The Expansion of Agriculture and Its Effects of Evapotranspiration in Brazil’s Newest Agricultural Frontier

Abstract:

Approximately half of the Cerrado has been deforested in Brazil’s drive to develop export-oriented mechanized agriculture. We focus our analysis on Brazil’s newest–and potentially final–agricultural frontier, Mapitoba. Using MODIS Enhanced Vegetation Index (EVI) data, we map land-use change within Mapitoba between 2003 and 2013 with 87% accuracy. During our study period, row-crop agriculture more than doubled, expanding from 1.2 to 2.5 million ha. We use MODIS evapotranspiration (ET) data and quantify the impacts of agricultural conversion on ET in Mapitoba. Monthly ET was, on average, 26 mm mo^-1 higher over areas of natural vegetation for all months except January, February, and March. These 26 mm mo^-1 equate to a 22% (April) to 77% (September) difference in ET rates depending on the month. In January and February, ET occurs at similar (~100%) or slightly higher (~107%) rates over row-crop agriculture than natural vegetation. ET is negatively correlated with single-cropped agricultural area for August through December and April through July across all years. Single-cropped area is positively correlated with ET in February across all years, and January and March across most years. Double-cropping is positively correlated with ET across all years during January, April, and May, and a majority of the study period during February, March, and June. The change in dry season (June-August) ET is linearly related (R² = 0.81) to the cumulative amount of land converted to row-crop agriculture. For every new 1000 ha of row-crops, 1.7 million m³ less water is recycled back to the atmosphere. If row-crop were to expand onto the 8.2 million ha of remnant Cerrado suitable for agriculture in Mapitoba, we estimate an additional reduction of 14 km³ of water each year during these 3 months alone. Land-use-change-induced climate feedbacks may extend the dry season and threaten both the health of the natural vegeation and sustainabiltity of continued agricultural production.