09/18/07 Affecting Ground Water

Affecting Ground Water. I'm Greg Martin with today's Line On Agriculture. We all depend on water but it's crucial to the Ag industry. If it doesn't fall from the sky, it's pumped from rivers, reservoirs, or wells. But changing climate patterns can have a substantial impact on the amount of water available and that is what ARS Scientist Tim Green has been studying. GREEN: Greenhouse gases are increasing, climate appears to be changing and these models are predicting that it will even more so continue to change. We used a climate model out of Australia and used it to predict what would happen under a doubling of CO2, how would that effect climates and not only long term changes in temperature but looking at long term equilibriums. If you had a doubling, how would it affect other weather variables like rainfall? According to Green, there are a great many variables when it comes to how much water from rainfall gets used or stored. GREEN: The interesting part of our study in that paper was that if you look at soil and plant systems and how they process the water that infiltrates into the ground, say a 20% increase in average annual rainfall doesn't translate to a 20% increase in water that goes below the root zone because the plants respond differently in different climates and CO2 in the atmosphere itself affects how much water a plant will use. What all this means is that an increase in CO2 levels in the atmosphere has an impact on how fast groundwater supplies recharge. In most cases, the models show that they will recharge faster with a higher CO2 level. In addition, Green says that even rainfall patterns can be changed. GREEN: So when we looked at simulated climates, we found that for example in a subtropical area we had much longer drought periods which is something that phenomenologically, people are deserving in different areas of the world that  wow our droughts are getting longer or we're getting more intense rainfalls in different periods. So the change in duration and frequency of droughts and also in the frequency and duration of wet periods have a big effect on how the soil/plant system responds. Green attributes these changes in the models to the human factor. GREEN: What is clear is that if you look at historical changes in greenhouse gases that there is a human effect in the timescale of a couple hundred years, you'll see a dramatic increase. That's today's Line On Agriculture. I'm Greg Martin on the Northwest Ag Information Network.