Thomas Condom

The Altiplano is an endoreic catchment (196 000 km2) of the Central Andes. At present, the wet season corresponds to the southward displacement of the intertropical convergence zone (I.T.C.Z.). The annual rainfall decreases from the north (about 800 mm.yr-1) to the south (about 200 mm.yr-1). The studied sub-catchment is the northern one of Titicaca lake (56 275 km2). Over the last decades, the water level of this lake has fluctuated of few meters around 3810 m.a.s.l. and the mean value of the surface outflow was 50 m3/s. During the last 11 000 years, the lake level has dropped down to 3710 m. An hydrological annual balance model allows to simulate the time evolution of the water level according to different rainfall scenarios. This lumped model takes into account the modifications of the ratio between the lake area and the watershed area. Using present potential evaporation, this model shows that a 18% decrease of the rainfall induces a drop of 100 meters in 380 years. On the base of this annual model, we developed a second one with a three-month time step. It takes into account the reservoir effect of the soil. This model includes two parameters whose values were calibrated with the hydrological data available on the last 15 years. For another 10- year period, the computed lake levels are in good agreement with the observations. The computed altitude of the water level decreases, like for the first model, of 100 m when the annual rain amount is 18% less than the present amount. However, the duration to achieve this value is lower than with the annual mass balance model. It is 340 years when 80% of the rainfall concentrates on three months and it is 310 years when the rainfall amount is well distributed all over the year.

The estimation of precipitation over the broad range of scales of interest for climatologists, meteorologists and hydrologists is challenging in high altitudes of tropical regions, where the spatial variability of precipitation is important while in situ measurements remain scarce largely due to operational constraints. Three different types of rainfall products – ground based, satellite derived, RCM outputs – are compared here during the hydrological year 2012/13 in order to retrieve rainfall patterns at time scales ranging from sub-daily to annual over a watershed of approximately 10 000 km<sup>2</sup> in Peru. It is a high altitude catchment, located in the region of the Cordillera Blanca, with 41 % of its area above 4000 m a.s.l. and 340 km<sup>2</sup> glaciated. Daily in situ data are interpolated using a kriging with external drift (KED) algorithm; the satellite product is TRMM 3B42, which incorporates monthly gauge data; RCM outputs are obtained from W...

Long-term climate records are rare at high elevations in Southern Europe. Here, we reconstructed the evolution of Ossoue Glacier (42°46' N, 0.45 km<sup>2</sup>), located in the Pyrenees (3404 m a.s.l.), since the Little Ice Age (LIA). Glacier length, area, thickness and mass changes indicators were generated from historical datasets, topographic surveys, glaciological measurements (2001–2013), a GPR survey (2006) and stereoscopic satellite images (2013). The glacier has receded considerably since the end of the LIA, losing 40 % of its length and 60% of its area. Three periods of marked ice depletion can be identified: 1850–1890, 1928–1950 and 1983–2013, as well as two periods of stabilization or slightly growth: 1905–1928 and 1950–1983; these agree with climatic datasets (air temperature, precipitation, North Atlantic Oscillation, Atlantic Multidecadal Oscillation). In the early 2000s, the area of the glacier dropped below 50% of its area at the end of the LIA. Geode...

Thanks to the IRD (Institut de Recherche pour l’Environnement, France) and local Andean institutions, a permanent observation network including glaciological mass balance, hydrological balance and locally, energy balance, could be maintained from 1991-1995 to date on a dozen of glaciers from Bolivia, Peru and Ecuador. We present a very synthetic view of the main fields investigated and the results focusing on the nature, intensity and coherence of the glacier shrinkage signal observed since the last 1970s and its linkage with climate evolution at regional scale. Some prospective features of this scientific program held in cooperation with the respective countries are presented. Regarding the sustainability of the network in the future, we think that it will be achieved thank to a strengthening of local institutions and the permanent support of international organizations.

The Andean Altiplano is an endoreic basin (196 000 km^2) of large latitudinal extension from 14^o to 23^oS. It consists of two smaller catchments separated by the Ulloma strait. The northern basin (14^o--17^oS) includes Lake Titicaca, perennial from the final Pleistocene. The southern catchment (17^o--22^oS) includes the Salar de Uyuni which is a thick and large salt crust attesting to the existence of the paleolake Tauca, dated 15 000 BP. The main question is whether the major inflow to this paleolake came as surface runoff from the northern catchment (Lat

ABSTRACT Some authors showed that for a fixed 0°C isotherm altitude, the ELA of the Peruvian and Bolivian glaciers from 5 to 20°S can be derived from a log-normal expression of the mid-annual rainfall amount (P). We present an extrapolation of this method to the entire Andes from 0°S to 50°S on the base of data from four glaciers: (i) Antizana (Equator, 0°29'S,78°09'W); (ii) Zongo (Bolivia, 16°15'S, 68°07'W), (iii) Sajama (Bolivia, 18°06'S, 68°50'W), and (iv) Glaciar de los Tres (Argentina, 49°20'S, 73°00'W). First, we determine the altitude of the annual 0°C isotherm from the altitudinal gradient of temperature and from the mean annual temperature measured by a meteorological station situated close to the glacier. Then, using this altitude and the mid-annual precipitation amount, we calculate the ELA. The expression allows to take into account the inter-annual variation of the isotherm 0°C altitude. The values of the ELA computed on the base of (P) and (T) differ by less than 200 m from those derived from glacier mass balance measurements or satellite imageries. This result validates the methodology for the instrumented period. This parsimonious method can then be applied to past climatological conditions on the Altiplano. For example during the Late Glacial Maximum, the relationship allows the elaboration of precipitation/temperature schemes that explain the glacier advance of 800 to 1000 m on the Altiplano. The annual temperature would be comprised between 0.6 and 3.3 °C, while the annual precipitation would be comprised between 700 and 1000 mm/yr.

ABSTRACT Hydro-sedimentology development is a great challenge in Peru due to limited data as well as sparse and confidential information. This study aimed to quantify and to understand the suspended sediment yield from the west-central Andes Mountains and to identify the main erosion-control factors and their relevance. The Tablachaca River (3132 km2) and the Santa River (6815 km2), located in two adjacent Andes catchments, showed similar statistical daily rainfall and discharge variability but large differences in specific suspended-sediment yield (SSY). In order to investigate the main erosion factors, daily water discharge and suspended sediment concentration (SSC) datasets of the Santa and Tablachaca rivers were analysed. Mining activity in specific lithologies was identified as the major factor that controls the high SSY of the Tablachaca (2204 t km2 yr-1), which is four times greater than the Santa's SSY. These results show that the analysis of control factors of regional SSY at the Andes scale should be done carefully. Indeed, spatial data at kilometric scale and also daily water discharge and SSC time series are needed to define the main erosion factors along the entire Andean range.

A model was developed for estimating the delay between a change in climatic conditions and the corresponding fall of water level in large lakes. The input data include: rainfall, temperature, extraterrestrial radiation and astronomical mid-month daylight hours. The model uses two empirical coefficients for computing the potential evaporation and one parameter for the soil capacity. The case studies are two subcatchments of the Altiplano (196 000 km2), in which the central low points are Lake Titicaca and a salar corresponding to the desiccation of the Tauca palaeolake. During the Holocene, the two catchments experienced a 100 m fall in water level corresponding to a decrease in water surface area of 3586 km2 and 55 000 km2, respectively. Under modern climatic conditions with a marked rainy season, the model allows simulation of water levels in good agreement with the observations: 3810 m a.s.l. for Lake Titicaca and lack of permanent wide ponds in the southern subcatchment. Simulations were carried out under different climatic conditions that might explain the Holocene fall in water level. Computed results show quite different behaviour for the two subcatchments. For the northern subcatchment, the time required for the 100 m fall in lake-level ranges between 200 and 2000 years when, compared with the present conditions, (i) the rainfall is decreased by 15% (640 mm/year), or (ii) the temperature is increased by 5.5 °C, or (iii) rainfall is distributed equally over the year. For the southern subcatchment (Tauca palaeolake), the time required for a 100 m decrease in water level ranges between 50 and 100 years. This decrease requires precipitation values lower than 330 mm/year.