|LEE, SANGCHUL - University Of Maryland|
|YEO, IN-YOUNG - Collaborator|
|HIVELY, DEAN - Us Geological Survey (USGS)|
|LANG, MEGAN - Us Fish And Wildlife Service|
|SHARIFI, AMIR - University Of Maryland|
Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2017
Publication Date: 6/25/2018
Citation: Lee, S., Yeo, I., Sadeghi, A.M., McCarty, G.W., Hively, D., Lang, M., Sharifi, A. 2018. Comparative analysis of hydrological responses of two adjacent watersheds to climate variability and change scenarios using SWAT model. Hydrology and Earth System Sciences. 22(1):689-708.
Interpretive Summary: Despite of significant restoration efforts, the health of the Chesapeake Bay continues to deteriorate, due in part to the excessive nutrients and sediment loadings from agricultural land. This problem is expected to exacerbate by climate change impacts. The focus of this study was to evaluate the impacts of climate variability and changes on hydrological processes in agricultural lands and to understand how those impacts influence nitrate export from two adjacent agricultural watersheds that are similar in size, but different in soil characteristics, using Soil and Water Assessment Tool (SWAT) model. Climate sensitive scenarios were tested, including increased in carbon dioxide, increased precipitation, and increased air temperature. A SWAT model was first calibrated and validated, using historic records of monthly stream flow and nitrate loads over 2001-2014. We then used the SWAT simulations from 2001 to 2014, as a baseline scenario, and compared the results from the predicted model scenarios from two watersheds. Differences in hydrological response observed was primarily due to the contrasting land use and soil characteristics of the two watersheds, which greatly affected the water and nutrient transport mechanisms and pathways. Overall, the model results showed that under climate change scenarios, annual stream flow and nitrate loads were expected to increase by 40% and 39%, respectively, compared to the baseline scenario. Furthermore, water and nitrate budgets in the watershed with more percentage of croplands were more variable to climate sensitivity and change scenarios, especially during summer crop growing seasons due to sensitive crop responses to modified climate conditions. Watershed managers and regulators can use the results of this study to better implement their conservation practices in the face of climate change.
Technical Abstract: The Chesapeake Bay (CB) is the largest and most productive estuary in the United States (US). Despite significant restoration efforts, the health of the Bay has continued to deteriorate, primarily due to excessive nutrient and sediment loadings from agricultural land. The water quality problem is expected to exacerbate under climate variability and changes. However, relative impacts of climate change on agricultural land and resulted nutrient loads are largely unknown. This study evaluates the impacts of potential climate variability and changes on the hydrological processes and nitrate export from two adjacent agricultural watersheds in the Coastal Plain of Chesapeake Bay Watersheds (CBW), using Soil and Water Assessment Tool (SWAT). We prepared six climate sensitive scenarios to assess the individual effects of variations in CO2 (590 and 850 ppm), precipitation (11 and 21 %) and temperature (2.9 and 5.0 °C) and considered the predicted climate change scenarios by Special Report on Emissions Scenarios (SRES) A2 scenario and five general circulation models (GCMs). SWAT was calibrated and validated using historic records of monthly stream flow and nitrate loads over 2001-2014, and calibration results were satisfactory to reproduce observed streamflow and nitrate loads for both watersheds. Using the SWAT simulation from 2001 to 2014 as a baseline, results under climate sensitivity and change scenarios were analyzed for annual and seasonal water and nitrate budgets, and compared for two watersheds. Difference in hydrological responses from two watersheds was primarily due to contrasting land use and soil characteristics, which greatly affected the water and nutrient transport mechanisms and pathways. Precipitation increase of 21% and elevated CO2 concentration by 850 ppm resulted in the greatest increase in stream flow and nitrate loads by ~ 50 % and ~ 52 %, respectively, in comparison to the baseline scenario. Temperature increase of 5.0 °C reduced stream flow and nitrate loads by ~ 12 % and ~ 13 %, respectively. Under climate change scenarios, annual stream flow and nitrate loads were expected to increase by 40 % and 39 %, respectively, compared to the baseline scenario. Water and nitrate budgets in the watershed with more percentage of croplands were more variable to climate sensitivity and change scenarios, especially during summer crop growing seasons due to sensitive crop responses to modified climate conditions. The watershed dominated by poorly-drained soils showed lower variation in nitrate export compared to one dominated by well-drained soils during winter seasons, due to a greater denitrification potential. Climate change could alter current agricultural activities strongly associated with hydrological processes and require more efficient conservation practices to adapt to modified conditions. To cope with climate change-driven modification in this region, a comprehensive understanding on agricultural activities and conservation practices under climate change would be required.