The impact of elevation and flow dynamics on hydrological drought and wet spell characteristics in semi-arid southeast Arizona

Identification and understanding of the dominant control mechanisms of hydrological extremes has drawn worldwide attention in recent decades. However, detailed understanding of drought and wet spells within semi-arid regions has been hampered by the fact that identification is difficult for no flow conditions. Classification methods that have been developed for regions with perennial flow, do not work for ephemeral semi-arid rivers, while approaches for arid environments have difficulties to deal with seasonal runoff. Recently, a method was presented to identify hydrological extremes within semi-arid regions, by combining approaches developed for perennial flow and arid environments. However, this combined approach shows difficulties to identify drought and wet spells within semi-arid domains with a yearly precipitation cycle (e.g. monsoon). The current paper proposes to modify the combined method and make it suitable for these domains. The modified combined approach presented here to identify hydrological extremes was applied to decade-long discharge observations from 12 different locations within the San Pedro basin in southeastern Arizona. These locations correspond to catchments covering multiple elevation bands and runoff characteristics. Southern Arizona receives the majority of its rainfall from the summertime North American Monsoon (NAM), with frontal systems providing additional precipitation in winter. Using the modified method, the identified droughts and wet spells last longer compared to the previously defined combined procedure, and drought generally does not only start in spring at the end of the dry season. Furthermore, results show that if a drought or wet spell starts during the NAM or post-NAM season, it will generally last longer as compared to one that starts in winter or spring. This specifically holds for catchments with no perennial flow. By increasing the flow averaging interval, the new method also enables to observe multi-year drought and wet spells patterns. For the precipitation limited semi-arid San Pedro basin results show that multi-year wet spell and drought are rare. This is caused by the strong impact of the summertime NAM that generally acts both as a start and reset button for both types of hydrological extremes.

Comentarios sobre el patrón de asentamiento en el valle del Río Verde-San Pedro (Aguascalientes) durante el Epiclásico

Este trabajo presenta los resultados de un primer estudio sobre la distribución de los asentamientos prehispánicos del valle del Río Verde-San Pedro (Aguascalientes). Las investigaciones dieron como resultado un inventario de 24 asentamientos, cuyos datos fueron incorporados a un Sistema de Información Geográfica (SIG). Con la captura de variables en el SIG se pudieron establecer distinciones preliminares sobre el grado de jerarquía e integración entre estos asentamientos. Se espera que los resultados de estos estudios contribuyan a la discusión de los diferentes ritmos de crecimiento e interacción que pudieron tener las sociedades del septentrión mesoamericano durante el Epiclásico.Abstract: In this paper we show the results from an initial study on the distribution of pre-Hispanic settlements in the landscape of the Río Verde-San Pedro Basin, Aguascalientes. The investigations resulted in an inventory of 24 settlements whose data were incorporated into a Geographic Information System (GIS). With the capture of variables in the GIS, we were able to make preliminary distinctions about the degree of hierarchy and integration between these settlements. With this study we expect to contribute to the discussion of the different rates of growth and interaction that northern Mesoamerican societies might have experienced during Epiclassic.Résumé : Cet article présente les résultats d’une première étude sur la distribution des établissements préhispaniques de la vallée du Río Verde-San Pedro (Aguascalientes). Ces recherches ont permis de réaliser l’inventaire de 24 établissements, dont les caractéristiques ont été incorporées à un Système d’Information Géographique (SIG). Grâce à la saisie de ces variables sur le SIG, certaines distinctions préliminaires ont pu être établies quant au degré de hiérarchie et d’intégration entre ces différents établissements. Nous espérons que les résultats de cette étude contribueront à la discussion concernant les rythmes de croissance et d’interaction que connurent les sociétés du septentrion mésoaméricain durant l’Épiclassique.