**Figure 5.**

*River flow levels and ecological functions [75].*

between the analyzed periods. This can be attributed to the use of the resource for agriculture and by the population after the construction of the little dams. For this hydrometric station, there is a significant decrease in precipitation of −38.57% in March and − 19.84% in April, which coincides with the maximum decrease in flows in this segment in the postimpact period. However, the increase in precipitation was observed for this area in the month of February (47.24%), without the increase in flows as should be expected, which is explained by the use of the resource by the population, nullifying the positive effect of climate change or increase of precipitation percentage on the availability of water for the river (**Figure 6**).

The average monthly flow of the Ticumán Station (middle part of the Yautepec River subbasin), for the preimpact period (1951–1980; 30 years) and postimpact period (1981–2011; 29 years), indicates a significant alteration in the hydrological regime only for the June and November months (**Figure 7**).

For this area, there is a nonsignificant increase in precipitation of 14.04% (September) and 19.63% (November) that coincides with the percentage increases in flows. However, in December, a decrease in the flows percentage of 70% can associated with the use of the resource for activities of anthropic type. Therefore, these variations with a negative tendency in the flow cannot be attributed to the effects of climate change, but to human influence.

On Las Estacas Station, the precipitation percentage variation between the preimpact period and postimpact period was significant for January (−18.8%) and April (−2.9%).

### **Figure 6.**

*The average monthly flow percentage and precipitation variation between the preimpact period (1949–1979) and postimpact period (1980–2011) at the Oaxtepec Station.*

### **Figure 7.**

*The average monthly flow percentage and precipitation variation between the preimpact period (1951–1980) and the postimpact period (1981–2011) at the Ticumán Station.*

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

### **Figure 8.**

*The flows monthly average percentage and precipitation variation between the preimpact period (1968–1988) and postimpact period (1989–2011) on las Estacas Station.*

The flows monthly average percentage for the Las Estacas Station (lower part of the Yautepec River Sub-basin), for the preimpact period (1968–1988; 21 years) and the postimpact period (1989–2011; 22 years), indicates a significant decrement in the flows on April (−5.9%), July (−4.8%), August (−8.5%), and September (−7.7%). This behavior does not coincide with the increase in rainfall from May to September (between 6.8% and 14.04%). Variations in precipitation and flows for this period (July–October) can be attributed to human influence and the effects of climate change (**Figure 8**).

The monthly average flows for the El Almeal Station (upper part) of the Cuautla River subbasin for the preimpact period (1948–1978; 31 years) and postimpact period (1979–2011; 32 years) indicate a significant alteration in the hydrological regime in all months of the year (**Figure 9**).

Coincidentally, in this area there is a significant decrease in precipitation percentages throughout the year (except November), ranging from −29.65% for January to −0.39% in August. Aspect that can be associated with the depletion of flow rates during the year for this season indicates the effects of climate change on the availability of water for the Cuautla River.

### **4.3 Environmental flows and indicators of hydrological alteration**

Increase of low extreme flow rates, decrease of low flow rates, loss of the high flow pulses, small floods, or large floods at the Oaxtepec Hydrometric Station were observed. The hydrological changes occurred in the average monthly flows and the days with

### **Figure 9.**

*The flows monthly average percentage and precipitation variation between the preimpact period (1968–1988) and postimpact period (1989–2011) at the Almeal Station.*

minimum and maximum flow (**Figure 10**). As well as in the number and duration of low flow pulses, in the increase in high pulses, changes in the rates of variation (to negative), and reversals of the flows. The loss of the frequency, magnitude, and periodicity of the flows during the year indicates the abuse in the use of the resource for agriculture and by the population after the construction of the dams (**Figure 12**).

### **Figure 10.**

*List of 34-parameter environmental flow components (EFCs) [63], Figure 11.*

### **Figure 11.**

*V7 IHA software 34 IHA parameters and their impact on the environment [73].*

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

**Figure 12.**

*Ecological flows and hydrological alteration indicators at the Oaxtepec Station.*

At the Ticumán hydrometric station, the environmental flows do not observe significant changes. However, the hydrological alteration indexes indicate a decrease in the average flows of January, June, August, and September (rains), as well as in the minimum daily flows with a duration of 3, 7, and 30 days. Also, an increase in the date of the maximum flow, in the duration of the high flow pulses, and a rise in rate flow. The base flow and low flow pulses 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 (**Figure 13**).

In Las Estacas hydrometric station (Yautepec River), the environmental flows show alterations in the postimpact period for the small and large floods, in the low flows and high flow pulses. The IHA show changes in the small and large floods for the postimpact period (1980–2000). Also, largest significant decreases in average flows in May, July, October, and November and increases in August and September point out a tendency to extreme weather due to climate change. In addition, decreases in the minimum and maximum daily flows with a duration of 3, 7, 30, and 90 days. The duration of high flow pulses and the rate of increase in flow can be associated with the torrential rains. On the contrary, an increase in the base flow, changes on the date of the maximum flow, and the rate flows decrease indicate shift of the start rainy season. The average flows and the number of investments of the flow can be attributed to human influence and climate change (**Figure 14**).

In El Almeal hydrometric station (Cuautla River), the environmental flows show great changes between the preimpact and the postimpact period. The IHA point out significant differences in all the components of ecological flow, except for the average

**Figure 13.** *Ecological flows and hydrological alteration indicators of the Ticumán Station.*

**Figure 14.**

*Ecological flows and hydrological alteration indicators of las Estacas Station.*

**Figure 15.** *Ecological flows and hydrological alteration indicators of the El Almeal Station.*

flows of March and December, and in the number of investments of the flow. The low extreme flows increased and became more frequent, the low flows and the high flow pulses practically disappeared, as well as small and large floods in the postimpact period, modifications that can be explained by human influence. Changes in the flow averages for the whole year were observed, in the duration of the days with minimum and maximum flow, an increase in the rate of the base flow, as well as in the number of flows pulses (high and low). Also, in the flow rates (increase and decrease in flows), on investments, the shorter duration of low pulses, a situation that reflects an alteration in all components of environmental flows. Therefore, modifications that can be explained by human influence (**Figure 15**). The calculations above lead to the construction of the diagram below (**Figure 16**).

### **4.4 Regression analysis and R2 of monthly flows**

The regression analysis of monthly flows for Yautepec and Cuautla subbasins in Hidrometric Stations of study period is shown in **Table 3**. All hydrometric stations showed a negative trend throughout the year. Only Las Estacas (January–April, dry season) and Ticumán (May–September, rainy season) showed a positive trend in flows, respectively. These stations are located in the middle and lower part of the Yautepec subbasin where annual, permanent, and semipermanent irrigation agriculture and secondary tree, shrub, and lowland forest vegetation predominate

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

**Figure 16.**

*Use of the sustainability boundary approach (SBA) to set sustainable water management targets [76].*

(**Figure 17**). This behavior can be explained by the use of some diversions to irrigate crops in the area during the dry season in Las Estacas and the positive tendency in Ticumán Station on rainy season could be explained for climatic change effect, as can be observed in **Figure 4** during this period, above all in June and July. The Almeal Station in the intermediate part of the Cuautla subbasin with annual, permanent, and semipermanent irrigation agriculture presents the highest values of R<sup>2</sup> (0.23 in October to 0.54 in May) coinciding with the greatest decreases in the percentages of precipitation (**Figure 4**). Aspects that show the synergistic effect of climate change and human influence on the availability of water for rivers.

ARMA (autoregressive moving average) flows analysis of the hydrometric stations.

For the Oaxtepec station, the ARMA analysis of the flow data indicates a homogeneous distribution of the residues with an AR coefficient = −824,201 at P ≤ 0.0517. However, some events of large floods generate some alterations on residuals and show some cyclicity (**Figure 18**).

For the Ticumán Station, the ARMA analysis of the flow data indicates a homogeneous distribution of the residues with an AR coefficient = −8893 at P ≤ 0.1115 and shows also some cyclicity (**Figure 19**).

For the Las Estacas Station, the ARMA analysis of the flow data indicates a homogeneous distribution of the residues with an AR coefficient = −79,086 at P ≤ − 0.2077. However, some events of large floods generate some alterations on residuals (**Figure 20**), and the cyclicity of the large floods is not clear.

For the El Almeal Station, the ARMA analysis of the flow data indicates a homogeneous distribution of the residues with an AR coefficient = −8940 at P ≤ − 0.1069. However, some events of large floods generate some alterations on residuals (**Figure 21**).


**Table 3.**

 *Monthly flows regression analysis of hydrometric stations Yautepec and Cuautla subbasins, and value of R2 during the all study period.*

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

### **Figure 17.**

*Vegetation and land use of Yautepec and Cuautla subbasins.*

**Figure 18.** *ARMA analysis of flows of Oaxtepec Station.*

**Figure 19.** *ARMA analysis of flows of Ticumán Station.*
