Monitoring agricultural cropping patterns across the Laurentian Great Lakes Basin using MODIS-NDVI data

The Moderate Resolution Imaging Spectrometer (MODIS) Normalized Difference Vegetation Index (NDVI) 16-day composite data product (MOD12Q) was used to develop annual cropland and cropspecific map products (corn, soybeans, and wheat) for the Laurentian Great Lakes Basin (GLB). The crop area distributions and changes in crop rotations were characterized by comparing annual crop map products for 2005, 2006, and 2007. The total acreages for corn and soybeans were relatively balanced for calendar years 2005 (31,462 km and 31,283 km, respectively) and 2006 (30,766 km and 30,972 km, respectively). Conversely, corn acreage increased approximately 21% from 2006 to 2007, while soybean and wheat acreage decreased approximately 9% and 21%, respectively. Two-year crop rotational change analyses were conducted for the 2005–2006 and 2006–2007 time periods. The large increase in corn acreages for 2007 introduced crop rotation changes across the GLB. Compared to 2005–2006, crop rotation patterns for 2006–2007 resulted in increased corn–corn, soybean–corn, and wheat–corn rotations. The increased corn acreages could have potential negative impacts on nutrient loadings, pesticide exposures, and sediment-mediated habitat degradation. Increased in US corn acreages in 2007 were related to new biofuel mandates, while Canadian increases were attributed to higher world-wide corn prices. Additional study is needed to determine the potential impacts of increases in corn-based ethanol agricultural production on watershed ecosystems and receiving waters. Published by Elsevier B.V. at both local and regional scales (Hodge, 2002; Huston and Marland, 2003; Pimentel and Patzek, 2005; Searchinger et al., 2008). Environmental assessments often need site-specific information about crop distributions (e.g., SWAT, 2007). Researchers are * Corresponding author. Tel.: +1 919 541 4256. E-mail address: [email protected] (R.S. Lunetta). 1 Current address: Humboldt State University, Office of Research and Graduate Studies, Arcata, CA 95521, United States. 0303-2434/$ – see front matter . Published by Elsevier B.V. doi:10.1016/j.jag.2009.11.005 pattern of crop change are generally unavailable from the estimated agricultural statistics. Researchers are thus forced to use unrealistic assumptions of crop distributions and crop rotation patterns, which may lead to high uncertainties in modeling predictions of potential environmental impacts. Themapping of crops using remote sensor data has shown good potential for characterizing the extent, distribution and condition of croplands (Moran et al., 1997; Frolking et al., 1999; Doraiswamy et al., 2005; Thenkabail et al., 2009). The Moderate Resolution Imaging Spectroradiometer (MODIS) data, which combine moderate spatial resolution (250 m) and a high temporal resolution (1–2 day repeat cycle), were found to be particularly useful to differentiate general cropland versus non-cropland and to categorize individual croptypes (Lobell andAsner, 2004;Changetal., 2007; is among themost industrialized regions in theworld, the southern portions of the GLB are prime areas for corn, soybean and other types of agricultural crop production (USEPA, 2008). GLB R.S. Lunetta et al. / International Journal of Applied Earth Observation and Geoinformation 12 (2010) 81–88 82 Wardlow et al., 2007; Wardlow and Egbert, 2008). The phenologybased categorization (or time-series analysis) of MODIS-NDVI (Normalized Difference Vegetation Index) is one of the most used approaches (DeFries and Townshend, 1994; Shao et al., 2010; Hansen et al., 2003). Most previous MODIS-NDVI crop-mapping applications have focused on single year crop mapping efforts. MODIS-NDVI datasets have rarely been used to study the crop changes or rotations overmultiple years. The potential ofmulti-year MODIS-NDVI crop mapping has not yet been fully exploited. The principle objective of this research was to examine the cropland changes across the Great Lakes Basin (GLB) using map products derived from MODIS-NDVI data. The GLB is a region thought to have undergone significant changes in cropping patterns, because the US government implemented substantial subsidies to encourage corn ethanol production during the study period (2005–2007). Research questions of interest included the following: (1) how did crop acreage distributions (i.e., corn, soybean, and wheat) change through the GLB? (2) Was there a change in crop rotational patterns due to increased corn ethanol demand? (3) If yes, were there any geographic differences associated with variations in crop rotation patterns across the GLB (i.e., US versus Canadian)? The answers to these questions are particularly important for identifying areas or regions with a high potential for environmental degradation. Two specific research objectives of this paper were to map annual crop distributions across the GLB for 2005, 2006, and 2007, and compare the two-year crop change or rotation patterns for 2005–2006 and 2006–2007.