It’s unusual for the southwestern states to be affected by hurricanes. Most years, predominant wind patterns in the Eastern Pacific Ocean steer storms away from the region. But about once every five years – like this year – the ocean winds change direction.
And those shifting winds steer hurricanes closer to northwestern Mexico, making them more likely to head northwards and track across the southwestern U.S.
Pacific hurricanes have typically degraded to tropical storms by the time they reach the Colorado Plateau. But when they do, the moisture-laden weather fronts can bring as much as a quarter of the average annual rainfall. That increased fall moisture can bring both short- and long-term change to our aridland ecosystems.
Fast-growing plants like grasses increase their uptake of CO2 from the atmosphere, while soils release less of the greenhouse gas. So for a brief spell at least, up to eight times more carbon may be stored by the land surface.
But there are longer-term effects too. For example, on ponderosa pines. Over the last 40 years, almost all the successful establishment of newly germinated pine seedlings has been concentrated in four years with abundant fall moisture: 1973, ‘79, ‘83, and 1990. And the width of annual growth rings of mature ponderosas has been well above average in those years too.
So with the surge of moisture on the plateau this fall, it’s likely that 2014 will be another bumper year for ponderosa pines – young and old.
Earth Notes is produced by KNAU and the Sustainable Communities Program at Northern Arizona University.