No, aliens aren't changing the weather. Short for evapotranspiration, ET measures the water heading in the opposite direction of the rain. Tim Baker, a Missouri horticulture blogger, wrote in the Marshall Democrat-News about measuring ET. Water evaporates from the soil (the E) as well as transpirates from plant leaves (the T). Combining ET measurements, water leaving the soil, with rainfall measurements, water entering the soil, gives meteorologists a better picture of the water cycle and is an important planning tool for farmers and water resource managers.
Cocorahs, the volunteer network of amateur weather observers in the United States, Puerto Rico and Canada, began a pilot project in 2011 to measure ET. It has rolled out ET observations across its network. As more amateurs set up their own $222 ET observatories, professional meteorologists will get better at forecasting drought.