Characterizing the Predictability and Sensitivity of Streamflow to Monsoon Season Precipitation
Research Need: In the Western US, warm-season precipitation has historically provided a secondary water source to snowmelt runoff (Serreze et al., 1999). However, increasing temperatures and decreasing snowpack suggest that it may gain importance for water resources management. As such, there is an interest in understanding the predictability of warm-season precipitation, as well as the sensitivity of water resources and management to this source.
Understanding the predictability of warm-season precipitation is of particular interest in the U.S. Southwest, a region that is influenced by the North American Monsoon in summer (Adams and Comrie 1997). One of the barriers to using monsoon forecasts has been their low skill in simulating precipitation. However, it has been recommended that any examination of monsoon should consider large-scale circulation, rather than examining precipitation directly (Seneviratne et al. 2012). To this point, Prein (2019) identified large-scale conditions over the U.S. Southwest associated with monsoon precipitation anomalies, and found that they are robustly captured by NCAR's Community Earth System Model (CESM) and other general circulation models. This provides motivation to evaluate monsoon circulation patterns in forecast ensemble products.
There is also a need to understand the sensitivity and potential usability of a warm-season forecast for water management. Recent work on the Rio Grande showed that although monsoon season streamflow volumes vary from year-to-year, they are an important contribution to water supply ( Towler et al. 2019). Nevertheless, in the Rio Grande, as in other snowmelt-driven basins in the West, seasonal water supply forecasts used to make operational decisions are mainly based upon snowpack, and don't explicitly consider any information about monsoon precipitation. As such, it is critical to identify the potential value of a probabilistic monsoon forecast for ongoing Reclamation management activities
Need and Benefit
Water resources are limited in many Reclamation regions, and understanding warm-season precipitation predictability and the sensitivity of water operations to that information can help Reclamation make better use of available water. Previous work by this project team on identifying large-scale monsoon circulation patterns to predict monsoon characteristics has shown promise in an area for which very little predictive information has been available in the past.. Evaluating the skill of these patterns in available forecast ensemble products and gaining insight into how they could be implemented in practice provides critical information that can be used to improve Reclamation planning and management.
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