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Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Precipitation impacts on earthen architecture for better implementation of cultural resource management in the US Southwest

item HART, S. - Us National Park Service
item RAYMOND, K. - Us National Park Service
item Williams, Christopher - Jason
item Johnson, Justin
item DEGAYNER, J. - Us National Park Service
item GUEBARD, M.C. - Us National Park Service

Submitted to: Heritage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2021
Publication Date: 11/4/2021
Citation: Hart, S., Raymond, K., Williams, C.J., Johnson, J.C., Degayner, J., Guebard, M. 2021. Precipitation impacts on earthen architecture for better implementation of cultural resource management in the US Southwest. Heritage Science. 9. Article 143.

Interpretive Summary: Projected increases in the intensity of monsoonal rainfall events in the southwestern US raise substantial concerns for the preservation of culturally important adobe architecture. Some of these historical resources have undergone significant degradation in recent years associated with changing rainfall amounts and intensity. The US Department of the Interior, National Park Service (NPS) requires improved understanding of the rainfall amounts and intensities that drive erosion and degradation of historical adobe construction. Such information is critical to predicting the potential impacts of rainfall events and targeting strategies to prevent and mitigate associated damage to these cultural resources. Scientists with the US Department of Agriculture, Agricultural Research Service and the NPS conducted rainfall simulation experiments on adobe test walls to quantify adobe erosion rates under various rainfall intensities and storm types. Adobe wall erosion during short-duration, high-intensity rainfall simulations increased exponentially with increasing rainfall intensity. Significant wall erosion also occurred under low-intensity, long-duration rainfall, but erosion for these events was less than that observed for the more intense short-duration rainfall events. Observations of erosion processes during the experiments provide new insight into mechanisms of adobe wall degradation during precipitation over various rainfall intensities. The study results and new knowledge will help NPS park managers make informed decisions about the protection and preservation of culturally important adobe architecture amidst changing climate and associated precipitation trajectories.

Technical Abstract: Changing seasonal precipitation patterns prompted by climate change are likely causing increasing degradation of adobe architecture in the American Southwest. This deterioration includes surface erosion and catastrophic collapse. This study examines the impact of changing rainfall patterns on untreated adobe walls to understand how damage occurs and anticipate future impacts. To complete the study, we constructed 20 adobe test walls. Using a portable rain simulator, each wall was subjected to two rainfall experiments: high-intensity rainfall simulations (rain intensity variable) and low-intensity rainfall simulations (rain event number variable). Wall-degradation metrics (material loss, volume loss, affected surface area, and cavity depth) were calculated for each wall using pre- and post-simulation LiDAR scans. Internal wall moisture was also measured with embedded volumetric water content sensors. In the high-intensity experiment, the lines of best-fit for material loss and affected surface area show that surface erosion increases with rain intensity, while cavity depth remains consistent. Linear models and post-hoc tests indicate material loss and affected surface area is significantly different for each high-intensity rainfall treatment. Furthermore, the interior of each wall remained relatively dry demonstrating that rain intensity is not a strong predictor of interior wall moisture. In the low-intensity rainfall experiment, the rainfall simulations yielded statistically similar erosion and interior wall moisture results. Greater infiltration occurred under low-intensity long-duration rain conditions, while greater surficial damage occurred under high-intensity rain conditions. In conclusion, changing weather regimes are bringing more intense rainfall events to the arid American Southwest. This study suggests that more frequent high intensity rain events will cause increasing damage to adobe walls. Resource managers will need to adapt current management strategies to account for this change.