NASAの衛星は雪がアメリカ南西部の地下水損失を相殺しなかったことを発見した(NASA Satellites Find Snow Didn’t Offset Southwest US Groundwater Loss)

2024-06-17 NASA

＜関連情報＞

• https://www.nasa.gov/science-research/earth-science/nasa-satellites-find-snow-didnt-offset-southwest-us-groundwater-loss/
• https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL107913

降雪は米国西部のグレートベースンにおける地下水損失を補うが、乾燥化の進行を補うことはできない。 Snowfall Replenishes Groundwater Loss in the Great Basin of the Western United States, but Cannot Compensate for Increasing Aridification

Dorothy K. Hall, Bryant D. Loomis, Nicolo E. DiGirolamo, Barton A. Forman
Geophysical Research Letters  Published: 20 March 2024
DOI:https://doi.org/10.1029/2023GL107913

Abstract

There has been an acceleration of groundwater loss in the Great Basin (GB) of the western U.S. as determined from total water storage (TWS) measurements from the GRACE/FO satellite missions. From 2002 to 2023, there was a loss of TWS in the GB of ∼68.7 km³ which is more than six times the current volume of the Lake Mead Reservoir. In this arid/semi-arid region, groundwater is the primary factor contributing to the decade-scale decline in TWS. Stronger declining trends are found in the western versus the eastern GB. Snow loading is the major cause of seasonal fluctuations of TWS in the GB. Despite annual replenishment of groundwater by snow, the downward trend persists even in notable snow years. Likely causes include declining snow mass, upstream water diversions and increased evaporation/sublimation due to increasing temperatures. Dire consequences for humans and wildlife are associated with this large loss of groundwater.

Key Points

• Snow accumulation in the Great Basin (GB) triggers an increase in total water storage (TWS) while snow ablation triggers a drop in TWS
• There is an 68.7 km³ loss of groundwater in the GB from 2002 to 2023 which is more than six times greater than the current volume of Lake Mead
• The 2002–2023 TWS decline in the GB is more pronounced in the western GB than in the eastern GB

Plain Language Summary

The 21st Century megadrought in the southwestern U.S. caused a dramatic acceleration of groundwater loss in the Great Basin (GB) of the western U.S. as determined from changes in the Earth’s gravity measured by the GRACE satellites. Groundwater is a major component of total water storage (TWS) in the GB, but snowfall and snowmelt are the major causes of seasonal fluctuations of TWS. As a snowpack accumulates or melts, water is redistributed causing a rapid regional change in gravity that can be measured from space. From 2002 to 2023, there is a substantial loss of groundwater in the GB of ∼68.7 km³ which is more than six times the current volume of water in the Lake Mead Reservoir in Arizona/Nevada. Stronger declining trends of groundwater loss are found in the western part of the GB while weaker declining trends are found in the eastern part. Despite annual replenishment by snowfall, even in notable snow years like 2010–2011, 2016–2017, 2018–2019, and 2022–2023, the downward trend of groundwater depletion persists. Likely causes for this decline include declining snow mass, upstream water diversions and increased evaporation/sublimation due to increasing air and surface temperatures. Groundwater depletion is associated with dire consequences for humans and wildlife.