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Title: Climate change impact on critical source area (CSAs) identification in a Maryland watershed

item RENKENBERGER, JAISON - University Of Maryland
item MONTAS, HUBERT - University Of Maryland
item LEISNHAM, PAUL - University Of Maryland
item CHANSE, VICTORIA - University Of Maryland
item SHIRMOHAMMADI, ADEL - University Of Maryland
item Sadeghi, Ali
item BRUBAKER, KAYE - University Of Maryland
item ROCKLER, AMANDA - University Of Maryland
item HUTSON, THOMAS - University Of Maryland
item LANSING, DAVID - University Of Maryland

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2016
Publication Date: 1/23/2017
Citation: Renkenberger, J., Montas, H., Leisnham, P., Chanse, V., Shirmohammadi, A., Sadeghi, A.M., Brubaker, K., Rockler, A., Hutson, T., Lansing, D. 2017. Climate change impact on critical source area (CSAs) identification in a Maryland watershed. Transactions of the ASABE. doi:10.13031/trans.59.11677.

Interpretive Summary: This study evaluated the potential effects of climate change on the distribution of runoff, sediment, nitrogen and phosphorus Critical Source Areas (CSAs) in an agricultural watershed that flows into the Chesapeake Bay. The Bay’s location in the US Northeast climate region is expected to cause it to receive the largest increases in annual rainfall and storm intensity of the conterminous US. The spatial and weather data were used to develop input files for the SWAT hydrologic model which was then calibrated against the watershed outlet stream flow of USGS data. The primary objective of this study was to advance our ability on the identification of the CSAs within the watershed that believed to contribute most of the pollutants such as excess nitrogen, phosphorus and/or sediment to the watershed’s estuaries. This method along with the validated SWAT model would help the implementation of best management practices (BMPs) to be focused on specific areas to minimize cost-to-benefits ratios that are aimed at sustaining the health and productivity of agricultural watersheds and ecosystems. This study resulted in the development of a more efficient approach for targeting CSAs or “hotspots” and also enables us to show substantial reduction of pollutants from these targeted areas into the Bay’s estuaries, as they relate to the impact of climate change scenarios.

Technical Abstract: The potential impacts of climate change on Critical Source Areas (CSAs) of surface runoff, sediments, nitrogen and phosphorus, were evaluated in an agricultural watershed of the Chesapeake Bay drainage basin, in the US Northeast climate region. The SWAT model was calibrated for the study watershed and used to establish its baseline response and constituent CSAs under current climate. The calibrated model was then subjected to weather time series downscaled from the CMIP3 GFDL CM2.1 Atmosphere-Ocean Global Circulation Model (AOGCM) for IPCC SRES scenarios B1 (low emissions), A1B (medium emissions) and A2 (high emissions) to predict the watershed’s response to climate change and identify how constituent CSAs may change under future climate. The utility of targeting Best Management Practices (BMPs) to CSAs was assessed by computing advantage ratios that relate the fraction of watershed-generated constituents that emanate from CSAs to the fraction of watershed area occupied by these CSAs. Results indicated that, under current conditions, CSAs occupying 11% to 21% of the watershed area contribute 31% to 45% of constituents, corresponding to advantage ratios of 1.5:1 for runoff control and approximately 3:1 for other constituents. Under climate change scenario B1, constituent yields were predicted to increase by factors of 1.5 to 1.8 at the watershed outlet, from an increase in annual rainfall of 25% predicted by the AOGCM, over current conditions. Under scenarios A1B and A2, constituent yields were predicted to increase by factors of 1.8 to 2.3 over current conditions, from an increase of 30% in annual rainfall. The area of runoff CSAs was predicted to more than triple with climate change, leading to negligible advantage of targeting runoff control BMPs to CSAs under future climate. The areas of sediment, nitrogen and phosphorus CSAs were predicted to increase by factors of 2 to 3 with climate change, causing BMP-targeting advantage ratios to decrease from approximately 3:1 (baseline) to 2:1 (future). While advantage ratios for suspended and dissolved constituents remain favorable, even under future climate, the much larger area predicted to be covered by CSAs (2 to 3 times current values) suggests that stakeholder involvement and community-oriented participatory approaches will be increasingly important for achieving Bay TMDLs with climate change.