Space-time trends in U.S. meteorological droughts

Abstract

Understanding droughts in a climate context remains a major challenge. Over the United States, different choices of observations and metrics have often produced diametrically opposite insights. This paper focuses on understanding and characterizing meteorological droughts from station measurements of precipitation. The Standardized Precipitation Index is computed and analyzed to obtain drought severity, duration and frequency. Average drought severity trends are found to be uncertain and data-dependent. Furthermore, the mean and spatial variance do not show any discernible non-stationary behavior. However, the spatial coverage of extreme meteorological droughts in the United States exhibits an increasing trend over nearly all of the last century. Furthermore, the coverage over the last half decade exceeds that of the dust bowl era. Previous literature suggests that climate extremes do not necessarily follow the trends or uncertainties exhibited by the averages. While this possibility has been suggested for droughts, this paper for the first time clearly delineates and differentiates the trends in the mean, variability and extremes of meteorological droughts in the United States, and uncovers the trends in the spatial coverage of extremes. Multiple data sets, as well as years exhibiting large, and possibly anomalous, droughts are carefully examined to characterize trends and uncertainties. Nonlinear dependence among meteorological drought attributes necessitates the use of copula-based tools from probability theory. Severity-duration-frequency curves are generated to demonstrate how these insights may be translated to design and policy. 3

Rising synchrony controls western North American ecosystems

“…Instead, synchrony trends appear to be driven by variability in the North Pacific High and its effects on precipitation and meridional winds. This is consistent with Ganguli and Ganguly (2016) who found that drought, as defined only by precipitation and not temperature, had over the past century increased in spatial coverage across the southwestern region of the United States.…”

Spatial and temporal patterns of drought in the Continental U.S. during the past century

“…Further, the results with discrete time periods are sensitive to the choice of periods selected for comparison. The results are found to vary with the periods selected for comparison [ Ganguli and Ganguly , ]. In order to assess the temporal variation of drought characteristics, a moving window approach is applied by generating sequential 40 year moving windows (e.g., 1900–1939, 1901–1940, …, 1973–2012, 74 windows or the PDSI_d data set and 1948–1987, …, 1969–2008, 22 windows for the PDSI_s data set), following the approach proposed by Liu et al [].…”

“…For example, a region with decreasing D may have an increasing trend in S [Andreadis and Lettenmaier, 2006]. More recent studies [Sheffield et al, 2009;Ganguli and Ganguly, 2015;Liu et al, 2016] studied multiple drought characteristics (D, S, and I), but none of these studies have analyzed the trends for each drought characteristic individually. In this study, trends in D, S, and I are analyzed for CONUS.…”

“…Some recent studies analyzed drought characteristics separately with long and short return periods [e.g., Ganguli and Ganguly, 2015;Ge et al, 2016;Liu et al, 2016] and compared drought characteristics under a given return period in different time periods (e.g., 1900-1954versus 1955-2012in Ge et al [2016] and 1926-1969versus 1970-2013and 1950-1979versus 1980in Ganguli and Ganguly [2015). The use of two segmented periods provides a comparison of only two values which are representative of drought conditions in that period.…”

Spatio‐temporal drought patterns of multiple drought indices based on precipitation and soil moisture: A case study in South Korea

“…Many studies have been conducted to estimate the onset, persistence and termination of drought events using meteorological and hydrological variables (Ganguli and Ganguly, ; Mo, ; Shukla et al , , among others). Drough features such as duration, severity and intensity are commonly characterized by drought indices, which provide a more comprehensive perspective for drought monitoring and management compared to the direct use of hydro‐meteorological variables (e.g., precipitation, soil moisture [SM] and streamflow; Zargar et al , ).…”