Harold Edwin Hurst (1 January 1880 – 7 December 1978) was a British hydrologist. Hurst's (1951) study on measuring the long-term storage capacity of reservoirs documented the presence of long-range dependence in hydrology, especially concerning the fluctuations of the water level in the Nile River. In doing so, he developed the empirical rescaled range methodology for measuring long-range dependence. Much of Hurst's research was motivated by his empirical observations of the Nile. The Hurst exponent, which has been used in other fields, such as finance and cardiology, was named after him.