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Article: Plant water use in a changing climate: why it matters (part 1). Julie Kray

by Julie Kray

These days, most of us don’t often pause long enough to think about the value of the natural resources that sustain life as we know it. Where would we be without water, for instance? We all drink it. H2O is essential to our daily biochemical functions, and the same is true for all other living things. Without water, we would also be foodless, as everything from rice to lettuce to potato chips to steak incorporates water along the way before it arrives on our plates or in our grocery stores. And even though doing the dishes or the laundry, or flushing the toilet are fairly mundane tasks for those of us in developed parts of the world, things would quickly get pretty unhygienic and unhealthy around here without water. With 6.8 million human beings on the planet and counting, we need clean fresh water and lots of it.

What we may not often think about is exactly how much water plants use, all over the world, in agricultural and natural environments. Over large areas, water use by plant communities can really add up. Some plants have remarkable abilities to find water sources with their roots, and conserve water during dry times. Plants develop these sorts of adaptations in response to long-term climate patterns where they grow. But how might plants deal with a rapid change in rainfall amount or seasonality, as is forecast for many places around the earth as our planet warms up?

This is the question that motivated my graduate research at C.S.U. It’s something that water planners think about constantly when they are trying to determine how much water is available to support growing human populations in different regions. Accurate estimates of plant water use are necessary to build water budgets that will tell us exactly how much is locally available for drinking water supplies, agriculture, or industry. But we don’t yet know how climate changes will affect plant water consumption in different regions. Like the plants themselves, our water budgets will probably have to adjust.

I had the fantastic opportunity to study water use of native plant communities in the awe-inspiring San Luis Valley (SLV) of southern Colorado, which is famous for its organic potato production, serves as a lay-over spot for migrating sandhill cranes, and is home to the wild and wonderful Great Sand Dunes National Park. The SLV is also the most arid region in Colorado, receiving only 7-8 inches of precipitation a year, on average. There is very little surface water (streams/rivers), and yet, the SLV is not a desert… a vast aquifer stores almost 1 billion acre-feet of groundwater that is relied upon by native plants and agricultural operations. Our best estimate of current groundwater use by native plant communities in the SLV is about 355,000 acre-feet per year (or 115 billion gallons per year). This is as much water as a city of 2 million people would use in a year! Is this groundwater consumption by native plant communities likely to increase or decrease as plants adjust to future climate conditions in the SLV? And how do we begin to answer this important question?  (on to part 2…)