In a typical year, California gets almost a fifth of its energy from dams on its rivers and streams. But the last several years have been anything but typical: the ongoing drought has shrunk the state's reservoirs and cut the amount of hydro power the state can generate by about a third.

And since our consumption of energy hasn't dropped to make up the shortfall, says a report released this week by the Pacific Institute, California has stepped up its consumption of power from plants that burn expensive, carbon-polluting natural gas to fill the gap left by the drought.

As a result, says the report, ratepayers are shelling out almost half a billion additional dollars per year, and emissions of carbon dioxide and other pollutants from California power plants have risen significantly.

The report, entitled "Impacts of California's Ongoing Drought: Hydroelectricity Generation," also cites increased imports of out of state electricity (likely increasing the state's coal footprint) and more wind and solar as other ways in which the state's power managers have been dealing with the hydropower shortfall.

"This severe drought has many negative consequences. One of them that receives little attention is how the drought has fundamentally changed the way our electricity is produced," said the report's author, Pacific Institute President Peter Gleick.

The report's worth reading for its overview of California's in-state power generation as well. Our state is very much hooked on natural gas even in non-drought years, but as this Pacific Institute pie chart based on data from the California Energy Commission shows, the drier it gets the gassier our energy mix becomes:

Before you look at that razor-thin one percent of California's power mix filled by burning coal and start thinking our state was nearly coal-free in 2013, remember that in-state generation isn't the whole story. According to the California Energy Commission, we imported enough coal-fired power from out of state in 2013 to make up almost 8 percent of the state's total use for that year. The Pacific Institute chose to omit imported energy from its calculations because a lot of the electrical power the state imports -- around 12.5 percent in 2013 -- isn't assignable to a specific energy source.

Still, both the in-state generation figures in the chart above and the Energy Commission's total figures for 2013 show that in that year, well into the current drought, hydro power's contribution to in-state generation was around 12 percent.

That's including output from hydroelectric plants of 30 megawatts and larger, which are counted in a separate "large hydro" category by the state, and those smaller than 30 megawatts, which are considered "small hydro" and counted along with wind, geothermal, and solar in the state's renewable energy totals.

By comparison, check out this similar graph we put together from 2011's stats:

Nuclear power contributed only half the percentage of California in-state generation in 2013 that it did in 2011 because the San Onofre Nuclear Generating Station shut down in 2012, leaving Diablo Canyon as the state's sole source of nuclear power. Solar and wind together rose by a cumulative three percentage points. Coal went down by a percentage point, and geothermal and biomass stayed the same.

But the really stark difference between 2011 and 2013 is in the relative output of hydro and natural gas. Hydroelectric power was 21 percent of the state's in-state generation in 2011, and dropped by nine percentage points to 12 percent in 2013 -- a power loss equivalent to San Onofre going offline.

And natural gas's share of the total rose from 45 to 61 percent to make up the difference, meaning a concomitant increase in emissions and energy costs -- as much as $1.4 billion in increased ratepayer costs from 2011 through 2014, according to the Pacific Institute report. And that increased natural gas burning is likely making the threat of future extended droughts worse due to increased greenhouse gas emissions.

Admittedly, 2011 was a reasonably wet year with great hydropower output; a statistical outlier in a string of increasingly dry years since 2007. That just underscores the state's need to conserve both power and water as we face an unpredictable future.

"We hope this report prompts a lively debate on how to factor in a changing climate when we plan for electricity generation," said Gleick.