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Increase of precipitation intensity is the most definite and detectable hydrological consequence of a warmer climate. Among all U.S. regions, the Northeast has witnessed the strongest increase of extreme precipitation in the past five decades. This study examines the impact of climate changes during 1950–2011 on hydrological processes in the Northeast using the Connecticut River Basin as a case study. In addition to precipitation and river discharge data from observations, the Variable Infiltration Capacity (VIC) hydrological model is used to derive hydrological variables for which long-term observational data are not readily available. Our results show a clear increase of precipitation intensity, with substantial increase in both the number of days with greater than 10 mm precipitation and the simple daily intensity index. From 1950 to 2011, extreme precipitation amount (which is the total amount of precipitation from the upper 1% of daily precipitation) increased substantially, by 240% relative to the 1950 level. The weight of extreme precipitation as a fraction of total precipitation also increased, from about 10.6% in the 1950s to 30.4% in the 2000s. Despite the increase of precipitation extremes, the consecutive dry days experienced a slight decrease. Mean trend analysis shows indications of increasing precipitation amount, increasing discharge, increasing runoff ratios, increasing soil moisture, and a negligible evapotranspiration trend. Our simulations suggest that the basin is entering a wetter regime more subject to meteorological flood conditions than to drought conditions. A companion paper will investigate how these trends may persist or differ in the mid-21st century under continued warming. [ABSTRACT FROM AUTHOR]

Abstract: Hydrological time series increasingly exhibit non-stationarity, e.g., variables such as precipitation and streamflow values do not maintain a consistent mean over long periods, due to natural and anthropogenic changes. Detecting whether such shifts are gradual or abrupt is a growing concern for water resources planning and management. This paper shows that conventional trend and change-point tests do not adequately enable these two types of change to be distinguished. We propose a method for combining the rank correlations of the Mann–Kendall and Pettitt statistics to extract an indicator whose value determines whether a shift observed in a given time series is gradual or abrupt. This method allows the success rate to be independent of the length of record, and it is validated with Monte-Carlo experiments. The limitations caused by the short and noisy nature of hydroclimatic time series are discussed. As an application, the proposed method provides useful insights on changes in hydroclimatic variables in the United States during 1910–2009 using time series from 1217 stations in the United States Hydroclimatic Data Network (USHCN). [Copyright &y& Elsevier]

Abstract: Northern peatlands are among the most carbon-rich ecosystems on Earth, but many unanswered questions remain regarding linkages between their long-term developmental processes and climatic variability. In this paper, we present a detailed paleoecological reconstruction of the developmental history of a kettle peatland in northern Wisconsin, USA (Fallison Bog) based on 21 coring locations and temporally constrained by 69 radiocarbon dates. This record of within-basin developmental history is compared to a regional dataset containing estimated ages of peatland establishment for 75 core samples collected from 37 depressional peatlands throughout the Great Lakes Region. Finally, our data are used to develop a spatially explicit model of whole-system carbon accumulation in Fallison Bog, which distinguishes between carbon pools stored in limnic sediments and peat deposits. Results indicate that peatland development in Fallison Bog was episodic and spatially complex. Peatland development was related to the morphology of the underlying basin and characterized by pulses of both terrestrialization and paludification. Major episodes of terrestrialization centered on 4980 and 3180 years before A.D. 1850 (cal yr BP), with less extensive episodes occurring around 3840, 1060, 670, and 410 cal yr BP. Extensive peatland area developed by paludification of shallow portions of the basin around 2040 cal yr BP. The timing of peatland development within Fallison Bog was correlated with the timing of peatland development in other depressional peatlands across the Great Lakes Region (r = 0.70), suggesting a common climatic driver. Comparison of peatland development in Fallison Bog and independent paleoclimate records suggested that both millennial-scale and sub-centennial-scale variability in moisture balance influenced spatiotemporal patterns of peatland development. Model results indicated that Fallison Bog accumulated ∼6655 t of carbon during the Holocene, with 66% of this total stored in peat deposits that have accumulated in only the last ∼5000 years. Collectively, model results and the strong correlation between the timing of within-basin and regional pulses of peatland establishment imply that depressional peatlands likely experienced climate-sensitive and episodic changes in carbon accumulation rates during the Holocene, and similar dynamics could be expected in response to ongoing and future climatic change. [Copyright &y& Elsevier]