<P> Kabara can only function as a port in December to January when the river is in full flood . When the water levels are lower, boats dock at Korioumé which is linked to Timbuktu by 18 km (11 mi) of paved road . </P> <P> Timbuktu features a hot desert climate according to the Köppen Climate Classification . The weather is hot and dry throughout much of the year . Average daily maximum temperatures in the hottest months of the year--April, May and June--exceed 40 ° C (104 ° F). Lowest temperatures occur during the Northern hemisphere winter--December, January and February . However, average maximum temperatures do not drop below 30 ° C (86 ° F). These winter months are characterized by a dry, dusty trade wind blowing from the Saharan Tibesti Region southward to the Gulf of Guinea: picking up dust particles on their way, these winds limit visibility in what has been dubbed the' Harmattan Haze' . Additionally, when the dust settles in the city, sand builds up and desertification looms . </P> <Table> <Tr> <Th_colspan="14"> (hide) Climate data for Timbuktu (1950--2000, extremes 1897--present) </Th> </Tr> <Tr> <Th> Month </Th> <Th> Jan </Th> <Th> Feb </Th> <Th> Mar </Th> <Th> Apr </Th> <Th> May </Th> <Th> Jun </Th> <Th> Jul </Th> <Th> Aug </Th> <Th> Sep </Th> <Th> Oct </Th> <Th> Nov </Th> <Th> Dec </Th> <Th> Year </Th> </Tr> <Tr> <Th> Record high ° C (° F) </Th> <Td> 41.6 (106.9) </Td> <Td> 43.5 (110.3) </Td> <Td> 46.1 (115) </Td> <Td> 48.9 (120) </Td> <Td> 49.0 (120.2) </Td> <Td> 55.0 (131) </Td> <Td> 46.0 (114.8) </Td> <Td> 46.5 (115.7) </Td> <Td> 45.0 (113) </Td> <Td> 48.0 (118.4) </Td> <Td> 42.5 (108.5) </Td> <Td> 40.0 (104) </Td> <Td> 49.0 (120.2) </Td> </Tr> <Tr> <Th> Average high ° C (° F) </Th> <Td> 30.0 (86) </Td> <Td> 33.2 (91.8) </Td> <Td> 36.6 (97.9) </Td> <Td> 40.0 (104) </Td> <Td> 42.2 (108) </Td> <Td> 41.6 (106.9) </Td> <Td> 38.5 (101.3) </Td> <Td> 36.5 (97.7) </Td> <Td> 38.3 (100.9) </Td> <Td> 39.1 (102.4) </Td> <Td> 35.2 (95.4) </Td> <Td> 30.4 (86.7) </Td> <Td> 36.8 (98.2) </Td> </Tr> <Tr> <Th> Average low ° C (° F) </Th> <Td> 13.0 (55.4) </Td> <Td> 15.2 (59.4) </Td> <Td> 18.5 (65.3) </Td> <Td> 22.5 (72.5) </Td> <Td> 26.0 (78.8) </Td> <Td> 27.3 (81.1) </Td> <Td> 25.8 (78.4) </Td> <Td> 24.8 (76.6) </Td> <Td> 24.8 (76.6) </Td> <Td> 22.7 (72.9) </Td> <Td> 17.7 (63.9) </Td> <Td> 13.5 (56.3) </Td> <Td> 21.0 (69.8) </Td> </Tr> <Tr> <Th> Record low ° C (° F) </Th> <Td> 1.7 (35.1) </Td> <Td> 7.5 (45.5) </Td> <Td> 7.0 (44.6) </Td> <Td> 8.0 (46.4) </Td> <Td> 18.5 (65.3) </Td> <Td> 17.4 (63.3) </Td> <Td> 18.0 (64.4) </Td> <Td> 20.0 (68) </Td> <Td> 18.9 (66) </Td> <Td> 13.0 (55.4) </Td> <Td> 11.0 (51.8) </Td> <Td> 3.5 (38.3) </Td> <Td> 1.7 (35.1) </Td> </Tr> <Tr> <Th> Average rainfall mm (inches) </Th> <Td> 0.6 (0.024) </Td> <Td> 0.1 (0.004) </Td> <Td> 0.1 (0.004) </Td> <Td> 1.0 (0.039) </Td> <Td> 4.0 (0.157) </Td> <Td> 16.4 (0.646) </Td> <Td> 53.5 (2.106) </Td> <Td> 73.6 (2.898) </Td> <Td> 29.4 (1.157) </Td> <Td> 3.8 (0.15) </Td> <Td> 0.1 (0.004) </Td> <Td> 0.2 (0.008) </Td> <Td> 182.8 (7.197) </Td> </Tr> <Tr> <Th> Average rainy days (≥ 0.1 mm) </Th> <Td> 0.1 </Td> <Td> 0.1 </Td> <Td> 0.1 </Td> <Td> 0.6 </Td> <Td> 0.9 </Td> <Td> 3.2 </Td> <Td> 6.6 </Td> <Td> 8.1 </Td> <Td> 4.7 </Td> <Td> 0.8 </Td> <Td> 0.0 </Td> <Td> 0.1 </Td> <Td> 25.3 </Td> </Tr> <Tr> <Th> Mean monthly sunshine hours </Th> <Td> 263.9 </Td> <Td> 249.6 </Td> <Td> 269.9 </Td> <Td> 254.6 </Td> <Td> 275.3 </Td> <Td> 234.7 </Td> <Td> 248.6 </Td> <Td> 255.3 </Td> <Td> 248.9 </Td> <Td> 273.0 </Td> <Td> 274.0 </Td> <Td> 258.7 </Td> <Td> 3,106.5 </Td> </Tr> <Tr> <Td_colspan="14"> Source #1: World Meteorological Organization, NOAA (sun 1961--1990) </Td> </Tr> <Tr> <Td_colspan="14"> Source #2: Meteo Climat (record highs and lows) </Td> </Tr> </Table> <Tr> <Th_colspan="14"> (hide) Climate data for Timbuktu (1950--2000, extremes 1897--present) </Th> </Tr>

Why was timbuktu a major center of trade and cultural exchange