Variability of precipitation in the Atacama Desert: its causes and hydrological impact

Abstract

An analysis of the variability of rainfall at 27 stations and run-off at 4 stations between 18°and 28°S in the Atacama Desert has been carried out. A diagonal boundary zone between summer-and winter-dominated areas is related to the provenance of the rainfall: Amazonia to the north and east, and Pacific moisture to the south. It is shown that winter rainfall tends to be higher during El Niño years, while heavy summer rainfall tends to be more common during La Niña. However, rather than the precipitation being directly controlled by El Niño-Southern Oscillation (ENSO), previous studies have shown that it is the regional synoptic conditions towards the source areas that largely control temporal precipitation variations, and these are in turn either facilitated or inhibited by ENSO. The spatio-temporal variability of precipitation leads to a complex hydrological regime. Perennial rivers in the north and central Atacama Desert tend to flood in summer, especially during La Niña conditions, from source to sea. Perennial rivers in the south tend to flood in summer, but as a result of melt from the previous years snowfall, especially during El Niño conditions, again from source to sea. However, while inland areas may also experience flooding of ephemeral rivers in summer associated with La Niña, coastal areas on the other hand experience winter flooding of ephemeral rivers associated with El Niño. Surface water flood events, and groundwater recharge events reported in the literature, are generally less frequent than ENSO events, confirming the requirement for specific synoptic conditions and making the use of averages unsound for present-day hydrological studies and water resource evaluations.

Origin and development of theater-headed valleys in the Atacama Desert, northern Chile: Morphological analogs to martian valley networks

“…The cold Humboldt Current runs northward along the Pacific coast, cooling the near-surface air and creating a stable temperature profile, so moist air is trapped along the coast. In northern Chile, the annual precipitation and resulting fluvial dissection decline rapidly westward, with annual rainfall ranging from $20 cm/a at higher elevations to <0.1 cm/a near the coast (Houston and Hartley, 2003;Houston, 2006;Strecker et al, 2007;García et al, 2011). Long-term semiarid to hyperarid climates, arguably since the late Triassic (Clarke, 2006) or late Jurassic (Hartley et al, 2005), has combined with rapid uplift of the Andes since the Miocene (when the rain shadow and aridity were enhanced) to create a landscape in which tectonic features are unusually well expressed on the surface (Gregory-Wodzicki, 2000;Rech et al, 2006).…”

“…1a and 2). Intermittent runoff from the Andean headwaters is the only significant water source for most of the quebradas (e.g., Houston, 2006), so the few locally sourced tributaries to the lower reaches are typically shallow, very infrequently active, hanging, and partly mantled by aeolian sand.…”

Climate change along the arid coast of northern Chile

“…A shorter rainless period was also registered in Chañaral (26°21 S, 70°37 W) between 1956 and 1961 (data not shown here) and appears as a relatively dry phase between the 1950s and 1960s as far south as Copiapo. Several studies on the interannual rainfall variability in northern Chile have documented its close relationship with ENSO in the sense that anomalously wet years tend to occur during the warm (El Niño) episodes (Ortlieb, 1995;Garreaud and Rutllant, 1996;Vargas et al, 2000;Houston, 2006), although not every El Niño event results in an enhanced frequency of rainfall episodes, and the intensity of rainfall events is not necessarily influenced by the strength of El Niño (Ortlieb, 1995). The forcing mechanisms of anomalous winter rainfall that have been studied and described for central Chile (Rutllant and Fuenzalida, 1991;Montecinos and Aceituno, 2003) are also applicable for the coastal region further north.…”

Regionalization of patterns of flow intermittence from gauging station records

“…Many river networks in arid regions are entirely intermittent (Jacobson and Jacobson, 2013;Meirovich et al, 1998). Temporal patterns of flow intermittence range from near-perennial flow regimes with infrequent, short periods of zero flow to episodic flow regimes with rare flow events separated by long zero-flow periods (Crocker et al, 2003;Houston, 2006;Larned et al, 2011;Meirovich et al, 1998). In turn, the duration and frequency of zero-flow periods are increasingly viewed as the primary determinants of river ecosystem processes (Corti et al, 2011;Datry et al, 2011;Dieter et al, 2011) and biotic communities (Arscott et al, 2010;Datry, 2012;Davey and Kelly, 2007).…”