NEW STUDY POINTS TO LAG IN RAINS IN BOTH MEXICO AND SOUTHERN US.

This year, scientists predict that the normal monsoon season will be delayed. This could cause a disruption of normal desertic climate in the Sonora desert, a protected habitat, and to its most famous vegetation, the Saguaro Cactus.

The summer rains, which fall in northwestern Mexico, are expected to change pattern in the coming decades.  This phenomenon usually provides the region with 70% of the yearly rainfall, allowing for crop cultivation and other relief for almost 20 million people who live both in Mexico and the neighboring regions in the southern United States.

This study, which was done by Columbia University Earth Observatory and Nasa Goddard in conjuction, will provide a model for the prediction and management of water resources for the future.  

Most of the US's southern regions will suffer steady and drier summers as climate change worsens.  But this new model also shows that summer rain levels might keep steady for a while for the southern Arizona, northwestern Mexico regions.  

What will change is the timing of the torrential rains, from the current july-August pattern to say September-October.  This is a significant shift.  Although the monsoon are predicted to delilver a still healthy dose of rainfall, the timing is a problem for agriculture.

A later monsoon can significantly impact crop yield, as crops slow their growth with the advent of fall.  By prolonging the dry season of the summer, there could also be wildfires and water supply will fall.  

The climate change study show that the models predict that drier summer seasons will make it more difficult for monsoon clouds to form when the soil is dry, especially after a drier winter season and less snowfall, so that the monsoon can only form when there is enough moisture drifting in from the ocean, once the warmest summer air finally cools and draws the cooler ocean air in. 

The Sonoran Desert and Sky islands are two ecosystems that lie at the northern edge of the north American monsoon, and vegetation in these two environments range from saguaro cacti alone to boreal forests.  The scientists do not yet know how these vegetations will react to a delayed monsoon season.

The delay might also impact the regions economically, both in Mexico or Arizona, where there is not enough ground water and agriculture is almost totally dependant on rainfall.

A late monsoon in 2005 hampered the growth of grass in areas where ranchers have their beasts graze, so that in that year, supplemental feed had to be bought, increasing significantly the cost of meat.  

Although the amount of total rainfall during the monsoon is supposed to stay the same, there will be more evaporation due to the longer and hotter summer season, making water resources scarce for all usages.  

The study then, will allow the regional farmers and ranchers to adjust and cope with the changes if proper resource management is adopted.  Scientist warn not to get complacent about the fact that the rainfall amount will remain the same, because rain in the fall is not the same as rainfall in the summer.

Source : Science Daily 3.13.13