Soil is dry; irrigation delivery begins early
Dryland crop germination is stunted
Active fire season begins
Winter resort visitation is low; snowpack is minimal
Dryland pasture growth is stunted; producers give supplemental feed to cattle
Landscaping and gardens need irrigation earlier; wildlife patterns begin to change
Stock ponds and creeks are lower than usual
Grazing land is inadequate
Producers increase water efficiency methods and drought-resistant crops
Fire season is longer, with high burn intensity, dry fuels, and large fire spatial extent; more fire crews are on staff
Wine country tourism increases; lake- and river-based tourism declines; boat ramps close
Trees are stressed; plants increase reproductive mechanisms; wildlife diseases increase
Water temperature increases; programs to divert water to protect fish begin
River flows decrease; reservoir levels are low and banks are exposed
Livestock need expensive supplemental feed, cattle and horses are sold; little pasture remains, producers find it difficult to maintain organic meat requirements
Fruit trees bud early; producers begin irrigating in the winter
Federal water is not adequate to meet irrigation contracts; extracting supplemental groundwater is expensive
Dairy operations close
Fire season lasts year-round; fires occur in typically wet parts of state; burn bans are implemented
Ski and rafting business is low, mountain communities suffer
Orchard removal and well drilling company business increase; panning for gold increases
Low river levels impede fish migration and cause lower survival rates
Wildlife encroach on developed areas; little native food and water is available for bears, which hibernate less
Water sanitation is a concern, reservoir levels drop significantly, surface water is nearly dry, flows are very low; water theft occurs
Wells and aquifer levels decrease; homeowners drill new wells
Water conservation rebate programs increase; water use restrictions are implemented; water transfers increase
Water is inadequate for agriculture, wildlife, and urban needs; reservoirs are extremely low; hydropower is restricted
Fields are left fallow; orchards are removed; vegetable yields are low; honey harvest is small
Fire season is very costly; number of fires and area burned are extensive
Many recreational activities are affected
Fish rescue and relocation begins; pine beetle infestation occurs; forest mortality is high; wetlands dry up; survival of native plants and animals is low; fewer wildflowers bloom; wildlife death is widespread; algae blooms appear
Policy change; agriculture unemployment is high, food aid is needed
Poor air quality affects health; greenhouse gas emissions increase as hydropower production decreases; West Nile Virus outbreaks rise
Water shortages are widespread; surface water is depleted; federal irrigation water deliveries are extremely low; junior water rights are curtailed; water prices are extremely high; wells are dry, more and deeper wells are drilled; water quality is poor

The California drought monitor historically observed impacts, via Meg Bernhard. (and kinda @nontanne I guess)