The uncertain future of global freshwater resources
Projections regarding the future of conditions on Earth vary widely. Climate change, both human-induced and naturally-forced, is expected to have many far-reaching implications, including altering current global weather patterns and terrestrial freshwater supply. Already, terrestrial water fluxes have been affected by human demand and interventions. Examples of human-induced impacts include dam and reservoir building, water withdrawals from ground and surface water for agricultural, industrial, and municipal use, as well as environmental sanitation impacts. Since the 1970's, concurrent with rising global mean temperature, freshwater discharge from rivers to the world's oceans has been decreasing. In the United States, the Southwest (from the headwaters of the westernmost Colorado River to the Mexican border, encompassing California, Nevada, Utah, and Colorado) has experienced three extreme drought years since the start of the 21st century. Projections indicate that precipitation over the lower mid-latitude continental regions, including the southwestern United States, will continue to decrease as a result of continuing greenhouse gas emissions and increasing global mean temperature. Colorado River flow reached the ocean in mid-2014 as part of a restorative experiment agreed to by the United States and Mexico, but had not previously reached the ocean since 1998. Rivers in Australia, Africa, and Asia are experiencing the same phenomena, with human extraction impairing the river’s natural ability to meet the sea. There are political and technological techniques that could mediate regional decreases in freshwater supply. In particular, large changes in agricultural use are necessary to compensate for oncoming climate shifts and to ensure that the worldwide population has access to enough water for survival.