Intensification of the North American Monsoon rainfall as observed from a long-term high-density gauge network

Authors: Demaria, Eleonora; HAZENBERG, P. - University Of Arizona; Scott, Russell - Russ; Meles, Menberu; Nichols, Mary; Goodrich, David - Dave

Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2019
Publication Date: 5/16/2019
Citation: Demaria, E.M., Hazenberg, P., Scott, R.L., Meles, M.B., Nichols, M.H., Goodrich, D.C. 2019. Intensification of the North American Monsoon rainfall as observed from a long-term high-density gauge network. Geophysical Research Letters. 46(12):6839-6847. https://doi.org/10.1029/2019GL082461.
DOI: https://doi.org/10.1029/2019GL082461

Interpretive Summary: The North American Monsoon is an extremely important source of moisture for most of the semiarid lands in the southwest United States during the warm summer months. In southeastern Arizona, summer rainfall produced by the monsoon account by as much as 60% of the total annual precipitation. This rainfall is crucial for the health of natural ecosystems, but it is also responsible for extreme flooding that cause human and material losses. As the atmosphere warms, its capacity to hold moisture increases along with higher chances of more intense storms. Previous studies have found contradictory results regarding higher rainfall intensities in southwestern United states due to the lack of a dense network of rain gauges needed to capture the highly localized nature of the storms. Our study uses an unique dataset from an experimental watershed located in southeastern Arizona that has been measuring rainfall for more than 60 years. We find that rainfall has been more intense since the mid 1970s. Our analysis also shows that changes in monsoon rainfall intensities are hard to capture by a few isolated rain gauges and that in order to obtain statistically strong results a dense network of observation points is needed.

Technical Abstract: As the atmosphere gets warmer, rainfall intensification is expected across the planet with anticipated impacts on ecological and human systems. In the southwestern USA and northwestern Mexico, the highly variable and localized nature of rainfall during the North American Monsoon makes it difficult to detect temporal changes in rainfall intensities in response to climatic change. This study addresses this challenge by using the dense, sub-daily and daily observations from 59 rain gauges located in southeastern Arizona. We find an intensification of monsoon sub-daily rainfall intensities starting in the mid 1970s that has not been observed in previous studies or simulated with high-resolution climate models. Our results highlight the need for long-term, high spatiotemporal observations to detect environmental responses to a changing climate in highly-variable environments, and shows that analyses based on limited observations or gridded datasets fail to capture temporal changes potentially leading to erroneous conclusions.