Environment

FSI scholars approach their research on the environment from regulatory, economic and societal angles. The Center on Food Security and the Environment weighs the connection between climate change and agriculture; the impact of biofuel expansion on land and food supply; how to increase crop yields without expanding agricultural lands; and the trends in aquaculture. FSE’s research spans the globe – from the potential of smallholder irrigation to reduce hunger and improve development in sub-Saharan Africa to the devastation of drought on Iowa farms. David Lobell, a senior fellow at FSI and a recipient of a MacArthur “genius” grant, has looked at the impacts of increasing wheat and corn crops in Africa, South Asia, Mexico and the United States; and has studied the effects of extreme heat on the world’s staple crops.

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More than 820 million people around the world don’t have enough to eat and their hunger affects us all. “Without food security, you will have no other security,” said David Beasley, the executive director of the World Food Programme, to an audience of Stanford members and local residents on Oct. 1. 

Beasley along with predecessor Ertharin Cousin, a visiting scholar with Stanford’s Center of Food Security and the Environment, helped shape the United Nations’ anti-hunger program into the world’s largest hunger relief organization, feeding over 90 million people every year.

Beasley and Cousin spoke on the multifaceted challenges of 21st century humanitarian response at the Robert G. Wesson Lecture, organized by Stanford's Center on Food Security and the Environment.


View photos from the event



In March 2017, the Trump administration considered pulling U.S. funding, which provides 40 percent of the program’s support. But by arguing that food insecurity drives terrorist groups, like ISIS using food to recruit members, Beasley was able to keep US funding and raise money internationally.

“If you’re not going to do this out of the goodness of your heart, then you better do this out of your interest for national security,” said Beasley.

Though Cousin lauded the efficacy of Beasley’s efforts, she questioned whether promoting food security as a solution for global security could incite safety issues for World Food Programme workers. “How does that affect the building of awareness and does that create more problems for the people working on the ground?” she asked.

There are countries the World Food Programme has struggled to assist due to safety concerns. In June 2019, Beasley suspended aid from Yemen due to diversion of food from vulnerable people by Houthis. Safety was also a huge factor. “You can get shot and killed or stabbed in a heartbeat,” Beasley said.

The World Food Programme has encountered another complex situation in Venezuela, which is in the midst of its direst food crisis in history. Almost 90 percent of the country is living below the poverty line with a substantial cut in government assistance food programs.

Though Beasley could not provide detail due to the sensitive nature of negotiations, he believes a resolution will come soon. “We’re on the ground…in the middle of negotiations as we speak, and we’re making tremendous headway,”

Future efforts will focus on self-sustainability, which is crucial for long-term food security. The program has rehabilitated about 400,000 acres of otherwise unusable land because of flash floods or drought, allowing hundreds of thousands of people food and job security that would no longer need direct aid.

Both Beasley and Cousin agree that with the technology and wealth available, no child should go hungry and there should never be another famine on earth. “There are [people] who don’t know where their next meal is, and they’re marching towards death. That is absolutely inexcusable,” said Beasley.

When asked by Cousin what his takeaway from his experience as director has been, Beasley said, “Go love your neighbor, first and foremost. Please understand the suffering world out there, and don’t underestimate the power you have as an individual…I have so much hope for the future but at the same time, a great fear form what I see because of a lot of destabilization. The world is very fragile…Loving your neighbor is the most powerful weapon.”

By Gina Yu, Stanford Global Health Media Fellow

This story originally appeard on the Stanford Center for Innovation in Global Health's website.

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David Beasley at Stanford Oct. 1, 2019
UN World Food Programme Executive Director David Beasley speaks with his predecessor Ertharin Cousin at Stanford Oct. 1.
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Feeding a growing population while reducing negative environmental impacts is one of the greatest challenges of the coming decades. We show that microsatellite data can be used to detect the impact of sustainable intensification interventions at large scales and to target the fields that would benefit the most, thereby doubling yield gains. Our work reveals that satellite data provide a scalable approach to sustainably increase food production.

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Nature Sustainability
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David Lobell
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New research from David Lobell and team finds small satellites can help target agricultural interventions in locations where impact will be greatest.

Data from microsatellites can be used to detect and double the impact of sustainable interventions in agriculture at large scales, according to a new study led by the University of Michigan.

By being able to detect the impact and target interventions to locations where they will lead to the greatest increase or yield gains, satellite data can help increase food production in a low-cost and sustainable way.

According to the team of researchers from U-M, the International Maize and Wheat Improvement Center, and Stanford and Cornell universities, finding low cost ways to increase food production is critical given that feeding a growing population and increasing the yields of crops in a changing climate are some of the greatest challenges of the coming decades.

“Being able to use microsatellite data, to precisely target an intervention to the fields that would benefit the most at large scales will help us increase the efficacy of agricultural interventions,” said lead author Meha Jain, assistant professor at the U-M School for Environment and Sustainability.

Microsatellites are small, inexpensive, low-orbiting satellites that typically weigh 100 kilograms (220 pounds) or less.

“About 60-70% of total world food production comes from small holders, and they have the largest field-level yield gaps,” said Balwinder Singh, senior researcher at the International Maize and Wheat Improvement Center.

To show that the low-cost microsatellite imagery can quantify and enhance yield gains, the researchers conducted their study in small-holder wheat fields in the Eastern Indo-Gangetic Plains in India.

They ran an experiment on 127 farms using a split-plot design over multiple years. In one half of the field, the farmers applied nitrogen fertilizer using hand broadcasting, the typical fertilizer spreading method in this region. In the other half of the field, the farmers applied fertilizer using a new and low-cost fertilizer spreader.

To measure the impact of the intervention, the researchers then collected the crop-cut measures of yield, where the crop is harvested and weighed in field, often considered the gold standard for measuring crop yields. They also mapped field and regional yields using microsatellite and Landsat satellite data.

They found that without any increase in input, the spreader resulted in 4.5% yield gain across all fields, sites and years, closing about one-third of the existing yield gap. They also found that if they used microsatellite data to target the lowest yielding fields, they were able to double yield gains for the same intervention cost and effort.

“Being able to bring solutions to the farmers that will benefit most from them can greatly increase uptake and impact,” said David Lobell, professor of Earth System Science at Stanford University. “Too often, we’ve relied on blanket recommendations that only make sense for a small fraction of farmers. Hopefully, this study will generate more interest and investment in matching farmers to technologies that best suit their needs.”

The study also shows that the average profit from the gains was more than the amount of the spreader and 100% of the farmers were willing to pay for the technology again.

Jain said that many researchers are working on finding ways to close yield gaps and increase the production of low-yielding regions.

“A tool like satellite data that is scalable and low cost and can be applied across regions to map and increase yields of crops at large scale,” she said.

The study is published in the October issue of Nature Sustainability. Other researchers include Amit Srivastava and Shishpal Poonia of the International Maize and Wheat Improvement Center in New Delhi; Preeti Rao and Jennifer Blesh of the U-M School of Environment and Sustainability; Andrew McDonald of Cornell; and George Azzari and David Lobell of Stanford.

This story originally appeared on the Univeristy of Michigan's School for Environment and Sustainability website.

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David Beasley
Please join us for a conversation with United Nations World Food Programme Executive Director David Beasley, who will discuss "Challenges of 21st Century Humanitarian Response." The conversation will be moderated by his predecessor at the agency, Ertharin Cousin, a visiting fellow at the Center on Food Security and the Environment.

R.S.V.P.

As Executive Director of the World Foods Programme (WFP), Mr. Beasley serves at the level of Under-Secretary-General of the United Nations and is a member of the organization's Senior Management Group under the leadership of Secretary-General António Guterres. At WFP, he is putting to use four decades of leadership and communications skills to mobilize more financial support and public awareness for the global fight against hunger. Under his leadership, WFP kept four countries from slipping into famine in 2017 and is moving beyond emergency food assistance, to advance longer term development that brings peace and stability to troubled regions. Before coming to WFP in April 2017, Beasley spent a decade working with high-profile leaders and on-the-ground programme managers in more than 100 countries, directing projects designed to foster peace, reconciliation and economic progress.

David Beasley was elected at the age of 21 to the South Carolina House of Representatives (1979-1992) and as Governor of South Carolina (1995-1999), one of the youngest in the state’s history.  He received a Profile in Courage Award in 2003 from the John F. Kennedy Library Foundation and is a 1999 Fellow of the Institute of Politics at Harvard University’s Kennedy School of Government. Born in 1957, he attended Clemson University and holds a B.A. from the University of South Carolina, as well as a J.D. from the University of South Carolina School of Law.

The Conversation with David Beasley is co-sponsored by Stanford’s Freeman Spogli Institute for International Studies; the Center on Food Security and the Environment and the Annenberg Foundation Trust at Sunnylands.

 The lecture will be held at the David and Joan Traitel Building, 435 Lasuen Mall, Stanford University. For more information about the event, contact Sonal Singh at sonals@stanford.edu.

About the Wesson Lecture

The Wesson Lectureship was established at Stanford by the Freeman Spogli Institute for International Studies in 1988. It provides support for a public address at the university by a prominent scholar or practicing professional in the field of international relations. The series is made possible by a gift from the late Robert G. Wesson, a scholar of international affairs, prolific author, and senior research fellow at the Hoover Institution.

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Walter P. Falcon
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This posting, my eighth annual edition, comes again from our mid-sized corn, soybean, and cattle farm in Linn County, Iowa.  My wife and I may not be typical owners, but our farming operation is a fair representation of what is happening in rural America. The overwhelming reaction for 2019 is, “Wow, what a difference a year makes.”  In 2018, growing conditions were practically perfect; in 2019, almost nothing has gone right.

Not since the early 1980s can I recall seeing so many glum faces around the farmer coffee table at the local diner.   And it is more than just the lousy coffee that prompts the scowls. Our spring was the wettest in recorded history.  There was severe flooding from both the Mississippi and Missouri Rivers, and from most of the streams in between.  Plantings of corn and soybeans were delayed, and substantial acres did not get planted at all—more than 400,000 acres in Iowa alone.  About 75% of the corn is typically planted by May 15th in our region. This year, less than 25% was in the ground, and the wet cold soil left crops that were planted looking yellow and puny.

“Prevented acres” (those fields that farmers were prevented from planting) became a hot topic of conversation, as everyone re-read their crop-insurance contracts to see what was needed to qualify, and who actually determined what was prevented. Discussions on whether it was wiser financially to plant late, with expectations of a small crop that could well suffer frost damage, or whether to claim prevention, led to some very interesting new principles of cost accounting!  Calculations and comparisons were complex, but farmers who chose the prevent option received about $400 per acre. Those who planted very late, and rolled the dice with respect to their regular crop-insurance, still eagerly await harvest outcomes.

If April 15-June 15 was unbelievably wet, June 15-August 15 was unbelievably dry during the critical period for corn pollination and grain filling.  Rainfall was 4 inches less than normal, and inch-wide cracks opened in the soil. Corn on sandy knolls began to burn and many stalks failed to “shoot” ears. Many of the ears that were produced were small and poorly filled with kernels. Pastures also dried up, and we began feeding supplemental hay to our cow herd in July. During the week of August 18th, we finally received two inches of rain—too late to make much difference to the corn crop, but offering some hope for reasonable soybean yields. One of my more sacrilegious friends suggested that the mid-August rain was god’s way of suckering famers into farming for another year. 

To make matters worse, eastern Iowa now has a new invasive pathogen—tar spot in corn.  Tar spot is a fungus that literally blew in from Mexico.  Spores rode winds from a hurricane into Indiana and Illinois in 2016, and now they have migrated to Iowa.  Our corn varieties have little resistance to it, and while breeders will probably breed in resistance within a couple of years, farmers are now short-run losers.  Yesterday’s debate over coffee was whether, with both low crop prices and low expected yields, it paid to spray aerially for tar spot and other fungi. (The application costs about $25 per acre for both the fungicide and for flying it on.)  For our farm, we decided to take our chances on damages and not to spray. Who knows if that was the right decision.

Perhaps the only thing that farmers agree on is that NO ONE has a good grasp on the size of the U.S. corn crop—not farmers or traders, and certainly not the Department of Agriculture (USDA).  For whatever reasons, local producers believe that the USDA is fudging the expected numbers upward on both expected yields and planted acre, with consequent negative effects on corn markets. A sad sign of the times occurred during a recent mid-western tour of crop conditions.  The tour included members of USDA’s statistical team.  But after threats to their personal safety were deemed credible, the USDA recalled its members from the tour. No one whom I know ever thought that the comment “farmers were up in arms” would need to be taken literally.

More generally, the growing frustration and anger with Washington has replaced talk about the best new tractors and pickups—no one is buying.  Farmers were furious over the Environmental Protection Agency’s (EPA) decision to provide waivers on ethanol requirements for 31 refineries, and a failure to move more generally to an E15 standard.  And after a decades-long attempt to build an Asian soybean market, farmers feel seriously victimized by the President’s trade policy (though interestingly, it is often the USDA and the EPA rather than the President who are blamed). Farmers will certainly cash the checks from the new $14 billion Market Facilitation Plan, but they are extremely worried about the loss of long-term market shares.  Farmers who grow either soybeans or corn in our county this year will receive (potentially) $66 per acre. Only the first half ($33) of the payment is now guaranteed; the remaining half of the payment is conditional on what the USDA says are “market conditions and trade opportunities.” Farmers are still scratching their heads about the operational meaning of those concepts.

In some years, strong livestock profits help offset poor crop yields and prices. But 2019 has not been one of those years.  Whereas 2018 saw quite high profits from pigs, 2019 saw a decline in lean pork prices from $.92 per pound in May to $.62 in August. Pork exports were disrupted by trade arrangements with Mexico. And in China, despite needs arising from African swine fever, the 66% tariff caused a 4% decline in pork shipment from the U.S. during the first half of 2019. Cattle fared little better.  Prices for slaughter steers started at about $1.40 per pound in March. But by August, prices had slipped to about $1.05 per pound.  To add insult to injury, a fire caused temporary closure of a very large packing plant in Kansas, which slaughters about 6,000 head per day (5% of total U.S. capacity). This accident, in turn, caused an overnight drop of $0.10 per pound.  The $0.45 per pound drop in price between March and August of “what might have been” tallies up to the equivalent of about $500 per animal—the difference between very handsome profits and devastating losses.

Taken together, readers now understand why my report this year has taken the form of a lament. In a recent Farm Futures survey of 1,150 farmers, 53% said that 2019 was the worst year they had ever experienced. And readers will also understand why the Secretary of Agriculture, Sonny Perdue, was roundly booed for his attempt at humor during a recent farm tour: “What do you call two Iowa farmers locked in a basement—a ‘whine’ cellar.”

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The State Fair is a big deal for Iowans. (So big, in fact, that by law public schools cannot start until the Fair is over.)  In 2019, more than 1 million visitors participated in state-fair activities, which is remarkable in a state with a total population of only 3.2 million, and with only three cities of greater than 100,000 in population. Of course, this year’s attendance, in preparation for the Iowa political caucuses, was inflated by an invasion of politicians and media personnel! During fair week, 24 Democratic presidential candidates showed up—22 on a single weekend. They not only cluttered the fair concourses, but they also tied up the airway, internet, and transport systems.

It was quite a spectacle.  There were the obligatory candidate pictures—viewing the sculpted butter cow, eating corn dogs, turning steaks on a grill, and for the geographically venturesome, a shot in front of a corn ethanol plant. Some even tried the dill-pickle ice cream. And poor “Captain,” Iowa’s largest boar (1,254 pounds), was exhausted by week’s end by all of the celebrity photo ops!

With all of the visiting candidates, Soap Box Corner was unusually crowded.  Joe Biden and Elizabeth Warren essentially tied in the informal straw poll at the fair, with Pete Buttigieg and Bernie Sanders finishing third and fourth.  For the most part, candidates said what farmers wanted to hear. Speakers generally spoke in favor of ethanol (some even liked E15); were against the current trade policy; and were mostly silent on climate change. Wearing my professorial hat, I am not sure that many of them would pass Ag101—even using Stanford’s liberal grading standards. 

Few candidates spoke with much nuance about agriculture. Many seemed to be thinking about an agriculture that perhaps existed in Iowa during the 1960s—one in which younger farmers had farming systems producing a broad array of crop and livestock products. But that is hardly the current reality. What I found most surprising was the implicit view that Iowa’s 87,000 famers were a set of small homogeneous farm units. In fact, there are huge economic and political differences among three groups.

One set contains a sizable number of retired farms which typically own moderate amounts of land that they now rent to others.  For this group, health insurance, declining land rents and social security are uppermost in their minds.  A second group is a younger, more venturesome group of farmers, who may own 160 acres, but who are aggressively trying to buy or rent an additional 1,000-2,000 acres. They also carry large loans for land and for huge machinery inventories.  For them, trade policy, interest rates, crop insurance, and health insurance are central matters of concern.  There is also a third set, comprised of multiple family generations, often organized as family corporations, who are intermediate in their ownership patterns, debt obligations, and political concerns.  None of the three groups is very happy, but it is the second set that has local bankers worried, since delinquent farm loans have now risen to a 20-year high.

But farmers often sound like baseball players. “Just wait until next year.”

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Perhaps next year—god willing and the creek don’t rise—my report will be more upbeat.   At least we will know the outcome of the Iowa Caucuses. Maybe we will also know if the August 29 Bloomberg Report,“ U.S. Farmers May be Angrier, but Their Trump Love is Growing”, continues into 2020. But as 2016 showed, what farmers tell pollsters about their political preferences always deserves a fair amount of skepticism. On our farm, we will at least know the actual size of the 2019 corn crop, and whether our switch from Angus to Simmental bulls increased the rates-of-gain of our steers. 

In the meantime, it is back to Stanford—without a pitchfork—to duel with some of the brightest of the “Z” generation, and to work on a global food-security assessment for 2050.

 

During the academic year, Walter Falcon is the Helen C. Farnsworth Professor of International Agricultural Policy, Emeritus, at Stanford; and senior fellow, emeritus, at the the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment. He is the former deputy director of the Center on Food Security and the EnvironmentHe spends summer with his wife, Laura, on their farm near Marion, Iowa. (wpfalcon@stanford.edu

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Efficient responses to climate change require accurate estimates of both aggregate damages and where and to whom they occur. While specific case studies and simulations have suggested that climate change disproportionately affects the poor, large-scale direct evidence of the magnitude and origins of this disparity is lacking. Similarly, evidence on aggregate damages, which is a central input into the evaluation of mitigation policy, often relies on country-level data whose accuracy has been questioned. Here we assemble longitudinal data on economic output from over 11,000 districts across 37 countries, including previously nondigitized sources in multiple languages, to assess both the aggregate and distributional impacts of warming temperatures. We find that local-level growth in aggregate output responds non-linearly to temperature across all regions, with output peaking at cooler temperatures (<10°C) than estimated in earlier country analyses and declining steeply thereafter. Long difference estimates of the impact of longer-term (decadal) trends in temperature on income are larger than estimates from an annual panel model, providing additional evidence for growth effects. Impacts of a given temperature exposure do not vary meaningfully between rich and poor regions, but exposure to damaging temperatures is much more common in poor regions. These results indicate that additional warming will exacerbate inequality, particularly across countries, and that economic development alone will be unlikely to reduce damages, as commonly hypothesized. We estimate that since 2000, warming has already cost both the US and the EU at least $4 trillion in lost output, and tropical countries are >5% poorer than they would have been without this warming.

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National Bureau of Economic Research
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Marshall Burke
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Key messages:

  • The Congo Basin is rich in biodiversity and stores an estimated 25%-30% of the worlds tropical forest carbon stocks. As agricultural land becomes increasingly scarce in Southeast Asia, and regulatory pressures continue to intensify, the Congo Basin could become the next frontier for oil palm expansion. Most of the roughly 280 million hectares (Mha) of additional land suitable for oil palm in the Congo Basin are found in the Democratic Republic of Congo (60%), Cameroon (11%) and the Republic of Congo (10%).
  • Many heavily forested countries in the Congo Basin are setting national targets to increase production to meet national and regional demands. Land area allocated to oil palm increased by 40% in the Congo Basin and five additional top-producing countries in Africa between 1990 and 2017. Without intervention, future production increases in the region will likely come from expansion rather than intensification due to low crop and processing yields, possibly at the expense of forest.
  • Sustainability strategies initiated by companies and aimed at certifying palm oil mills are unlikely to be effective at curbing deforestation in the Congo Basin. Smallholder farmers are an engine of growth in the regions palm oil sector, and recent evidence suggests they are actively clearing forest to expand. Because of the proliferation of non-industrial processing facilities (artisanal mills), a substantial fraction of the palm oil produced by smallholders never passes through a company's jurisdiction. Smallholders are also disadvantaged by power imbalances and limited access to technical and financial resources. Including smallholders in sustainability strategies offers opportunities to achieve multisectoral goals.
  • Recommendations to improve the sustainability of the palm oil sector in the Congo Basin include (1) improving access to finance for smallholders and non-industrial mill managers; (2) implementing policies to safeguard natural resources and facilitate access to appropriate market opportunities that offer incentives to prevent future deforestation; (3) intensifying production by replanting aging plantations, rehabilitating abandoned plantations with disease-resistant and high-yielding varieties, and increasing fertilization, without further expansion into high conservation value or high carbon stock forest areas; and (4) improving processing capacity and extraction rates by upgrading mill technologies. Sustainable palm oil development in the Congo Basin will require careful consideration of the governance, institutional, environmental and socioeconomic factors that underpin the complex regional supply chains.
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Center for International Forestry Research Center for International Forestry Research
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Rosamond L. Naylor
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Accurate measurements of maize yields at field or subfield scales are useful for guiding agronomic practices and investments and policies for improving food security. Data on smallholder maize systems are currently sparse, but satellite remote sensing offers promise for accelerating learning about these systems. Here we document the use of Google Earth Engine (GEE) to build “wall-to-wall” 10 m resolution maps of (i) cropland presence, (ii) maize presence, and (iii) maize yields for the main 2017 maize season in Kenya and Tanzania. Mapping these outcomes at this scale is extremely challenging because of very heterogeneous landscapes, lack of cloud-free satellite imagery, and the low quantity of quality ground-based data in these regions.

First, we computed seasonal median composites of Sentinel-1 radar backscatter and Sentinel-2 optical reflectance measures for each pixel in the region, and used them to build both crop/non-crop and maize/non-maize Random Forest (RF) classifiers. Several thousand crop/non-crop labels were collected through an in-house GEE labeler, and thousands of crop type labels from the 2015–2017 growing seasons were obtained from various sources. Results show that the crop/non-crop classifier successfully identified cropland with over 85% out-of-sample accuracy in both countries, with Sentinel-1 being particularly useful for prediction. Among the cropped pixels, the maize/non-maize classier had an accuracy of 79% in Tanzania and 63% in Kenya.

To map maize yields, we build on past work using a scalable crop yield mapper (SCYM) that utilizes simulations from a crop model to train a regression that predicts yields from observations. Here we advance past approaches by (i) grouping simulations by Global Agro-Environmental Stratification (GAES) zones across the two countries, in order to account for landscape heterogeneity, (ii) utilizing gridded datasets on soil and sowing and harvest dates to setup model simulations in a scalable way; and (iii) utilizing all available satellite observations during the growing season in a parsimonious way by using harmonic regression fits implemented in GEE. SCYM estimates were able to capture about 50% of the variation in the yields at the district level in Western Kenya as measured by objective ground-based crop cuts.

Finally, we illustrated the utility of our yield maps with two case studies. First, we document the magnitude and interannual variability of spatial heterogeneity of yields in each district, and how it varies for different parts of the region. Second, we combine our estimates with recently released soil databases in the region to investigate the most important soil constraints in the region. Soil factors explain a high fraction (72%) of variation in predicted yields, with the predominant factor being soil nitrogen levels. Overall, this study illustrates the power of combining Sentinel-1 and Sentinel-2 imagery, the GEE platform, and advanced classification and yield mapping algorithms to advance understanding of smallholder agricultural systems.

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Remote Sensing of Environment
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George Azzari
Stefania Di Tommaso
Marshall Burke
David Lobell
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Low-intensity tillage has become more popular among farmers in the United States and many other regions. However, accurate data on when and where low-intensity tillage methods are being used remain scarce, and this scarcity impedes understanding of the factors affecting the adoption and the agronomic or environmental impacts of these practices. In this study, we used composites of satellite imagery from Landsat 5, 7, and 8, and Sentinel-1 in combination with producer data from about 5900 georeferenced fields to train a random forest classifier and generate annual large-scale maps of tillage intensity from 2005 to 2016. We tested different combinations of hyper-parameters using cross-validation, splitting the training and testing data alternatively by field, year, and state to assess the influence of clustering on validation results and evaluate the generalizability of the classification model. We found that the best model was able to map tillage practices across the entire North Central US region at 30 m-resolution with accuracies spanning between 75% and 79%, depending on the validation approach. We also found that although Sentinel-1 provides an independent measure that should be sensitive to surface moisture and roughness, it currently adds relatively little to classification performance beyond what is possible with Landsat. When aggregated to the state level, the satellite estimates of percentage low- and high-intensity tillage agreed well with a USDA survey on tillage practices in 2006 (R2 = 0.55). The satellite data also revealed clear increases in low-intensity tillage area for most counties in the past decade. Overall, the ability to accurately map spatial and temporal patterns in tillage should facilitate further study of this important practice in the United States, as well as other regions with fewer survey-based estimates.

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Remote Sensing of Environment
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George Azzari
David Lobell
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Fast, accurate and inexpensive estimates of crop yields at the field scale are useful for many applications. Based on the Google Earth Engine (GEE) platform, we recently developed a Scalable satellite-based Crop Yield Mapper (SCYM) that integrates crop simulations with satellite imagery and gridded weather data to generate 30 m resolution yield estimates for multiple crops in different regions. Existing versions of SCYM typically capture one-third to half of the variation in reported county-scale yields. Using rainfed maize in the US Midwest as an example, this study tested multiple approaches for improving SCYM’s accuracy, including (i) calibrating the phenology parameters of the crop model (APSIM) used to generate training samples for SCYM; (ii) using an ensemble of three crop models (APSIM-Maize, CERES-Maize, and Hybrid-Maize) instead of a single model; (iii) using simulated biomass from the crop models instead of simulated yields to train SCYM, with the former assuming a constant harvest index (HI). Results show substantial improvement in performance, as assessed using reported county yields by USDA-NASS, both from calibrating APSIM phenology parameters and from training SCYM on simulated biomass rather than yields. Using a multi-model ensemble further improves SCYM, although the benefit is limited. The proposed preferred version of SCYM on average captures 75% of the yield variation for 2001–2015 in the 3I states (i.e. Illinois, Indiana and Iowa) where SCYM is trained, with RMSE typically less than 1 t/ha, and explains 41% to 83% of multi-year yield variations when tested across nine Midwestern US states for 2008–2015. This level of accuracy is particularly notable given that only data from 2014 were used to calibrate phenology parameters. The yield estimates for multiple years in multiple states utilized 1184 Landsat tiles, but could be completed in about 2 h per year by using the GEE platform. All approaches tested in this study do not require any site-specific measurements, and thus can be readily extended to other regions and crops.

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Agricultural and Forest Meteorology
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George Azzari
David Lobell
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