Heat domes and heat waves take more water from reservoirs

The historic drought in California could be made worse as water levels fall in the state's reservoirs. Officials say accelerated evaporation is to blame, the good news they say is one records heatwave is not enough to do serious damage. 

"That increment increase, for a few days; it's not gonna make a big impact in our scheme of things," said East Bay MUD Water Supply engineer, Chris Potter.

According to officials, two things will make a difference. As the drought parches the land, it gets so dry, so deep that a lot of rain and snow runoff will likely not make it to reservoirs. 

"The soil drys out more quickly, and I think that will lead to less runoff," said Potter.

One good year of rain can erase several years of increased evaporation. 

"It's really varied. It's year by year, depending on many factors, not only temperature," said Valley Water Supply Operations Manager, Bassam Kassab. 

"Other factors are relative humidity, wind speed, solar radiation or demand," said Potter.

Over the last 60 years, Valley Water Supply reservoirs have lost between five and nine percent of the reservoir's contents. Overall temperatures are rising as well as the frequency and duration of extreme heat spells, which experts warn doesn't make the situation any better. 

"Assuming you have a series of heat waves down the road, it's gonna increase the evaporation per year," said Mr. Kassab.

It also increases water temperatures year over year.

"That can especially be problematic for fish and it can result in the death of eggs and larvae which again, we've seen," said Pacific Institute Research Director, Heather Cooley. "As temperatures go up, water use, crop water use, will go up or demand for that water will go up," said Ms. Cooley.

Water suppliers do factor climate change into their planning. To help conserve water, have focused more on above and below ground storage and purification of waste water.