less moisture is available to fall as rain...toの用法は？
（なぜ人間は森林破壊を心配するのか）
The losses are difficult to evaluate. However, the loss of tropical forests would have very far-reaching effects both on the countries concerned and on the whole world. The loss to
science of animal and plant species in the tropics would be far greater than in temperate regions because of the far greater numbers of species involved. Scientific study of all the innumerable plants and animals in the jungles is still very incomplete and there is much work to be done.
There are even more important reasons for some countries to preserve their forests. Trees take in a great deal of water through their roots and release this by transpiration back into the air. This helps to keep the air moist. When forests are removed the air becomes drier, less moisture is available to fall as rain and therefore agriculture suffers. Many savanna regions of the world are being turned into deserts, largely because trees are removed for firewood, or by animals that feed
on the grass, and the savanna vegetation cannot survive. It is replaced by desert conditions of no rainfall and almost no vegetation. Large-scale removal of jungles could have the same effect, and thus it is very important that forests should be preserved.
（質問）less moisture is available to fall as...の部分のto不定詞の用法が分かりません。
(1) mostureを説明する「形容詞的用法」
(2) availableを説明する「副詞的用法」
それともそれ以外ですか？何かこれと同じ用法の良い例文があれば宜しくお願いします。
お礼
早速の回答ありがとうございます。 available には「手に入る」のほか「利用できる」「使える」などの 意味もあり、「利用できる」という意味にはならないのでしょうか？ よく、アメリカではＴａｘｉに対し「Is this available ?] と云っていましたので、同じようにカードでも使えるのかと 思っていましたが・・・