Date of Award

January 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geography & Geographic Information Science

First Advisor

Paul E. Todhunter

Abstract

ABSTRACT

Although numerous studies have examined hydroclimatic and climatic changes in our national parks, no previous studies have examined historical temperature, precipitation and hydroclimatic changes at Theodore Roosevelt National Park (South Unit). Documenting historical trends in temperature, precipitation and hydroclimatic variables is important for understanding present and future changes in vegetation and wildlife.

I used 117 (1895 - 2011) years of temperature and precipitation data obtained from the PRISM data network to construct the historical climatic water budget time series based upon the Thornthwaite water-budget model. Trend lines and descriptive statistics are used to analyze the monthly, seasonal and annual climatic variables.

The results reveal positive trends in the mean annual (Tmean) and mean minimum (Tmin) air temperatures at the 95% significance level. The mean annual air temperature increased at a rate of 1.6°C per century, while the mean annual maximum (Tmax) and minimum air temperatures increased at rates of 0.9°C and 2.1°C per century, respectively, over the period of record (P-O-R). On a seasonal basis, a statistically significant positive trend was observed in all seasons for Tmin and three seasons (winter, fall, spring) for Tmean air temperatures. Tmax showed a significant positive trend for the summer and winter seasons. On a monthly basis, all months except June experienced a significant warming trend in the mean minimum air temperature. The various time series reveal a tendency toward climate warming with significantly warmer winter and summer periods. The warming is greater in the mean minimum temperature than in the mean maximum temperature in the time series, resulting in a statistically significant decrease of the diurnal temperature range (DTR). Annual precipitation has decreased at a rate of 13.8 mm per century over the same period, although the trend is not statistically significant. Negative precipitation trends were observed in the summer and winter seasons. The winter season trend was statistically significant with a rate of -11.2 mm per century.

The Thornthwaite water balance model output variables indicated a significant increase in the mean annual potential evapotranspiration, and annual moisture deficit, and a statistically significant decrease in annual actual evapotranspiration, annual snow storage and the annual ratio of actual to potential evapotranspiration. The study site's increasing temperature and decreasing precipitation are consistent with global warming projections, which are driving a higher moisture deficit.

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