km (65 mi) from Gao. The border with Niger is just south of the village of Labbézanga, a distance of 204 km (127 mi). The prime meridian marker runs right through Gao, Mali. There are also seasonal ferry services on the Niger River. A service between Gao and Koulikoro, a distance of 1380 km (860 mi), is managed by the Compagnie Malienne de Navigation (COMANAV). It usually operates from the end of July, after the annual rains when there is sufficient water in the river, until mid November. Smaller boats are able to operate for a longer season between Bourem and Ansongo. In the 1998 census, the population of the urban commune was 52,201. By the census in 2009 this had increased to 86,633, a 4.7% annual growth rate. For administrative purposes, the commune is divided into nine quartiers: Gadeye, Farandjiré, Aljanabanbia, Djoulabougou, Saneye, Sosso Koïra, Boulgoundjé, Château, and Djidara. The urban commune is bounded to the north by the commune of Soni Ali Ber, to the east by the commune of Anchawadi and to the south and west by the commune of Gounzoureye. Climate Gao features an arid climate under Köppen's climate classification. Gao's climate is hot and dry, with the only rainfall occurring between June and September. August is normally the wettest month. The average annual rainfall is only 220 mm, but there are large year-to-year variations. May is the hottest month, with an average daily high temperature of 43 °C. December and January are the coolest months, with daily low temperatures of 15 °C. From October to March during the dry period, the north-easterly Harmattan wind blows from the Sahara. With the low rainfall, the vegetation further away from the river is sparse and consists mainly of various species of Acacia (Acacia raddiana, Acacia nilotica, Acacia ehrenbergiana) and Balanites aegyptiaca. The herbaceous plants are dominated by Cenchrus biflorus and Panicum laetum. Annual flood of the Niger River Almost all the local agriculture depends on river water for irrigation. The annual flood of the Niger River is a result of the heavy rainfall in the headwaters of the Niger and Bani rivers in Guinea and the northern Ivory Coast. The rainfall in the headwater areas peaks in August but the flood water takes time to pass down the river system, through the Inner Niger Delta region and arrive at Gao. At Koulikoro the flood peaks in September, while