View source for 24-Month Study Model (24MS)

==Overview==

The 24-Month Study Model (24MS) is one of three [[river system models]] developed and maintained by Reclamation to support operational decision-making and planning for the Colorado River Basin. All three models are implemented in the RiverWare modeling platform and share some key features. The [[Mid-term Probabilistic Operations Model (MTOM)]] was developed directly from 24MS so the two models have very similar structures and operations. RiverWare is an object-oriented modeling platform in which the ''objects'' may be inflow points, river reaches, diversions, reservoirs, canals, pipelines, and other water-resource features. 

24MS is used for short-term (1-2 years) projections for operational decision-making, and is typically run in a deterministic mode, meaning that a single inflow scenario is used to generate a single output trace for analysis. The model is run every month to provide operational updates as inflow hydrology forecasts and demand projections evolve. 

The results of the monthly runs of 24MS are formatted by Reclamation as a standardized set of data tables totaling 17 pages, known as 24-Month Study Reports. However, the Upper Colorado and Lower Colorado regional offices package and distribute this set of data tables differently; Upper Colorado adds a 9-page narrative summary for the Upper Colorado reservoirs, while Lower Colorado adds a single cover page with very a brief summary. 

==Relevance==

The 24MS projections of Lake Powell and Lake Mead levels for the coming water year determine the tier for the Annual Operating Plan and thus also the annual release volume from Lake Powell, and any reductions in delivery to the from Lake Mead to the Lower Basin states and Mexico. This fact alone means that Lower Basin stakeholders avidly follow the 24-Month Study Reports, as do many Upper Basin stakeholders as well. 

==Model Structure and Operation==

[[File:MTOM_CRB_view.png|thumb|400px|Figure 1. While this shows the Mid-term Probabilistic Operations Model (MTOM) in ''object view'', MTOM's model structure and objects are very similar to those of the 24-Month Study Model (24MS), including the 12 reservoirs in the bullet list at left, which are shown with the purple triangles. (Source: Reclamation)]]

Basically, 24MS takes a projected inflow sequence and runs it through prescribed operational rules at 12 Reclamation reservoirs to project the monthly conditions at those reservoirs over the next 24 months. A total of 19 inflow points are used to represent both inflows to those reservoirs and intervening flows between reservoirs. 

The inflow sequences are provided by the NOAA Colorado Basin River Forecast Center (CBRFC) and are based on a blend of CBRFC's [[seasonal streamflow forecasts]] and average historical inflows, depending on (1) the month when 24MS is run, and (2) the future month that is projected. 

Upper Basin water demands are not explicitly modeled in 24MS (with three exceptions); instead, the inflow sequences from CBRFC have the expected Upper Basin diversions and consumptive use already subtracted from the flows that would have occurred under natural conditions. The exceptions are the Gunnison Tunnel, Azotea Tunnel, and Navajo Indian Irrigation Project, which are represented as separate diversions in 24MS. Lower Basin water demands are modeled based on monthly schedules provided by the water users. 

The output from 24MS consists of monthly projected elevations and storage, releases downstream, and hydropower generation (if applicable) for the following 12 reservoirs:
*Fontanelle
*Flaming Gorge
*Taylor Park
*Blue Mesa
*Morrow Point
*Crystal
*Vallecito
*Navajo
*Lake Powell
*Lake Mead
*Lake Mohave
*Lake Havasu

As suggested above, 24MS is run monthly with a single inflow sequence, representing the ''most probable'' inflows. The ''most probable'' run in August--specifically, its projected elevations of Powell and Mead on January 1st--is used to set the tier for the Annual Operating Plan. The release from Lake Powell may be subsequently adjusted based on the results of the April run (projected elevations on September 30th).

Additionally, four times a year (January, April, August, October), two additional 24MS runs are done, using ''probable minimum '' and ''probable maximum'' inflow sequences provided by CBRFC. These two runs, which represent 90% and 10% exceedance probabilities, help bracket the uncertainty in the main ''most probable'' run. Under the terms of the 2019 Drought Contingency Plans, whenever a ''probable minimum'' run shows Powell going below 3525' at any time in the next 24 months (as happened in January 2021), both of these additional 24MS runs are done monthly instead of four times per year to provide basin stakeholders with additional guidance to prepare for drought impacts.


==Data and Tools==

===24-Month Study Model Reports===

The output of the 24-Month Study Model is released monthly on about the 15tt of the month. 

Upper Colorado Region


*[[Mid-term Probabilistic Operations Model (MTOM)]] 
*[[Colorado River Simulation System (CRSS)]]

==Additional Resources==

===State of the Science Report===

[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_3.pdf Chapter 3] of the State of the Science report, ''Primary Planning Tools,'' describes the three primary Reclamation system models in detail. 

==Research Directions==



==New and Notable Research (2020-present)==

'''[<URL FOR PAPER>]'''

''Summary''