**4. Results**

### **4.1 Precipitation**

The variation average monthly in the precipitation between the preimpact and postimpact periods in the Yautepec and Cuautla subbasins indicates the largest decreases in February for Tepoztlán (−71.58%) and Nexpa (−66.67%). However, the greatest increases in precipitation were observed in the dry season on the Nexpa station with 62.94% (March); Oaxtepec with 47.24% (February); Totolalpan with 45.49% (January); and Yautepec with 35.50% in February (**Figure 4**).

The months with the highest percentage decreases in precipitation during the year were: February, April, November, and December in the east of the Cuautla subbasin (Alpalocan, Tecajec, and Tecomalco, respectively). However, the northern part (Tetelcino) showed the greatest increases in the winter season (January, February, and March, with 72.76, 47.72, and 98.10%, respectively; **Figure 2**). The month of February was the most favored with respect to the increase in rainfall in the northern part of the Yautepec and Cuautla river subbasins, where annual seasonal agriculture predominates and the dominant vegetation is the pine and oyamel forest. On the contrary, the month of October (high part of the subbasins) was the most affected by the decreases in precipitation.

### **4.2 Water availability for ecological flows**

Flows should be interpreted as below (**Figure 5**).

In the upper basin of the Yautepec River (Oaxtepec Station), the monthly averages of the flows (preimpact period 1949–1979; 31 years) and the postimpact period (1980–2011; 26 years) indicate the significantly decrease in the availability of water

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

### **Figure 4.**

*The percentage variation of the monthly rainfall between the preimpact and postimpact periods for the Yautepec and Cuautla river subbasins.*
