90% chance of rain: downpour as event
- Publisher:
- Birkhäuser
- Publication Type:
- Chapter
- Citation:
- Drawing Climate: Visualising Invisible Elements of Architecture, 2021, pp. 98-117
- Issue Date:
- 2021-11-08
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| Filename | Description | Size | |||
|---|---|---|---|---|---|
| 10.1515_9783035623611-006.pdf | Published version | 1.54 MB |
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Rainfall arrives in many guises. It can be destructive or mundane, a cause for celebration or terror. As a climatic certainty, precipitation cannot be ignored by architects, but as a source of design expression its status is contentious. Unlike sun or wind, the downpour tends to be excluded from architectural representations in the twentieth century: after all, how does one draw a condition that is incalculable in terms of direction,
intensity and duration? How, for example, could a designer represent crucial distinctions between a week of steady rain and a thirty minute flash flooding event? A common way of experiencing urban rainfall is through a series of increasingly certain probabilities (for example, 90 % chance of precipitation on Friday) that culminate in an event represented on a screen by electronically generated blobs of colour, updated as close to real time
as possible (Figure 2). Cycles of urban life rely on short-term probabilities in order to avoid disruption to daily activities; here, the weather tomorrow is critical for one’s schedule rather than rain predicted for next week. For activities that rely on longer cycles, it can be more important to know the probability of rain over the next six to twelve months. For agricultural production this is certainly true and for those in charge of water supply where the catchment and storage of rainfall is the primary source of potable water; the same holds true for bushfire planning, which needs to calculate the build-up of fuel loads in the absence of rain. For architects and urban planners, such a timeframe can extend to decades
and sometimes centuries. The likelihood of a 1-in-20 or 1-in-100-year rainfall event determines the minimum sizing for a building’s gutters and downpipes. A 1-in-100 or even 1000-year event becomes the motivating factor behind flood control and coastal protection systems.
Differences between short- and long-term probabilities also exemplify the separation of weather from climate; the event of the downpour itself is experienced as weather against long-term shifts in the probability of rainfall. The fact that these events are occurring more frequently today as a result of a changing global climate has resulted in a marked shift in attitude by designers towards the event of rainfall. Here, the former notion of control of the downpour by buildings has become supplanted by concepts of resilience.
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