This calendar graph of the San Pedro River clearly shows the increased seasonal occurrence of spring droughts (indicated by the red lines), most evident from 1980 to present. Before 1970, the perennial river was exactly that -- groundwater recharge continued to feed its flows deep into spring. What's the solution? Ground water conservation wouldn't hurt. Can you see how even river recharge from the summer monsoons seems affected over the past couple decades, too. That may be a result of changes, i.e. intensification, of land use.