Five Hundred Years of Hydrological Drought in the Upper Colorado River Basin¹

Abstract

This article evaluates drought scenarios of the Upper Colorado River basin (UCRB) considering multiple drought variables for the past 500 years and positions the current drought in terms of the magnitude and frequency. Drought characteristics were developed considering water‐year data of UCRB’s streamflow, and basin‐wide averages of the Palmer Hydrological Drought Index (PHDI) and the Palmer Z Index. Streamflow and drought indices were reconstructed for the last 500 years using a principal component regression model based on tree‐ring data. The reconstructed streamflow showed higher variability as compared with reconstructed PHDI and reconstructed Palmer Z Index. The magnitude and severity of all droughts were obtained for the last 500 years for historical and reconstructed drought variables and ranked accordingly. The frequency of the current drought was obtained by considering two different drought frequency statistical approaches and three different methods of determining the beginning and end of the drought period (annual, 5‐year moving, and ten year moving average). It was concluded that the current drought is the worst in the observed record period (1923‐2004), but 6th to 14th largest in terms of magnitude and 1st to 12th considering severity in the past 500 years. Similarly, the current drought has a return period ranging from 37 to 103 years based on how the drought period was determined. It was concluded that if the 10‐year moving average is used for defining the drought period, the current drought appears less severe in terms of magnitude and severity in the last 500 years compared with the results using 1‐ and 5‐year averages.

Development of the Soil Moisture Index to Quantify Agricultural Drought and Its “User Friendliness” in Severity-Area-Duration Assessment

“…Guttman et al (1992) and Alley (1985) reported that PDSI depicted spatially does not identify areas of equal hydrologic drought intensity owing to the variability of precipitation and groundwater levels over large areas. It suggests that PDSI, Palmer hydrologic drought index (PHDI), and streamflow and their relationship to climate signals such as El Niño-Southern Oscillation (ENSO) provides only a broad framework for regional hydrologic drought dynamics (Piechota and Dracup 1996;Timilsena et al 2007;Tsakiris and Vangelis 2004). Therefore, an approach that is fundamentally linked to soil moisture and its measurement in the vadose zone, can only serve to enhance our ability to quantify local drought, especially during the crop-growing season, for the obvious linkages with evapotranspiration, precipitation, and deep soil moisture as reported in many studies (e.g., Sandvig and Phillips 2006;Hong and Kalnay 2000;Sheffield et al 2004;Entekhabi et al 1992;Koster et al 2004).…”

Development of streamflow projections under changing climate conditions over Colorado River basin headwaters

“…From 2000 through 2010, the Colorado River Basin has experienced the driest period on record and one the worst droughts in history (e.g, Timilsena et al, 2007). At the beginning of water year 1999 (October 1998), water storage in the Colorado River Basin was at 94 % capacity; in particular, the two largest reservoirs within the system, Lake Powell and Lake Mead, were at 98 % and 91 % capacity, respectively.…”

Analytical procedures for weekly hydrological droughts: a case of Canadian rivers

“…Likewise, the term "intensity" (ratio of severity to duration) has been used interchangeably with magnitude (Dracup et al, 1980;Panu & Sharma, 2002). Use of the term magnitude in the hydrological drought context seems to be gaining momentum (Timilsena et al, 2007;Lopez-Moreno et al, 2009). In view of the changing trend in the nomenclature of drought parameters, the term magnitude shall be used in place of severity, and the ratio of magnitude to duration shall be termed drought intensity in this study.…”