[en] Reconstructing past climatic variations can lead to a better understanding of possible future precipitation and groundwater recharge patterns. Work so far has led to several new insights into past climate variability and will provide input into the hydrologic modeling effort in progress for the Waste Management Program. Short-term reconstructions (0 to 350 y) suggest that the basin and range of the southwestern United States have the driest, least variable precipitation record. The Pacific Northwest shows higher variability and several trends lasting for more then 25 y. The Southern High Plains have even more variability, but the upper Midwest and Southwest vary most and have the highest precipitation amounts. Pollen and lake level data from the literature suggest that the Southwest was wetter during at least part of the last glacial maximum than it is today