Articles | Volume 19, issue 3
Technical note
02 Mar 2015
Technical note |  | 02 Mar 2015

Technical Note: Higher-order statistical moments and a procedure that detects potentially anomalous years as two alternative methods describing alterations in continuous environmental data

I. Arismendi, S. L. Johnson, and J. B. Dunham

Abstract. Statistics of central tendency and dispersion may not capture relevant or desired characteristics of the distribution of continuous phenomena and, thus, they may not adequately describe temporal patterns of change. Here, we present two methodological approaches that can help to identify temporal changes in environmental regimes. First, we use higher-order statistical moments (skewness and kurtosis) to examine potential changes of empirical distributions at decadal extents. Second, we adapt a statistical procedure combining a non-metric multidimensional scaling technique and higher density region plots to detect potentially anomalous years. We illustrate the use of these approaches by examining long-term stream temperature data from minimally and highly human-influenced streams. In particular, we contrast predictions about thermal regime responses to changing climates and human-related water uses. Using these methods, we effectively diagnose years with unusual thermal variability and patterns in variability through time, as well as spatial variability linked to regional and local factors that influence stream temperature. Our findings highlight the complexity of responses of thermal regimes of streams and reveal their differential vulnerability to climate warming and human-related water uses. The two approaches presented here can be applied with a variety of other continuous phenomena to address historical changes, extreme events, and their associated ecological responses.

Short summary
We present tools to assess shifts in the distributional properties of continuous environmental variables and to identify potentially anomalous years. We demonstrate the utility of these tools using stream temperature as an illustrative example. We were able to examine seasonal and annual responses to climate and other human-related influences. These tools will be useful to characterize how regimes of continuous phenomena have changed in the past, or may respond in the future.