the average minimum temperature has been higher. Average precipitation during the same period was close to the average of the previous period, snowfall totals down only marginally with slightly higher rainfall. In order from the top: December, September, July and January have seen the highest average temperature increases. Part of this warming is likely attributed to increased urban growth surrounding the airport. An older study conducted in the 1990s analysed the heat island effect comparing data from selected regional stations, including both Downtown Toronto and Pearson Airport, enough for a large area of the old city limits, and parts of Etobicoke to have a different Köppen climate classification from the surrounding area. Statistics Topography Toronto has numerous hills and valleys that were carved out during the last Ice Age. The ravines are largely undeveloped, primarily as the result of Hurricane Hazel in 1954. A significant topographical feature is the old shoreline of the Glacial Lake Iroquois, known as the Iroquois Plain. The plain consists mostly of sand deposits and eroded shale and gently slopes about north from Lake Ontario. The Iroquois Plain joins Lake Ontario at the Scarborough Bluffs where erosion and the currents of Lake Ontario have carried sand deposits into Toronto Harbour to form the Toronto Islands. Above the Iroquois Plain, the topography includes two features: the South Slope and the Peel Plain. The South Slope is the southern part of an interlobular moraine the Oak Ridges Moraine. The South Slope has a gentle slope as well, and experiences relatively high runoff as water infiltration is relatively low. The Peel Plain is mostly clay and generally flatter than the South Slope. Water infiltration is also low. Historically, the Peel Plain and South Slope were considered to be high-quality agricultural lands, unlike the Iroquois Plain, which is very sandy. These areas are now heavily urbanized. Both Dufferin Street and Caledonia Road between Davenport Road and Eglinton Avenue, in the York district, run across numerous steep hills and valleys and the neighbourhood in this area is named Fairbank. Fairbank and Silverthorn to the west have often been compared with the many hills that make up San Francisco. However, parts of the hills and valleys are slightly levelled for GO Transit's Barrie line that runs through this area. Vaughan Road runs parallel to the buried Castle Frank Brook to the northeast. The Don River is categorized as an underfit river, given