Reconstructing a water balance for north Crestone Creek: streamflow variability and extremes in a snowmelt dominated internal drainage basin

May 2013.Includes bibliographical references.The San Luis Valley in Colorado is a semi-arid region that relies on streamflow from the surrounding mountain ranges for agricultural productivity and to recharge the important aquifer systems of the basin. The (North) Crestone Creek watershed is characteristic of the many small watersheds that drain the Sangre de Cristo Mountains on the eastern side of the valley providing water for local water users, wildlife, and augmentation of Rio Grande flows through the Closed Basin Project reclamation efforts. This study investigates the range of hydrologic variability and extremes in this area over the last 426 years using readily available historic hydrologic and paleo-climatic data derived from tree-rings and other sources. Streamflow and precipitation reconstructions were generated and compared to the historic period of observation. Water balance modeling was performed using historic and paleo-derived model inputs. The results of this study show that the drought conditions experienced in the San Luis Valley over the last decade are not unusual in the context of streamflow and precipitation reconstructions spanning hundreds of years. Past droughts were at least as intense as those in 1950 and 2002 and several droughts in the paleo-record were of much longer duration than any recorded in the instrumented period. These results are similar to those demonstrated in other paleo-hydrologic research from the western part of the San Luis Valley in Colorado and throughout the western United States. The water balance modeling provided a means to examine monthly changes to runoff and other hydrologic and state variables output by the model under differing past climate conditions. Together, the climate reconstructions and water balance model provide insight into regional water use sustainability and future development issues for a highly variable natural system