Published on Organic Gardening (http://www.organicgardening.com)
Compost encourages the formation of soil clusters that soak up water and hold it like a sponge.
Links:
[1] http://www.organicgardening.com/compost-protects-drought-380
[2] http://www.organicgardening.com/learn-and-grow/water-wiser