Warming climate may spread drying to a third of earth: Heat, not just rainfall, plays into new projections

Increasing heat is expected to extend dry conditions to far more farmland and cities by the end of the century than changes in rainfall alone, says a new study. Much of the concern about future drought under global warming has focused on rainfall projections, but higher evaporation rates may also play an important role as warmer temperatures wring more moisture from the soil, even in some places where rainfall is forecasted to increase, say the researchers.

The study is one of the first to use the latest climate simulations to model the effects of both changing rainfall and evaporation rates on future drought. Published this month in the journal Climate Dynamics, the study estimates that 12 percent of land will be subject to drought by 2100 through rainfall changes alone; but the drying will spread to 30 percent of land if higher evaporation rates from the added energy and humidity in the atmosphere is considered. An increase in evaporative drying means that even regions expected to get more rain, including important wheat, corn and rice belts in the western United States and southeastern China, will be at risk of drought. The study excludes Antarctica.

"We know from basic physics that warmer temperatures will help to dry things out," said the study's lead author, Benjamin Cook, a climate scientist with joint appointments at Columbia University's Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies. "Even if precipitation changes in the future are uncertain, there are good reasons to be concerned about water resources."

In its latest climate report, the International Panel on Climate Change (IPCC) warns that soil moisture is expected to decline globally and that already dry regions will be at greater risk of agricultural drought. The IPCC also predicts a strong chance of soil moisture drying in the Mediterranean, southwestern United States and southern African regions, consistent with the Climate Dynamics study.

Using two drought metric formulations, the study authors analyze projections of both rainfall and evaporative demand from the collection of climate model simulations completed for the IPCC's 2013 climate report. Both metrics agree that increased evaporative drying will probably tip marginally wet regions at mid-latitudes like the U.S. Great Plains and a swath of southeastern China into aridity. If precipitation were the only consideration, these great agricultural centers would not be considered at risk of drought. The researchers also say that dry zones in Central America, the Amazon and southern Africa will grow larger. In Europe, the summer aridity of Greece, Turkey, Italy and Spain is expected to extend farther north into continental Europe.

"For agriculture, the moisture balance in the soil is what really matters," said study coauthor Jason Smerdon, a climate scientist at Lamont-Doherty. "If rain increases slightly but temperatures also increase, drought is a potential consequence."

Today, while bad weather periodically lowers crop yields in some places, other regions are typically able to compensate to avert food shortages. In the warmer weather of the future, however, crops in multiple regions could wither simultaneously, the authors suggest. "Food-price shocks could become far more common," said study coauthor Richard Seager, a climate scientist at Lamont-Doherty. Large cities, especially in arid regions, will need to carefully manage their water supplies, he added.

The study builds on an emerging body of research looking at how evaporative demand influences hydroclimate. "It confirms something we've suspected for a long time," said Toby Ault, a climate scientist at Cornell University, who was not involved in the study. "Temperature alone can make drought more widespread. Studies like this give us a few new powerful tools to plan for and adapt to climate change."

Rainfall changes do not tell the whole story, agrees University of New South Wales researcher Steven Sherwood, in a recent Perspectives piece in the leading journal Science. "Many regions will get more rain, but it appears that few will get enough to keep pace with the growing evaporative demand."

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African dust changes India's rainfall: Dust can affect planet's climate, research shows

A new analysis of satellite data reveals a link between dust in North Africa and West Asia and stronger monsoons in India. The study shows that dust in the air absorbs sunlight west of India, warming the air and strengthening the winds carrying moisture eastward. This results in more monsoon rainfall about a week later in India. The results explain one way that dust can affect the climate, filling in previously unknown details about Earth's system.

The study also shows that natural airborne particles can influence rainfall in unexpected ways, with changes in one location rapidly affecting weather thousands of miles away. The researchers analyzed satellite data and performed computer modeling of the region to tease out the role of dust on the Indian monsoon, they report March 16 in Nature Geoscience.

India relies heavily on its summer monsoon rains. "The difference between a monsoon flood year or a dry year is about 10 percent of the average summer rainfall in central India. Variations driven by dust may be strong enough to explain some of that year-to-year variation," said climate scientist Phil Rasch of the Department of Energy's Pacific Northwest National Laboratory.

Rasch, V. Vinoj of the Indian Institute of Technology Bhubaneswar, India, and their coauthors wanted to explore a correlation that appeared in satellite records: higher amounts of small particles called aerosols over North Africa, West Asia, and the Arabian Sea seemed to be connected to stronger rainfall over India around the same time. The team wanted to see if they could verify this and determine how those particles might affect rainfall.

To explore the connection, the team used a computer model called CAM5 and focused on the area. The model included humanmade aerosols from pollution, and natural sea salt and dust aerosols. First, the team ran the model and noted a similar connection: more aerosols in the west meant more rainfall in the east. Then they systematically turned off the contribution of each aerosol type and looked to see if the connection remained.

Dust turned out to be the necessary ingredient. The condition that re-created stronger rainfall in India was the rise of dust in North Africa and the Arabian peninsula.

To see how quickly dust worked, they ran short computer simulations with and without dust emissions. Without dust emissions, the atmospheric dust disappeared within a week compared to the simulation with dust emissions and rainfall declined in central India as well. This indicated the effect happens over a short period of time.

But there was one more mystery, how did dust do this to rainfall? To explore possibilities, the team zoomed in on the regional conditions such as air temperature and water transport through the air.

Their likeliest possibility focused on the fact that dust can absorb sunlight that would normally reach the surface, warming the air instead. This warmer dust-laden air draws moist air from the tropics northward, and strengthens the prevailing winds that move moisture from the Arabian Sea into India, where it falls as rain.

Although dust plays a role in strengthening monsoons, this natural phenomenon does not overpower many other processes that also influence monsoons, said Rasch. Other extremely important factors include the effect of temperature differences between land and ocean, land use changes, global warming, and local effects of pollution aerosols around India that can heat and cool the air, and also affect clouds, he said.

"The strength of monsoons have been declining for the last 50 years," he said. "The dust effect is unlikely to explain the systematic decline, but it may contribute."

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Ohio Record Rainfall, Flooding Causing Algae Problems for Waterways (ContributorNetwork)

Going "green" isn't always a good thing. Due to record amounts of spring rainfall, a coating of green algae known as cyan bacteria has invaded at least 20 public beaches, lakes and ponds in Ohio. The toxic blue-green sticky film occurs when water becomes polluted with sewage, manure and fertilizer.

Indiana Prairie Reporter notes the Ohio Department of Natural Resources (ODNR) is offering financial assistance to farmers battling an overflow of manure-based fertilizer due to spring flooding. Cleaning up the manure seepage will likely prevent the contamination from encompassing more public and private waterways.

Memorial Day is the unofficial kick-off for outdoor summer fun and coveted eco-tourism business around the state. Ohio State Park beaches are popular day and weekend getaways even when the economy is good. The struggling economy has boosted state park visitation for the last several years. A decline in visitors would have a financial impact for campground, cabin and outdoor recreation rental businesses. The algae problem will impact the rural Hocking Hills area of southern Ohio to the northern shores of Lake Erie, the two largest outdoor tourist attractions in the Midwest.

Heavy April showers and flood waters washed phosphorus-infused sediment from agricultural areas into waterways last year as well. The rainfall run-off issue in 2011 has already surpassed the algae growth which occurred in all of 2010 in Ohio. Per studies by University of Toledo ecologists, harmful algal blooms are expected to make a return appearance in Lake Erie again this summer, according to the Columbus Dispatch. The warmth and sunshine which any Ohioans have been seeking will only exasperate algae growth. Fishing is not only an enjoyable way to spend an afternoon on Lake Erie but a means of putting food on the table for angler-related businesses. Decaying fish floating on the top of the lake will not only deter fishermen but disrupt the fragile economy in the Buckeye State.

Fortunately, no safety warnings affecting human health have yet been issued due to the growing algae problem. Water may be deemed safe for swimming if the concentrations of the green ilk are determined to be low enough not to be harmful if accidentally ingested while in the water.

Last year, tourists were met with warning signs when visiting state park beaches at Hake Hope, Burr Oak and Grand Lake state parks. Thousands of hikers at the Hocking Hills State Park were not deterred by the pending algae over the holiday weekend and cooled off in waterfall overflows at Ash Cave and Old Man's Cave with both their small children and four-legged family members. The thick canopy of trees and cooler temperatures along cave trails are protected from the direct sunlight algae needs to flourish.

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