The scientific legacy of Harold Edwin Hurst (1880\u20131978)

Emanating from his remarkable characterization of long-term variability in geophysical records in the early 1950s, Hurst\u2019s scientific legacy to hydrology and other disciplines is explored. A statistical explanation of the so-called \u201cHurst Phenomenon\u201d did not emerge until 1968 when Mandelbrot and co-authors proposed fractional Gaussian noise based on the hypothesis of infinite memory. A vibrant hydrological literature ensued where alternative modelling representations were explored and debated, e.g. ARMA models, the Broken Line model, shifting mean models with no memory, FARIMA models, and Hurst-Kolmogorov dynamics, acknowledging a link with the work of Kolmogorov in 1940. The diffusion of Hurst\u2019s work beyond hydrology is summarized by discipline and citations, showing that he arguably has the largest scientific footprint of any hydrologist in the last century. Its particular relevance to the modelling of long-term climatic variability in the era of climate change is discussed. Links to various long-term modes of variability in the climate system, driven by fluctuations in sea surface temperatures and ocean dynamics, are explored. Several issues related to the Hurst Phenomenon in hydrology remain as a challenge for future research. Editor M. Acreman; Associate editor A. Carstean

Evaluation of the sustainability of water withdrawals in the United States, 1995 to 2025

To evaluate the long term sustainability of water withdrawals in the United States, a county level analysis of the availability of renewable water resources was conducted, and the magnitudes of human withdrawals from surface water and ground water sources and the stored water requirements during the warmest months of the year were evaluated. Estimates of growth in population and electricity generation were then used to estimate the change in withdrawals assuming that the rates of water use either remain at their current levels (the business as usual scenario) or that they exhibit improvements in efficiency at the same rate as observed over 1975 to 1995 (the improved efficiency scenario). The estimates show several areas, notably the Southwest and major metropolitan areas throughout the United States, as being likely to have significant new storage requirements with the business-as-usual scenario, under the condition of average water availability. These new requirements could be substantially eliminated under the improved efficiency scenario, thus indicating the importance of water use efficiency in meeting future requirements. The national assessment identified regions of potential water sustainability concern; these regions can be the subject of more targeted data collection and analyses in the future

Dynamics of Liénard optoelectronic oscillators

In this chapter we present a comprehensive study on the dynamics of novel nonlinear optoelectronic oscillators (OEO) modeled by Liénard OEO systems. The OEO dynamical systems are based on negative differential resistance resonant tunneling diode oscillators incorporating a photoconductive region and laser diodes. The modeling results are in a good agreement with the wide variety dynamics that has been observed in recent experimental work spanning from self-sustained relaxation oscillations to injection locking and chaotic behaviors in both electrical and optical domains. Potential applications range from generation of periodic and chaotic signals for chaos-based communication schemes to highly stabilized OEOs for microwave-photonic systems