Around the world, global warming is starting to have a serious impact on rainfall in the subtropics and middle latitudes. The tropical atmospheric circulation known as the Hadley Cell is expanding toward the poles. This expansion is causing clouds and storms to move further north. And as a result, regions in the middle latitudes are starting to dry out.
According to The World Resources Institute:
A changing climate means less rain and lower water supplies in regions where many people live and much of the planet’s food is produced: the mid-latitudes of the Northern and Southern hemispheres, including the U.S. Southwest, southern Europe and parts of the Middle East, southern Africa, Australia and Chile.
Such a fundamental shift in global weather patterns due to human-caused climate change is expected to reduce the food and water security of numerous nations. The World Resources Institute recently warned that food and water crises were imminent as a result. And, apparently, these kinds of changes to the world’s weather are already generating profound shocks in parts of the U.S.
Colorado River and California Droughts Expected to Persist
For the Colorado River, this combined warming and movement of clouds northward has produced a 16-year-long drought. Hotter average seasons result in greater rates of evaporation. So even if rainfall averages remain, grounds, lands and rivers are drier. But the Hadley Cell’s expansion has also moved rain bearing weather systems north.
It’s a compounding drying influence that has pushed Lake Mead, the nation’s largest reservoir, to record low levels. And states dependent on the great river’s water supply for farming and industry are now involved in negotiations to avert a water crisis in 2018. Forecasts predict a 50 percent possibility that Lake Mead’s water levels will fall below its mandatory rationing line. Such an event would result in water cut-offs for Arizona and Nevada.
(Over recent years, the U.S. has experienced numerous severe and long-running droughts. These worsening drought conditions have impacted everything from Colorado River levels to wildfires, to the health of forests, to commerce on the Mississippi River, to the productivity of state agriculture. As human fossil fuel burning continues, atmospheric changes will force rainfall toward the poles which will tend to further worsen drought conditions in middle-latitude regions like the lower 48 states of the U.S. Image source: Drought Monitor.)
In an attempt to prevent crisis in the coming months, California and other Colorado River states are attempting to cut water consumption now. Such a planned regional belt-tightening would help to avert conflict over the Colorado River’s dwindling stores and smooth out any losses over time. But, sadly, climate conditions are only likely to continue to worsen — increasing the risk of mandatory rationing for 2019, 2020 and beyond.
In California, a five-year-long drought that is the worst in state history now threatens to enter its 6th year. Rains during 2016 did help to reduce the severity of drought conditions for some parts of the state. And during recent days, a series of Pacific storms has helped to deliver moisture to some northern and central regions. However, with record warmth settling in over the Arctic and with a La Nina developing in the Pacific, long range forecasts indicate a high risk that California will experience a warm, dry winter. Such predicted conditions would result in a persistence of the present drought with continued impacts to the state’s forests and agriculture.
Southeastern Drought Expected to Expand
(Drought conditions are expected to worsen across the US Southeast this fall and winter. Drought in the Colorado River region is expected to persist or worsen. Drought in California and in parts of the US Northeast is expected to persist. Image Source: Climate Prediction Center.)
Further east, a flash drought that has settled into the US south is expected to worsen over the coming months. Abnormal warmth in the range of 5-15 degrees (F) above average for the region during the past month has combined with dry weather to spur severe to extreme drought conditions over a six state area. Now, parts of Tennessee, North Carolina, South Carolina, Georgia, Alabama and Mississippi are under the gun — with drought zones expected to persist or expand through at least early February.
US Drought Conditions to Worsen as the Globe Warms
In total, more than 120 million people in the lower 48 states are experiencing drought. And the systemic impacts of multi-year, persistent droughts are widespread and growing. This drying is consistent with the impacts associated with a warming climate. And, unfortunately, such worsening of droughts is likely to continue until atmospheric warming is halted and/or reversed.
Hat tip to Wili