Severe drought no longer caused just by nature
Recent research has focused on natural areas, such as the effects of climate change on drought under natural conditions. However, the validity of these studies is questionable if our world is strongly altered and managed by people.
“The traditional approach to drought research — focusing on natural phenomena - leads to poor prediction and management of this complex interdisciplinary phenomenon. The complexity of the issue and lack of data and information make it hard, but that is no reason to pretend that the water system is completely natural and we can ignore water use by people in quantifying drought.”
Dr. Van Loon added that in California, one of the big questions is how much rain is needed to end the drought. It was particularly important to take into account human activity, such as groundwater abstraction and water transfers, when calculating how much rain is needed.
“We can see the water system as a bucket of water half-empty due to drought, which needs to be filled up to its original level,” she said. “We can calculate how much rain is needed to fill up the bucket, but at the same time we are constantly taking water out of the bucket and putting water in.”
The water science researchers say that defining the causes of drought is crucial in deciding whether management should focus on making changes to cope with climate-induced drought (adaptation) or tackling the actions that lead to human-induced drought (mitigation).
Innovative scientific methodology is needed to pull apart different causes of drought. Research should also analyze the impacts of drought on society, how society responds to water shortages and the effect of these responses on drought.
Direct effects of people on drought are water abstraction, reservoir building and water transfer.
Indirect effects are changes to the land surface made by people that can affect the development of drought by altering hydrological processes. These can include evaporation from land to air (evapotranspiration) and the rate at which water penetrates the soil (infiltration), as well as surface runoff and storage of water.
These direct and indirect influences can be long-term (big engineering projects for reservoirs or gradual urbanization) and short-term (more efficient irrigation methods, different crops). Short term adaptation to drought can decrease the severity of the next drought or even cause within drought changes influencing the drought end.
A better understanding of how public perception of drought and strategies to tackle climate-induced factors is also needed. Large drought impact databases currently being compiled for the United States and Europe, together with improved data analysis methods should help in this area.
“Whilst human activity can contribute to worsening drought, society can also play its part in tackling water shortages. However, we can only begin to take positive global action against drought when evaluating the relationship between nature and people and its impact,” said Dr. Van Loon.
Pertinent facts:
- Recent drought in China, which has reduced farmers’ profits, is linked to policy changes on water rights and access, as well as water pollution. Industries such as agriculture, forestry, and leisure depend on regional ecosystems - how land is managed can affect how drought hits. Increasing fertilizer use and growing more crops in Northern China, for example, is leading to drier soils during the growing season.
- The current drought affecting south east Brazil, including the cities of São Paulo and Rio de Janeiro has been described as the worst drought in eighty years. It has been made worse by human activity such as deforestation, the growth of towns and reservoir construction.
— Read more in Anne F. Van Loon et al., “Drought in the Anthropocene,” Nature Geoscience 9 (2 February 2016): 89-91 (DOI: 10.1038/ngeo2646)
