The La Nina we are in now is the most intense La Nina in many years.



La Nina, the yang to El Nino's yin, is a semi-cyclical pattern of the tropical Pacific ocean and atmosphere. Cool water wells up along the equator at higher than normal rates. The cool water reinforces the pattern of strong trade winds which reinforces the strong upwelling. La Nina lasts one year, sometimes two.

Warm tropical Pacific temperatures and cool Atlantic temperatures bring winds that take Atlantic moisture into north America.



Before the super El Nino of 1997 there was a period of about 20 years of frequent El Ninos and weak La Ninas. Since the La Nina of 1998, El Ninos have been weaker and La Ninas stronger. The Tropical Atlantic ocean warmed after 1997 and the tropical central and east Pacific cooled.

Water temperature oscillations between the north Atlantic and the north Pacific occur naturally. However, as we will see, increasing levels of greenhouse gases can tip the natural balance, just as natural changes have tipped the balance in the past.

The cooling of the eastern North Pacific and warming of the North Atlantic has caused a drought in the southwest since 1998.

Cool Pacific and warm Atlantic temperatures divert Atlantic moisture from north America to the Pacific ocean causing north American droughts.



When the tropical Atlantic and Caribbean sea are warmer than normal and the tropical eastern Pacific ocean is cooler than normal, moisture bearing winds are diverted from north America to central America, causing north American droughts.

The Colorado River is the largest river in the southwest. The ongoing drought has dramatically reduced its flow causing a precipitous decline in the water level of lake Mead, the reservoir designed with the largest storage volume on the Colorado.

Lake Mead's level has plummeted approximately 140 feet since the year 2000. At the end of September, 2010 Lake Mead's level was equal to its lowest level since it was filled.

The dock to nowhere and the Lake Mead bathtub ring show water levels down over 100 feet.



Growing populations are increasing demand for water in the southwest at the same time as climate change is bringing hotter and drier weather. Lake Mead is rapidly drying up as a result of the increasing demand and decreasing supply of water.

Historical and anthropological records show that drought conditions in western north America much more severe than any drought since European occupationoccurred during the medieval warm period.

The western United States is experiencing a severe multiyear drought that is unprecedented in some hydroclimatic records. Using gridded drought reconstructions that cover most of the western United States over the past 1200 years, we show that this drought pales in comparison to an earlier period of elevated aridity and epic drought in AD 900 to 1300, an interval broadly consistent with the Medieval Warm Period. If elevated aridity in the western United States is a natural response to climate warming, then any trend toward warmer temperatures in the future could lead to a serious long-term increase in aridity over western North America.

Extreme drought contributed to the fracturing of the civilization of the Mesa Verde Anasazi.

Photo: Amerind Foundation

In an effort to draw together the skein of causes and effects, Dr. Kohler and members of the Village Ecodynamics Project are collaborating with archaeologists at Crow Canyon on a computer simulation of population changes in southwest Colorado from 600 to around 1300. Juxtaposing data on rainfall, temperature, soil productivity, human metabolic needs and diet, gleaned from an analysis of trash heaps and human waste, the model suggests a sobering conclusion: As Anasazi society became more complex, it also became more fragile. Corn was domesticated and then wild turkeys, an important protein source. With more to eat, the populations grew and aggregated into villages. Religious and political institutions sprung up. When crops began dying and violence increased, the inhabitants clustered even closer. By the time the drought of 1275 hit, the Anasazi had become far more dependent on agriculture than during earlier droughts. And they had become more dependent on each other.

The Anasazi abandoned Mesa Verde, never to return although heavy rains returned in the early 14th century.

Las Vegas is as vulnerable to water shortages as Mesa Verde was. Las Vegas gets 90% of its water from Lake Mead. Las Vegas is trying to find sources of the water in northern Nevada, but those sources are from arid areas also affected by drought.

Las Vegas was first settled for its springs, springs that made it an oasis in the desert. Although those springs have decades since run dry, water is still the most import resource to Las Vegas and the dry Southwest. And by all indications the region is only going to get dryer. Scientists predict devastating effects from global warming, conservationists are calling for a halt to growth in Southern Nevada as a way to preserve supplies and water managers are looking to ever more creative ways to reduce reliance on the overburdened Colorado River. A Colorado River reservoir at Lake Mead is the source of 90 percent of the valley's water supply. Water levels there have fallen steadily for nearly a decade.

Lake Mead 1985 vs 2010 viewed by satellite.



The strong drought in western north America that has been worsening since the year 2000 is the beginning of a mega-drought caused by anthropogenic climate change according to a new report published by National Center for Atmospheric Research (NCAR) scientist Aiguo Dai.

The detailed analysis concludes that warming temperatures associated with climate change will likely create increasingly dry conditions across much of the globe in the next 30 years, possibly reaching a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times.

Drought is deepening and spreading across the U.S.



The top 2 panels show normal conditions from 1950 to 1984. The middle 2 panels show drought developing in the west from 2000 to 2010 and deepening and spreading from 2030 to 2039. The lower panels predict devastating drought, catastrophic failure of water supplies and crops across the continental United States in the last half of the century if climate change goes unchecked.

Dai turned to results from the 22 computer models used by the IPCC in its 2007 report to gather projections about temperature, precipitation, humidity, wind speed, and Earth’s radiative balance, based on current projections of greenhouse gas emissions. He then fed the information into the Palmer model to calculate the PDSI index. A reading of +0.5 to - 0.5 on the index indicates normal conditions, while a reading at or below - 4 indicates extreme drought. The most index ranges from +10 to - 10 for current climate conditions, although readings below - 6 are exceedingly rare, even during short periods of time in small areas. By the 2030s, the results indicated that some regions in the United States and overseas could experience particularly severe conditions, with average decadal readings potentially dropping to - 4 to - 6 in much of the central and western United States as well as several regions overseas, and - 8 or lower in parts of the Mediterranean. By the end of the century, many populated areas, including parts of the United States, could face readings in the range of - 8 to - 10, and much of the Mediterranean could fall to - 15 to - 20. Such readings would be almost unprecedented.

Dai's forecasts of global drought have significant uncertainties a the detail level. However, in areas with a long history of recurrent drought such as the western United States uncertainties are less. When we understand the processes and conditions that caused previous droughts and can show by numerical modeling that we are recreating those conditions, we gain confidence in the model's predictions.

When data show the drought started in 2000, that's a strong indication that the model's results should be taken seriously.

In 20 years extreme drought as bad or worse than the dust bowl will spread across the United States, much of Europe and much of the southern hemisphere if greenhouse gas emissions aren't abated.



Humans didn't cause the drought conditions, but they caused the dust bowl. History shows the folly of denying that human actions can have wide scale effects. History never repeats itself exactly. Broad lessons must be learned from history to prevent the next catastrophe. Poor soil management in Texas and Oklahoma created a national crisis. Now, greenhouse gas emissions are causing a global crisis. Drought maps and Lake Mead show the crisis has already begun. We have very little time left to stop the return to dust bowl drought conditions.

Poor soil management caused the dust bowl catastrophe.

NOAA

Water, as we know, is a precious resource - in the arid western portions of Texas and Oklahoma battles about water rights are waged even today. When the expected rains do not materialize, the precariousness of water supplies becomes even more evident. In 1931, the cyclical drought of the High Plains wrecked havoc. The overuse of land by tractors and single crop farming methods, coupled with major erosion by wind and dryness, caused the fragile top layer of soil to drift away. What remained was a barren landscape of sand dunes and piles of dead animals.



Those who cannot remember the past are condemned to repeat it.

