Inter-Annual and Seasonal Variability of Flows: Delivering Climate-Smart Environmental Flow Reference Values

Abstract

Environmental flow (eflow) reference values play a key role in environmental water science and practice. In Mexico, eflow assessments are set by a norm in which the frequency of occurrence is the managing factor to integrate inter-annual and seasonal flow variability components into environmental water reserves. However, the frequency parameters have been used indistinctively between streamflow types. In this study, flow variability contributions in 40 rivers were evaluated based on hydrology, climate, and geography. Multivariate assessments were conducted based on a standardized contribution index for the river types grouping (principal components) and significant differences (one-way PERMANOVA). Eflow requirements for water allocation were calculated for different management objectives according to the frequency-of-occurrence baseline and an adjustment to reflect the differences between river types. Results reveal that there are significant differences in the flow variability between hydrological conditions and streamflow types (p-values < 0.05). The performance assessment reveals that the new frequency of occurrence delivers climate-smart reference values at least at an acceptable level (for 85–87% of the cases, r2 ≥ 0.8, slope ≤ 3.1), strengthening eflow assessments and implementations.

Water Reserves for the Environment: A Strategic and Temporal Analysis (2012–2022) for the Implementation of Environmental Flows in Mexico

“…In summary, this standard recognizes that the seasonal and interannual variability of the natural hydrological regime, in terms of attributes such as magnitude, frequency, duration, timing, and rate of change, as well as its components of ordinary and extraordinary flows, are essential for the development of ecological processes, functions, and ecosystem services. It also acknowledges that as water resources are used and the regime is modified, the biological-ecological condition of the ecosystem degrades [13,[17][18][19]. Apart from the various environmental flow assessment methods used for water planning and management or research purposes (e.g., hydrological, ecohydrological, habitat simulation, or holistic approaches) [16,36,37], the environmental flows are assessed based on the assignment of environmental or management objectives.…”

“…Although similar environmental flow estimations are currently available and could inform implementation progress against water scarcity, they are global-scale-model-derived, display significant gaps or inconsistencies in arid, and semiarid climates, and limit confidence in their relevance in countries like Mexico [43][44][45]. This assessment is based on systematic analyses of outcomes reported in scientific literature that have demonstrated consistency between hydrological, ecohydrological, and holistic methods generated in nearly 300 case studies in Mexico [13,[17][18][19].…”

“…These reference values are expressed as percentages of the mean annual runoff and are recognized in the international literature solely for water planning purposes, even when the source of information comes from monthly or annual-scale precipitation runoff models, as is the case in Mexico. Thus, for the purpose of this research, the approximation is appropriate (look-up tables, [16][17][18][19]37]). Water reserve calculations were performed using the global database in Microsoft Excel.…”

“…More than ten years after the initiative to allocate water to the environment started, studies have been developed to systematize experiences regarding the performance of methods for the evaluation and the implementation of environmental flows, and the commitment to continue reserving water in the country has been reaffirmed [13,[17][18][19][20][21]. Currently, however, no research has been conducted on changes in the key variables for establishing water reserves and implementing the Mexican Norm NMX-AA-159-SCFI-2012, even though it establishes the desired conservation state of basins based on demand for water use and ecological importance at that time [11,22].…”

Kızılırmak Havzasında Hidrolik Yapıların Planlanmasında Nehir Akımlarının Mevsimselliğinin Belirlenmesi

“…Variability tests and PCA method were used. As a result, seasonality and variability of river flows were evaluated in terms of climate-smart environmental flow reference values [15]. Eng et al identified five distinct seasonality patterns in the zero-flow events in the United States and strong correlation patterns with historical variations in climate [16].…”