|Cloud Kigo©Alan Summers, Bradford on Avon 13th June 2013|
a light rain patters across
your nightingale floors
Publication Credits: Asahi Shimbun (Japan, 2013)
"In search of the ultimate season word to associate with clouds, Alan Summers observes how “rain writes its own story across floorboards that sing like a bird.” I like the idea of the cloud kigo. Readers will too. It is always my pleasure to work with you on haiku.”
David McMurray writes a haiku column for the Asahi Newspaper (Asahi Shimbun, Japan). He is also Professor of Intercultural Studies at The International University of Kagoshima (Japan) where he lectures on international haiku.
“season is the soul of haiku”
William J. Higginson (The Haiku Seasons, p20)
The Haiku Seasons
Poetry of the Natural World
by: William J. Higginson
"The Haiku Seasons presents the historical and modern Japanese usage of seasonal themes in poetry. It shows, as nothing else in the literature has done, the growing dialogue between poets in Japan and other countries...An extremely valuable work!"
—Elizabeth Searle Lamb, retired editor, Frogpond
A Little About the Kigo Technique in Haiku
by Alan Summers
Japanese kigo are a strong allusion device (there are others) and can contain cultural and emotional tones of extreme intensity within Japan. The possibilities of kigo as a tool or device of choice, can be equally considered as valid, as any other technique of haiku.
Kisetsu (season, seasonal aspect)
The seasons. The seasonal aspect of the vocabulary (kigo) and subject matter (kidai) of traditional tanka, renga, and haiku; a deep feeling for the passage of time, as known through the objects and events of the seasonal cycle. 
Season words, and the Japanese kigo system, are not only derived from observations of nature, they can allude to a country’s historical, cultural, and literary past.
Haiku are 'seasonal' rather than 'nature' centered poems. If looked at in this way it allows for urban seasonal markers and seasonal celebrations; in other words from this perspective it would be legitimate to compose haiku centered on the human world because the human world is also seasonal.
I feel that non-Japanese haiku can achieve an aspect of kisetsu  with seasonal words and phrases.
 William J. Higginson with Penny Harter, The Haiku Handbook: How to Write, Share, and Teach Haiku, published by Kodansha International. Copyright (C) 1989 by William J. Higginson. (p289 & 291)