Record snowfall in recent years has not been enough to offset long-term drying conditions and increasing groundwater demands in the U.S. Southwest, according to a new analysis of NASA satellite data.

Declining water levels in the Great Salt Lake and Lake Mead have been testaments to a megadrought afflicting western North America since 2000. But surface water only accounts for a fraction of the Great Basin watershed, which covers most of Nevada and large portions of California, Utah, and Oregon. Far more of the region’s water is underground. That has historically made it difficult to track the impact of droughts on the overall water content of the Great Basin.