Presentations 2016

The effects of climate change on groundwater extraction for agriculture and land-use change

University of California at Davis

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The management of groundwater resources is an issue that reaches far and wide; regions around the world are struggling with ways to reign in extraction from aquifers that have been deemed over-exploited, and many of the world's most productive agricultural basins depend almost exclusively on groundwater. The food consumers that eat, the farmers who produce that food, and the local economies supporting that production are all affected by the availability of groundwater. Worldwide, about 60 percent of groundwater withdrawn is used in agriculture, and in some countries, the percent of groundwater extracted for irrigation can be as high as 90 percent. Thus, any investigation into the economics of groundwater must consider the agricultural industry. The proposed research focuses exclusively on the groundwater used for agriculture.Climate change has the potential to impact groundwater availability in several ways. For example, it may cause farmers to change the crops they plant or the amount of water they apply, both of which have implications for water availability. Climate change also affect water availability directly by changes in precipitation and evapotranspiration patterns. In this paper, we analyze the effects of changes in temperature, precipitation, and humidity on groundwater extraction for agriculture using an econometric model of a farmer’s irrigation water pumping decision that accounts for both the intensive (water use) and extensive margins (crop acreage). Our research focuses on the groundwater used for agriculture in the High Plains (Ogallala) Aquifer system of the Midwestern United States. We find that changes in climate variables will influence crop selection decisions, crop acreage allocation decisions, technology adoption, and the demand for water by farmers. We also find that such changes in behavior can affect the diversity of crops planted, potentially impacting agricultural biodiversity.According to our preliminary results, water intensity decreases in rainy years. Farmers tend to plant more corn and soybeans after rainy years, as evidenced by a significant positive coefficients a total precipitation over the last 3 years on the crop acreage regressions for these crops. Farmers planting more than one type of crop tend to increase acreage of alfalfa, sorghum and wheat in warmer/dryer years and increase acreage of corn and soybeans in colder/wetter years. High temperatures in March can trigger the installation of central pivots with sprinklers: also true for rain in May/June. We find mixed results for crop acreage and water use in the regressions with monthly variables. Farmers tend to diversify crop acreage in warmer/dryer years. The outcome of this research provides a better understanding of how changes in temperature, precipitation, and humidity affect the availability of groundwater for agricultural use and of how agriculture can adapt to these changes. We are also able to see how such adaptation measures affect crop diversity, one of the main components of agricultural biodiversity.