Fertilizer management is key to realizing yield and water quality benefits from cover cropping.
Crop field with dark clouds in the sky; Credit: Dave Hoefler via Unsplash
Authors: Cibin Raj and Marali Kalra
What is the issue?
In the coming decades, the watersheds of the Chesapeake Bay region are expected to experience rising temperatures and more extreme precipitation events, which has the potential to impact crop yields and worsen existing water quality problems. Simultaneously, the region is undergoing a trend toward urbanization, which places additional stress on agricultural systems in the watershed. Hydrology and water quality models like the Soil and Water Assessment Tool (SWAT) can help us understand how these long-term climate and land use changes will affect agricultural production and water quality in the region.
What did we find and why does it matter?
Figure 1. Decreases in annual average crop nutrient uptake over the three 30-year evaluation periods: past (1991-2020), near future (2021-2050), and far future (2051-2080). Bar heights show ensemble averages while ranges show ensemble range.
Increasing heat stress causes a steady decline in crop yield over time across the Susquehanna River Basin (SRB), the largest tributary to Chesapeake Bay. For example, corn yield is estimated to decline by 15% in the future (2051-2080) compared to the current yield. Rising summer temperatures (annual average temperature rising from 10 degrees Celsius in the period 1991-2020 to 13 degrees Celsius in 2051-2080) is projected to inhibit crop growth, leading to decreased nutrient uptake (Figure 1) and increasing nutrient losses from agricultural fields (Figure 2).
Water quality is also projected to worsen over the course of the simulation period. Annual average sediment load at the SRB watershed outlet is projected to be 21% higher between 2051 and 2080 than between 1991 and 2020. Total nitrogen load is projected to increase by 10% and total phosphorus load by 22%.
Figure 2. Upward trends in losses of organic N and leached N from agricultural lands in the SRB over the period 1991-2080. Blue lines show ensemble means, gray shading shows ensemble range.
These results show that future climate and land use change will have substantial negative impacts on both agricultural productivity and downstream water quality. Farmers will need to adjust planting and harvest times to minimize summer temperature stress on crops, while watershed managers in the Chesapeake Bay watershed will need to prepare for accelerating water quality challenges in the future.
What did we do?
We developed a SWAT model for the SRB using Coupled Model Intercomparison Project Phase 6 (CMIP6) precipitation and temperature projection data, which consist of historical and projected values from an ensemble of 7 general circulation models (GCMs), and USGS urbanization projections for the Chesapeake Bay, based on land use change data for 2017, 2025, 2035, 2045, and 2055 at the NHD+ (national hydrology dataset) catchment scale, and then aggregated to the hydrologic unit code level 12 (HUC12) scale for use in SWAT. We simulated crop yield and nutrient losses in the SRB over the period 1991-2080. We divided the simulation period into three 30-year time periods (recent past 1991-2020, near future 2021-2050, far future 2051-2080) and computed time period averages for all values to help distinguish long-term trends from short-term variability.
Publications completed for this work
Marali, K., & Cibin, R. (in preparation). Effects of indicator selection on apparent ecosystem health: A case study of climate and land use change in the Susquehanna River Basin.
Rohith, A. N., & Cibin, R. (2024). An extremes-weighted empirical quantile mapping for global climate model data bias correction for improved emphasis on extremes. Theoretical and Applied Climatology, 155(6), 5515–5523. https://doi.org/10.1007/s00704-024-04965-z
Rohith, A. N., Mejia, A., & Cibin, R. (2024). The selection of global climate models for regional impact studies should consider information from historical simulations and future projections. Earth Systems and Environment, 8(3), 693–703. https://doi.org/10.1007/s41748-024-00410-3
