Increases in Growing Degree Days in the Alpine Desert of the San Luis Valley, Colorado

Most alpine ecosystem climate change studies identify changes in biota, several report abiotic factors and conditions, few report temperature changes, and few to none discuss growing degree days (GDD) changes. This study provides results of data analysis on changes in number of GDD in the alpine desert of the San Luis Valley (SLV) whose community is dominated by an irrigated agricultural region. Analysis indicates significant increases (p?<?0.05) in annual and growing season GDD₁₀, GDD_4.4 (potato), and GDD_5.5 (alfalfa) during 1994–2007 compared to 1958–1993. With one exception, all stations experienced significant increases in mean annual daily GDD between 0.12 and 0.50 day^?2 and growing season GDD day^?2 0.21 and 0.81. Higher temperatures increase numbers of GDD, quickening growth of crops and maturity at the cost of reduced yield and quality. Increases in GDD indicate the Valley’s agricultural region and economy may experience negative impacts as yields decrease and water use increases.