Environmental impact of irrigation

An irrigation scheme draws water from groundwater, rivers, lakes, or overland flow, and distributes it over a certain area.

[3] Increases or decreases in irrigation are a key area of concern in precipitationshed studies, that examine how significant modifications to the delivery of evaporation to the atmosphere can alter downwind rainfall.

The reduced downstream river flow may cause: Increased groundwater recharge stems from the unavoidable deep percolation losses in the irrigation scheme.

The sediment from the delta has built up to form a giant aquifer during flood season and retains water in the wetlands.

The Sanmenxia reservoir is part of a larger man-made project of hydroelectric dams called the Three Gorge Project [12] In 1998, uncertain calculations and heavy sediment greatly affected the reservoir's ability to fulfill its flood-control function properly [13] This also reduces the downstream river water quality.

Pastoralists and nomadic tribes may find their land and water resources blocked by new irrigation developments without having legal recourse.

[17] The Manatali reservoir formed by the Manantali dam in Mali intersects the migration routes of nomadic pastoralists and destroyed 43000 ha of savannah, probably leading to overgrazing and erosion elsewhere.

The depletion of groundwater aquifers, which is caused by the suppression of the seasonal flood cycle, is damaging the forests downstream of the dam.

Some notable examples include: The effects of irrigation on the water table, soil salinity, and salinity of drainage and groundwater, and the effects of mitigative measures can be simulated and predicted using agro-hydro-salinity models like SaltMod and SahysMod[24] Irrigation can have a variety of negative impacts on ecology and socioeconomy, which may be mitigated in a number of ways.

It was stated that the impacts would mostly "be localized, minimal, a short term occurring during the construction and operation phases of the Project".

The original primary purposes of the irrigation project were to reduce poverty, improve food security, create local employment, increase household income and enhance the sustainability of land use.

[36] Due to this careful planning, this project was successful both in improving the socioeconomic conditions in the region and ensuring that land and water are sustainable into the future.

The first environmental effect is increased crop growth, such as in the Rubaksa gardens in Ethiopia
The irrigation that grows crops, especially in dry countries, can also be responsible for taxing aquifers beyond their capacities. Groundwater depletion is embedded in the international food trade, with countries exporting crops grown from overexploited aquifers and setting up potential future food crises if the aquifers run dry.
Countries with the highest share of water withdrawal by agriculture in total withdrawal.
Looking over the shoulder of a Peruvian farmer in the Huarmey delta at waterlogged and salinised irrigated land with a poor crop stand.
This illustrates an environmental impact of upstream irrigation developments causing an increased flow of groundwater to this lower-lying area, leading to adverse conditions.
Within a long period of groundwater depletion in California's Central Valley , short periods of recovery have been mostly driven by extreme weather events that typically caused flooding and had negative social, environmental and economic consequences. [ 8 ]
Water becomes scarce for nomadic pastoralist in Baluchistan due to new irrigation developments
Lake Manantali, 477 km 2 , displaced 12,000 people.
Flooding as a consequence of land subsidence