The observation of the physical environment for long periods can expose changes in hydrological systems behavior, to anticipate problems that manifest themselves with greater intensity in the future. The northern part of Mexico is characterized by been an arid or semi-arid region, hence water scarcity is its natural condition; however, these areas can be even deeply affected by changes in climate. In this region, specifically the Hydrologic Region “Closed Basins of the North”, in the State of Chihuahua, where the Carmen river basin is located. This land area of just over 4,500 km2, from inception to where the dam “Las Lajas” is located. From this dam an irrigation district is supplied, hence, analysis of the effects of climate change in the surface water availability could be very useful, to take preventive measures to help cope with adverse conditions opportunely.
This reservoir has hydrometric records available since 1968, so it was possible to determine the monthly natural flows until 2012, by mass conservation equation, as established in the Mexican Official Standard NOM-011-CNA-2015. The behavior of natural flows shows a rise in the first nine years of the time series, and then a period of stability until 2012.
Regarding the behavior of the annual precipitation in the basin, the records shows a tendency to increase from 1968 to 1991, then it exhibits a decrease in the time series from 1992 to year 2012. Using the natural flows time series as well as the annual precipitation ones, was possible to determine the evolution of the annual runoff coefficient for the entire period of study, showing a clear upward trend.
The runoff coefficient exhibits high dependence on physical factors such as precipitation, vegetation cover and land use, soil type and its characteristics and geomorphological parameters of the basin, including the slope of the basin and of the main channel, among others. Analysis of cartographic databases from the National Institute of Statistics, Geography and Informatics in Mexico, it was observed that the basin suffered modifications in its natural cover, some naturally originated probably due to changes in the regime of precipitation and temperature, and other anthropogenic such as clearing land to establish agricultural areas.
As results of the research, there were changes in the surface hydrologic system, both in the climate (precipitation regime) and in the physical conditions of the basin. However, natural flows have preserved relatively stable, probably because the decrease in annual rainfall was compensate by the increase in the values of the annual runoff coefficient (caused by the physical changes in the basin, or changes in the rainfall intensity).
All the knowledge regarding on how the hydrologic systems could been altered by changes in the climate, would be useful to diminish adverse effects to the socioeconomic activities. Finally, the alteration of the surface hydrologic system, surely have produced alterations in the groundwater system that is associated to the first. This issue was outside the scope of the work, but it represents an area of opportunity for future research.