Date of Award

Fall 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil & Environmental Engineering

Program/Concentration

Civil Engineering

Committee Director

Xixi wang

Committee Member

Gangfeng Ma

Committee Member

Hua Liu

Call Number for Print

Special Collections; LD4331.E542 Y36 2014

Abstract

Climate, which is the most important factor that influences Net Primary Productivity, has been detected changing all over the world. The confounding effects of step change invalidate the stationarity assumption of commonly used trend analysis methods such as the Mann-Kendall test technique, so previous studies have failed to explain inconsistencies between detected trends and observed large anomalies. In this research, by formulating a trend analysis approach that considers nonstationary due to step changes, trends and extreme occurrences of precipitation, temperature, and runoff in annual, seasonal, and monthly scales were analyzed in a mid-latitude Eurasian steppe watershed in northeast China, and how runoff and NPP responds to climate trends were also examined in the study watershed.

The results indicate that annual precipitation and runoff underwent a marginal step jump around 1994, and annual average temperature underwent a marginal step jump around 1987. If this step change was included in a conventional trend analysis, it could lead to misleading results with regard to the detected trends and their start years.

Both low-frequency and high-frequency precipitation events in the study watershed occurred more often after than before 1994; High average and maximum temperatures, that were higher than 75th percentile of daily average and maximum temperature, occurred more often after than before 1987 in the study watershed, probably as either a result or an indicator of climate change.

In response to these precipitation changes, the study watershed had distinctly different precipitation-runoff relationships for observed annual precipitations of less than 300 mm, between 300 and 400 mm, and greater than 400 mm. The annual NPP and May-July precipitation varied synchronically.

The annual NPP and the precipitation in summer, especially in June and July varied synchronically. In addition, from year to year, a decreasing summer average or maximum temperature was generally associated with a decreasing NPP, and vice versa. Minimum temperature in any time scale and annual NPP showed little positive correlation based on this study except September minimum temperature.

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DOI

10.25777/7mbr-rz06

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