The Corps Water Management System (CWMS) includes four interrelated models to assist with water management for the basin:

- GeoHMS (Geospatial Hydrologic Modeling Extension)
- ResSIM (Reservoir System Simulation)
- RAS (River Analysis System)
- FIA (Flood Impact Analysis)

The climate of California is the result of three major factors peculiar to the location and physiography of the state. These are the latitude, the influence of the Pacific Ocean, and the orientation and extreme range of topography of the State. The influence of the Pacific Ocean gives the immediate coastal areas a true maritime climate. However, the mountain ranges, which shut off the Sacramento Basin from the ocean and the interior of the continent, cause unusually wide variations and abrupt discontinuities in climate within the basin.

Topography is the most important influence on areal distribution of precipitation in California. The pattern of average precipitation in California reflects the influence of the physical configuration of the land surface. Precipitation is heavy on the windward side of the coastal ranges because of lifting of the moisture-bearing winds over the mountains. The Central Valley to the east of the coastal ranges has a drier, more continental cllmate, but the western slope of the Sierr Nevada is a region of normally heay precipitation. These latter mountains lie across the path followed by moist air moving inland and reach a much higher elevation than the coastal ranges. Major state-wide storms in California result when the deep southwest wind current in the warm moist sector of a Pacific storm is superimposed upon the efficient rain-producing mechanism of California topography. These major storms pass through California only during the fall, winter and spring, with maximum frequency during the winter.

The climate of the valley floor is characterized by mild wlnters with moderate precipitation, and hot, dry summers. The mountain watershed has colder winters, heavy rain and snowfall, and warm, dry summers. Maximum and minimum temperatures of 118 °F and 17 °F, respectively, have been recorded on the valley floor. Normal annual precipitation varies from less than 15 inches on the Valley floor to over 90 inches in the Sierra Nevada. Approximately 85% of the precipitation occurs during the period of November through April. Precipitation normally falls as rain below the 5,000 ft level and as snow above, although occasionally there is rain over almost the entire area