The Impact of Rainfall on Drinking Water Quality in Antananarivo, Madagascar
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bioRxiv preprint doi: https://doi.org/10.1101/666826; this version posted June 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 1 The impact of rainfall on drinking water quality in Antananarivo, Madagascar 2 3 Alexandra BASTARAUD 1, Emeline PERTHAME 2, Jean-Marius 4 RAKOTONDRAMANGA 3, Jackson MAHAZOSAOTRA 1, Noro RAVAONINDRINA 1, and 5 Ronan JAMBOU 4,* 6 7 1 Food Hygiene and Environment Laboratory, Institut Pasteur of Madagascar, 8 Antananarivo, Madagascar; [email protected] 9 2 The Center of Bioinformatics, Biostatistics and Integrative Biology (C3BI), Institut 10 Pasteur Paris, France; [email protected] 11 3 Epidemiology Department Institut Pasteur of Madagascar, Antananarivo, 12 Madagascar; [email protected] 13 4 Parasites and vectors insects Department, Institut Pasteur Paris, France; 14 [email protected] 15 16 Corresponding author: 17 Ronan Jambou, Parasites and vectors insects Department, Institut Pasteur Paris, France 18 [email protected]; Tel.: +225-77-92-32-04 19 bioRxiv preprint doi: https://doi.org/10.1101/666826; this version posted June 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 2 of 34 20 Abstract 21 Low-income cities that are subject to high population pressure and vulnerable to 22 climate events often have a low capacity to continuously deliver safe drinking water. Here 23 we report the findings of a 32-year investigation of the temporal dynamics of indicators of 24 drinking water quality in the city of Antananarivo, where we assess the long-term evolution 25 of supplied water quality and characterize the interactions between climate conditions and 26 the full-scale supply system. A total of 25,467 water samples were collected every week 27 at different points in the supplied drinking water system. Samples were analyzed for total 28 coliforms (TC), Escherichia coli (EC), intestinal Enterococci (IE), and spores of Clostridia 29 (SSRC). Nine-hundred-eighty-one samples that were identified as positive for one or more 30 indicators were unevenly distributed across the series. The breakpoint method identified 31 four periods when the time series displayed changes in the level and profile of 32 contamination (i) and the monthly pattern of contamination (ii), with more direct effects of 33 rainfall on the quality of supplied drinking water. The modeling showed significantly 34 different lags among indicators of bacteria occurrence after cumulative rainfall, which 35 range from 4 to 8 weeks. Among the effects of low-income urbanization, a rapid 36 demographic transition and urban watershed degradation are progressively affecting the 37 quality of supplied water and resulting in the more direct effects of rainfall events. bioRxiv preprint doi: https://doi.org/10.1101/666826; this version posted June 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 3 of 34 38 Introduction 39 A poor capacity to provide safe drinking water, regardless of weather conditions, is of 40 growing concern in low-income areas vulnerable to climate change [1,2]. Indeed, under 41 global forecasts, some parts of the globe will experience increased frequency and intensity 42 of rainfall [3] with increasing difficulties to limit storm impacts, such as flooding or increased 43 run-off [4,5]. These events are associated with elevated turbidity [6–8] and dissolved 44 organic matter in water sources [9], which can overwhelm treatment plans [10]. Indeed, 45 extreme rainfall regimes are likely to be associated with drinking water contaminations 46 [6,10], and this is predicted to be worsened by climate change [11]. Contaminated water is 47 the main factor of diarrhea in children, and it is evident that an integrated approach to 48 improving water supply will have an impact on the health of the population [12]. 49 However, the relationship between rainfall patterns and water microbial quality is 50 complex, involving an interplay between the type of water supply, the type of water source, 51 and the treatment technology applied to water [13]. Also, susceptibility to climate change 52 is reinforced by rapid and unplanned urbanization, poor sanitation, erosion, and low level 53 of maintenance of the supply network [14]. Thus, the nature and the depth of the link 54 between rainfall and water quality is not expected to be stationary. Rather, these should 55 vary with the infrastructure and environmental changes, the time scale of study (yearly, 56 season or day to day), and the rainfall patterns. Rainfall is a seasonal phenomenon with 57 significant inter-annual variability [15] related to climate variations [16], extreme climatic 58 events [6], intra-annual variability or distribution of water [17], change in duration of spells 59 of continuous rain or no-rain events, and the total amount of water delivered during each 60 wet spell [15]. Combined or selective impacts of these factors also depend on the 61 catchment’s characteristics. bioRxiv preprint doi: https://doi.org/10.1101/666826; this version posted June 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 4 of 34 62 Due to its diverse landscape, Madagascar is exposed to a variety of weather and 63 climate phenomena, already submitted to significant variability [18]. Antananarivo, the 64 capital of Madagascar (Commune Urbaine d’Antananarivo - CUA), is witnessing rapid 65 urbanization due to the arrival of 100,000 additional inhabitants per year. This evolution 66 increases the technical constraints on infrastructure, and local services are already 67 deficient [19]. Water supply on Madagascar only dates back since the colonial period 68 (1952) and is outpaced by urban expansion and population growth. Consequently, home 69 connections are still limited, and a network of about 900 standpipes supply un-piped 70 households. In this context, storm events, heavy rainfall, and runoff can increased water 71 turbidity and microbiological contamination [20]. Un- or insufficiently filtered, inadequately, 72 and even adequately disinfected drinking water is thus susceptible to microbiological 73 contamination [21]. Water utilities are required to monitor microbial indicators to assess the 74 effectiveness of the treatment process (i.e., spores of Clostridia), the safety of end drinking 75 water (i.e., Escherichia coli, intestinal enterococci), and the biological stability of 76 microorganism communities in piped water (i.e., total coliforms) [21]. All changes impacting 77 the water source, or the treatment process can affect these indicators and the drinking 78 water quality. Characterizing the interplay between rainfall pattern and drinking water 79 characteristics will highlight needs in monitoring and priorities in improving water 80 production. 81 Due to its geographic setting, its demographic burden, and its environmental transition, 82 Antananarivo is a suitable example for setting up new strategies to survey water treatment 83 based on predictive mathematic models. Predictive models could also be used to adapt 84 the activities of dispensaries based on the burden of diarrhea. First, we analyzed how the 85 water quality had evolved over the last 30 years, and then how the rainfall pattern has 86 impacted long-term water quality in the supply system under environmental and technical 87 shifts. We also focused on the current week-to-week relationship between rainfall patterns bioRxiv preprint doi: https://doi.org/10.1101/666826; this version posted June 10, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. 5 of 34 88 characteristics and water quality to determine the main factors regulating water 89 contamination. 90 Materials and Methods 91 CUA and its drinking-water supply system 92 Site of study 93 Antananarivo is located in the central highlands of Madagascar at 1,300 m altitude 94 (18°55’ S latitude and 47°32' Longitude). The city is nestled among twelve hills and lies in 95 the natural floodplain of the Ikopa River, which skirts the city to the south and west (Fig. 96 1). The river and its tributaries play an important role in rice-dominated agricultural 97 production. The metropolitan area spreads over 220 km2, with an estimated population of 98 3,058 million inhabitants in 2018 [22]. This area currently experiences significant 99 challenges due to flooding during the rainy season. 100 101 Fig 1. Location of Mandroseza Lake inside the limits of Antananarivo. 102 103 Climate 104 Antananarivo experiments a subtropical highland climate, warm and temperate 105 classified as Cwb by the Köppen-Geiger system [23]. Summers are rainy, with most of the 106 precipitations falling in December, January, and February. The winters are dry, especially 107 in June, July, and August. The dry season occurs from May to September (i.e., from week 108 no.14 to no.40), and the wet season from November to April (i.e., from week no.41 to 109 no.13). From 1985 to 2017, the annual average of rainfall was above 1500 mm with 110 extremes in January (above 300 mm) and June (less than 10 mm).