The Andes Chap. 1 - Geographical context Chap. 2 - Large scale climate

Transcription

1 The Andes Chap. 1 - Geographical context Chap. 2 - Large scale climate René D. Garreaud Geophysics Department Universidad de Chile Center for Climate and Resilience Research, CR2

2 We all love the Andes.. More than 6000 km long, from the Caribbean sea to Patagonia Very tall mountain, specially at tropical/subtropical (>5000 m ASL) Water tower for 50 Millions people in seven countries A nearly 2D mountain when considering synopuc-scale flow Exposed to easterlies and deep convecuon at low lautudes Exposed to westerlies and frontal systems in midlautudes Plenty of paleo-records (glaciers, trees, lake sediments.) Many mysteries to be solved Nonetheless Its extreme geography set the stage for hydromet. hazards Under sampled (meteorology + hidrology) Highly sensiuve to climate change

3 Basic Features Topography PrecipitaUon PopulaUon (2015) Σ 50 Mill Eq Merida Caracas Medellin Cali Quito Cuenca Bogota S 20 S 12.1 Huaraz Lima 1.5 Cuzco Juliaca La Paz Arequipa 1.5 Oruro Tarija Calama Salta Santa Cruz 30 S La Serena Tucuman 7.2 San;ago Mendoza S 50 S m ASL >5000 < 5 mm/yr >3000 < 50 p/km2 >1000 < 1 Villarica.8 Coyhaique Bariloche Esquel Natales

4 Basic Features

5 Climate Tectonics - Geomorphology Sea level Plenty of sediment transport Abundant rainfall Nazca Plate Wet slip Sea level Lidle sediment transport Deficient rainfall Nazca Plate Dry slip Adapted from Lamb and Davis; Nature 2003

6 Garreaud et al. 2009

7 Zonal (east-west) mean flow over the Andes Brown area: Terrain mean height Dashed line: 500 hpa, half of the atmosphere below! a. DJF b. JJA W Km 12 W E E Latitude Latitude

8 The complex mid- and low-level flow near the Andes CAO Choco LLJ SALLJET Coastal LLJ Jiang et al. 2013

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10 Another ocean to the east. Andes-Amazon connecuons Illustration of the components of surface water balance and atmospheric water balance for the observations and reanalysis datasets in the Andes and Amazonia sub regions of the Amazon River basin. Values are in units of mm.y-1. The arrow convention on the bottom left represents 1000 mm.y-1. Data source: Builes-Jaramillo and Poveda, 2018.

11 South America monsoonal regime and Altiplano rainfall Mean annual cycle Colors: OLR (proxy of precipitation) Streamlines: 200 hpa (~12 km) wind Bolivian High

12 Now you see it now you don t What controls the BH at submonthly Umescales

13 Summer Altiplano rainfall: Intraseasonal variability Falvey and Garreaud 2005

14 ConvecUve rainfall also exhibits a pronounced diurnal cycle

15 Seasonal march of the diurnal cycle of rainfall at 17 selected stauons in the tropical Andes of Colombia. The diurnal cycle is defined from 0700 to 0700 LST, and interpolated isolines indicate percent of total daily rainfall, with the color scale shown at the bodom. Boundaries of the neighboring (lel) Cauca and (right) Magdalena River valleys are shown in white. The inset at the bodom lel shows details of rain gauges located in the western flank of the Central range of the Andes. Source: Poveda et al. (2005).

16 Precipitacion en La-tudes medias Modest annual cycle in the extratropics

17 Where does it rain more? The elusive Orographic PrecipitaUon Gradient (OPG(laUtude)) Espinonza et al DistribuUon of mean annual rainfall over transect (around 6 N) along the three ranges of the Colombian Andes (Poveda)? DistribuUon of mean annual rainfall over transect (around 33 S) along the subtropical Andes

18 Central Chile climate P 300 mm/yr Short rainy season (JJA) T 15ºC (annual mean)

19 Central Chile Agriculture a miracle? P 300 mm/yr Short rainy season (JJA) T 15ºC (annual mean)

20 The Andean Credit Upper basin A km 2 P 900 mm/yr Lower basin, arable A km 2 P 300 mm/yr mm/yr mm/yr = mm/yr Lower basin, non arable A km 2 P 300 mm/yr

21 How does the spaual variability in surface parameters and meteorology affect water availability (e.g. river flow)? 1a 1b Daily mean river flow (m 3 /s) 600 Upper Maipo 3 Lower Mapocho San-ago rainfall [mm] 50 2a Jan Jul Jan Jul Jan 2b 0 Snowmelt regime, with strong year-to-year variability (1a versus 1b) Winter storms (2), non-linear (2a/2b), with sudden peak flow (3)

22 Other forms of Andean Credit Dr Wouter Buytaert:

23 Other forms of Andean Credit Sillitoe and Perello, 2005

24 But living close to the Andes has its risk Flooding of Mocoa, Putumayo, Colombia, on April 1st, 2017 At least 300 fataliues. Landslide SanUago foothills, May 3, 1993 At least 100 fataliues.

25 Interannual variability : Major ENSO impacts along the Andes Weder-JFMA Stronger upper- Level ST Jet Warmer - DJF Drier/Warmer DJF Weakened ST High Blocking High H H Weder-OND Weder-JJA Drier-DJF Colder EN years Storm Track Climo. Storm Track

26 Global Historical Climate Network (GHCN) PrecipitaUon Mean Temperature All stauons (anyume, any length) Century-long stauons (Ti<1905, Tf>1995, missdata<20%)

27 Hydro/met observing system in the high Andes Current coverage (DGA+DMC, pink circles) is reasonable in the central valley but dramaucally low at higher elevauons, where most of the water accumulauon takes place

28 How much really rains in the central Andes? Different products, different places

29 Regular sounding stauons Lima La Paz

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32 Mountain induced circulauon: subsidence west of the Andes Tropical Easterlies Subtropical Westerlies Extratropical Westerlies

33 Basic Features Central Andes Glaciers Tropical Glaciers La Paz Seasonal snow Pack / Glaciers Bogota Quito Arequipa Salta NPI + SPI 0 C DJF Andes crest height Lima San;ago Natales 0 C JJA Precipita;on atop of the Andes (mm/yr)