Date of Award

June 2017

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering


Charles T. Driscoll


Climate change, Flow indicator, Northeastern United States, Regime shift, Teleconnection, Urban development

Subject Categories



In this dissertation, the scale-dependency of hydrologic responses due to changing climate and regime shifts of large-scale circulation patterns and their teleconnection patterns were evaluated using long-term precipitation and discharge records in sub-basins with no development, and extensive development and riverine impoundments of the Merrimack River watershed. The Merrimack (New Hampshire-Massachusetts) is a 13,000 km2 forested (67%) watershed located in the northeastern United States. The overarching goal of this dissertation was to assess hydrologic responses to the potential effects of changing climate in sub-basins experiencing a range of development in order to help guide sustainable water management in the Merrimack River watershed and other northeastern basins. The objective of this research was to integrate hydroclimatic observations across basin size and anthropogenic disturbances (i.e. river regulation and land development) to understand the dynamic of hydrologic alterations under a changing climate.

This dissertation consists of three research phases. In phase I, I assessed the interacting hydrologic responses to changing climate, watershed physical characteristics, river regulation, and land development under dry, average, and wet hydrologic conditions using long-term precipitation and discharge data of the Merrimack River watershed. I found that the effects of basin scale were limited to high (exceedance probability of less than 15%) and low (exceedance probability of greater than 60%) discharge events and were expressed as lagged discharge in larger sub-basins and earlier discharge in smaller headwater catchments. Annual discharge responded to increases in annual precipitation regardless of river regulation or land development. In general, the temporal trends showed greater decreasing trends in discharge under dry and greater increasing trends in discharge under wet hydrologic conditions compared to average years.

In phase II, I explored the effects of Atlantic Multi-decadal Oscillation (AMO: metric of Sea Surface Temperature anomalies of the North Atlantic Ocean typically over 0-80°N) and North Atlantic Oscillation (NAO: metric of Sea-Level Pressure anomalies over the Atlantic sector 20°-80°N, 90°W-40°E) regime shifts on hydrologic responses to evaluate whether the intensified inter-annual variability in discharge is explained by natural climate cycles. I focused on AMO and NAO regime shifts of the early 1950s, 1970s, and 2000s and the effects on hydrology of the Merrimack River watershed. AMO regime shifts were strongly synchronized and preceded both precipitation and discharge across all study sites by one to two years, while NAO regime shifts indicated weaker associations. I found that all responses tended towards greater extremes from each regime shift to the next. Across many different ecological discharge indicators, high percentile values increased across regimes, while low percentile values decreased between regimes (with a few exceptions).

In phase III, I evaluated the potential for discharge estimation considering annual or seasonal AMO and NAO teleconnection patterns with precipitation and discharge. When AMO was extremely positive (greater than 0.2), the magnitudes of annual precipitation and discharge correlation coefficients with AMO were obscured by river regulation or land development. In contrast, during the extreme negative phase of AMO (less than 0.2), river regulation and land development amplified the effects of changing climate on precipitation and discharge variations. AMO was positively associated with precipitation and discharge, while NAO showed a negative linkage. AMO positive phase was correspondent with average-to-wet discharge conditions at headwater catchments. When basin scale increased, confidence in the estimation of discharge conditions decreased for downstream developed sub-basins compared to headwater undisturbed catchments.

The results from this research indicated that the Merrimack River watershed is expected to experience increases in discharge in the future and changing in timing and the seasonal distribution of this discharge; therefore development should be avoided on flood plains. Furthermore, the current reservoir storage capacity in the Merrimack should be improved in order to accommodate excess water input and minimize flood damage. Future research should target changes in the magnitude and timing of high discharge events in order to develop adaptation strategies for aging hydraulic infrastructure in the region. This dissertation will provide information for watershed planners and managers to inform future sustainable water use in the Merrimack River watershed and other northeastern basins.


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