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A study conducted in northwest India has claimed that the new irrigation systems in arid regions may benefit farmers but can also increase the local malaria risk for more than a decade despite intensive and costly use of insecticides.
According to the researchers, the new University of Michigan-led study's findings demonstrate the need to include a strong, binding commitment to finance and implement long-term public health and safety programs when building large-scale irrigation projects.
Lead author and U-M graduate student Andres Baeza, who works in the laboratory of Mercedes Pascual in the Department of Ecology and Evolutionary Biology said that in these dry, fragile ecosystems, where increase in water availability from rainfall is the limiting factor for malaria transmission, irrigation infrastructure can drastically alter mosquito population abundance to levels above the threshold needed to maintain malaria transmission.
He said that the results have highlight the need for considering health impacts in the long-term planning, assessment and mitigation of projects related to water resources.
The researchers studied changes in land use and malaria risk around a large irrigation project under construction in a semi-arid area in the northeast part of the Indian state of Gujarat. Water from the project is eventually expected to cover more than 47 million acres and will benefit about a million farmers.
Malaria risk in arid regions often rises when irrigation is introduced, due to increased amounts of standing water that serve as mosquito breeding sites.
The new study demonstrates that this transition phase from high risk to low disease prevalence can last more than a decade. The study is the first to combine satellite imagery of vegetation cover with public health records of malaria cases over a large region to track changes that occur as a mega-irrigation project progresses.
Pascual said that by following the changes in malaria incidence, vegetation and socioeconomic data at the level of sub-districts, they identified a transition phase toward sustainable low malaria risk lasting for more than a decade and characterized by an enhanced environmental malaria risk despite intensive mosquito control efforts.
Pascual said that the findings show that environmental methods for sustainable disease control are urgently needed. Several of these methods-including intermittent irrigation and periodic flushing of canals-have proved to be affordable, effective and feasible to implement at local levels.
In the study, the researchers examined epidemiological data on microscopically confirmed malaria cases from rural areas, some dating back to 1997. Using satellite imagery, the researchers were able to discriminate irrigated crops from non-irrigated crops by their spectral signature.
They were then able to determine how levels of malaria changed as the massive irrigation project progressed. They showed that elevated disease risk-despite heavy use of insecticides-is concentrated in the areas adjacent to the main irrigation canal that have experienced the most pronounced change in irrigation levels in the last decade.
They tied the remote sensing and epidemiological findings to various socioeconomic factors. In general, the high-risk areas had a lower proportion of literate people and more limited access to sources of clean drinking water.
The findings are set to be published online in the Proceedings of the National Academy of Sciences.