Background

Climate variability and climate change are related to changes in the climate regime, with effects on the hydrological cycle. The intense rains in short periods in the basin of Metztitlán River cause the river to quickly fill its discharge vessel (Lake Metztitlán) and flood Irrigation District 08 and nearby towns.

Goals

This study undertook a long-term hydrological analysis of the Metztitlán watershed to identify signs of climate change by looking at statistical means, and it defined the limits of greatest flood risk in order to understand the affected locations. We also calculated the environmental flow and the probable discharge volumes of the Metztitlán River.

Methods

The historical tendency of the runoffs from 1937 to 2008 was estimated using the Regime Shift Detection software; the environmental flow and the probable discharge volumes were evaluated based on the Tennant method.

Results

The analysis showed the mean annual runoff regime: Maximum extreme rainfall occurred in 1944, 1955, 1998, and 1999; and minimum rainfall occurred in 1950 and 1997. In the mean monthly runoff regime, seven and five changes were observed in the ten and five-year longitude cuts, respectively. These imply a downward trend of runoffs in the dry period, and an upward trend in the rainy period in recent years.

Conclusions

We were unable to detect any signs that might have allowed us to link these changes with climate change, although we did find a certain relationship with the El Niño-Southern Oscillation phenomenon. The highest flood risk limits lie between 1246 and 1258 meters above sea level; the susceptible populations are El Pedregal de Zaragoza, San Cristóbal, Tlacotepec, Tlatepexe, and Tecruz de Cozapa. The estimations of environmental flows indicate higher reserves for September and October and the release of excessive volumes throughout the year.