**5. Discussion**

The impact of climate change on aquatic ecosystems was seen as early as 1999 in eight US regions [77]. In the Fifth Evaluation Report of the Intergovernmental

**Figure 20.** *ARMA analysis of flows of las Estacas Station.*

**Figure 21.** *ARMA analysis of flows of El Almeal Station.*

Panel on Climate Change, MacAlister and Subramanyam mentioned that 93% of the impacts associated with climate change will affect aquatic ecosystems [78, 79]. Environmental flows, using the Brisbane definition [30], were incorporated into the "water stress" indicator 6.4.2 [80]. Environmental flows are the source of the "natural" versus "managed" ecosystem support and, as can be seen below (**Figure 22**), due to climate change or direct human intervention, their impact tends to zero as the managed contribution increases to a plateau.

In a study of the Huangqihai River basin in Inner Mongolia, China, it was found that environmental flow requirements (EFRs) contribute to the determination of water scarcity using the QQE indicator that combines the status of quantity, quality, and EFR [82] while if the environmental flow protection is low, 53 countries experience different levels of water shortage, and if it is high, we have an increase to 101 countries [83]. A similar result was found when water withdrawals were replaced by water consumption plus environmental flows where in a global river basin examination for the period 1996–2005, 201 out of 405 river basins examined presented intense water scarcity for at least 1 month per year [84]. Using the environmental water

**Figure 22.** *Benefits from natural (environmental flows) and managed systems [81].*

### *Water Availability for the Environmental Flow in Two Rivers of Mexico under Climate Change DOI: http://dx.doi.org/10.5772/intechopen.104881*

requirement (EWR) as the sum of environmental low-flow requirement (LFR) and environmental high-flow requirement (HFR) shows that if freshwater-dependent ecosystems are to stay in fair condition, 20–50% of the mean annual river flow has to be allocated to them [85]. Hence, it can be said that the constraint of finiteness of water resources imposes a socioeconomic choice regarding water allocation between human use and environmental flow at global, regional, country, and locality levels, which perhaps can be regulated via a scalable framework although the country level plays a decisive role as water is a strategic economic good. Mexico determines the volume of water that is allocated for ecological protection on the basis of the Environmental Flow Mexican Norm (e-flows, NMX-AA-159-SCFI-2012, ratified in 2017) regarding the formation and disposition of environmental water reserves (EWR) 12 of which have a 50-year duration to date (2021), and 75% of them meet up to the theoretical minimum requirement of norm implementation [86].

Annual maximum flood events depend in part on runoff generation and flow routing as seen in [87], while precision moisture estimation [88] may add to the description of the biotic state. Also rainfall and temperature trends analysis [89] plays a determinate role in this description as well. Increases in the winter rainfall in the northern and southern part of the Yautepec and Cuautla River (February) are different as shown by the historic records of the preimpact period. As well as, for the middle part of the subbasin of the Yautepec River where the shrubby secondary vegetation of low deciduous forest predominates and the permanent and semipermanent annual irrigation agriculture. The decreases in rainfall at the end of the rainy season (October) show a climate change in coincidence with other authors and pointed out as one of the most urgent threats to sustainable development worldwide [90]. The significant decrease in the percentage of precipitation for all months of the year at the Oaxtepec and Las Estacas weather stations indicates the synergistic effect of climate change and the use of the resource by the population (mainly agriculture). On the contrary, the effects on the flow depletion can only be associated with the use of the resource by human influence on Ticumán station. The impacts of climate change are exacerbated by rapid population growth, an example of which is seen below (**Figure 23**), rapid urbanization and chaotic economic development, particularly where water demands already exceed limited supplies.

Likewise, climate change is altering precipitation and thawing patterns, affecting the frequency and magnitude of river flows, floods and droughts, and contributing to more extreme weather events and forest fires around the world in a coincident way

### **Figure 23.** *Population statistics in the Cuautla area [91, 92].*

in the subbasins of the Yautepec and Cuautla River [79]. The hydroperiod determines the presence of certain plants and animals in the different strata of the riparian zone and the riverbed, being the dominant factor that makes the difference in the riverbank and riverbeds, and constitutes the most important variable in the corridor structure river [93, 94]. The changes in base flow and low flow pulses on subbasins indicate a tendency toward drought conditions or a tendency to extreme climate and the synergic effect of climate with use of the water by human influence. Moreover, the duration of high flow pulses and the rate of increase in flow can be associated with the torrential rains, as well as the increase in the base flow, changes in the date of the maximum flow, and the rate flows decrease indicate shift of the start rainy season. Variable flow was seen in 52 rivers worldwide whose patterns of flow variability were often correlated with climate [95]. Extreme events, e.g., unusual floods/droughts, may alter the physicochemical conditions under which biotic communities undergo long-term development [96]. Therefore, hydroperiod models are a useful tool in the analysis of the distributions of organisms during the year and the modifications caused by human activity. These models should be studied through comparative multidisciplinary studies to determine the real problems derived from global change in the freshwater systems and to determine the real influence of global warming on the regional climatic conditions of the planet and its influence on river ecosystems [57, 58]. Therefore, the dimensions and processes observed in the development of the watersheds, among them the environmental flows, must be approached in a systemic way, starting from integrative and articulating approaches to generate the actions for the management, conservation, and recovery of the freshwater. As well as, the vulnerability maps and lines of action for climate change adaptation [56, 97].
