Impact of anthropogenic activities on hydroclimatological variables

Kuk Hyun Ahn, Purdue University

Abstract

The natural environment has been significantly affected by anthropogenic activities. Between 1700s and 2000s, agricultural land area had quintupled and the extent of natural vegetation was globally reduced by half. Furthermore many scientists argue that the recent rise in CO2 levels in the atmosphere is mainly due to anthropogenic activities. Anthropogenic activities may also play a crucial role in the change of the hydro-climatologic variables. In this study, impact of anthropogenic activities on two representative hydro-climatologic variables, temperature and streamflow, is investigated. The variations in temperature occur over larger spatial and time scale, and hence the United States is adopted for studying the impact on temperature. The continental United States includes most of the existing climate types in its large size and geographic variety. On the other hand, streamflow is affected by local environmental factors, including land cover condition and dam construction, and thus it is investigated based on a small regional area. The three objectives of this study are to: (1) evaluate the impact of anthropogenic activities on temperature in the continental U. S., and compare the impact of anthropogenic activities with natural variability using the AR4 climate models, (2) quantify the change in streamflow by considering both the natural factors and anthropogenic activities, and (3) investigate the impact of land cover change on extreme streamflow. The first objective is to detect the changes in temperature in the continental United States (CONUS) and attribute these changes to anthropogenic activities by applying the Detection and Attribution methodology. The CONUS is divided into ten regions by using the K-mean clustering method. For each region, the Mann-Kendall trend analysis is used to examine the magnitude of change in observed temperature data as well as the data from eight climate models and an ensemble from all climate model outputs. Then the optimal fingerprint method is used to analyze the impact of anthropogenic activities on temperature changes. The results show the trends in the observed temperature of the entire CONUS over the 20th century lie inside the range expected from natural internal climate variability. In the regional analysis, the western U.S. is affected the most from the anthropogenic activities, based on both the results from the optimal fingerprint based detection and attribution analysis, and from comparison of trend between observed and simulated data using the Mann-Kendall test. In the second objective, the roles of climate impact and anthropogenic activities on streamflow are evaluated using historical streamflow records, in conjunction with trend analysis and hydrologic modeling. In this study, four U.S. states, including Indiana, New York, Arizona and Georgia area used to represent various level of human activity based on population change and diverse climate conditions. Four hydrologic modeling methods, including linear regression, hydrologic simulation, annual balance, and Budyko analysis are then used to quantify the amount of climate impact and anthropogenic activities on streamflow. In conclusion, the results indicate that the impact of anthropogenic activities is higher on streamflow at most gauging stations in all four states compared to climate impact. The third objective is to investigate the effect of land cover change on the duration and severity of high and low flows by using the Soil Water Assessment Tool (SWAT) model and copulas. High and low flows are defined in terms of percentiles of streamflow. Two watersheds, which have different dominant land covers within the Ohio River basin, are employed to carry out this study. The results show that land cover change explicitly affects the duration and severity of both high and low flows. Increase in the forest area leads to a decrease in the duration and severity in high flow; its significant impact is observed in extreme high flows. Overall, the results presented in the dissertation indicate that the impact of anthropogenic activities plays an important role in the hydrologic system and certainly should be considered for a better understanding of the hydrologic system.

Degree

Ph.D.

Advisors

Venkatesh, Purdue University.

Subject Area

Hydrologic sciences|Climate Change|Civil engineering

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