NEWS NOTES ON SUSTAINABLE WATER RESOURCESWater Availability Issueshttps://www.fs.fed.us/rm/pubs_journals/2019/rmrs_2019_brown_t001.pdf  &ld...

NEWS NOTES ON SUSTAINABLE WATER RESOURCESWater Availability Issueshttps://www.fs.fed.us/rm/pubs_journals/2019/rmrs_2019_brown_t001.pdf  “This study estimates the likelihood of water shortages over the remainder of the 21st century in 204 watersheds covering the contiguous United States. The estimates are based on monthly projections of water demand and renewable water supply in light of population growth and climate change, taking into account water storage and transbasin diversion capacities. The study then examines several possible adaptations to projected shortages, including water withdrawal efficiency improvements, reservoir storage enhancements, demand reductions, instream flow reductions, and groundwater depletions. Results provide a broad measure of the relative efficacy of the adaptation measures and show when and where the measures are likely to be helpful.  Although there remains substantial uncertainty about future precipitation and thus water yield, climate change and population growth are likely to present serious challenges in some regions of the U.S., notably the central and southern Great Plains, the Southwest and central Rocky Mountain States, and California, and also some areas in the South (especially Florida) and Midwest. The continued reductions in per‐capita water withdrawal rates assumed here, which follow trends established over the past three decades, are essential but insufficient to avoid impending shortages. Attention will therefore focus on the other options examined here—additional reservoir storage capacity, groundwater mining, instream flow reduction, and ag‐to‐urban transfers—all of which have serious external costs. Of these four options, the first has limited promise, especially where most needed. Simulations show that major additions to storage capacity are ineffectual in the most vulnerable basins due to a lack of water to fill the reservoirs. The other three options, however, can be quite effective in many locations, indicating that pressures to implement them will mount as shortages become more severe.”  Trends in water use for the U.S. are shown at https://www.usgs.gov/mission-areas/water-resources/science/trends-water-use?qt-science_center_objects=0#qt-science_center_objects“Total withdrawals for all categories of use in 2015 were estimated to be 322 billion gallons per day (Bgal/d), a level of withdrawal not reported since before 1970. Total withdrawals in 2015 were 9 percent less than in 2010, continuing a sharp but steady downward trend since 2005. Freshwater withdrawals were also 9 percent less than in 2015.The drop in total withdrawals in 2015 was primarily caused by significant decreases in withdrawals for thermoelectric power (28.8 Bgal/d), which accounted for 89 percent of the decrease in total withdrawals. The decrease in public-supply withdrawals accounted for another 9 percent of the decline in total withdrawals. Categories of use with larger withdrawals in 2015 than in 2010 were irrigation and mining. The increase in irrigation withdrawals was only about 2 percent greater than 2010 levels, partly resulting from updated 2010 data, and mining withdrawals were corrected downward for 2010.”