Abstract
AbstractNorthern 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.
Highlights
Rainfall in Northern Chile is highly irregular at seasonal and annual scales (Romero et al, 2013)
The multivariate regression models are linear, and the coefficients are obtained by means of the minimum mean square error method
The Concentration Index (CI) exhibits a direct relationship with latitude and inverse relationships with elevation, distance to the Amazon Basin and the orientation and curvature of the surface
Summary
Rainfall in Northern Chile is highly irregular at seasonal and annual scales (Romero et al, 2013). Considering the intraseasonal level, precipitation in Northern Chile during the austral summer responds to an excess of latent heat in the atmosphere and incoming radiation from the ground, generating vertical air instability and convection (Sarricolea and Romero, 2015) Such a configuration of the upper levels is known as the Bolivian High (250 hPa), and activates the South American monsoon as well as areas where dry seasons are absolute with no recorded rainfall close to the Pacific coast (Sarricolea and Romero 2015). In the study area of Northern Chile (17oS – 29oS), general warming trends may have direct implications in the hydrological cycle (Held and Soden, 2006), exacerbating the acknowledged situation of drought (Sarricolea and Romero, 2015; Sarricolea et al, 2017a) In this region, national policies are focused on developing economic activities that increase water demand (lithium and copper mining activities in the Atacama Desert) but are indispensable to the country. A recent study (Zappalà et al, 2018) has identified concrete changes in spatial rainfall patterns in the Amazon Basin connected to a northward shift of the inter-tropical convergence zone (ITCZ), as well as a widening of the rainfall band in the western Pacific Ocean during the period 1979-2016
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