With each issue, Trib+Water brings you an interview with experts on water-related issues. Here is this week's subject:
Bridget R. Scanlon is a senior research scientist at the Bureau of Economic Geology in the Jackson School of Geosciences at the University of Texas at Austin. Her research group evaluates variations in water resources in response to droughts and floods at various scales using GRACE satellite data, surface hydrologic data and groundwater level data. They are currently examining different approaches to coping with drought by comparing data from Texas and California.
Editor's note: This interview has been edited for length and clarity.
Trib+Water: How do the California and Texas droughts compare?
Bridget R. Scanlon: Each drought is different even in the same place. The Texas drought started off very intense in 2011. We’ve been in drought throughout most of the four years since.
The California drought started out gradually in 2012, and has been intensifying. California gets much of its precipitation in the winter from the snowpack. That provides a good forecast for drought in the summer. The 2012 snowpack was about 52 percent of the long-term average. The snowpack this year was only 5 percent of the long-term average. They know in spring if they are going to have a lot of drought problems in the summer.
We don’t have that kind of forecasting mechanism. At UT, we have a forecast that combines new satellite soil moisture data, and they are predicting a wet summer in Texas, a greater than 90 percent probability of a wet summer throughout Texas.
Trib+Water: Do the two droughts have any similarities?
Scanlon: The one thing that is similar about these is the long-term nature of these droughts. You start out with a meteorological drought because of low rainfall and then you build up. That results in low soil moisture, causing an agricultural drought, with a cumulative deficit over time. That results in low runoff that decreases over time. When that accumulates, you end up with a large-scale hydrological drought.
It builds on each other. Sometimes when we have close to normal rainfall, we wonder why are we still in a drought, and our reservoirs are still low. That makes it difficult for people to understand. Above-average rainfall impacts the meteorological drought, but we could still have a large deficit in the reservoirs that is going to take way above normal rainfall conditions to overcome.
Trib+Water: What are the tools being used to monitor and predict these conditions?
Scanlon: Traditionally, we relied on ground-based data like precipitation gauges, runoff gauges and reservoir storage data. But now we have some new tools to evaluate drought conditions.
One of those is the GRACE satellite, the Gravity Recovery and Climate Experiment. We can measure how much water we have in storage over the entire state. That provides a good regional perspective on drought, recovery and the overall status of water storage, which includes reservoirs, soil moisture and groundwater.
The Center for Space Research at the University of Texas is one of the lead institutions that helped develop GRACE and is responsible for maintaining the monitoring data.
The GRACE data showed us that in 2011 we had a large decrease in water storage in the state. It was almost 50 million acre feet. We use about 18 million acre feet of water a year in the state, on average. So that is a large decrease.
We saw with GRACE that we had a fair recovery in the fall of 2011 through spring 2012, but then it decreased again in 2012. It has remained on average pretty low, until recently. We have seen a recovery. It is similar to what we saw toward the end of 2011. It gives us an overall picture of what is going on.
Trib+Water: Are the attempted remedies for drought playing out differently in California than in Texas?
Scanlon: California and Texas are fairly different, in that California has an integrated canal aqueduct pipeline system where they transport water from the wet regions in the North to the very dry regions in the South.
However, recently, because of endangered species issues, they have been reducing the delivery from the North to the South during drought. Having that integrated system is almost amplifying the drought impacts, because they provide water when it's so wet and they reduce it when it is dry.
One way of dealing with that is to store water when it is wet, so that it is available when it is dry. We are trying to manage these extreme wet and dry periods. We end up having too much water when we don’t need it and too little when we do.
Traditionally, we have stored water in reservoirs. In California and Texas, most of our reservoirs were built by the mid-70s and we haven’t built very many reservoirs since that time. But our population has continued to grow both in California and Texas.
The current Legislature is evaluating a bill to help incentivize aquifer storage and recovery in Texas. We have more opportunities to do that in the state to store more water in these aquifers.
Trib+Water: How much impact could the recent rains have on the status of water in the state?
Scanlon: The Texas Water Development Board’s database shows the reservoir storage in state is at 79 percent of capacity, as an average over the entire state. It is moving in the right direction. It has increased a few percent within the last month.
A wet summer could keep moving this in the right direction, but these bumps and dips will continue. It seems that maybe we have had enough rain to replenish the soil moisture deficit. The rain that we get would then run off and move into the reservoirs, but we still have to consider that the Colorado River basin is at 34 percent of capacity. Buchanan and Travis reservoirs are now at 40 percent of capacity. They have a fair ways to go. It depends where we get the rain to see if they can be replenished.
[Editor's note: This interview was conducted before the Memorial Day rains. The statewide reservoir supply is now at 83 percent of capacity. The Colorado River basin is now at 48 percent of capacity. The Buchanan and Travis reservoirs are now at 65 percent of capacity.]
Trib+Water: What is your perspective on the state of water in Texas?
Scanlon: One way of dealing with water issues, we focus a lot on being about to predict a drought and floods. But I think we need to be ready. We can’t rely totally on being able to predict these things and we can’t react very fast. It takes a long time to develop infrastructure and mechanisms to deal with these extremes of droughts and floods. And we have had these forever.
A way to deal with water management during dry periods is to reduce demand or increase supply, or store more water. We are getting much better at conserving water. Other ways we can deal with that is considering reusing and recycling municipal wastewater. We can also try to learn to manage stormwater better.
To increase supply, we are looking at brackish water resources in the state and also seawater desalination to increase supplies. Conjunctive use, using surface water during wet periods and shifting to using more groundwater during dry periods, is another way to deal with it. An extension of that is to store excess surface water in groundwater aquifers for use during dry periods.
The main approach to reducing vulnerability to drought shortage and enhancing drought resistance is to have a large number of techniques in your portfolio that you can use.