattern, Sudanese low pressure system is extremely weak and it crosses the southern areas of the Arabian Peninsula in east-west direction. Moreover in this pattern, a cyclone system covers South Eastern areas of the Arabian Peninsula.