disclosure question

I'm under contract to sell my home in Littleton, Colorado. All of the disclosures have been completed and signed by both parties. The home currently backs to open space, which is one of the attractive features of the home. However, yesterday I received a letter in the mail from the county in which the property is located, indicating that a developer has applied for rezoning of some of that open space, so that a storage facility up to 40 feet tall can be constructed on it. Honestly, I really didn't know who owned that land that I think of as "open space", and in my mind, it's up to the buyer to perform their due diligence and investigate those matters to achieve a comfort level with the purchase. On the other hand, since my marketing included statements about "backs to open space", I sort of feel the need to disclose this news to the buyer, before we close. My question is, am I obligated to disclose something like this? What is my risk if I don't disclose it?