Q&A: How can SEI tools help California prepare for a “new normal” of drought?

Well, right now California is experiencing one of its most severe droughts. Recent research is suggesting that this is likely more intense due to human-caused climate change.

Another factor that differentiates it from droughts in the past is that water demands may have become less flexible as the easiest conservation measures have been applied and agricultural demands have shifted to perennial crops that require irrigation every year. So there’s less cushion, if you will, for ensuring everyone is allotted the water they’re entitled through water rights.

As the drought progressed through the irrigation season, different basins around the state have had to have curtailment orders issued, which means that certain water rights holders are unable to divert surface water any longer.

The reason that has to be done is that California’s water rights system is a first in time, first in right system, in which the oldest water rights – those that were claimed the earliest – have senior priority. And they have to be protected relative to more junior water rights, so it’s the responsibility of the State Water Resources Control Board to determine when certain water rights can no longer divert in order to protect the water rights of the more senior water right holders.

The State Water Resources Control Board is the central authority for the water rights.

But of course, the hydrologic conditions are different in each basin, so not every basin has had to be curtailed. Some basins are curtailed almost every year.

It’s just that this year, some of the larger basins and some basins that aren’t curtailed very frequently have been curtailed, so it’s impacting a lot of people in ways that they’re not used to being affected.

This is obviously a real challenge and growers have put their crops in and gotten part way through an irrigation season. Now they’re unable to divert surface water, so they may have to rely on groundwater if they can to protect their economic investment. It makes for a very difficult situation.

Others have pointed out that the forecast for inflows into the reservoirs this year turned out to be overly optimistic and people are investigating why that is.

A leading theory is that soil moisture in the mountains had gotten so low due to the previous year being a dry year – as well as this past winter – that the snow melt that was generated as the snow pack melted just infiltrated into the ground and never moved into the streams. There is a need for better forecasting under these extremely dry conditions. And I think there’s a need for better linkage between those forecasts and the models that are used to study water allocations throughout the state, particularly throughout the Central Valley.

Over the past eight years or so, SEI has been developing water allocation models for various parts of California.

What we do is create these water allocation models and basically, it’s a platform for comparing the supplies and demands for water. It helps us determine when and where shortages may occur, where water users may not receive enough water.

What’s new in our more recent work in these models is that we’re working with the State’s water rights database, eWRIMS, to create an explicit representation of every water right in these basins. So now we’re starting to bring tools online that can tell a water manager which water rights will be impacted by water shortages. And it’s possible to explore what may happen to water availability for each water right under a range of hydrologic conditions.

This type of tool needs to be connected to the seasonal and long-range forecasts that are being developed so that when we’re in wintertime and early spring, models can take these forecasts and give us some sense of what type of water allocation we can expect in the coming months, down to which water right may be impacted by any shortage that may occur.

In some parts of the state – the main agricultural areas– the demands for water are fairly well known. They can be estimated using information such as crop maps, which can be obtained from satellite information, and our understanding of the weather, and how that impacts crops and how much water they use.

A particularly difficult area for estimating demands that we’ve been working on more recently are watersheds like the ones along the northern coast, where there are many small demands that are usually just for very small agricultural operations or domestic use. We’ve been developing tools at SEI that can help estimate those demands based on the water rights that are in that basin.

An important first piece of information in doing any type of analysis around a drought is to try to characterize the demand for water. This gives us a first approximation of what the demands may be just by looking at the water rights.

That’s right. I think it’s the case that in wet years and when demands were smaller relative to the supply, it wasn’t an issue, so no one had to focus on it like they have to focus on it now.

It’s when you get to these really dry years and when you’ve had growing demand over time that there’s going to be conflict over water supply because there’s not enough for everyone.

What we’re really trying to do is methodically account for every legal water right and put that into a framework we where we can compare it to the supply or what we think the supply might be. And then that, again, gives us a first approximation of what might happen during a drought.

Droughts will happen no matter what, but based on my review of recent research, climatologists are feeling much more confident that human-induced climate change will make those droughts more severe. What that means is we’re going to see severe droughts more frequently than we have in the past.

It also may be that the time period in which California was developed was a relatively wet period in the in the longer historical record. This is based on tree ring data going back a thousand years. Researchers can see that this is a relatively wet period in which we’ve built up our whole system and our whole expectation for what’s normal or average.

And it may well be that it’s not that wet normally and that would be another argument for us to prepare for more droughts.

With the forecasting tools we’re developing at SEI, we can at least anticipate what’s to come and adapt accordingly.