<human>:  With respect to the California Drought, what is the cause of the drought?
<bot>: The cause of the drought is a combination of a long-term trend of reduced precipitation and a short-term trend of increased evapotranspiration. The long-term trend is due to a combination of global warming and a decrease in the amount of water stored in the snowpack in the Sierra Nevada Mountains. The short-term trend is due to a combination of increased temperatures and increased evaporation from the soil.