In August 2021, the Intergovernmental Panel on Climate Change (IPCC) released its report of working group 1. It reiterated that human-caused greenhouse gas emissions are almost entirely responsible for global warming. As a result of climate-induced warming, the global water cycle has intensified. The water cycle is the continuous movement of water through evaporation, precipitation, condensation (rain, snow), infiltration (seeping into the ground and into aquifers), and subsurface flow. The intensification of the water cycle means, broadly, more extreme rainfall as well as worse droughts, while parts of the ocean – the major reservoir of water – will become fresher and others saltier. The extremes will become more extreme.
What does intensification of the global water cycle mean for societies, economies and nature? How are people and nature impacted by these changes, and how are they adapting? Are current adaptation measures effective in reducing climate-related risks, and would they remain effective at higher levels of global warming?
Half the world’s population already experience water insecurity due to several climatic and non-climatic factors. Intensification of the water cycle has worsened existing water insecurities for many people, particularly in developing countries. Almost half a billion people are experiencing unfamiliar wet conditions compared to the long-term rainfall average. About 700 million people live in places where maximum one-day precipitation has increased compared to the long-term average since the 1950s.
Every increment of global warming is likely to intensify water-related risks, with 3 to 4 billion people projected to experience physical water scarcity at 2°C and 4°C global warming levels respectively. Most at risk are regions with existing water insecurities like the Middle East, South Asia and Sub-Saharan Africa. We are seeing floods and droughts worsened by poor land management practices. From 1970 to 2019, only 7% of all disaster events were drought-related, yet they caused 34% of all disaster-related deaths. In the same period, 31% of all economic losses were flood-related. Overall, a large majority of the world’s population is experiencing climate change first and foremost through water impacts.
A large majority of the world’s population is experiencing climate change first and foremost through water impacts
Damages from droughts and floods are projected to increase with every degree of global warming. The global population exposed to exceptionally severe droughts is projected to rise from 3% to 8% over the 21st century under some scenarios, while direct flood damages are projected to increase by 4 to 5 times at 4°C temperature rise from pre-industrial times compared to 1.5°C.
Agriculture and energy production has been impacted by the ongoing intensification of the water cycle. Droughts have caused a loss of yields in approximately three-fourths of the global harvested area since the mid-1980s. Capacity utilisation of power plants has declined by 4-5% on an average during drought years compared to long term average values since the 1980s. These impacts are projected to intensify at higher levels of warming. Water-related hazards and disasters affect vulnerable populations – the poor, women, children, indigenous peoples, ethnic minorities and the elderly – disproportionately. This is especially so in developing countries due to high levels of existing vulnerabilities that stem from decades, if not centuries, of marginalisation, including from colonial times.
Water at heart of adaptation to climate change
Around 60% of the adaptation interventions to deal with climate change impacts are in response to water-related hazards such as floods, droughts, faster melting of glaciers, rainfall variability, groundwater depletion and so on. Other adaptation moves including irrigation, water storage, soil moisture conservation, rainwater harvesting, drought and flood-resistant crops are also all about water.
Current adaptation measures have many beneficial outcomes, but some serious risks too
In developing countries, most of these adaptation measures are autonomous and in the agricultural sector. In contrast, adaptation responses in developed countries are planned and in the urban sector. In both, water is at the heart of climate change adaptation in both developed and developing countries. Current adaptation options in the water sector have many beneficial outcomes – economic and livelihood benefits such as increased incomes or crop yields; ecological benefits like better soil moisture conservation; and positive socioeconomic and institutional outcomes such as increased capacities and voices of communities in decision making.
However, the effectiveness of current adaptation measures to the intensification of the water cycle in reducing climate risks are not always apparent. Some of them can also be maladaptive in the medium to long term.
The worse the warming, the less we can adapt
More important, the effectiveness of most of these adaptation options decreases beyond 1.5°C to 2°C warming. This again underscores the need for mitigation of greenhouse gas emissions to keep temperature rise within the 2°C ceiling (striving towards 1.5°C) pledged by all governments in the Paris Agreement. At higher levels of warming, adaptation in many systems and locations will simply not be possible. In high mountain regions like the Hindu Kush Himalayas and in Small Island Developing States limits to adaptation will be reached sooner than elsewhere.
Be careful while mitigating
Many mitigation measures such as carbon capture and storage, bio-energy, afforestation and reforestation can also have a significant water footprint. Mitigate we must, but water intensity of mitigation must be managed in socially and politically acceptable ways. Water professionals will need a seat at tables where mitigation decisions are made.
Climate change impacts on the water cycle have permeated through all sectors of the economy and society. The majority of the world’s population, particularly those dependent on climate-sensitive livelihood activities like agriculture, feel the impacts of climate change first and foremost through water-related changes.
As a result, adaptation solutions are also forged in response to water-related hazards. People are adapting to climate change impacts on water in myriad ways. Judicious and equitable water use is integral to the solution.
There is an urgent need to expand good adaptation solutions related to water. For this, we must fill the finance gap and put much more money into adaptation than we do now. There is also an urgent need to build capacity of people so that these solutions are replicated. Water is at the heart of climate change adaptation.
This write up is based on the executive summary of Chapter 4 in the IPCC AR6 WGII Report