Book excerpt: The Water Availability Modeling (WAM) System maintained by the Texas Commission on Environmental Quality (TCEQ) consists of the Water Rights Analysis Package (WRAP) and datasets for all the river basins of Texas. The modeling system is used to support long-term regional and statewide planning and evaluation of water right permit applications. The research is designed to explore and improve WRAP/WAM capabilities as a decision-support tool for drought management. The WRAP/WAM model for the Colorado River Basin is applied in this research in both long-term planning and short-term conditional reliability modeling (CRM) modes. A strategy using iterative long-term simulations is developed for modeling water management plans that combine interruptible and firm water supply commitments. The methodology is tested and demonstrated by application to the LCRA System. Improvements in water supply reliabilities provided by off-channel storage are also investigated in the simulation study. The research is designed to explore and improve modeling capabilities in general, not to support specific decisions regarding water management in this particular river basin. CRM features in WRAP provide short-term storage frequency and supply reliability analyses conditioned on preceding reservoir storage and can be employed as a decision-support tool for water management during drought or operational planning studies for preparing for future drought. The research explores alternative methods and combinations of options for performing various CRM tasks and develops several additional new options. Climate teleconnection patterns, drought indices, and flow persistence are investigated from the perspective of potential improvements to WRAP/WAM CRM capabilities. The literature regarding climate cycles and metrics for identifying these cycles is reviewed. Correlation analyses are performed to analyze the relationship between flows at selected sites on the Colorado River and various climate cycle indices. The correlations are generally found to be fairly weak. The Rapid Intervention Program (RIP) is designed for improving on-farm irrigation management strategies. A new interactive web interface tool being developed by other researchers at Texas A&M University, called the Irrigation Water-Use Efficiency Maximizer (IWEM), will link WRAP with RIP. WRAP CRM methods are tested and compared to determine the optimal combination of options for use with the IWEM platform. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155724