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How does climate change affect water and agriculture?

According to the latest assessment report on impacts, vulnerability and adaptation by the UN Intergovernmental Panel on Climate Change (IPCC),

 

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans.

IPCC, AR5 WGII, Technical Summary, October 2014

 

Scientists say that ecosystems and many human systems are vulnerable and exposed to climate-related extremes, such as heat waves, droughts, floods, cyclones, and wildfires.

 

Impacts of such climate-related extremes include alteration of ecosystems, disruption of food production and water supply, damage to infrastructure and settlements, morbidity and mortality, and consequences for mental health and human well-being.

IPCC, AR5 WGII, Technical Summary, October 2014

In the map below, the IPCC summarizes the observed impacts of climate change on human and natural systems at local and regional scale. Drop and tractor icons represent impacts for hydrogeological and food production systems respectively.

WGII_AR5_FigTS-2_p1
Figure TS 2, Technical Summary, IPCC Working Group II, IPCC Fifth Assessment Report, 2014.

CLIMATE CHANGE AND WATER

 

At global level climate change impacts on the overall water cycle (evaporation and precipitation) and affects availability and demand of water resources. Changing precipitation or melting snow and ice alter hydrological systems, affecting quantity and quality. Glaciers shrinking affects runoff and water resources downstream.

National and local impacts largely depend on local water availability, demand and management. The unequal distribution of freshwater resources and their local exploitation involve that the pressure on those resources deeply varies region by region, as well as local climate impacts.

Aqueduct Global Maps-Baseline-water-stress-World Resources Institute
Aqueduct Global Maps, World Resources Institute. More on WRI website: www.wri.org/our-work/project/aqueduct

The IPCC said impacts of drought have increased mostly due to increased water demand, while there is no evidence that surface water and groundwater drought freqency hase changed over the last few decades.

Future local impacts are more difficult to assess than global trends. The IPCC estimated that for each degree of global warming, approximately 7% of the global population is projected to be exposed to a decrease of renewable water resources of at least 20%. Climate change is also projected to reduce renewable surface water and groundwater significantly in most subtropical regions, intensifying competition for water among all systems and sectors involved (ecosystems, settlements, agriculture, industry and energy production), while water sources are projected to increase at high latitude.

Problems with water are basically linked to “too much or too little”. The IPCC concluded that climate change is projected to impact on the frequency and magnitude of both floods and droughts.

[…] flood hazards will increase over more than half of the globe, in particular in central and eastern Siberia, parts of Southeast Asia including India, tropical Africa, and northern South America, but decreases are projected in parts of northern and Eastern Europe, Anatolia, central and East Asia, central North America, and southern South America.

[…] By the end of the 21st century meteorological droughts (less rainfall) and agricultural droughts (drier soil) are projected to become longer, or more frequent, or both, in some regions and some seasons, because of reduced rainfall or increased evaporation or both. […] Droughts are projected to intensify in southern Europe and the Mediterranean region, central Europe, central and southern North America, Central America, northeast Brazil, and southern Africa. In dry regions, more intense droughts will stress water supply systems. In wetter regions, more intense seasonal droughts can be managed by current water supply systems and by adaptation; for example, demand can be reduced by using water more efficiently, or supply can be increased by increasing the storage capacity in reservoirs.

IPCC, AR5 WGII, Chapter 3, October 2014

 

CLIMATE CHANGE AND AGRICULTURE

 

Agriculture and climate change are inextricably linked: crop yield, biodiversity, water use, as well as soil health are directly affected by the changing climate.

Impacts on agriculture are caused by climate factors, such as the warming and drying trend, extreme temperature and precipitation, carbon dioxide fertilization and ocean acidification, but non-climate factors also play a key role in how agricultural systems are hit: soil fertility, irrigation methods, fertilizers, demography, local economical and societal structures.

Indirect climate impacts include increased competition from weeds, expansion of pathogens and insect pest ranges and seasons, and other alterations in crop agroecosystems.

The IPCC highlighted that  the net effect of climate change on world agriculture is likely to be negative,  even if some regions and crops could benefit from it.

Based on many studies covering a wide range of regions and crops, negative impacts of climate change on crop yields have been more common than positive impacts (high confidence). The smaller number of studies showing positive impacts relate mainly to high-latitude regions, though it is not yet clear whether the balance of impacts has been negative or positive in these regions. Climate change has negatively affected wheat and maize yields for many regions and in the global aggregate (medium confidence). Effects on rice and soybean yield have been smaller in major production regions and globally, with a median change of zero across all available data, which are fewer for soy compared to the other crops.

IPCC, AR5 WGII, Chapter 7, October 2014

The key risks for the future are reductions in mean crop yields because of climate change and increases in yields variability (that also affect global food prices), scientists say.

With or without adaptation, negative impacts on average yields become likely from the 2030 with median yield impacts of 0 to -2% per decade projected for the rest of the century, and after 2050 the risk of more severe impacts increases.

IPCC, AR5 WGII, Chapter 7, October 2014

Local impacts of climate change on crops and food production systems depend largely on the adaptation measures undertaken, and this will be increasingly so in the future. In the next updates on this blog we will go deeper into the complex issues related to water use, food production and climate change.

 

(Image: Fishing with a lift net, Bangladesh. Photo credit: Wikipedia)

 

About Water and Food Production series: We depend on water for everything we do. The houses we live in, the clothes we wear and, significantly, the food we eat. Sustainable use of water will become ever more important as the population continues to rise and climate change makes secure access to water less predictable. As such, understanding the complex connections between water and food production is crucial to addressing one of the greatest challenges we face as humans and to exploring practical and innovative solutions. In 2015, Best Climate Practices provides a platform for discussing problems and solutions on water management, food security, farming, agricultural emissions and much more.