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Document Type

Thesis - University Access Only

Award Date

2015

Degree Name

Master of Science (MS)

Department / School

Agricultural and Biosystems Engineering

First Advisor

Laurent Ahiablame

Abstract

In recent years, there has been a considerable conversion of grasslands to croplands, along with concerns over the effects of climate change on streamflow trends in South Dakota (SD). This study investigated the impacts of variability in climate and land use change on water resources in SD by (1) estimating the relative proportion of different flow components in streamflow; (2) evaluating long-term trends in hydro-climatology; (3) assessing decadal variation in streamflow and rainfall; and (4) examining relationships among streamflow, rainfall, and land use. The relative proportions of baseflow and direct runoff in streamflow were estimated from daily streamflow records using the Web-based Hydrograph Analysis Tool (WHAT) program. Long-term streamflow trends from 1951 to 2013 was assessed for 18 selected SD watersheds using a modified Mann-Kendall test for different streamflow conditions (low-moderate-high). Rainfall trends from 21 rain gauging stations located within 50-km of the streamflow gauging stations were also assessed for the same study period. While the modified Mann- Kendall test was applied to estimate streamflow and rainfall trends for the entire study period, the nonparametric Wilcoxon change test was used to evaluate decadal streamflow and rainfall variation between seven decades from the 1950s to 2010s. The nonparametric xi Spearman correlation test and the concept of elasticity were used to examine streamflowrainfall- land use (grassland) relationships in the studied watersheds. Results showed that baseflow contributed 50% to 80% of total streamflow in the majority of eastern and western streams (83% of eastern streams, 58% of western streams), while direct runoff contributed 50% to 80% of total streamflow mostly in western streams (33% western streams, 17% eastern streams). At the same time, baseflow and direct runoff contribution in total streamflow varied between 44% and 80%, and 22% and 56%, respectively in western watersheds, while in eastern watersheds, baseflow and direct runoff contribution in total streamflow varied between 48% and 72%, and 27% and 52% respectively. These results suggest that streamflow was more dependent on baseflow contributions compared to direct runoff in the majority of the western and eastern watersheds. Streamflow trend analysis indicated that SD watersheds exhibited increasing trends in low (50% of watersheds had increasing 1-day minimum and 7-day minimum flow trends) and medium flow conditions (56% watersheds had increasing trends in median daily flow and 39% of watersheds had incraesing trends in daily average flow) whereas, for high flow conditions less than 35% watersheds had incraesing trends in 1-day maximum and 7-day maximum flow. Twenty eight percent of all streams located in eastern SD exhibited significant upward trends in annual streamflow, whereas very few western watersheds showed a significant upward trend (12% of all streams), implying that eastern SD is getting wetter over time. Streamflow change analysis revealed that between the1980s and 1990s, half of the studied watersheds throughout SD showed a significant decline in annual streamflow, whereas, streamflow increased significantly in western watersheds between the 1990s and 2000s. According to the xii elasticity assessment, streamflow is highly influenced by rainfall across the state (84% of eastern watersheds and 59% of western watersheds). Findings from the elasticity analysis revealed that a 10% increase in annual rainfall can increase annual streamflow by 11% to 30% in more than half (62%) of the SD watersheds. In addition, high elasticities were found between grasslands change and annual streamflow in 17% of western watersheds that might be explained by the abrupt grassland conversion and a small percentage of grassland area in western watersheds. Results from streamflow elasticity analysis were comparable to correlation analysis results, which exhibited a significant correlation between annual streamflow and annual rainfall in 78% of watersheds, while streamflow was significantly correlated with land use in 50% of the studied watersheds. In addition, streamflow appears to be more correlated to rainfall in western South Dakota, while equal number of eastern watersheds were correlated with rainfall or grassland area.

Library of Congress Subject Headings

Streamflow--South Dakota
Landscape changes--South Dakota
Land use, Rural--South Dakota
Climatic changes

Description

Includes bibliographical references (pages 101-127)

Format

application/pdf

Number of Pages

139

Publisher

South Dakota State University

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Rights Statement

In Copyright