The Fourth National Climate Assessment includes projections for temperature increases that can cause cause droughts and decrease the winter storage of water to cover summer needs.
The report uses the do-nothing RCP 8.5 projection, and calculates the temperature increases for 2050 and 2100 for various areas in the US. We concentrate on the Western temperatures. Here are some results for temperature increases in degrees C, from Table 8.2 of Chapter 8.
Area/Date. 2050. 2100
Rockies. 1.1. 4.5
Sierra Nevada 1.1. 4.5
Western US. 1.3. 5.2
The 5.2 degrees C increase is 9.36 degrees F.
Update: Dec. 7, 2017. A new study published in Nature magazine that adds the restriction of upper atmosphere data, raises the global mean temperature by 0.5 degrees C for RCP 8.5 in the year 2100. This may have to be added to the above projections. The RCP 6.0 and RCP 4.5 added 0.4 degrees C by 2100. The ranges around the new central values were also narrowed.
The report also shows the decline with time of the water equivalent of the snow pack in the do-nothing future of RCP 8.5.
Area/Date. 2050. 2100
Rockies. -17%. -65%
Sierra Nevada. -22%. -89%
Western US. -22%. -70%
Since Southern California gets water both from the Colorado River from the Rockies, and from the Sierra Nevada through the California Water Project, we have to do our best to slow climate change and to encourage to help others to do so. The California population is also rapidly increasing.
About the increased forest fire activity, the report says that there is a low to medium confidence for a detectable human climate change contribution in the Western US. However, housing developments in forest and brush areas, as well as more power lines, can contribute to the fires.
