Interannual variability of North American Monsoon hydroclimate and application to water management in the Pecos River Basin
The North American Monsoon (NAM) is the large-scale atmospheric circulation system responsible for up to 55% of the annual precipitation in the southwestern U.S. These summer thunderstorms, however, are highly variable and predicting the variability in the strength, location, and timing of monsoonal precipitation and streamflow is understandably very important for efficient water resources management.
This research, comprised of three main components, analyzes the spatial and temporal variability of NAM precipitation and streamflow; and using this information it develops a statistical forecasting framework which is then integrated with a decision support system to evaluate water management strategies on the Pecos River Basin. First, the interannual variability of precipitation and streamflow in the NAM region of southwest U.S. is studied and large-scale and local climate features that drive the variability are diagnosed using robust Spearman rank correlation analysis and Kendall Theil slope estimators. These analyses led to the proposal of the following hypothesis: antecedent Pacific sea surface temperatures (SSTs) modulate the winter/spring hydroclimate and land conditions of the NAM region, thus playing an important role in setting up the land-ocean temperature gradient (the key driver of the NAM), and, consequently, in modulating monsoonal rainfall and precipitation. This offers increased hopes of long-lead forecasts of summer hydrologic conditions in the NAM region. The second component of this study develops a framework for generating ensemble forecasts of spring and summer streamflow at five lead times using the large-scale climate information obtained from the diagnostics. In the third, and final, component of this study, streamflow exceedance probabilities calculated from the ensemble forecasts are used in a decision support system, modeled with RiverWare, to evaluate various water management options for reservoir releases, irrigation diversions and inter-state spill in the Pecos River Basin. The Pecos River receives a significant portion of its annual streamflow in the summertime from monsoon thunderstorms, however operations on the river do not utilize forecasts of this important moisture source. The research framework developed here demonstrates significant improvements to water management though decreased reservoir spills and increased irrigation water delivery.