The internal renewable water resources of rivers and aquifers amount to 44,000 km3/year, and the volume of water intake (in all sectors) exceeds 4,000 km3/year, which is almost 10%. The local effects of physical water scarcity and freshwater pollution are spreading at an increasing rate. In many cases, the first sign of water scarcity due to an increase in water intake is a decrease in the groundwater level.
As a universal indicator of physical water scarcity, a summary indicator is used that characterizes the level of water stress. At the global level, the indicator averaged 18% in 2018, but this average indicator hides significant regional differences. In Europe, the level of water stress is low - 8.3%.
For comparison, in East and West Asia it ranges from 45 to 70 percent, in Central and South Asia it is more than 70 percent, and in North Africa it exceeds 100 percent. The use of non-traditional sources in agriculture, such as reuse and desalination of water, is still small, but growing, especially in areas with water scarcity, such as the Middle East–West Asia.
The level of water stress is high in all basins where intensive irrigated agriculture is practiced and there are densely populated cities that compete for water, especially where the available freshwater resources are scarce due to climatic conditions. In order to get a complete picture of the situation with water scarcity, it is recommended that countries make a breakdown of data by sub-basins. Basins where the level of water stress is high or critical are located in regions with high water stress, such as North Africa, North America, Central and South Asia, as well as on the west coast of Latin America. In countries with a high level of water stress, agricultural activities significantly exacerbate this problem. In Central Asia, the Middle East, West Asia and North Africa, water intake for agriculture accounts for a significant part of the total volume of water taken.
The water stress caused by water abstraction for agriculture illustrates the critical importance of the Nile and other river basins in the Arabian Peninsula and South Asia. The consequences become visible in detail when distributed to areas equipped for irrigation.
The volume of available freshwater resources per capita and the volume of fresh water taken per capita
The dynamics of the distribution of freshwater resources per capita generally corresponds to population growth. Between 2000 and 2018, the volume of water resources per capita decreased by about 20 percent. In particular, in sub-Saharan Africa 41%, Central Asia 30%, West Asia 29% and North Africa 26%. The region where this indicator decreased the least was Europe - 3%. As for demand, the regions with the largest volumes of water intake per capita were Central Asia and North America. Total water abstraction per capita for the period from 2000 to 2018 decreased everywhere except Central America and the Caribbean, South America and Southeast Asia. It is expected that with population growth, these trends will continue – partly due to an increase in water productivity, including in agriculture, and partly due to the prevalence of water scarcity caused by prolonged dry periods in areas with high population density.
Depletion of groundwater
The consolidated country-level reporting for 2018 shows that the volume of groundwater abstracted worldwide for the needs of irrigated agriculture is estimated at 820 km3 per year. This is 19% more than in 2010, when this figure was estimated at 688 km3. Groundwater abstraction for the needs of irrigated agriculture accounts for more than 30 percent of the volume of fresh water abstraction in agriculture and continues to grow by about 2.2 percent per year. The increase in consumption on irrigated lands, which can be attributed to groundwater, is estimated at 43 percent, which is explained by a much lower level of water losses from the conduit during irrigation with groundwater.
The possibility of using groundwater is already limited. They are intensively exploited in most of the most important continental aquifers and along highly productive coastal plains, where salinization is a constant threat.
The presence of water stress in irrigated areas significantly correlates with intensive use of groundwater and depletion of aquifers. It is believed that such a level of exploitation of groundwater causes the loss of their reserves in the amount of 250 km3 per year and, more importantly, the loss of the function and usefulness of the aquifer for farmers if the groundwater level falls. If the recharge of aquifers is insignificant or absent, the consequences for local production and livelihoods can be very serious. Modeling the impact of these processes on the production of irrigated crops shows that groundwater depletion will continue to pose major problems in East Asia, the Middle East and West Asia, North America and South Asia.
Pollution of water resources related to agricultural activities
Water pollution is a growing global crisis, the consequences of which directly affect health, economic development and food security. And although the main culprits here are other anthropogenic factors, in particular the development of settlements (urbanization) and industry, in many countries agriculture has become the main source of pollution. The deterioration of water quality poses a serious threat to food safety and food security.
It is estimated that currently about 2,520 km3 of wastewater is discharged into the environment annually, of which 330 km3/year is urban wastewater, 660 km3/year is industrial (including cooling water) and 1,260 km3/year is agricultural. The anthropogenic impact on the soils of arable lands and pastures has reached such a scale that they no longer cope with their task of retaining and decomposing pollutants carried with water, as a result of which the nitrogen content, salinity and biological oxygen demand in fresh water are often increased.
The volume of agricultural use of artificial fertilizers containing reactive forms of nitrogen has been growing since 2000, when they amounted to about 81 million tons; the peak was reached in 2017 (110 million tons), and in 2018 there was a slight decrease. Industrial fertilizer production and biological nitrogen fixation in agriculture account for 80 percent of anthropogenic nitrogen fixation. The global growth rate of phosphorus use in agriculture is low: in 2000, the volume of use was 32 million tons, in 2016 they reached a peak of 45 million tons, after which a noticeable decline began. It is estimated that the total amount of phosphorus entering water bodies as a result of anthropogenic use is about 1.47 million tons per year, with 62 percent coming from point sources (domestic and industrial), and 38 percent from diffuse sources (agriculture). Agricultural use of potash peaked in 2018, amounting to almost 39 million tons (in 2000 – 22 million tons).
Of particular concern are new chemical pollutants, such as pesticides, pharmaceuticals for animal husbandry and plastic particles, as well as the possible development of antimicrobial resistance, for which regulation and monitoring are currently virtually non-existent.
Reduction of available water resources per capita
More than 733 million people, i.e. almost 10 percent of the world's population, live in countries where the level of water stress is high or critical. Between 2018 and 2020, the number of those living in areas with critical water scarcity increased from 6 percent to 7 percent, but where water scarcity is high, this figure decreased from 4 percent to 2 percent. About 1.2 billion people live in areas where agriculture is experiencing great problems due to serious water shortages and shortages due to frequent droughts on non-irrigated arable lands and pasture areas or with a high level of water stress on irrigated lands.
As the population increases, the amount of available natural resources per capita decreases. In sub-Saharan Africa, water availability per capita has decreased by 40 percent over the past decade, and the area of agricultural land has decreased from 0.80 to 0.64 hectares per capita between 2000 and 2017. In North, South and West Africa, there is less than 1,700 m3 of water per capita – this is the level at which the country's ability to meet water needs for food production and other sectors is at risk. At the same time, more than 286 river basins and about 600 aquifers cross the borders of countries. However, more than 60 percent of transboundary river basins and even more aquifers are still being exploited without any mechanisms of joint adaptive transboundary use that would solve the problem of resource allocation and control water pollution.