Controls on peak discharge at the lower course of Ameca River (Puerto Vallarta graben, west-central Mexico) and its relation to flooding

- The largest peak discharges (~ 50%) take place during normal phase of ENSO.
- The amount of rainfall accumulated for two-weeks is critical for the magnitude of peak discharges.
- A discharge > 1140 m3 s− 1 inundates with > 0.5 m of depth the lower course of Ameca River (~ 5.7 km2).
- The number of hurricanes and tropical storms and rainfall are the highest in the summer of normal phase of ENSO.

Rivers are dynamic features sensitive to climatic oscillations. While in some settings the warm (El Niño) and cold (La Niña) phases of ENSO are related with an increase in peak discharge events, in other zones like subtropical rivers, floods are caused by different meteorological events. Here we evaluate the potential controls on river peak discharge of the Ameca River, within a tectonically active landscape located on west-central Mexico, by using stream discharge and rainfall data spanning ~ 60 years. We evaluated the flooding produced by maximum peak discharges in the landscape by simulating different flood scenarios using the solver Nays2DFlood (http://i-ric.org). Our results indicate that the warm, cold and normal phases of ENSO, as well as moderate meteorological events, coincide with the highest peak discharges recorded on stream gauging stations. Further analysis of rainfall data reveals that the largest peak discharges are positively correlated with the amount of rainfall accumulated two weeks before the day of the peak discharge. Our flood simulations indicate that when stream discharge exceeds ~ 1114 m3 s− 1, a column of water > 0.5 m of depth inundates ~ 2.5 km2 of Ameca's floodplain. Such condition can leave the inhabitants in hazardous condition and damage the infrastructure. We found that the highest peak discharges in the Ameca River are produced in summer and in all phases of ENSO, however, these events are more frequent in the normal phase of ENSO (~ 50%), followed by the phase of La Niña (~ 37%). Our results highlight the importance of seasonal rainfall in the geomorphic work of the subtropical rivers of west-central Mexico.