Application of Climate Assessment Tool (CAT) to Estimate Climate Variability Impacts on Nutrient Loading from Local...

Area of Science:

• Environmental Science
• Hydrology
• Climate Science

Background:

• Global climate models (GCMs) offer future climate scenarios but often lack the spatial-temporal resolution for accurate local watershed impact assessments.
• Downscaling and disaggregating GCM data for local watersheds presents significant challenges, potentially compromising the reliability of hydrological and water quality projections.

Purpose of the Study:

• To apply the US-EPA's Climate Assessment Tool (CAT) for generating localized climate variability scenarios using historical data.
• To assess the impact of projected extreme rainfall and temperature increases on nitrate-nitrogen (NO3-N) and orthophosphate (PO4) loads in the Lower Yazoo River Watershed (LYRW).

Main Methods:

• Utilized the Climate Assessment Tool (CAT) to create localized climate variability scenarios based on historical meteorological data.
• Employed the Hydrological Simulation Program-FORTRAN (HSPF) model, integrated with CAT-generated scenarios, to simulate hydrological processes and nutrient loads.
• Developed specific scenarios for increased rainfall rates, air temperature, and extreme summer rainfall events.

Main Results:

• A 10% and 20% increase in rainfall rate led to a 9.1% and 18% rise in NO3-N loads, and a 12% and 24% rise in PO4 loads, respectively.
• Combined increases in air temperature and rainfall amplified nutrient loads, with a 2.0°C and 20% rainfall increase raising NO3-N by 20% and PO4 by 26%.
• Extreme summer rainfall events (≥10% rainfall increase) significantly elevated monthly NO3-N and PO4 loads by 31% and 41%, respectively.

Conclusions:

• Extreme rainfall events pose a substantial threat to water quality by drastically increasing nutrient loads.
• The Climate Assessment Tool (CAT) is a valuable and flexible instrument for tailoring historical climate data to predict local watershed responses to climate variability.
• Accurate, localized climate impact assessments are crucial for effective water resource management and mitigation strategies in vulnerable watersheds.