Dayton
Dayton Geography & Climate
Geography
Dayton stands where the Mad River, the Stillwater and Wolf Creek join the Great Miami, on flat glaciated ground in south-west Ohio.
Four rivers
The confluence gave the city water power, transport and, repeatedly, catastrophic floods. All four converge within about two kilometres of downtown, which concentrates the runoff from a large catchment into one place. The valley floor is broad and flat and the rivers are shallow and braided, so when they rise they spread rather than deepen.
The aquifer
Beneath the city lies the buried valley aquifer, a channel of sand and gravel left by a pre-glacial river and refilled by the ice sheets, which holds an exceptional quantity of easily pumped groundwater. Dayton draws its entire water supply from it, and the capacity was a substantial reason heavy industry located here.
Flat and open
Glacial till plain in every direction, rising gently to the east where the land becomes rolling. The flatness is why the Wright brothers could use Huffman Prairie as a flying field — an unobstructed cow pasture a short streetcar ride from town.
The dams
Five dry dams upstream, built after 1913, stand empty most of the year and fill only to hold back a flood crest. They are earthen, enormous and among the earliest such systems in the world.
Huffman Prairie
A flat, poorly drained cow pasture east of the city, about 34 hectares, ringed by trees and crossed by a streetcar line. It was unpromising ground — too small, too soft, with unreliable wind — which is precisely why using it forced the Wrights to solve turning and landing rather than relying on a long straight run. It is still open grassland, inside the air force base, and can be visited.
The Little Miami
East of the city, a scenic river in a gorge with a long recreational trail along it.
Climate Patterns
Dayton has a humid continental climate typical of south-west Ohio, with four distinct seasons and a genuinely active spring.
Summer
June to August is hot and humid, with highs of 28 to 30°C and dew points that make it feel warmer. Thunderstorms are frequent and often arrive in organised lines in the late afternoon and evening. The flat open country means there is no relief nearby.
Winter
December to February is cold: highs of 3 to 5°C and lows around minus 6°C, with roughly 60 centimetres of snow across many small falls rather than a few large ones. Ice storms are the more disruptive event, bringing down power lines.
Severe weather
This part of Ohio sits at the eastern edge of the region where violent tornadoes occur, and Dayton has been hit. On Memorial Day 2019 an outbreak produced fifteen tornadoes across the metropolitan area in a single night, including one that tracked through the northern suburbs and damaged thousands of buildings. Warnings are taken seriously here, sirens are tested monthly, and a warning means take shelter immediately.
Spring and autumn
Autumn is the better season — dry, clear and warm into late October. Spring is wet, volatile and the peak of storm season.
Flood risk now
The conservancy dams handle river flooding, but the flat ground and the extent of paving mean flash flooding from heavy rain remains a local problem, particularly in summer when a slow-moving storm can drop a great deal in an hour. The distinction matters: the 1913 kind of flood has been engineered out, the sudden kind has not.
Rainfall
Around 1,000 millimetres a year, fairly evenly distributed.