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(AlertNet) - Disputes over water are common around the world, exacerbated by climate change, growing populations, rapid urbanisation, increased irrigation and a rising demand for alternative energy sources such as hydroelectricity.
Following are a few of the regions where competition for water from major rivers systems is fuelling tension.
India is home to three major river systems -- the Ganges, Brahmaputra and the Indus -- which support 700 million people. As an upstream nation, it controls water flows to Bangladesh to the east and Pakistan to the west. The Indus supplies some 80 percent of Pakistan's irrigated land.
India and Pakistan are both building hydropower dams in disputed Kashmir along Kishanganga river. Pakistan fears India's dams will disrupt water flows.
India, for its part, is concerned that China is building dams along the Tsangpo river, which runs into India as the Brahmaputra.
Central Asia is one of the world's driest places, where, thanks to 70 years of Soviet planning, growing thirsty crops such as cotton and grain remain the main source of income for most people.
Disputes over water use from the Syr Daria and Amu Daria rivers have increased since independence in 1991. Problems are compounded by rising nationalism and lack of progress on a regional approach to replace Soviet-era systems of water management.
Kazakhstan, Turkmenistan and Uzbekistan need more water for growing populations and farming, while economically weaker Kyrgyzstan and Tajikistan want more control for hydropower and irrigation.
Afghanistan, linked to Central Asia by the Amu Daria, is claiming its own share of the water.
The countries of the Nile basin are Egypt, Sudan, South Sudan, Ethiopia, Eritrea, Uganda, Kenya, Democratic Republic of Congo, Burundi, Rwanda and Tanzania.
Egypt and Sudan control more than 90 percent of the Nile's waters due to colonial-era and other treaties but others in the basin want a bigger share.
Demand for irrigation has risen, with millions of hectares leased for large-scale farming. Dams have complicated access to water.
Water needs are expected to rise as the Nile basin population is projected to reach 654 million by 2030, up from 372 million in 2005, according to UN estimates.
TIGRIS-EUPHRATES RIVER SYSTEM
The Tigris-Euphrates basin is mainly shared by Turkey, Syria and Iraq, with many Tigris tributaries originating in Iran.
Iraq, struggling with water shortages due to aridity and years of drought, says hydroelectric dams and irrigation in Turkey, Iran and Syria have reduced the water flow in both rivers.
Increasing desertification, especially in Iraq, is compounding problems. A large amount of Euphrates' waters evaporate due to extreme heat. Contamination from pesticides, discharge of untreated sewage and excess salinity due to low water levels are all common.
Iraq, Syria and Iran want more equitable access and control from Turkey, where almost 98 percent of Euphrates waters originate. Despite some cooperation on common management, a final agreement has yet to be reached.
JORDAN RIVER BASIN
The river basin is highly stressed due to aridity in Jordan, Israel and Palestinian Territories.
All three discharge untreated or poorly treated sewage. The Mountain Aquifer - a key fresh water source for West Bank Palestinians and major Israeli cities - is threatened by decades of over-exploitation and groundwater pollution.
Despite efforts to cooperate, agreements to share water resources are complicated by the long-stalled Middle East peace process. Israel dominates the Palestinian water economy.
MEKONG RIVER BASIN
Most Mekong countries, especially China, have been planning and building hydropower dams since the late 1980s.
Thailand, Laos, Cambodia and Vietnam argue that China diverts or stores more than its fair share of water due to dam-building on the Upper Mekong.
There is growing concern about serious environmental damage to agriculture, fisheries and food security for some 60 million people due to plans by Laos and Cambodia to build more than 10 dams along the Lower Mekong.
Despite cooperation efforts by Cambodia, Thailand, Laos and Vietnam through the Mekong River Commission, national interests are getting in the way of joint river management.
Sources: Reuters, AlertNet, Institute of Peace and Conflict Studies, Brookings Institute, International Crisis Group, Nile Basin Research Programme, GRAIN, UNDP
(This factbox is part of a special multimedia report on water produced by AlertNet, a global humanitarian news service run by Thomson Reuters Foundation. Visit http://water.trust.org)
(Reporting by Astrid Zweynert; Editing by Sonya Hepinstall)
Our Standards: The Thomson Reuters Trust Principles.