Intensification of the North American Monsoon Rainfall as Observed From a Long‐Term High‐Density Gauge Network

Abstract

As the atmosphere gets warmer, rainfall intensification is expected across the planet with anticipated impacts on ecological and human systems. In the southwestern United States 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, subdaily, and daily observations from 59 rain gauges located in southeastern Arizona. We find an intensification of monsoon subdaily 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 show that analyses based on limited observations or gridded data sets fail to capture temporal changes potentially leading to erroneous conclusions.

Changing Climate Drives Divergent and Nonlinear Shifts in Flowering Phenology across Elevations

“…The considerable increase in precipitation variability in the Southwest could exacerbate the effects of drought by reducing growth and increasing mortality [35]. In addition, the increasing intensity of monsoon storms [36] will likely result in greater run-off, which means less moisture available to vegetation. In the study area, several dominant species have declined in abundance, particularly Carnegiea gigantea (saguaro), Juniperus deppeana var.…”

“…A second goal is to determine whether changing temperature and precipitation patterns are responsible for any community-specific changes in phenology. Since the late 1990s, the study area has been impacted by a long-term warm drought that is characterized by not only precipitation deficits but also rising temperatures, increasing precipitation intensity, and increasing precipitation variability [33][34][35][36]. This drought and longer-term climatic changes could be affecting communities and subpopulations along this gradient differently, in part because of species-and population-specific responses and spatial environmental variation that could modulate the changing abiotic conditions.…”

The impact of elevation and flow dynamics on hydrological drought and wet spell characteristics in semi-arid southeast Arizona

“…The southwest US has been drying out during recent decades, with seasonal and inter-annual precipitation variability during the North American Monsoon (NAM) becoming more extreme (Prein et al, 2015;Solander et al, 2017;Luong et al, 2017). This also holds for the San Pedro, with increasing temperatures and an increased number of extreme precipitation events (Demaria et al, 2019). Section 2.2 explained that long-term observations available for the San Pedro, show no statistically significant changes in measured runoff after 1960.…”

“…These latter drought have been related to increases in temperature over the last 25 years (e.g. Easterling et al, 2007;Woodhouse et al, 2010;Demaria et al, 2019), while some of the earlier peaks in hydrological extremes have been related to long-term variations in sea surface temperature (e.g. Ropelewski and Halpert, 1986;Sheppard et al, 2002;Ciancarelli et al, 2014).…”

“…For the southwest US increases in agricultural demand and a rapidly growing urban population have impacted this relatively water scarce region, affecting available streamflow and groundwater resources. Observations show a drying out of the southwest US during recent decades, with seasonal and inter-annual precipitation variability during the North American Monsoon (NAM) becoming more extreme (Luong et al, 2017;Demaria et al, 2019). As urbanization and population are expected to further increase, this drying can potentially cause serious water availability challenges, with an expected increase in the frequency and severity of drought (Seager et al, 2007(Seager et al, , 2015Cayan et al, 2010;Garfin et al, 2013;Cook et al, 2015;Jones and Gutzler, 2016;Berardy and Chester, 2017).…”