Land Use and Land Cover Change and Potential Implications for Water Levels of the Great Salt Lake

The Great Salt Lake has shrunk significantly in volume since non-native settlement started. Most of that shrinkage has occurred in recent years. There are many adverse consequences associated with the shrinking of the lake, so avoiding the lake drying completely is desirable. To prevent this from happening, the causes of the drying need to be determined. Previous studies suggest that drying is due to a combination of water diversion for agricultural and municipal use and a decades-long drought. While municipal water use has been mentioned in other studies, it has sometimes been presented as a solution to the drying of the lake. As agriculture uses more water per hectare than urban areas, a prevalent notion is that urban expansion results in water savings. This viewpoint assumes that urban areas are predominantly developed on agricultural land. In this paper we quantify land use change in the Great Salt Lake basin over the last ~40 years and associated likely water diversion quantities based on average irrigation needs for different crops and for urban areas. We determine whether recent urbanization has occurred on natural or agricultural lands and has therefore increased or decreased water demand. Our results show that the cultivated crop area in Salt Lake County decreased markedly in the 2002–2007 and 2018–2023 periods, while developed land increased far more than the decrease in agricultural land. For the 2008–2023 period, far more natural land uses have been converted to urban uses than conversions from agricultural land, meaning that water demand has increased with urbanization. Also, alfalfa has a high water demand and has increased in area. Nevertheless, the increased irrigation water use from the alfalfa area has been smaller than the increase in water use from urban development. Results show that for the four most populous counties, >75% of land use change from 2008 to 2023 has resulted in a net increase in water use. Even for the more agricultural Cache County, Utah, and Franklin County, Idaho, >50% of land use change resulted in a net increase in water use. The results of this study have important implications for the planning of future urban development if the Great Salt Lake is to be preserved.