Analysis of soil moisture trends in the Salt River watershed of central Arizona     

Bohumil M. Svoma  Robert C. Balling Jr.  Andrew W. Ellis 《Theoretical and Applied Climatology》2010,102(1-2):159-169

In this investigation, we generate estimates of soil moisture for the Salt River basin on which the expanding city of Phoenix, Arizona relies upon for nearly half of its water supply. While previous empirical studies have produced mixed results concerning recent drought trends in the southwestern USA, our results support the many numerical climate models which predict that this region will become drier in response to the buildup of greenhouse gases. Over the period 1895–2007, we found that soil moisture levels revealed no significant change. However, if we restrict the study to the period 1980–2007, soil moisture levels have decreased at a highly statistically significant rate. We could find little evidence that the trend is associated with variations in El Niño–Southern Oscillation and the Pacific Decadal Oscillation. Increasing surface pressure over our study area during the latter half of the twentieth century may be a catalyst for the drier conditions.  相似文献   

Expansion of the northern hemisphere subtropical high pressure belt: trends and linkages to precipitation and drought     

Bohumil M. Svoma  Daniel S. Krahenbuhl  Chad E. Bush  Jonny W. Malloy  Joshua R. White  Melissa A. Wagner 《自然地理学》2013,34(3):174-187

A critical issue in research concerning long-term climate change is the relationship between circulation features and global temperature variations. We establish that the annual areal size of the northern hemisphere subtropical high pressure belt (SHPB), as defined by seven 500-hPa height isohypses, shares over 70% of the variability with global annual near-surface air temperature since 1948. The area enclosed by the 5850-m isohypse of the 500-hPa surface in the northern hemisphere has more than doubled since the 1950s, with greatest increases over northern Africa, the Middle East and India. A long-term historical run of a coupled global climate model shows rapidly increasing SHPB annual sizes, since the mid-1970s. Since the SHPB’s descending air produces increased aridity, SHPB expansion may transition humid regions to more arid lands. To examine this aspect, first, variations in recorded precipitation using a gridded database for the region experiencing expansion of the SHPB show a decrease in precipitation (though significant only at the 88% confidence level) over the last 60?years. Second, variations in a 0.5° spatial resolution monthly drought index, the Standardized Precipitation Evapotranspiration Index, are highly correlated (+0.78) with annual variations in the area enclosed by the 500-hPa height isohypses. These results support those of previous investigations that suggest further northward expansion of the northern hemisphere subtropical dry zones with continued global climate change.  相似文献   

An anthropogenic signal in Phoenix, Arizona winter precipitation   总被引：1，自引：0，他引：1  

Bohumil M. Svoma  Robert C. Balling Jr 《Theoretical and Applied Climatology》2009,98(3-4):315-321

Many other investigators have shown pronounced weekly cycles in atmospheric composition, particularly in large urban settings. A substantial body of literature shows that the varying concentrations of fine atmospheric aerosols (particulate matter (PM)_2.5) impact precipitation processes; generally, higher concentrations of these aerosols tend to depress winter precipitation especially in short-lived, shallow, and orographic clouds. Phoenix, Arizona has a large population relying heavily on motor vehicles as the primary means of transportation. This results in a strong weekly cycle of PM_2.5 concentrations with a maximum on Wednesday and Thursday and a distinctive minimum on the weekend. To determine any influence on rainfall, we analyze daily precipitation records from 291 stations in the Phoenix area and find a strong weekly cycle in winter precipitation frequencies with maximum values on Sunday and minimum values on Thursday. The weekly cycle in precipitation frequency strengthens slightly moving eastward (downwind) across the metropolitan area as well as with increasing proximity to the metropolitan area. These results strongly suggest that human activity is influencing winter precipitation primarily by the suppressing effect of PM_2.5.  相似文献