Culture and Ecology of Chaco Canyon and the San Juan Basin

Environment and Natural Resources 33LaPlsta Mta."'" "'~.1AS1N",CCPCfUION COftfOUasJuanChuaksMta.Mta.Nt40Iun20 mil ..Zuni Mta.Mt. TaylorFigure 2.4. Precipitation contours for the San Juan Basin. (Taken from Windes 1993:Figure 2.3.(1983:Plate IV) mapped the precipitation contours forthe San Juan Basin; these are presented here as Figure2.4.Data on temperature and precipitation in the SanJuan Basin are generally limited to the past century.During this recent time, temperatures rose until thelate 1960s and then declined (Gillespie 1985). Therewas a similar trend in increased rainfall during Julyand August, but the correlations between these twotrends are weak. Both rising trends occurred whenglobal temperatures were cooling and there weregenerally weak westerly circulation patterns. Thesedata do not fit the model presented by Bryson andBaerries (1968), who suggested reduced July rainfallwhen westerlies are slightly expanded. Whenevaluated against the models of Euler et al. (1979),and Rose et al. (1982), who proposed either summerorwinter-dominant precipitation, the data show nonegative correlation over the past 40 years betweenamounts of summer and winter precipitation, both ofwhich peaked in the 1960s (Gillespie 1985).