Spatial distribution and trends of different precipitation variability indices based on daily data in Northern Chile between 1966 and 2015

Northern Chile is one of the most arid regions in the world, as it includes the Atacama Desert. At high elevations, most precipitation is observed only during a short period of the year, from December until March. This renders water availability a major concern for policymakers. Accumulated rainfall varies considerably from one year to another, and for this reason, climate projections have a very low degree of confidence in this area. Consequently, in this region, it is more interesting to study the irregularity of precipitation itself than accumulated rainfall values, as they express in a clearer way the behaviour of precipitation. According to daily data from 161 meteorological stations, four irregularity indices of precipitation were calculated: concentration index, entropy, persistence index, and fractal dimension. These indices were measured according to observed values, and their spatial distribution was subsequently determined by interpolating following multivariate regression models that consider different geographical variables such as latitude, distance to the Amazon Basin, elevation, orientation, and curvature. The temporal trends of each index and for each meteorological station were also calculated, displaying different results depending on the latitude and elevation. These changes agree with the observed modifications on the inter‐tropical atmospheric circulation and with changes in the precipitation diurnal cycle. These results will help improve climate projections for this region, in the process facilitating the development of more accurate climate models and informing the formulation of water management policies.The authors want to thank the FONDECYT Project 11160059, the CLICES Project (CGL2017‐83866‐C3‐2‐R), and the Climatology Group (2017 SGR 1362, Catalan Government) for their support

Spatial behaviour of daily observed extreme temperatures in Northern Chile (1966-2015): data quality, warming trends, and its orographic and latitudinal effects

According to the Intergovernmental Panel on Climate Change (IPCC), Northern Chile will be one of the most affected territories by changes in the atmospheric dynamics in next years. These climate change effects will be noticed in several ways, and temperatures will be one of the most sensitive variables to these changes, and with high importance because of their relationship with the hydrological cycle in one of the most arid regions in the world. Extreme temperatures of 77 observatories have been analysed by the calculation of 14 indices and their temporal trends. Also, the relationship of these indices between them, between observatories, with elevation and latitude has been taken into consideration, while they imply significant differences of the behaviour of the analysed indices. The results showed general warming trends but with particular differences depending on the behaviour of minimum temperatures. Examining the relationship between the indices and elevation, it appears that this variable has more implications in minimum temperatures. The analysis showed significant correlations also between the indices and latitude, agreeing with not evident general warming trends in the intertropical area of Northern Chile. Considering the different behaviours of the trends and their relationships with latitude and elevations, it has to be analysed in the future the possible existing relations with the spatial and temporal changes in the hydrological cycle such as precipitations.The authors want to thank the FONDECYT Project 11160059, the UTA-Mayor Project 5755-17, the CLICES Project (CGL2017-83866-C3-2-R) and the Climatology Group (2014SGR300, Catalan Government)

Synoptic attributions of extreme precipitation in the Atacama Desert (Chile)

Northern Chile is a region characterised by an extremely dry climate; however, there is a brief rainy season from December to March (austral summer), mainly above 3000 m a.s.l. It is interesting to consider where the humid air masses that generate such rain come from. For this purpose, daily precipitation data from 161 meteorological stations located in this area (18° S–19° S) were considered, and four clusters formed by k-means clustering. For each cluster, days of extreme precipitation (above 90th percentile) were selected to obtain flow strength (F), direction (D), and vorticity (Z) for each event according to the Jenkinson and Collison (JC) method. The back trajectory, for the previous 72 h, of air masses affecting the centroid of each cluster was determined by means of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The analyses were carried out at sea level (1013 hPa) and in the middle (500 hPa) and upper (250 hPa) troposphere. Surface circulation was not a determining factor in the occurrence of extreme events, but it did influence circulation at 500 and 250 hPa. For stations located in the northern Altiplano, moisture advection from the Amazon basin is evident due to the configuration of the Bolivian high—an upper level anticyclone that develops over the Bolivian Altiplano during austral summer. For stations located in the southern part of the study area, the main source of moisture is the Pacific Ocean, and the weather is related to the arrival of frontal systems and to the configuration of cut-off low pressure systems in the mid-troposphere.The authors want to thank the FONDECYT Project 11160059 of the Chilean Government, the Climatology Group (2017SGR1362, Catalan Government) and the CLICES Project (CGL2017-83866-C3-2-R) for the institutional support. R.S.N. is funded by the Spanish Ministry of Science and Innovation (grant no. FJCI-2017-31595)

Spatial distribution and trends of different precipitation variability indices based on daily data in Northern Chile between 1966 and 2015

Northern Chile is one of the most arid regions in the world, as it includes the Atacama Desert. At high elevations, most precipitation is observed only during a short period of the year, from December until March. This renders water availability a major concern for policymakers. Accumulated rainfall varies considerably from one year to another, and for this reason, climate projections have a very low degree of confidence in this area. Consequently, in this region, it is more interesting to study the irregularity of precipitation itself than accumulated rainfall values, as they express in a clearer way the behaviour of precipitation. According to daily data from 161 meteorological stations, four irregularity indices of precipitation were calculated: concentration index, entropy, persistence index, and fractal dimension. These indices were measured according to observed values, and their spatial distribution was subsequently determined by interpolating following multivariate regression models that consider different geographical variables such as latitude, distance to the Amazon Basin, elevation, orientation, and curvature. The temporal trends of each index and for each meteorological station were also calculated, displaying different results depending on the latitude and elevation. These changes agree with the observed modifications on the inter-tropical atmospheric circulation and with changes in the precipitation diurnal cycle. These results will help improve climate projections for this region, in the process facilitating the development of more accurate climate models and informing the formulation of water management policies