with the help of example higlight the ill effect of irrigation
Answers
An irrigation scheme draws water from groundwater, rivers, lakes or overland flow, and distributes it over an area. Hydrological, or direct, effects of doing this[1] include reduction in downstream river flow, increased evaporation in the irrigated area, increased level in the water table as groundwater recharge in the area is increased and flow increased in the irrigated area. Likewise, irrigation has immediate effects on the provision of moisture to the atmosphere, inducing atmospheric instabilities and increasing downwind rainfall,[2] or in other cases modifies the atmospheric circulation, delivering rain to different downwind areas.[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.
Explanation:
ndirect effects are those that have consequences that take longer to develop and may also be longer-lasting. The indirect effects of irrigation include the following:
Waterlogging
Soil salination
Ecological damage
Socioeconomic impacts
The indirect effects of waterlogging and soil salination occur directly on the land being irrigated. The ecological and socioeconomic consequences take longer to happen but can be more far-reaching.
Some irrigation schemes use water wells for irrigation. As a result, the overall water level decreases. This may cause water mining, land/soil subsidence, and, along the coast, saltwater intrusion.
Irrigated land area worldwide occupies about 16% of the total agricultural area and the crop yield of irrigated land is roughly 40% of the total yield. In other words, irrigated land produces 2.5 times more product than non-irrigated land. This article will discuss some of the environmental and socioeconomic impacts of irrigation
Adverse impacts
Reduced river flow
The reduced downstream river flow may cause:
reduced downstream flooding
disappearance of ecologically and economically important wetlands or flood forests[6]
reduced availability of industrial, municipal, household, and drinking water
reduced shipping routes. Water withdrawal poses a serious threat to the Ganges. In India, barrages control all of the tributaries to the Ganges and divert roughly 60 percent of river flow to irrigation[6]
reduced fishing opportunities. The Indus River in Pakistan faces scarcity due to over-extraction of water for agriculture. The Indus is inhabited by 25 amphibian species and 147 fish species of which 22 are found nowhere else in the world. It harbors the endangered Indus River dolphin, one of the world’s rarest mammals. Fish populations, the main source of protein and overall life support systems for many communities, are also being threatened[6]
reduced discharge into the sea, which may have various consequences like coastal erosion (e.g. in Ghana[7]) and salt water intrusion in delta's and estuaries (e.g. in Egypt, see Aswan dam). Current water withdrawal from the river Nile for irrigation is so high that, despite its size, in dry periods the river does not reach the sea.[6] The Aral Sea has suffered an "environmental catastrophe" due to the interception of river water for irrigation purposes.
Increased groundwater recharge, waterlogging, soil salinity
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.
Increased groundwater recharge stems from the unavoidable deep percolation losses occurring in the irrigation scheme. The lower the irrigation efficiency, the higher the losses. Although fairly high irrigation efficiencies of 70% or more (i.e. losses of 30% or less) can occur with sophisticated techniques like sprinkler irrigation and drip irrigation, or by well managed surface irrigation, in practice the losses are commonly in the order of 40% to 60%. This may cause the following issues: