Modeling prehistoric climatic variability and agricultural production in southwestern Colorado: A GIS approach

TitleModeling prehistoric climatic variability and agricultural production in southwestern Colorado: A GIS approach
Publication TypeThesis
Year of Publication1990
AuthorsWest, CV
Academic DepartmentAnthropology
UniversityWashington State University

A model with high temporal and spatial resolution has been developed for a 1816 km$\sp2$ area of southwestern Colorado to examine the potential effects of past climatic variation on dryland maize agriculture and sustainable population during the late Mesa Verde Anasazi occupation of the area (A.D. 901-1300). The data generated by the model are used to evaluate a question of long standing in the Northern Southwest: whether climatic variability was severe enough to disrupt agriculture and promote the abandonment of the Northern San Juan Region toward the end of the 13th century.

The model incorporates techniques and data sets that have not been used together before. Long regional dendroclimatic records are used to retrodict 1070 years (A.D. 901-1970) of June Palmer Drought Severity Indices (PDSI)--measures of stored soil moisture--for area-specific soils. Reconstructed PDSIs are reexpressed in terms of their local equivalent in potential maize yield. The integration, quantification, and visual display of these productivity values are coordinated through geographic information systems (GIS) technology. The method results in the production of (1) annual maps depicting the variable character of the potential agricultural environment and (2) annual values for total maize productivity, which can be translated into the population size and density that can be potentially supported on that yield. From these, multiple year estimates of a sustainable population or carrying capacity are made.

The results indicate that there was always enough productive land somewhere in the study area to support thousands of persons (e.g., 31,363 persons or 21 persons/km$\sp2$ minimum in the 1470.36 km$\sp2$ study area over the 400-year period), even in the documented dry times of the middle 12th and late 13th centuries. It would seem, therefore, that climatic variability was never so extreme in the Mesa Verde area that decreased agricultural production can be cited as the sole or even primary cause of the 13th century depopulation of the region.