Date of Award

8-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical and Civil Engineering

First Advisor

Nicolas Velasquez

Second Advisor

Paul J. Cosentino

Third Advisor

Gary A. Zarillo

Fourth Advisor

Troy V. Nguyen

Abstract

Streamflow in Florida watersheds is influenced by both land cover change and rainfall variability, but separating their contributions is difficult because both have changed over recent decades. This study evaluated rainfall trends and land cover change to determine which better explains flood and drought threshold exceedance across 27 USGS streamflow gauges within the St. Johns River Water Management District (SJRWMD) from 1985 to 2025. Streamflow was characterized using change-point, trend, and variability analyses with a six-threshold exceedance framework. Land cover was quantified using the National Land Cover Database (NLCD), rainfall characteristics were derived from the Analysis of Records for Calibration (AORC) dataset, and within- and between-watershed attribution analyses were performed. Results showed that rainfall controls year-to-year flood and drought exceedance within individual watersheds, with annual rainfall volume as the strongest predictor. In contrast, long-term rainfall and land cover trends explained little variation in exceedance among watersheds. Land cover trends were unrelated to exceedance trends, while rainfall trends showed only weak relationships with drought exceedance. These findings indicate that rainfall is the dominant driver of year-to-year streamflow variability in eastern Florida, whereas explaining long-term watershed differences will likely require a longer observational record, greater rainfall and land cover variability, or hydrologic modeling.

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