The devastating 2011 drought left 301million trees dead across Texas and while a drought can certainly increase tree problems of insects and disease, the real bottom line is that trees need water. And right now, most of them arenโt getting enough. Water allows trees to transport nutrients from their roots to their leaves. Almost all of the water moving through a tree is used to keep stomata open, which are the pores that let in carbon dioxide, allowing a tree to carry out photosynthesis. Without water, known as hydraulic failure, trees have to depend on stored sugars and starches and theyโll run out if the drought continues long enough. There are other reasons trees die during drought, according to this study by the National Science Foundation, but lack of water leads the list.