Frequency of occurrence of flow regime components: a hydrology-based approach for environmental flow assessments and water allocation for the environment

What Do Environmental Flows Mean for Long-term Freshwater Ecosystems’ Protection? Assessment of the Mexican Water Reserves for the Environment Program

“…This regulatory instrument is a three-level hierarchical framework that aims to find a balance between water use and freshwater ecosystem conservation [20,30,31]. It sets the ecological, hydrological, and water management principles for both people and nature-from a public policy perspective-to conduct eflow assessments, from relatively simple and cheap (i.e., "look-up tables" and hydrology-based) to more comprehensive and expensive methodologies (i.e., ecohydrology-, habitat simulation-and holistic-based) [21,22,27].…”

“…The EWRs were assessed based on the theoretical eflow requirements according to the methodology stated in the Mexican Standard's Appendix D (application 2). This ecohydrology-based methodology was selected because it is grounded in the frequency-of-occurrence of eflow components, recognized by the environmental water science and a state-of-the-art practice [11,22,[24][25][26][27]. Monthly-scale of very dry, dry, average, and wet seasonal ordinary low-flows conditions (Solf) were assessed [21,22].…”

“…This ecohydrology-based methodology was selected because it is grounded in the frequency-of-occurrence of eflow components, recognized by the environmental water science and a state-of-the-art practice [11,22,[24][25][26][27]. Monthly-scale of very dry, dry, average, and wet seasonal ordinary low-flows conditions (Solf) were assessed [21,22]. Likewise, a daily-scale flood regime (Fr) encompassing three peak flows at a magnitude of 1-, 1.5-, and 5-year return period was evaluated [21,22].…”

“…Monthly-scale of very dry, dry, average, and wet seasonal ordinary low-flows conditions (Solf) were assessed [21,22]. Likewise, a daily-scale flood regime (Fr) encompassing three peak flows at a magnitude of 1-, 1.5-, and 5-year return period was evaluated [21,22]. The characteristic duration (hours) was also calculated, as this flow attribute is required to integrate eflow needs into annual-based volumes (million cubic meters, hm 3 ) [21,22].…”

“…Furthermore, their implementation, together with a complementary suite of policy, legislative, regulatory, financial, scientific, and cultural measures holds the potential for reaching trade-offs among sustainable water usage and ecosystem protection [5,[10][11][12][13][14][15][16]. The present research article focuses on the assessment of the implementation of the Mexican eflow policy in 2012-2018, which aimed to enact environmental water reserves (EWR) [17][18][19], an annual-based volume designated to remain in the environment for ecological protection for up to 50 years [20][21][22].…”