The Limarí River Basin
The semi-arid Limarí River Basin, located in the Region of Coquimbo is bounded by the Pacific Ocean and the high Andes. The area’s climate records show vast spatial, intra- and inter-annual climate variations. Mean annual precipitation has a strong geographical modulation, ranging between approx. 43 and 270 mm per year from the coastal area to the Andes, with an average of only 125.7 mm (Oyarzún, 2010; Verbist et al., 2010).
The seasonal cycle of rainfall is well pronounced, as almost 85% of annual precipitation falls between May and June (Souvignet et al., 2010). Extended dry spells are a common feature and dry periods without precipitation may last from one up to multi-years (Favier et al., 2009). This inter-annual variability of rainfall is linked to ENSO (El Niño Southern Oscillation), with often positive rainfall anomalies during El Niño events and below normal rainfall during La Niña conditions (Verbist et al., 2010). This frequently causes a natural shortage of water availability, leading to meteorological droughts.
Temperature also displays a strong seasonality. Minimum temperatures occur in June-August, coinciding with precipitation maximums and hence snowfall above 1000m of elevation. The central climate station in Ovalle between 1965-2009 recorded a mean annual temperature of 16,6 °C with a minimum of 9, 4°C and a maximum of 23,8°C. Furthermore, spatial temperature variation is strong depending on elevation and the South-North gradient.
THE Enso phenomenon and its impact on climate variability in central chile
The El Niño–Southern Oscillation (ENSO) is a well-known phenomenon in dry Central Chile. The irregular – every 2-7 years – El Niño and La Niña years originate in the tropical Pacific and are accompanied by interactions between the ocean and the atmosphere and teleconnections over the tropical Indian and Pacific Oceans. They have clear signals in sea surface temperature (SST), atmospheric pressure patterns and a varying strength of the Pacific trade winds.
While El Niño years account for higher sea surface temperatures and lower air pressure in the Eastern Pacific, La Niña conditions are generated by cold sea surface temperatures originating in the tropical Pacific (Mc Phaden et al., 2006; Tudhope et al. 2001). Higher El Niño SSTs lead to higher evaporation rates and hence to above-average rainfall in the eastern Pacific and Central Chile during winter and late spring. At the same time, it causes severe droughts in eastern Australia and storms along the equator. Measuring sea surface temperature and atmospheric pressure enables the prediction of El Niño and la Niña events more than several months ahead (Montecinos & Aceituno 2003). On the other hand, La Niña years lead to dry conditions in Central Chile in winter and late spring. However, there is no reliable correlation between the ENSO index value and precipitation rates.
It is believed that ENSO is sensitive to global warming. Tudhope et al. (2001) analyzed annually banded corals from Papua New Guinea to determine how ENSO has varied in response to both glacial and interglacial conditions during the past 130,000 years. They have found that in the past century, the ENSO signals have been stronger than during the seven earlier cool (glacial) and warm (interglacial) periods analyzed and they suggest that this change might be due to glacial retreat and solar forcing (Tudhope et al., 2001). Gomez et al. (2011) conducted a further paleoclimatic analysis of high-resolution Lake Tutira storm sediment records for the past 6800 years and derived historical rainfall events indicating ENSO patterns with teleconnections to records from New Zealand, the tropical Pacific and Antarctica. They also suggest that solar radiation strength plays a crucial role and therefore might be the reason for the accelerated ENSO cycle during the recent decades (Gomez et al., 2011).
hydrology and water infrastructure
During the passage of cold fronts, the 0°C isotherm typically is located at about 2.500 masl. permitting snow accumulation in the upper half of the basins during winter. The upper watersheds in the basins are therefore typically snowmelt dominated, and due to the time lag between snow accumulation and melt, maximum river discharge is reached during late spring and summer month (October-January) (Vicuna et al., 2010). In lower altitudes, in wet years a two peak hydrograph is observed, where the first peak is a response to liquid precipitation, whereas the second peak in spring is related to snow or glacier melt (see Favier et al., 2009). The Hurtado River drains the driest north-eastern part of the basin, filling the Recoleta Reservoir which has a capacity of 100 million m³. The Rio Grande has a much larger drainage area of 544m² due to the southern contributions of the Río Rapel (Álvarez et al., 2006; Oyarzún, 2010). The Guatulame River is regulated through the Cogotí reservoir with 150 million m³ storage capacity. The river runoff from Río Guatulame downstream of the Cogotí reservoir and from the Río Grande is stored by the reservoir La Paloma, with a storage capacity of 750 million m³. Hence, the whole basin is regulated through the three reservoirs forming the ‘La Paloma’-System with a potential total capacity of 1 billion m³, to store and distribute the available water throughout the year and to irrigate 48.000 hectares of cropland (Parga et al., 2005; Álvarez, 2006; Oyarzún, 2010).
References and further reading:
ÁLVAREZ, P., KRETSCHMER, N., OYARZUN, R. (2006): “Water Management for Irrigation in Chile: Causes and Consequences” paper presented at the international water fair “Wasser Berlin 2006”.
FAVIER, V., FALVEY, M., RABATEL, A., PRADERIO, E. and D. LÓPEZ (2009): Interpreting discrepancies between discharge and precipitation in high-altitude area of Chile’s Norte Chico region (26–32°S), Water Resources Research, 45, W02424, doi:10.1029/2008WR006802.
GOMEZ, B.; CARTER, L.; ORPIN, A.R.; COBB, K.M.; PAGE, M.J.; TRUSTRUM; N.A.; PALMER A.S. (2011): ENSO/SAM interactions during the middle and late Holocene, The Holocene, DOI: 10.1177/0959683611405241.
MC PHADEN, M. J., ZEBIAK, S.E., GLANTZ, M. H., (2006); ENSO as an Integrating Concept in Earth Science, Science 15 December 2006: 314 (5806), 1740-1745. [DOI:10.1126/science.1132588].
MONTECINOS, A.; P. ACEITUNO (2003): Seasonality of the ENSO-related rainfall variability in central Chile and associated circulation anomalies. Journal of Climate, 16, 281-296.
OYARZUN, R. (2010) Estudio de caso: Cuenca del Limarí, Región de Coquimbo, Chile, Compilación Resumida de Antecedentes, Centro de Estudios Avanzados en Zonas Aridas- Universidad de la Serena (CEAZA-ULS).
PARGA, F., LEÓN A., VARGAS, X., FUSTER, R. (2005) El índice de pobreza hídrica aplicado a la cuenca del Río Limarí en Chile semiárido, volumen XI; El Agua en Iberoamérica en 2005. Assessed athttp://www.cricyt.edu.ar/ladyot/publicaciones/cyted_libro_XII/articulos/093.pdf on the 15th of August 2011.
PEEL, M.C., FINALYSON, B.L. and MC MAHON, T.A. (2007): Updated World Map of the Köppen‐Geiger Climate Classification. Hydrology and Earth System Sciences, 11(5): 1633‐1644.
SOUVIGNET, M., GAESE, H., RIBBE, L., KRETSCHMER, N. & OYARZUN, R. (2010): Statistical downscaling of precipitation and temperature in north-central Chile: an assessment of possible climate change impacts in an arid Andean watershed, Hydrological Sciences Journal, vol. 55, no. 1, pp. 41-57.
TUDHOPE, A.W., CHILCOTT, C. P., MC CULLOCH, M.T., COOK, E.R., CHAPPELL, J.; ELLAM, R. M.; LEA, D.W.; LOUGH, J.M. and SHIMMIELD, G.B. (2001): Variability in the El Niño Southern Oscillation Through a Glacial-Interglacial Cycle; Science, Vol. 291, 23.
VERBIST, K., ROBERTSON, A.W., CORNELIS, W., GABRIELS, D. (2010): Seasonal predictability of daily rainfall characteristics in central-northern Chile for dry-land management, Journal for Applied Meteorology and Climate, 49(9), 1938-1955.
VICUñA, S., GARREAUD, R.D. & MC PHEE, J. (2010): "Climate change impacts on the hydrology of a snowmelt driven basin in semiarid Chile", Climatic Change, vol. 105, no. 3-4, pp. 469-488.