Water-hungry Los Angeles is pumping so much groundwater that the area is rising and falling each year in tune with the seasons, according to a report published today in the journal Nature. Using global positioning system satellites, a research team from the U.S. Geological Survey calculated that some parts of the L.A. area have been sinking half an inch a year, while others are rising a quarter-inch every year. In some parts, the seasonal difference can be more than 4 inches, rising in the fall and early spring, and falling in the summer.