The effects on public health of climate change adaptation responses: a systematic review of evidence from low- and middle-income countries

We included 99 studies that were conducted in 66 different LMICs and reported 1117 unique measurements or mentions of the effect on human health or intermediate health outcomes of adaptation responses (figure 1). Thirty-eight studies reported quantitative health outcomes and were available for both quantitative analysis and narrative synthesis. Sixty-one studies provided only qualitative data and are reported here through narrative synthesis.

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We identified seven climate hazard categories and nine climate change response categories (table 1). Adaptation response categories were further grouped into three aggregate categories (improving community resilience, policy, governance and finance, and disaster risk reduction). The studies reported on five health outcomes and three intermediate health outcomes with the remainder of studies grouped into an 'other health outcomes' category.

The most common reported climate hazards were drought (59 studies), extreme precipitation (46 studies), increased heat (32 studies), and precipitation variability (43 studies). The most common adaptation responses were related to behaviour change (50 studies), green infrastructure (including certain climate smart agriculture (CSA) activities (37 studies)), new technologies (32 studies), and other infrastructural improvements (31 studies). The most commonly reported health outcomes were related to infectious diseases (17 studies). No study reported on the ex ante defined category of maternal and child health outcomes. The evidence base was largest for studies evaluating the effect of adaptation responses on intermediate health outcomes, especially outcomes related to food security (46 studies) and water, sanitation and hygiene (WASH; 16 studies) (table 1). Studies typically reported multiple combinations of climate hazards, health outcomes, and adaptation responses, and a total of 1117 data points were extracted. The size of the evidence base, for all possible combinations of climate hazards, adaptation responses and health outcomes, is depicted by the number of studies in figure 2 and number of reported outcomes (including multiple outcomes reported by individual studies) in figure 3. The identified exposure—adaptation—health outcome pathways evaluated in each study are listed in the supplementary materials along with disaggregated data on the specific health outcomes evaluated in each study.

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Among the identified studies in LMIC settings, the majority were reporting on studies conducted in Asia (49 studies, with India (n = 11) and Bangladesh (n = 14) as most frequently reported countries) and Africa (38 studies, with Ethiopia (n = 9) as most frequently reported country). Seven studies were global studies, and one study assessed health outcomes in 57 small island states (figure 4).

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We identified two studies with a 'category 1' study design, and a relatively small number (n = 24) of studies assessed as category 2. The majority of studies were assessed as 'category 3' and 'category 4' study designs (49 and 24 studies, respectively). Studies reporting on food security showed the highest proportion of 'category 1' and 'category 2' study, and these typically reported more contextual details as well as more comprehensive quantitative analysis of the effects on health of the evaluated climate change adaptation responses (figure 5).

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Given the distribution of the evidence, we focus our evidence synthesis on the three most commonly reported outcomes namely, infectious disease, WASH and food security.

3.4.1. Infectious disease

3.4.2. WASH indicators

Forty-six studies reported on the effects of adaptation responses on food security and malnutrition. Geography: Studies reported on Africa (28), Asia (11), Oceania (3) and on the global context (4). Twelve studies were conducted in coastal settings, of which five focussed on rural areas, and seven studies focussed on both urban and rural settings. 24 rural studies, and two urban-rural combination studies reported on non-coastal settings; two studies did not report on urbanicity. Study populations: Twenty studies assessed the effect in the general population and 20 reported on farmers, one study looked into male versus female led households. Study design and category: The majority of studies (35) used a cross-sectional study design, five studies were reviews, four studies were longitudinal and two studies were empirical modelling studies. Nearly 30% of the included evidence base derives from studies in category 1 or 2 (figure 5).

Climate hazards: The majority of studies reported responses droughts (29), precipitation variability (18) and extreme precipitation and inland flooding (18) while also a considerable number of studies focussed on more general climate change impacts (19). Adaptation responses: The most commonly evaluated adaptation responses were related to behaviour change approaches (20), technological advances (19), and ecosystem responses or green infrastructure, including CSA (17). Approximately half of the studies (24) evaluated a combination of adaptation strategies. Pathways to health: Reported adaptation responses fell into three categories: expanding agricultural produce to different/additional products (including tree planting); cultivation of climate resilient crop varieties or the application of climate resilient agricultural management strategies; and enhanced storage or preservation techniques of foodstuffs for consumption at times of reduced food supply. The disaggregated food security indicators that fall under each of these categories can be found in the supplementary table (supplementary files).

Thirty-eight studies (all 33 studies in study design category 1, 2 and 3 and in addition five studies in 'category 4') reported the effectiveness of adaptation responses; 24 reported a beneficial response; two negative responses and 12 reported mixed responses. Eighteen studies reported quantitative information on change in food security indicators (as result of the adaptation response) in 117 individual outcome measurements. Reported changes in food security indicators from adaptation responses ranged from −18% to +133% with two outliers reporting on larger food security improvements. Reported improvements in production due to climate change adaptations were, on average, higher in middle-income countries (28.7% (95% CI 22.5–34.8)) than in low-income countries (17.9% (95% CI 6.03–29.8)) after removing outliers (figure 6).

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The studies reported a large variety of food security outcomes, often evaluating multiple combinations of climate exposures, and therefore the results could not be pooled. The largest food security improvements were reported from projects that evaluated the impact of climate resilient crop varieties (often under the heading of CSA), and advancements in agricultural management.

3.5.1. Other health outcomes

Nearly a 3rd (n = 31) of papers reported on maladaptations related to the evaluated climate change responses [32]. These maladaptations can be summarised in four themes. First, there are a number of papers describing maladaptation related to gender inequalities. For example, there were major differences reported in enablers and barriers to uptake of some adaptation responses between men and women. Increased and excessive workload on women related to the climate change adaptation response was mentioned frequently, whilst others (especially migration related responses) were reported to more danger to women and/or female headed households. Secondly, a number of studies report that improved resilience and positive effects on health at the individual level, did not necessarily translate into improvements of resilience of the system, especially when certain underlying systemic problems (e.g. education and size of the livestock herd) were not addressed. For that reason, several studies expressed their concerns over the longer-term benefits of the adaptation responses evaluated. A 3rd category related to unexpected or hidden co-harms including the perceived reduction of well-being related to infrastructural development, negative health and environmental consequences of self-driven diversification (for example coral mining) and stress and emotional pressure related to migration. Finally, a 4th category of reported maladaptations was related to pre-existing socio-economic disparities and inequalities and associated maladaptation of responses. This was frequently mentioned in adaptation strategies involving loans, whereby the poorest households particularly struggled to make their repayments. Some non-financial adaptation responses that required a relatively high investment costs were also reported to have limited uptake among the poorest households.

Our study has identified a disparate and limited evidence base on the effects on health of climate change adaptation responses in LMICs. There is a concerning lack of ex ante formal evaluations of climate change adaptation responses and our review found only 38 studies in total that reported quantitative data, precluding limited pooled analysis. Evaluation timelines were typically short with no studies reporting on longer term health outcomes (greater than 12 months). Furthermore, the methods and results of many included studies were frequently poorly reported. The majority of papers evaluated adaptation responses to extreme weather events: evaluation of adaptation options for gradual climate change were scarce, while evidence on these are also of pivotal importance to safeguard population health. We identified a very limited evidence base on major health indicators such as all-cause mortality, and no evidence on other important outcomes in LMICs including maternal and child health.

The largest evidence base reported on the effect of adaptation responses on infectious disease, and indicators of WASH and food security. There is limited evidence that some climate change adaptation responses improved WASH and food security outcomes and this may be important for future response planning. The preponderance of positive outcomes reported in included studies suggests that reporting and publication bias is likely, further limiting the opportunities to provide a robust evidence synthesis and draw valid conclusions. It is noteworthy that a wide spectrum of maladaptations were reported underlining the need to understand the contextual determinants of successful adaptation responses for improved population health.

There has been a growing recognition, over the past decade, that the effects of climate change adaptation responses on health need to be understood in more detail [33]. However, the evidence base, specifically in LMICs, and our knowledge on specific barriers and enabler for success, remains relatively small. In 2011, a systematic search of United Nations Framework Convention on Climate Change (UNFCCC) initiatives to identify evidence on tangible adaptations and their effects on health concluded that adaptation actions were largely at groundwork stage and that implications for health were absent in initiatives of any of the 38 contributing countries [21]. Furthermore, consideration for the special needs of vulnerable groups was broadly underdeveloped. Similar to the current study, they found that WASH and food security outcomes were priority themes. A 2014 report [22] evaluated 54 published studies related to national-level adaptation planning with a specific focus on infectious disease risks in OECD countries and identified a lack of consideration of the needs of vulnerable population groups as well as very limited evidence on local context-specific factors that could influence adaptation. The authors argue that a possible reason for evidence paucity could be linked to the lack of available funding and timelines for evaluation, and/or an evaluation component not being considered as a priority in climate change adaptation action. A more recent systematic review of grey literature on the effects on health of climate change adaptation in ten OECD countries suggested that governments primarily address infectious disease and heat-related risks posed by climate change [20]. Finally, a review of project reports from the 1st 5 years of implementation (2008–2013) of multinational health adaptation projects in ten LMICs identified that countries remain insufficiently prepared to prevent additional health burdens resulting from climate change [33].

Our study extends the current evidence base by including the most recent published literature and specifically focussing on LMICs. We conclude that evidence paucity remains a significant problem with major knowledge gaps and limitations in socio-economic, demographic and vulnerability aspects. The clear and concerning lack of evidence, notably the lack of measured quantitative information, poses major challenges for evidence-based decision-making regarding climate change adaptation options.

We propose a number of priorities for study planning, reporting and publishing that—if adopted over the coming years—would be major leverage points for enabling high-quality, comprehensive and valid data synthesis through systematic reviews of the literature.

Study planning—A major reason for data paucity may relate to research capacity and preparedness for data collection. As many countries in Sub-Saharan Africa and South and South-East Asia are disproportionately affected by climate change, improving the research capacity in these countries to conduct climate change adaptation evaluations, should be prioritised. This includes both preparation (e.g. set-up and protocols for data collection) prior to the occurrence of climate hazards (including disasters) as well as tailor-made research training that incorporates a careful consideration of contextual factors or hazards that could affect climate change adaptation evaluations. Interactive webinars and training materials on accessible platforms could improve access to curricula on research and evaluation training and encourage continuous improvement and adaptation of the training materials by the climate change adaptation community.

Funding—Formal evaluations are resource-intensive and a lack of available funding will directly limit the conduct of high-quality evaluations. We urge research funders to acknowledge the crucial importance of evidence on the effects on health of climate change adaptation for evidence-based decision making over the coming years. This would also enable the evaluation of longer-term health impacts of adaptation options and allow more in-depth data analysis linked to existing (routinely collected) health data.

Study protocol guidance and reporting templates—We strongly advocate for the development of clear and open access data collection and reporting templates for climate change adaptation evaluations—and in particular those that that aim to measure effects on health. The use of experimental designs, such as community based randomised controlled (or step-wedge) trials should be actively encouraged. Reporting should be standardised to capture a minimum set of data, including (but not limited to) study context, full details and quantification of health outcome, equity indicators, maladaptation, and financial and time costs of the adaptations.

Context and equality—Further research should investigate not only the types of adaptation measures adopted, but quantify how effective they are in achieving the goals formulated, among different groups in society, and how feasible implementation of the options are in various context.

Tackling reporting and publication bias—We strongly encourage journals editors, medical associations, funders, researchers, and NGO representatives to prioritise identifying solutions for reporting and publication bias in this literature. An international repository of climate adaptation strategies and reports that is readily accessible may support the dissemination of key findings, lessons learned, and best practices.

Evidence-based decision making is a critical cornerstone of public policy. With the rapidly extending knowledge base on health and climate change, assessments to inform public policy are increasingly time and resource intensive. For example, the IPCC AR6 is expected in 2021 and 2022, almost 8 years since AR5 was published.

We have the knowledge, skills and techniques to perform comprehensive synthesis on a rolling basis—especially when computer assisted screening methodologies are applied alongside human screening. Such state-of-the-art synthesis of evidence will be crucial for development, implementation and decision-making around climate change adaptation responses and further stresses the importance of designing, conducting and clear reporting of climate change adaptation evaluations.

Information and knowledge on health adaptation can be found in traditionally difficult-to-access sources, including grey literature, policy and project evaluations, (archived) websites, and social media platforms. Extending the knowledge base on health adaptation can make use of advancements in digital methods and tools; web scraping can extend the scope of literature included; (pre-)trained algorithms can help predict relevant information sources, and advancements in automated translations could significantly decrease English reporting bias [34].

We present a comprehensive systematic review and synthesis of published evidence on the effects on health of climate change adaptation responses—focussing on LMICs. The collated evidence provides important insights into the available published literature. The database of studies—on which analyses are based—is available in the supplementary material and forms a timely and substantial contribution to current climate change adaptation literature. However, there are several important limitations that need to be considered when interpreting the findings.

First, the evidence base is relatively restricted both in scale and in quality. The limited scale of the evidence base, reduced our ability to synthesise findings across multiple studies, which in turn restricts direct use of data for evidence-based decision making. The limited quality of the evidence base, with very few studies being graded as study design category 1 (i.e. ex ante formal evaluations of a defined adaptation responses), means that confidence in the reliability and strength of the findings is reduced. Second, there are limitations in the way in which the studies were identified. The original GAMI project was not designed specifically to answer the question on the effects on human health of climate change adaptation responses. While screening of the GAMI database of 48 813 papers for relevant studies was systematic, it is possible that some relevant papers were not included in the original GAMI database. It could be important to explore whether relevant climate-health literature is being indexed under very specific terms not captured by GAMI search terms (i.e. studies not using 'adaptation' or 'risk' in their abstracts and titles). Other biases, including those relating to reporting, publication and language, are common concerns in reviews of this nature and should be considered. Information on costs as well as barriers and enablers of adaptation options was not extracted from the included studies, as this was beyond the scope of this study. Given the data paucity on specific adaptation option such data would, however, give merely anecdotal evidence and costs could vary greatly from country to country. Finally, the review focuses on the currently available (and limited) scientific literature, meaning it does not include grey literature sources, nor does it provide much information on newly emergent areas of research. Recent areas of particular research activity include for example a focus on antimicrobial resistance and climate change, as well as a rapidly emerging literature on post-COVID19 climate governance. An update to this review in 3–5 years would certainly reveal several new priority areas.