Abstract
BackgroundThe association between irrigation and the proliferation of adult mosquitoes including malaria vectors is well known; however, irrigation schemes are treated as homogenous spatio-temporal units, with little consideration for how larval breeding varies across space and time. The objective of this study was to estimate the spatio-temporal distribution of pools of water facilitating breeding at the Bwanje Valley Irrigation Scheme (BVIS) in Malawi, Africa as a function of environmental and anthropogenic characteristics.MethodsIrrigation structure and land cover were quantified during the dry and rainy seasons of 2016 and 2017, respectively. These data were combined with soil type, irrigation scheduling, drainage, and maintenance to model suitability for mosquito breeding across the landscape under three scenarios: rainy season, dry season with limited water resources, and a dry season with abundant water resources.ResultsResults demonstrate seasonal, asymmetrical breeding potential and areas of maximum breeding potential as a function of environmental characteristics and anthropogenic influence in each scenario. The highest percentage of suitable area for breeding occurs during the rainy season; however, findings show that it is not merely the amount of water in an irrigated landscape, but the management of water resources that determines the aggregation of water bodies. In each scenario, timing and direction of irrigation along with inefficient drainage render the westernmost portion of BVIS the area of highest breeding opportunity, which expands and contracts seasonally in response to water resource availability and management decisions.ConclusionsChanges in the geography of breeding potential across irrigated spaces can have profound effects on the distribution of malaria risk for those living in close proximity to irrigated agricultural schemes. The methods presented are generalizable across geographies for estimating spatio-temporal distributions of breeding risk for mosquitoes in irrigated schemes, presenting an opportunity for greater geographically targeted strategies for management.
Highlights
The association between irrigation and the proliferation of adult mosquitoes including malaria vectors is well known; irrigation schemes are treated as homogenous spatio-temporal units, with little consideration for how larval breeding varies across space and time
Rainy season Pervasive mosquito breeding occurs within plots across Bwanje Valley Irrigation Scheme (BVIS) during the rainy season as a function of: (1) abundant water resources for rice cultivation both through precipitation and irrigation; (2) the soil’s susceptibility to ponding; and (3) regular irrigation following BVIS’ standard rainy season schedule
Between irrigation application periods, drying out of plots situated furthest from the branching and main canals were observed in WSA3, which was a noted source of frustration among farmers whose plots were located in this area
Summary
The association between irrigation and the proliferation of adult mosquitoes including malaria vectors is well known; irrigation schemes are treated as homogenous spatio-temporal units, with little consideration for how larval breeding varies across space and time. Irrigation is a prominent tool for ensuring food security through enhancing agricultural productivity [1, 2] and is often discussed in relationship to the health and economic benefits for smallholder farmers, or more generally, developing countries. Increased erosion, salinization, deterioration of water quality, proliferation of aquatic weeds, and eutrophication are associated with the expansion of irrigated agriculture [9, 10]. The capacity for irrigation development across subSaharan Africa (SSA) is considerable, with only 14% of irrigation potential developed across the region [11]. Despite a period of reticence to further expand irrigation by governments and donors, recent years have brought a renewed interest in irrigation potential, in light of food insecurity concerns [11]
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