According to the respondents, ACHA project investments in water management infrastructure reduced flood frequency and impact. This logically provided for higher agricultural productivity (e.g. the recorded increase in the value of vegetable production) and contributed to lower levels of severe food insecurity and debt, suggesting significant benefits of improved water management. We did expect benefits to arise, but had not formulated expectations about the scale of benefits. The fact that respondents reported both decreased and increased flood frequency, and decreased and increased impacts, suggests that respondent bias was unlikely to have occurred (i.e. it does not indicate that respondents answered questions according to what they thought interviewers wanted to hear). Data are also corroborated by key informant interviews with APSARA staff (wherein flooding frequency and impact did vary across the Park). We acknowledge that the 3-year time frame for assessment (limited to ACHA project time frame) may not provide a sufficient time period to detect impact. 

The benefits of effective SEPL management (i.e. maintenance of water services) clearly support agricultural productivity and improved health outcomes in the lower part of the catchment through food security. While protection of the Park has enabled regulation on deforestation within its boundaries, it has also attracted tourists and most likely resulted in increased population growth in Siem Reap, adding pressure on groundwater resources needed to support the temples. This project demonstrates that while synergies between biodiversity protection and economic development exist that can strengthen SEPL management, new challenges may be created whose mitigation requires a broader landscape focus.

Focus group data from the upper catchment contributed to the understanding of the linkages between water, loss of forests, and human health. Discussions about forest change beyond the Park boundary, compared to the benefit of forests protected within the Park, provide three clear lessons for SEPL management. Firstly, a loss of forest coverage impacts human health. Some of these impacts are direct (e.g. shade trees), whereas others are indirect. Indirect changes include a change in land use from forest to rice, cassava, and cashew nut cultivation. The negative impacts of these crops on soil fertility often result in increased rates of agricultural input use (Mahanty & Milne, 2016). Increased health risks are attributed to the use of agricultural inputs. The respondents’ awareness of these linkages bodes well for improved SEPL management in the future. Discussions about pathways forward indicated that alternatives do exist that improve water quality and ameliorate health impacts (e.g. traditional composts). Health impacts are particularly important for pregnant women who are more vulnerable, and for women in general who are more susceptible to increases in temperature (WHO, 2014).

Secondly, the loss of biodiversity and land-use changes are clearly associated with development pressure, with participants shifting to higher value cash crops, and complaining about their ability to control the use of forests by “outsiders”. Cash crops such as cassava are low labour-intensive, enabling migration of family members for part of the year to supplement household income in the country of origin of migrants (Eliste & Zorya, 2015). Studies from Siem Reap (e.g. Jacobson et al., 2019; Jacobson, 2020) indicate that migration results in a loss of agricultural labour. Losses of agricultural labour can result in less intensive production, or smaller production areas, which can result in lower total production and food availability. This can further exacerbate existing food insecurity for remaining members, in addition to other reported impacts on human health, such as increasing violence against women and children. Outsider use of forests is indicative of the rural-urban poverty divide, whereby the urban poor in Cambodia improved their share of disposable income by nearly twice as much as the urban rich between 2009 and 2017, whereas the rural poor improved it by only 30% as much as the rural rich. Illegal and “outsider” use of forests is an option for rural poor to advance themselves; restricting forest degradation therefore requires carefully targeted development initiatives for this group. Identifying and working with vulnerable groups who engage in deforestation in meaningful ways remain a critical development challenge.

Lastly, the potential impacts of any future deforestation in the upper catchment, coupled with climate change, are expected to result in water shortages and affect temple stability in the Park (Chim et al., 2021). Likewise, any further deforestation in the upper catchment is predicted to also affect the economic benefits from tourism (Chim et al., 2021). This could severely affect tourism benefits associated with the Park, estimated at 4.9 billion USD in 2019 (Ministry of Tourism, 2019). It would also impact the ability to sustain the cultural service benefits associated with the ACHA project in the Park, and could affect the ability to sustain food security benefits within the Park due to the impact on groundwater reserves. 

Future challenges to SEPL management include the accelerating pressures of climate change, alongside livelihood development placing further pressure on water resources. Further lower flows in the Mekong River are anticipated to undergo proposed hydroelectric development (Hecht et al., 2019); this will affect the flood pulse in the Tonle Sap lake, reducing groundwater levels. This compounds changes that result from extractive uses of water. The ability to sustain ACHA project benefits therefore depends on additional interventions that address the concomitant impacts of development, climate change, as well as unknown impacts of the COVID-19 pandemic. Tourism during the pandemic has all but ended, declining by 95.5% between June 2019 and June 2020,11 with an estimated forgone annual provincial revenue of 1.3 billion USD.12 The COVID-19 pandemic has also resulted in many migrants returning home, with remittance losses for many; for example, reported rates of migration in Siem Reap province prior to the pandemic were up to 46% of households, with an average remittance of 284 USD (Jacobson et al., 2019); loss of remittances is also likely to affect debt sustainability, and places increased pressures on food availability. These socio-economic challenges are likely to hinder the ability to maintain biodiversity and the benefits derived from ACHA in the future. In recent years, the physical extent of ancient Angkorian water management infrastructure beyond existing protected area boundaries has been studied by scientists (Evans, 2016), although knowledge of it likely persisted through traditional mechanisms. Continued investment in its reinvigoration beyond the Park boundaries is therefore likely to support the whole of landscape management.

Addressing the links between environmental health and human well-being requires recognition that management interventions might need to occur at locations different from where the impacts of poor management are experienced. For example, the impacts of forest degradation are experienced in the Park in terms of lower groundwater levels. However, the most important sites for action are probably in the upper catchment where deforestation is higher, and the mid-catchment where groundwater recharge can be maximised through water-efficient agriculture. In addition to the obvious focus on water, we identified four other strategic directions to enhance environmental health and human well-being outcomes through sustainably managing landscapes.

First, we advocate for community-based natural resource management (CBNRM) to enhance SEPL management in the upper catchment, and complement existing management of the Park in the lower catchment. CBNRM recognises that environmental protection requires the survivability of communities as stewards of the natural environment. Criteria for successful CBNRM include (1) local recognition of problems and initiation of projects, (2) economic incentives for environmental management, (3) alternative livelihoods that combat the opportunity costs of environmental protection, (4) autonomy of decision-making, and (5) capacity development (Measham & Lumbasi, 2013).

Our analysis demonstrated that community and government staff acknowledged the importance of ecosystem services to livelihoods and well-being (criterion 1). Economic incentives for protection exist as evidenced from economic analysis of water infrastructure management in the Park (criterion 2). However, it is unclear whether these will outweigh the opportunity costs of further actions to limit land-use change and protect forests (criterion 3). Payment for Ecosystem Services (Redford & Adams, 2009) could reduce the rate of land-use change, but the benefit distribution as well as the identification of appropriate buyers of services will be critical. The opportunity cost balance could also be addressed through a more nuanced understanding of vulnerability. This will ensure that even those who are contributing to negative impacts, but doing so inevitably due to their vulnerability, could benefit from development projects so as to be compensated for missed opportunities and ensure that their livelihoods are sustainable. This will be particularly important given the emerging economic impacts of the COVID-19 pandemic. For example, those from outside of forest communities may be more vulnerable than those within, leading them to engage in forest clearing. In development projects, these people, as well as people within forest communities, need to be considered as beneficiaries.

For autonomy (criterion 4), some mechanisms already exist that could be strengthened to protect forests. Management committees for Community Protected Areas and Community Forestry Areas (examples of which exist in the upper catchment) have the ability to set regulations on forest use, but lack resources and a mandate to address regulation breaches. Legal provisions also exist that could support community-based management of water, but these have had limited application (Mak, 2017). Capacity development is also needed, as identified by community members (criterion 5). We propose community-based monitoring of disaster risk reduction and environmental health (e.g. Rainforth & Harmsworth, 2019) as one mechanism for incorporating and improving knowledge and autonomy in management.

Second, we also advocate for nature-based solutions (NBS). NBS specifically promote nature as a means of mitigating climate change and adapting to it (Nesshover et al., 2017). Solutions relevant to the Park include actions that strengthen ecosystem service provision while providing alternative livelihoods. For example, riparian planting could reduce erosion of river banks. It also has the potential to provide food (fruit trees) and jobs in nursery production, as well as shade trees to reduce heat stress. Alternatively, instream structures could be built that slow the speed of water travel across the landscape and increase production yields through soil moisture retention. Health impacts could be ameliorated through the promotion of organic compost instead of chemical inputs. This could take advantage of existing aquatic plants, and potentially improve production returns through organic certification.

Third, we advocate for economic diversification. Economic diversification is considered critical for resilience building (Davidson et al., 2016), and lessening the risk of livelihood failure during times of uncertainty and crisis. Smallholder
reliance on one or two key crops heightens risks associated with climate change. Market supply-chain development and careful selection of alternatives in horticultural production will be important, given the market competitiveness of imported fruits and vegetables in Cambodia (World Bank, 2015). Unique heritage crops such as tiger-hand potato, and high-value land-efficient crops such as pepper and moringa, could provide niche market opportunities.

Lastly, we advocate for improved disaster preparedness. Disaster management in Cambodia is in its infancy (ESCAP, 2016). Understanding the temporal-spatial dimensions of disasters within the catchment, and facilitating preparedness for sudden and slow on-set events (i.e. emergency responsiveness, preparedness, and adaptation), will enhance resilience. This includes planning for emergency water and food reserves (i.e. rice), adaptation in crop varieties and crop choices, and preparedness for emergency livelihoods (e.g. tuber crop stems and rice seed).