NASA Harvest Partner Investigates Underestimated Cropland Burning in Ukraine
Despite being illegal, cropland burning within Ukraine, and its associated environmental and public health detriments, is still widespread. A recent study co-authored by a team including NASA Harvest’s Dr. Sergii Skakun found that official government estimates of cropland burned area do not account for the overwhelming majority of actual burnings. Given the severe impact that cropland burning has on air quality and human health, as well as the importance of accurately monitoring agricultural CO2 emissions, it is vital that methods for effective cropland burning are created and implemented.
The team, consisting of the University of Maryland’s Dr. Joanne V Hall, Dr. Louis Giglio, and Dr. Sergii Skakun; the Regional Eastern Europe Fire Monitoring Center’s Dr. Sergiy V Zibtsev and Dr. Viktor Myroniuk as well as Dr. Oleksandr Zhuravel [FAO], Dr. Johann Georg Goldammer [Global Fire Monitoring Center], and Dr. Nataliia Kussul [Space Research Institute NAS Ukraine], created a new technique utilizing an open-access Earth observation (EO) dataset to create a reliable crop burning detection methodology within Ukraine.
More than 70% of the land within Ukraine is classified as agricultural and just under half of the total land area in the country is used to actively grow crops. Cropland burning is a practice that occurs in heavily agricultural areas to quickly remove post-harvest stubble and allow for rapid second plantings. The practice, while allowing for quickened planting turnarounds, has harmful impacts on air quality including the production of black carbon. Agricultural fires are the single largest source of black carbon, creating more than a third of the pollutant, which is heavily responsible for increased melting in polar regions. In addition to the environmental harm, black carbon poses a significant direct harm to humans, being only second behind cookstoves, in causing air-pollution illnesses and deaths.
This harm has led to cropland burning coming under severe restrictions by numerous governments. The European Union has banned the practice and this regulation has limited its occurrence on the continent. Lithuania, for instance, has reduced the amount of cropland burned by 90% since joining the EU.
Outside of the EU’s authority however, cropland burning persists, particularly so in Ukraine, which saw ~7.5% of its total land area burned in recent years. Despite its illegality within the country, potential fines up to $5800 USD and years in prison, cropland burning occurs approximately 300 times more often than in other European countries. Given the negative consequences, it is vital that accurate monitoring and recording of cropland burning happen in Ukraine. Improved understanding of the severity of the problem is necessary to effectively combat it.
Agricultural fires captured in March 2017
Currently one of the major sources of global fire monitoring is from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the Terra and Aqua satellites circling the globe on a daily basis. The sensor detects temperature and reflection anomalies as it observes the earth’s surface and records fire location, date, time, the radiative strength of the anomaly, and the confidence that the anomaly is a fire. With Terra and Aqua strategically planned to cover the entire Earth’s surface every 24 hours, MODIS fire products are able to catch many fires as they occur.
Additionally, MODIS data is used to create a Burned Area (BA) product. By analyzing rapid changes in the Earth’s surface reflectance, recently created BA is mapped on a per pixel basis for the globe. Despite these benefits, MODIS fire and BA products have their limitations. Given the coarse resolution of MODIS sensors (each pixel equals approximately 1 km), smaller fires can avoid detection. However, the illegal nature of cropland burning leads to large amounts of obfuscation when it comes to collecting official government surveys. This reticence on the part of citizens, as well as the difficulties in conducting the surveys, mean that, despite its limitations, EO-based fire detection remains a desirable option for cropland burning detection.
Seeking more refined estimates, the team developed a new technique for estimating cropland BA within Ukraine. To do so, they switched from MODIS to another open-access, but finer spatial resolution EO dataset produced by the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor which maps the entire surface of the earth every 24 hours as it travels on the Suomi NPP satellite. With a spatial resolution of 375m (compared to MODIS’ 1000m), VIIRS allows for detection of much smaller fires and improved mapping of fire perimeters.
The team also manually mapped more than 40,000 cropland field boundaries within preselected known agricultural zones in Ukraine. Each field was then categorized based on a visual determination of cropland burning from Landsat 8, Sentinel-2 and Planet imagery, the percentage of BA per pixel, and the presence/absence of VIIRS active fire detections. This manually created reference data was then used to create a conversion algorithm that allowed for the estimation of BA across the entirety of Ukraine, on a monthly timescale, using only collected VIIRS active fire detections.
This figure from the article shows the reference areas where data was collected. Two enlarged panels show zoomed in sections of reference areas A (predominantly maize) and G (predominantly soybean).The classification system displays the team's confidence in the burn: 1 and 2 indicating burned area; 3 indicating ambiguity; 4 showing no burn' and with 5 excluded as non-cropland.
Results from the study found that there are two main burning periods within Ukraine. The first occurs in March-April, after the snowmelt, primarily in the northern and central oblasts. The second peak is larger, is associated with the winter wheat harvests in the south of the country, and occurs in July and August. Mid-June of 2016 and 2017 specifically saw fires start in the southwestern oblast Odes’ka, before moving eastward by the end of the month. Fire detections would begin to spread to northwestern oblasts through August in both years.
Investigating the spread of the cropland burning does provide a potential solution to the problem. The five oblasts with the highest amounts of recorded burning (all within the south of the country) are also heavily productive, with the five oblasts being among the country’s highest producers of wheat. This heavy productivity is what drives the burning as it produces a large amount of crop residue which must later be dealt with.
A renewable energy policy of the nearby EU could help provide an alternative to burning however. The policy aims to increase biofuels to 20% of its non-fossil fuel energy sources. If financial incentives are created for local farmers to sell their crop residue as future biofuels to EU countries, the possibility of decreased burning exists.
Moving from the spread of fire to calculating burned area across the country, the team found significant underestimation of the amount of cropland burning that occurs within Ukraine. Compared to the newly developed technique, MODIS-based estimates underestimated the total area between 30%-63% depending on the year.
More shockingly, official government estimates were found to be 95%-99% lower than the VIIRS-obtained estimates. In other words, MODIS-based methods miss ⅓ to ⅗ of all cropland burning within the country, while official government inventories miss nearly all cropland burning.
The negative environmental and public health consequences of cropland burning only sharpen the failure of conventional government accounting to properly inventory the practice. Further, Ukraine is expected to experience increased warming by the middle of the 21st century accompanied with decreased summer precipitation. These conditions make the possibility of wildfires only more likely, particularly those caused by errant cropland burning. Agricultural-based fires have already caused significant wildfires including a 2020 1000km2 blaze that intruded into the Chernobyl Exclusion Zone.
The full paper can be accessed here.