Economic growth in Vietnam has shifted food consumption patterns to incorporate more livestock products (meat, dairy products, and eggs) [1
]. With the growing demand for livestock products, livestock farming is expanding in Vietnam and is among the fastest growing agricultural production subsectors in Vietnam [1
]. In 2015, livestock accounted for 28% of value added from the agriculture sector. The development and intensification of this subsector has led to an increase in the total animal population during the past decade. In 2016, Vietnam had 29 million pigs, 5.5 million cattle, 2.5 million buffalos, and 361 million poultry [2
]. The largest population increases compared to 2005 have been in poultry (increased by 65% with 142 million head added), followed by pigs (increased by 8% with 2 million head added); while numbers of cattle and buffalo have fluctuated slightly.
The development and intensification of livestock farming helps to ensure national food security and boosts economic growth. However, this sector is also a significant contributor to environmental pollution in general and air pollution in particular. Livestock farming contributes significantly to global greenhouse gas (GHG) emissions [3
] by releasing methane (CH4
) and nitrous oxide (N2
O), as well as air pollutants, mostly ammonia (NH3
), into the atmosphere. Livestock farming is the largest emissions source of NH3
], which plays a major role in eutrophication and acidification [7
]. The Food and Agriculture Organization (FAO) has estimated that 18% of global GHG emissions originate from the livestock sector.
Vietnam is listed among the 20 countries with the highest GHG emissions in the UNFCCC and FAOSTAT databases [8
]. Emissions from livestock farming account for approximately 20% of greenhouse gas emissions from agricultural activities in Vietnam according to the National GHG emissions inventory for 2010 [9
]. Emissions from enteric digestion are responsible for half of all livestock emissions, with the other half originating from manure management, one of the fastest-growing sources of GHG emissions in Vietnam during 1994–2010 [5
]. An inventory of CH4
emissions from livestock in Asia in 2000 [10
] showed that poultry emitted the largest amounts of CH4
in Vietnam, followed by cattle, buffalo, and pigs. A CH4
O emissions inventory for South, Southeast, and East Asia was recently conducted [11
] using emissions inventory methodologies from the International Panel on Climate Change (IPCC) 1997 Guidelines for National Emission Inventory, and ranked Vietnam in 6th place for NH3
emissions and 7th place for CH4
O emissions among the 23 countries studied. An estimate of air pollutants and GHGs over Asia aggregated Vietnam within the Southeast Asia region [12
]. To the best of our knowledge, no emissions inventory has been conducted for CH4
O in Vietnam using IPCC 2006 methodologies. Previous studies estimating livestock farming emissions in Vietnam have been conducted at the provincial scale or for one type of pollutant (such as GHG or air pollutant). Examples of such studies include estimates of CH4
emissions from cattle in Daklak province [13
emissions from cattle in Quang Ngai province, with mitigation scenarios [14
], and GHG and pollutants from livestock farming within a ward of Hung Yen province [15
It is important to develop a historical inventory and projections of future livestock GHG and air pollutants to improve our understanding of the evolution of emissions and their associated impact on air quality. In this study, we focused on the Red River Delta (RRD) region, which is among the largest livestock farming centers in Vietnam. This region contained 8726 livestock farms in 2016, accounting for 42% of all livestock farms in the country [2
]. RRD contains the largest number of pigs and poultry, with populations of 7.4 million and 93.7 million head, respectively (account for 26% of country’s total). This inventory attempts to quantify emissions of CH4
O, and NH3
produced by livestock farming, in RRD from 2000 to 2030 at a 5-years resolution using the IPCC 2006 Guidelines for National Emission Inventory [16
] and regional or country-specific emission factors wherever applicable. Its results are designed to provide input to more comprehensive studies about regional air quality, for example using an air dispersion model and the Greenhouse Gases—Air Pollution Interactions and Synergies (GAINS) model.
Emission factor is a very important element to the accuracy of the estimations in emission inventory. Default methane emission factors for enteric fermentation in IPCC 2006 Guidelines for Asia is 68 kg head−1
for dairy cattle and 47 kg head−1
for other cattle. We used emission factors from studies of References [25
], which were derived from the RUMINANT model (Tier 3 methodology). These emission factors are higher for dairy cattle and lower for other cattle compared to the default values in IPCC 2006 (see Table A4
, Appendix A
). These emission factor discrepancies were mainly due to higher milk yields from dairy cattle and lower weight in beef cattle in the studied area. Another study [10
] used IPCC 1997 default emission factors, which are lower than IPCC 2006 values for both dairy and non-dairy cattle.
Previous studies [11
] have used a manure management CH4
emission factor of 16 kg head−1
for dairy cattle in a temperate climate region with annual average temperature ranging from 15 to 25 °C. However, the IPCC 2006 guidelines provide CH4
emission factors for temperatures classified at a finer scale. We calculated the annual average temperature for the RRD region to be approximately 25 °C using historical data from three monitoring stations in the region. According to the IPCC 2006 guidelines, the manure management CH4
emission factor for dairy cattle is 26 kg head−1
, much higher than the value used in previous inventories.
O emission factors used in this study are presented in Table A4
, and expressed in emission per animal head per year to be able to compare with the ones used in previous studies. Some studies have used IPCC 1997 default N2
O emission factors for each animal type (e.g., Reference [11
]), which were calculated based on proportional regional values of manure production. Our calculation resulted in higher emission factors for all animals except horses and goats; these are “pasture animals”, for which N2
O emissions are not accounted for as livestock but instead for soil management. Our emission factors for dairy cattle and poultry were an order of magnitude higher than those used previously [11
]. We used the IPCC 2006 default values for dairy and non-dairy cattle to calculate emission factors, resulting in higher values than those obtained using the IPCC 1997 guidelines due to the incorporation of different manure management systems and the more detailed classification systems employed in the IPCC 2006 guidelines.
Pig husbandry is the largest GHG and NH3
emitter in the RRD region, which is responsible for about half of total GHG emissions (in CO2
eq) and about 46% NH3 emissions from livestock in 2015. This is an atypical situation compared to neighboring countries. In the emission inventory for South, South East and East Asia for 2000 [11
], cattle was the largest emitter for CH4
O and NH3
emissions, with a share of 56%, 30% and 33% respectively. Study of Reference [32
] in Indonesia has also shown cattle as the major contributor to GHG emissions in the 2005–2015 period. Our results provide a reminder that regarding agricultural sector emission mitigation, policies in the Red River Delta should not be copied from other countries.
The production of emissions from livestock farming depends on various factors including feeding practices, housing systems, and manure management systems. Detailed historical data on the feed composition for each animal type and the proportions of manure managed by different management systems are needed to obtain more accurate emissions estimates. However, these data are not yet systematically collected or well documented for emissions inventory purposes. Improving the quantity and quality of data and research related to livestock farming will help to improve emissions monitoring in this sector.
Currently, environmental protection regulations for livestock farming in Vietnam mainly focus on water quality, not air quality. There is a national technical standard for wastewater from livestock farming in Vietnam, but no specific regulations with respect to manure management and air quality. In practice, compliance with and enforcement of related environmental regulations in the livestock sector are currently weak [1
]. The significant contributions to GHG and air pollutant emissions from this sector deserve more attention.
In this study, we estimated CH4, N2O, and NH3 emissions from livestock farming in the RRD, northern Vietnam from 2000 to 2015 and projected future emissions to 2030. This inventory and projection yielded emissions by animal type and by province. The results of our emissions inventory indicate that livestock farming in RRD contributes significantly to GHGs and NH3 emissions. The emissions inventory and projection showed an upward trend in GHG and NH3 emissions during 2000–2030. The GWP of CH4 and N2O emissions was 5.9 MtCO2eq in 2030, representing 33% of GHG emissions from livestock nationwide. Pig farming contributed the largest proportion of GHG and NH3 emissions, at 50%. Cattle were responsible for the second largest share of GHG emissions, whereas poultry contributed most of the remaining NH3 emissions. This study also provides the provincial emissions levels for CH4, N2O and NH3. Understanding the level of emissions emitted in the RRD region and the contribution of different type of livestock as well as the spatial distribution of emissions by province is a first step to developing effective mitigation strategies for reducing GHG and NH3 emission in the RRD region. Furthermore, this inventory provides an input to implementing regional air dispersion modeling for air pollution impact assessments in the RRD region.