Spatial extent of the North American Monsoon: Increased cross‐regional linkages via atmospheric pathways

Abstract

[1] The North American monsoon is a key feature affecting summer climate over Southwestern North America. During the monsoon, evapotranspiration from the Southwest promotes transference of water to the atmosphere which is subsequently distributed across the continent -linking the SW to other regions via atmospheric hydrologic connectivity. However, the degree to which atmospheric connectivity redistributes monsoonal terrestrial moisture throughout the continent and its sensitivity to climate disturbances such as drought is uncertain. We tracked the trajectory of moisture evapotranspired within the semiarid Southwest during the monsoon season using a Lagrangian analytical model. Southwest moisture was advected north-east accounting for $15% of precipitation in adjacent Great Plains regions. During recent drought (2000 -2003), this amount decreased by 45%. Our results illustrate that the spatial extent of the North American monsoon is larger than normally considered when accounting for hydrologic connectivity via soil moisture redistribution through atmospheric pathways.

Oceanic sources of continental precipitation and the correlation with sea surface temperature

“…During AprilSeptember these oceanic source areas are weaker, and continental moisture recycling becomes important [see also, e.g., Bisselink and Dolman, 2008;Dominguez et al, 2009;van der Ent et al, 2010]. Two other regions with strong seasonal patterns are regions 4 and 5 (near South America), which only are significant moisture sources during November-May.…”

“…This is always an arbitrary choice, and most studies have chosen it in terms of a certain flux but did not provide information on how much moisture the area within a boundary receives as a percentage of the source region's evaporation (forward tracking) or precipitation (backward tracking) [e.g., Sodemann et al, 2008;Dirmeyer et al, 2009a ;Dominguez et al, 2009 ;Drumond et al, 2010 ;Gimeno et al, 2010]. We like to argue that this information is crucial in assessing the spatial extent of a source region's influence.…”

“…However, this question is highly relevant for a wide range of disciplines in Earth sciences. It is of importance for seasonal weather forecasting [see, e.g., Dominguez et al, 2009;Tuinenburg et al, 2011;van den Hurk et al, 2012], land and water management [see, e.g., Bagley et al, 2012 ;Keys et al, 2012;Spracklen et al, 2012;Tuinenburg et al, 2012], as well as for our understanding of the role of the hydrological cycle in our climate system [see, e.g., Dominguez and Kumar, 2008 ;Dirmeyer et al, 2009b ;van den Hurk and van Meijgaard, 2009;Goessling and Reick, 2011 ;Durkee et al, 2012].…”

“…[4] Many of these atmospheric moisture tracking studies focused on a particular basin, country, or terrestrial region and identified the moisture sources or sinks for that region taking account of interannual or seasonal variability [e.g., Druyan and Koster, 1989;Numaguti, 1999;Yoshimura et al, 2004;Bosilovich and Chern, 2006;Nieto et al, 2006;Sodemann et al, 2008;Dominguez et al, 2009;Drumond et al, 2010;Gangoiti et al, 2011aGangoiti et al, , 2011bBagley et al, 2012;Keys et al, 2012;Tuinenburg et al, 2012]. More global characterizations of moisture sources showed the import and export of water vapor between nations [Dirmeyer et al, 2009a], or the oceanic versus terrestrial contributions to continental precipitation [e.g., van der Ent et al, 2010;Goessling and Reick, 2011] [5] Our own recent work [van der Ent et al, 2010;van der Ent and Savenije, 2011] showed that globally about 40% of the precipitation on land originates from continental rather than oceanic evaporation.…”

Spatiotemporal dynamics of global drought

“…Land-atmospheric feedback mechanisms, such as precipitation recycling [e.g. Rodriguez-Iturbe et al, 1991a,b;Eltahir and Bras, 1996] have been linked to the intensification and persistence [Giannini et al, 2003;Wu and Kinter, 2009;D'Odorico et al, 2013;Roundy et al, 2013], and even propagation of droughts within a continent [Dominguez et al, 2009;Sheffield et al, 2009;Sheffield and Wood, 2011]. Thus, in order to understand better how droughts evolve within a region, it is also important to take into account its surroundings, and the regions to which it is atmospherically connected.…”