Actual Climatic Conditions in ERB. Online Resource 1 corresponding to:

Transcription

1 Actual Climatic Conditions in ERB. Online Resource 1 corresponding to: Article Title: Climatic Trends and Impact of Climate Change on Agriculture in an Arid Andean Valley. Journal Name: CLIMATIC CHANGE Authors: Melitta Fiebig-Wittmaack 1,2, Orlando Astudillo, Elaine Wheaton, Virginia Wittrock, César Perez, Antonio Ibacache Affiliations and address of the corresponding author: 1. Departamento de Matemática, Universidad de La Serena, La Serena, Chile 2. Centro de Estudios Avanzados en Zonas Áridas (CEAZA), La Serena, Chile melitta.fiebig@userena.cl 1

2 1 Temperature The cold Humboldt Current and other factors produce temperature anomalies which can present challenges for agriculture. An example of an anomaly is the maximum (minimum) temperature increases (decreases) with the altitude along the ERB, from the lower coastal sites to the higher sites in the valley. On average, the annual minimum (maximum) near-surface air temperatures at coastal stations can be 2-7 C higher (3-7 C lower) than those of the km inland stations (Fiebig-Wittmaack et al. 2008). The daily vertical temperature profiles were obtained from radiosonde data launched in parallel from La Serena site at the coast and Vicuña inland (Figure1) during several short campaigns (Kalthoff et al. 2002; Kalthoff et al. 2006; Khodayar et al. 2008). The results showed that this anomalous behavior of the temperature holds up to approximately 1600 m.a.s.l. and then the temperature decreases with altitude at the usual thermal gradient (Fiebig-Wittmaack et al. 2008). 2 Hydrological characteristics A major portion of the precipitation in the watershed occurs between May and August, but the greater runoff, controlled by snow-ice melting, takes place in spring (SON)- summer (DJF) because the water stored in the mountains is gradually released then. Most of the precipitation in the Andean zone, above 3500 m, occurs as snowfall with an average water-equivalent of 180 mm yr -1 (annual average for the period ) and a peak of 740 mm in 1987, coinciding with an El Niño year (Zavala et al. 2008). Because of the extremely low rainfall in the cultivated area of the ERB an integrated irrigation system with dams and irrigation channels has been constructed. The most important infrastructure is the Embalse Puclaro reservoir, at 550 m.a.s.l. The construction of the dam was completed in 1999 and the reservoir was filled with water in the subsequent years. Another smaller and older dam is located farther upstream, the La Laguna dam at 3200 m.a.s.l. 2

3 Even though the annual rainfall is low in the ERB, extreme precipitation events do occur. In these cases, large amounts of precipitation, for example 40 mm, during a short period (1-3 days) are recorded. Then the water volumes in the basin gain destructive power and result in flooding and mudslides that cause considerable damage (Pérez et al. 2008). But these extreme events are rare: for example, during the period only eight such extreme precipitation events are recorded at the Vicuña site. 3 Evapotranspiration and Dew In the middle of the ERB, the actual evaporation is very high, but the areas with natural vegetation as compared with cultivated fields with good irrigation techniques, exhibit completely different evapo-transpiration behaviors. On average, the first type of area has accumulated annual evapo-transpiration amounts of 65 mm yr -1 (which is about 65% of the annual precipitation). In contrast, the second type of area has accumulated annual evapo-transpiration amounts of 750 mm yr -1 (Kalthoff et al. 2006). Due to the wind systems in the ERB, transport of moist marine air from the Pacific coast to the Elqui valley supplies enough moisture in the boundary layer so that nocturnal dew occurs regularly. The annual nocturnal sum of dew amounts to 5-10 mm yr -1 which represents the same order of magnitude as precipitation in dry years. As dew does not show the interannual variability of precipitation, it is well known that dew serves as an important additional source of water for natural vegetation in the coastal sector, as in several arid and semiarid environments (Munn 1966; Downing et al. 1994; Jacobs et al. 1999; Kalthoff et al. 2006). 4 Drought Climatic characteristics of the ERB include periodic droughts (Downing et al. 1994; Pérez et al. 2008). Two types of droughts occur in this area, that is, those affecting unirrigated areas and the areas with irrigation infrastructure. Drought can affect these two areas in quite different ways. For the unirrigated areas, drought is a consequence of low precipitation amounts in the area, i. e. meteorological drought. For the areas with irrigation infrastructure drought is a consequence of decreased river runoff, induced by low snowfall amounts and ice melting in the high Andes Mountains, i.e. hydrological drought. 3

4 As a result, the drought for the unirrigated areas has almost no relation with the drought in the irrigated areas where the main agrarian productivity occurs. For example, during 2007, all the precipitation monitoring stations of the Chilean national water management institution (Dirección General de Aguas (DGA)) at the ERB located at less than 2000 m.a.s.l. showed a precipitation deficit about 40 %, but the Andean La Laguna station showed a precipitation surplus of about 70 % of the annual mean precipitation (average over the last 30 years). Effectively during these years in the ERB the unirrigated areas have had a drought problem, but the areas with irrigation infrastructure did not have any drought problems as a consequence of abundant snow-melt in the high Andes. Additional References Fiebig-Wittmaack M, Pérez C, Lazo E (2008): Aspectos climáticos del Valle del Elqui (Climatic aspects of the Elqui valley). In: Cepeda J (ed) (2008) Los sistema naturales de la cuenca del Río Elqui (Región de Coquimbo, Chile): Vulnerabilidad y cambio del clima (The natural systems in the Elqui river basin (Coquimbo, Chile): Vulnerability and climate change). Ediciones Universidad de La Serena, Chile [ Available from Universidad de La Serena, Dirección de Investigación, Casilla 599, La Serena, Chile.] pp Jacobs A F G, Heusinkveld B G, Berkowicz S M (1999) Dew deposition and drying in a desert system: a simple simulation model. Journal of Arid Environments 42: Kalthoff N, Bischoff- Gauß I, Fiebig-Wittmaack M, Fiedler F, Thürauf J, Novoa E, Pizarro C, Castillo R, Gallardo L, Rondanelli R, Kohler M (2002) Mesoscale Wind Regimes in Chile at 30ºS. J Appl Meteor 41: Munn R E (1966) Descriptive Micrometeorology. Academic Press, New York. Pérez C, Fiebig-Wittmaack M, Cepeda J, Pizarro-Araya J (2008) Desastres naturales y plagas en el valle del Elqui (Natural hazards and plagues in the Elqui valley). In: Cepeda J (ed) Los sistema naturales de la cuenca del Río Elqui (Región de Coquimbo, Chile): Vulnerabilidad y cambio del clima (The natural systems in the Elqui river basin 4

5 (Coquimbo, Chile): Vulnerability and climate change). Ediciones Universidad de La Serena. [ Available from Universidad de La Serena, Dirección de Investigación, Casilla 599, La Serena, Chile.] pp Zavala H, Trigos H (2008) Hidrología de la cuenca del río Elqui (Hydrology of the Elqui river watershed). In: Cepeda J (ed) Los sistema naturales de la cuenca del Río Elqui (Región de Coquimbo, Chile): Vulnerabilidad y cambio del clima (The natural systems in the Elqui river basin (Coquimbo, Chile): Vulnerability and climate change). Ediciones Universidad de La Serena. [ Available from Universidad de La Serena, Dirección de Investigación, Casilla 599, La Serena, Chile.] pp