New York Times: It’s a simple fact of life across the rural West, as it is here in Montana’s mountain-ringed Big Hole River Valley. Flooding river bottoms to grow hay sustains the economy but means less water in the river for the prized wild trout population. The competition for water is not new, but it is intensifying as the climate here gets warmer and drier. "The biggest worry for trout is that smaller streams will simply run dry in late summer and temperatures in the remaining pools will …