MATLAB Hydrological Index Tool (MHIT): A high performance library to calculate 171 ecologically relevant hydrological indices

•171 ecologically relevant hydrologic indices are being used to define environmental flow.•Several programs are available to determine environmental flow indices.•Current programs lack the required coding mechanism to be scalable to large area.•A new program was introduced that significantly reduces the computational time.

Ecologically relevant hydrologic indices are being used for developing environmental flow baselines. EflowStats is an R-package developed by the US Geological Survey that calculates 171 ecologically relevant hydrologic indices. Although EflowStats provides a set of easy to use functions, once it is applied to a large area with thousands of streams, it requires a long processing time. This particularly limits its application in problems that are dealing with optimizations, requiring evaluation of thousands of scenarios. As a result, a new package called MATLAB Hydrological Index Tool (MHIT) was developed, incorporating different technologies, such as vectorization, memoization, and parallelism to considerably reduce the processing time. Both EflowStats and MHIT were tested against a long-term (20 years) daily streamflow data set from the Saginaw River Watershed in Michigan. In summary, MHIT reduces the processing time by 227 times for the study area. Therefore, MHIT is much more suitable for dealing with Big Data.