Primarily a summer phenomenon, the Bay of Bengal branch of the Indian Monsoon brings the most monsoonal rainfall in Uttar Pradesh. Uttar Pradesh is affected primarily from the southwest monsoon. "Western disturbances" and North-East Monsoon also contribute small quantities towards the overall rainfall of the state. The rain in Uttar Pradesh can vary from an annual average of 1.700 mm in hilly areas to 840 mm in Uttar Pradesh. As a direct result of the monsoonal rainfall, excess rain can lead to floods and shortage to droughts. As such, these two phenomenons of floods and droughts are common in the state.