Climatic trends and impact of climate change on agriculture in an arid Andean valley

Little is known about climate change and its impacts for the arid coastal and mountainous regions in northern Chile. The Elqui river basin, part of the Norte Chico of Chile between 27oS and 33oS latitude, is located south of the hyper-arid Atacama desert. Despite water scarcity, agricultural development in this region has been enhanced by agronomic practices and the marketing of valuable products. This paper characterizes the actual climate conditions and presents an overview and analyses of past climate variability, and future possible climate trends, emphasizing those relevant to agriculture. Precipitation shows an important decrease during the first decades of the past century. Runoff shows decreasing trends for the first half of the past century and increases for 1960 to 1985. Drought appears to be increasing. Statistical downscaling was accomplished using the Long Ashton Research Station Weather Generator. Both future periods of 2011 to 2030 and 2046–65 showed trends to higher minimum and maximum temperature. The number of hot days (maximum temperature greater than or equal to 30°C) has a strong increasing trend during October to April. Even though the downscaled results for precipitation do not show trends, the continuation of the present trend of low amounts is a concern. We discuss some implications of climatic changes for agriculture and we emphasize the importance of adaptation, especially to deal with water scarcity.     

Evolution of the atmospheric boundary-layer structure of an arid Andes Valley

Summary The boundary-layer structure of the Elqui Valley is investigated, which is situated in the arid north of Chile and extends from the Pacific Ocean in the west to the Andes in the east. The climate is dominated by the south-eastern Pacific subtropical anticyclone and the cold Humboldt Current. This combination leads to considerable temperature and moisture gradients between the coast and the valley and results in the evolution of sea and valley wind systems. The contribution of these mesoscale wind systems to the heat and moisture budget of the valley atmosphere is estimated, based on radiosoundings performed near the coast and in the valley. Near the coast, a well-mixed cloud-topped boundary layer exists. Both, the temperature and the specific humidity do not change considerably during the day. In the stratus layer the potential temperature increases, while the specific humidity decreases slightly with height. The top of the thin stratus layer, about 300 m in depth, is marked by an inversion. Moderate sea breeze winds of 3–4 m s⁻¹ prevail in the sub-cloud and cloud layer during daytime, but no land breeze develops during the night. The nocturnal valley atmosphere is characterized by a strong and 900 m deep stably stratified boundary layer. During the day, no pronounced well-mixed layer with a capping inversion develops in the valley. Above a super-adiabatic surface layer of about 150 m depth, a stably stratified layer prevails throughout the day. However, heating can be observed within a layer above the surface 800 m deep. Heat and moisture budget estimations show that sensible heat flux convergence exceeds cold air advection in the morning, while both processes compensate each other around noon, such that the temperature evolution stagnates. In the afternoon, cold air advection predominates and leads to net cooling of the boundary layer. Furthermore, the advection of moist air results in the accumulation of moisture during the noon and afternoon period, while latent heat flux convergence is of minor relevance to the moisture budget of the boundary layer. Correspondence: Norbert Kalthoff, Institut für Meteorologie und Klimaforschung, Universit?t Karlsruhe/Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany     

Vulnerability and adaptation in a dryland community of the Elqui Valley, Chile

Livelihoods in drylands are already challenged by the demands of climate variability, and climate change is expected to have further implications for water resource availability in these regions. This paper characterizes the vulnerability of an irrigation-dependent agricultural community located in the Elqui River Basin of Northern Chile to water and climate-related conditions in light of climate change. The paper documents the exposures and sensitivities faced by the community in light of current water shortages, and identifies their ability to manage these exposures under a changing climate. The IPCC identifies potentially increased aridity in this region with climate change; furthermore, the Elqui River is fed by snowmelt and glaciers, and its flows will be affected by a warming climate. Community vulnerability occurs within a broader physical, economic, political and social context, and vulnerability in the community varies amongst occupations, resource uses and accessibility to water resources, making some more susceptible to changing conditions in the future. This case study highlights the need for adaptation to current land and water management practices to maintain livelihoods in the face of changes many people are not expecting.     

Towards an Open Source Analysis Toolbox for Street Network Comparison: Indicators,Tools and Results of a Comparison of OSM and the Official Austrian Reference Graph

This article presents a novel open source toolbox for street network comparison based on the Sextante geoprocessing framework for the open source Geographic Information System Quantum GIS (QGIS). In the spirit of open science, the toolbox enables researchers worldwide to assess the quality of street networks such as OpenStreetMap (OSM) by calculating key performance indicators commonly used in street network comparison studies. Additionally, we suggest two new performance indicators for turn restriction and one‐way street comparisons specifically aimed at testing street network quality for routing. We demonstrate the use of this toolbox by comparing OSM and the official Austrian reference graph “Graph Integration Platform” (GIP) in the greater Vienna region.     

Model Simulations of the Boundary-Layer Evolution over an Arid Andes Valley

The boundary layer of the Elqui valley in the arid north of Chile exhibits several interesting phenomena, such as a very shallow convective boundary layer (CBL) during the day. In the morning, warming is observed in and above the CBL, while the humidity decreases in the CBL. At midday, in and above the CBL of the valley, the temperature stagnates. In the afternoon in the CBL the temperature decreases and humidity increases, although the latent heat flux is very low. Because the characteristic features of the valley atmosphere are hard to interpret from observations alone, model simulations were applied. The simulations indicate that all components of the budget equations, i.e. the turbulent flux divergences, advection via the sea breeze, the upvalley and upslope wind systems, as well as subsidence, contribute to the evolution of the valley atmosphere.     

The influence of a storage lake in the Arid Elqui Valley in Chile on local climate

Summary High-resolution model simulations were performed with the quadruple-nested version of the mesoscale model KAMM to investigate the impact of the new storage lake ‘Embalse Puclaro’ on the arid environment. The storage lake covers an area of 1 to 2 km in width and about 7 km in length. Model simulations were performed for a summer and a winter day. Due to a change in the surface properties, the installation of the storage lake resulted in a modification of the energy balance. Above the lake area, a stably stratified atmosphere establishes during the day and unstable stratification during the night. During the day, the latent heat flux is similar to that of the replaced cultivated ground, but is higher at the night. The influence of the storage lake on temperature and humidity can be seen to a height of about 300 m above ground level. During the night, water vapour accumulation results in relative humidity values of 100%, as a result a greater number of days with fog above the storage lake is likely when compared to the surrounding area. The storage lake does not produce its own lake breeze during the day, because the larger-scale up-valley wind is too dominant. However, a significant modification of the nocturnal down-valley wind above the lake area can be observed, especially in summer. As a consequence of the larger-scale valley wind system, the influence of the storage lake on the temperature, humidity, and wind field can be identified up to about 4 km on the downwind side.