   Watching Climate Change - October 29, 2003 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County The current drought in the southwest has scientists looking at long-term data to understand where we have been and where we may be headed. Some of these data include measured precipitation and temperature, changes in ocean currents and temperatures, tree rings of both living and non-living trees, and coral reef data. These data allow climatologists to look back at climatic variation over the past 1,000 years. I recently attended an excellent lecture by University of Arizona Professor, Gregg Garfin. Gregg is affiliated with the Climate Assessment for the Southwest (CLIMAS), which is part of the Institute for the Study of Planet Earth. The CLIMAS mission is to: improve the ability of the region to respond sufficiently and appropriately to climatic events and climate changes. Below I will present some interesting information from CLIMAS. When looking at climate (and weather), ocean temperatures and currents drive the system. Warm water temperatures at the ocean surface allow water to evaporate more readily. Moisture laden air masses are transported by air currents to areas where they cause precipitation. Ocean currents and surface temperatures vary from place to place and year to year. The El Nino/La Nina (ENSO) is the best known of these ocean current/temperature systems. There are two additional ocean temperature oscillations that influence global weather patterns: the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). El Nino is a warming of the eastern and central equatorial Pacific Ocean which creates moist air masses that can potentially reach the southwestern US during winter months. La Nina is a cooling of the eastern and central equatorial Pacific Ocean and always results in dry winters for the southwest. These conditions alternate and occur on 2 to 7 year intervals. The PDO was discovered in the mid-1990s, is located in the northern Pacific, and occurs every 20 to 30 years. It also has a major influence on winter precipitation in the Southwest. Drought is not cyclic or regular, but it does occur in events that last 0.5 to 1.5 years. Drought also occurs in waves or regimes lasting 5 to 20 years. Notable droughts in recent history were during the 1900’s, 1950’s, and our current drought. A mega-drought occurred between 1571 and 1598. Paleoclimate records indicate that severe multiyear droughts in the southwest frequently coincided with prolonged La Nina conditions and negative phase (dry Southwest) PDO. We only need to look around us for evidence of severe drought. The recent tree mortality episodes are often blamed on bark beetles. However, the beetle mortality was really brought on by prolonged drought which weakened the trees. There is evidence in the dendrochronological (tree ring) record that shows widespread tree mortality has also occurred in the more distant past. Data also shows that temperatures are on the rise. Spring snow melt is occurring 1 to 2 weeks earlier now than it did 50 years ago. In fact, over much of the northern hemisphere, longer growing seasons have been noticed. Most of this temperature change is attributed to increases in minimum temperatures in both urban and rural areas. Climate models and researchers agree that temperature is increasing in the southwest. Given this, even if we continued to get “normal” precipitation, evaporative demand and early snow melt will exacerbate drought conditions. We have always known that drought is a normal part of our Arizona climate, but the latest data show that we may be in for drastic changes. This certainly strengthens the case for water management. For more information, consult the CLIMAS web site at www.ispe.arizona.edu. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |