Lunyu Xie Renmin University of China Sarah Lewis UC Berkeley Maximilian Auffhammer UC Berkeley Peter Berck UC Berkeley INTRODUCTION Why I mportant Crop yields are forecasted to decrease by 3046 before the end of the century even under the slowest ID: 1039703
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1. Crop Acreage Adaptation to Climate ChangeLunyu Xie, Renmin University of ChinaSarah Lewis, UC BerkeleyMaximilian Auffhammer, UC BerkeleyPeter Berck, UC Berkeley
2. INTRODUCTION
3. Why Important?Crop yields are forecasted to decrease by 30-46% before the end of the century even under the slowest climate warming scenario.Farmers may adapt to the expected yield changes by growing crops more suited to the new climate.Predicting adaptation behavior is therefore an important part of evaluating the effect of climate change on food and fiber production.
4. Research QuestionHow weather and soil determine crop location and how, in the face of warmer weather, crop adaptation varies across quality levels of soil.Panel data for 10 years from a group of US states situated in a north-south transect along the Mississippi-Missouri river system.
5. WhereParts of 6 states making up the cornbelt.Size. The line is 840km. Here to Bremen. Top to bottom, here to Marseille.
6. Figures 1: Observed Crop Coverage along the Mississippi-Missouri River SystemNotes: Graphs display observed coverage shares for corn, soy, rice, cotton, and other land use, in the six states along the Mississippi-Missouri river corridor. They are average shares over 2002-2010.
7. Figure 2: Distribution of Land Capability Classification (LCC) LevelsPrime agricultural soils are absent in southern Iowa and so largely is the corn-soy complex. Similarly, more optimal soils hug the river in Missouri and Arkansas, and so do rice and cotton. Notes: Land Capability Class (LCC) 1 is the best soil, which has the fewest limitations. Progressively lower classifications lead to more limited uses for the land. LCC 8 means soil conditions are such that agricultural planting is nearly impossible.
8. Compare Soil and Corn
9. Modern Econometric Studies…Nerlove’s (1956) examination of crop share response to crop pricesCoverage is a function of lagged coverage, crop price, input prices and other variables. Many ways to elaborate on this basic modelPriceEven the futures price is not predetermined! IV is likely needed always. Wheat rust, known to all but the econometrician.RiskOften the coefficient of variationSum-up conditionLogit in theory, but see below for the real problems with this.Spatial correlationOmitted variables change slowly over the landscape. Cause spatial autocorrelation.
10. DATA
11. Geospatially explicit data on Land coverSoil characteristicsWeatherClimate change scenarios 4km by 4km grid10 yearsIowa, Illinois, Mississippi, and part of Wisconsin, Missouri, and ArkansasData Summary
12. Data: Land UseCropland Data Layer (CDL) available annually from 2000 to 2010 (USDA NASS) for the six states. Land cover is divided intoMajor cropsOther crops Agricultural landNon-crop and wild land (denominator)Urban and water bodies
13. AccuracyThe limiting factor in accuracy is the number of ‘ground truthed’ plots. Large crops like corn and soy, high accuracy.Minor crops, like oats, pasture, irrigated pasture, low accuracyHence the aggregate category of wild and minor.
14. Data: Soil CharacteristicsUSDA’s U.S. General Soil Map (STATSGO2)Percent clay, sand, and silt, water holding capacity, pH value, electrical conductivity, slope, frost-free days, depth to water table, and depth to restrictive layerA classification system generated by the USDALand Capability Class (LCC)
15. Data: Weather VariablesPRISM data processed by Schlenker and Roberts (2009)A 4km by 4km spatial resolutionWith a daily level of temporal resolutionDegree days are calculated from daily highs and lows.Using a fitted sine curve to approximate the amount of hours the temperature is at or above a given threshold (Baskerville & Emin, 1969)
16. Fewer bins and more monthsWe process the degree days by broad bins,Above 10 planting, cotton above 15Above critical (e.g. 29 corn, 30 soy, and 32 cotton and rice.)And then classify weather further by months and planting or growing season.Add interaction between over 30c and precip. By month.
17. Weather has cross section variationNorth to SouthCold to hotEast to WestWet to dry
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20. Comparison: Sweden is drier than Midwest
21. Data: Climate Change ScenariosClimate Wizard (http://www.climatewizard.org/)Ensemble average, SRES emission scenarioA1B and A2PDF’s of 4km squares, for 2080, of Temperature and Precipitation
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23. ECONOMETRIC SYSTEM
24. …… (1)where is the fraction of land in year that was allocated to crop , within each of our 4km grid cells, ; is a vector of determinate factors of revenue from planting crop on plot at year ; is a vector of coefficients; is an error term; is a suitable transformation with its domain on the unit interval. A Proportion Type Model
25. Considerations for a transformation for a proportions modelsLinear estimation.Many observations zero, many > zero.No need to interpret as choice model.Outside option, land not in major crops well measured.
26. Choice of Form to estimateBerry 1994 (within logit framework): We use a ratio transformation (not logit): .We estimate by tobit. Share of residual land, S0, is never zero.
27. Expected shares We simulate () by taking draws from a left truncated normal distribution with mean 0, standard deviation and truncation at . We calculate for each draw and take the averages.
28. Heteroscedasticity, which would make straightforward tobit estimation inconsistent.Solution: estimate local Tobit models, each for only one county and its neighbors.Neighbors of county : counties whose centroids are within 70 km distance of the centroid of county . Spatial Correlation
29. Where is the share of crop planted at grid cell in year ; is a vector of substitute crop shares planted in year ; is a vector of soil conditions; is a vector of degree days by month in the last growing season (April through November in year ); is a vector of degree days by month in the current planting season (April through June in year ) is a vector of precipitation by month in the last growing season; is a vector of precipitation by month in the current planting season; are vectors of interactions of degree days above 30 oc and precipitation levels in the same month. Explanatory Variables
30. ESTIMATION RESULTS
31. Significance
32. Simulation for Unit Change in WeatherFigure 4: Distribution of Crop Share Changes with Unit Change in Temperature and Precipitation
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35. How Soil Affects Crop Adaptation…
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38. CLIMATE CHANGE IMPACTS
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44. CONCLUSION
45. Rice and cotton spread north, while the average shares of corn and soy decrease in the north and increase in the south. There is less crop adaptation on prime soils than on lower quality soils. A significant makeover of major crop distribution is not likely to happen.