Characterizing and understanding the variability of streamflow drought indicators within the USA

Variability patterns of the annual frequency and timing of low streamflow days across the United States and their linkage to regional and large‐scale climate

“…There were three unique clusters, where low‐flow days mostly occurred in the summer and early fall months, which could be generated by climate extremes. The potential driving mechanisms were discussed in Pournasiri Poshtiri et al (), where they concluded that in the Western United States, precipitation deficit seems to play the key role, leading in declining the soil moisture and generating low flows in summer–fall (Pournasiri Poshtiri et al, ). However, in the Central and Western regions, where the vegetation coverage is denser, increased evaporation during the warm season tend to drive low flows in summer and fall (Pournasiri Poshtiri et al, ).…”

“…We run the PAM algorithm for a given number of K values and calculate SC each time for each station i . Then, we use the average of all SC for the evaluation of the number of clusters and determine the optimal number of clusters (e.g., Bernard et al, ; Pournasiri Poshtiri et al, ).…”

“…HCDN‐2009 represents headwater‐type stations whose flows are minimally impacted by human development (Lins, ). This data network is a valuable indication of observed natural streamflow records and has been employed in many streamflow studies (Frei, Kunkel, & Matonse, ; Kam & Sheffield, ; Newman et al, ; Pournasiri Poshtiri et al, ; Pournasiri Poshtiri & Pal, ; Pournasiri Poshtiri & Pal, ; Rossi, Whipple, & Vivoni, ; Timilsena, Piechota, Tootle, & Singh, ; Vidal et al, ). We define the climate year to be from April to March for all the analyses; this is so streamflow from the entire dry season are included in the annual values (Cravotta, ; Martin & Arihood, ; Martin, Fowler, & Arihood, ; United States Environmental Protection Agency, ).…”

“…Most natural streams within the U.S. experience annual variation of low‐flow events (Pournasiri Poshtiri, Towler, & Pal, ). Observed natural low‐flow records indicated a gradual drying tendency of headwater locations in several major river basins of the United States (Pournasiri Poshtiri & Pal, ).…”

“…They found that the co‐occurrence of warm and dry winter conditions leads to significantly longer, more severe summer low‐flow events and shorter winter low‐flow events (Dierauer et al, ). Recently, a study by Pournasiri Poshtiri et al () compared the spatial variability of low‐flow magnitude indicators versus deficit indictors, showing that magnitude indicators are significantly different from the deficit indicators, although they show similar linkages to the regional climate and meteorological drought (Pournasiri Poshtiri et al, ).…”