Analysis of RCP8.5 Projections of Precipitation and Temperatures in Chilean Basins

Abstract:

In order to explain the uncertainty of future water availability in Chilean basins we study time series of daily precipitation and mean daily temperature projected by global circulation models (GCMs) in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report. Representative Concentration Pathway, RCP 8.5, characterized by increasing greenhouse gas emissions over time is taken for the analysis.

Data from four GCMs (MPI-ESM-LR, CSIRO-MK3.6, CMCC-CMS, BCC-CSM1.1) is used and downscaled spatial and temporally to local gages sites using standard statistical procedures. The model selection procedure was based on the preservation of the observed precipitation and temperature regimes for the base line period through the comparison of the average monthly values of the observed and spatial downscaled variables normalized respect to annual values for one of the sites. Base line data is defined for the period 1975-2005 and two future periods are studied: near future stands for 2015-2045 and far ahead future stands for 2045-2075. For the analysis we consider hydrologic year starting on April and ending on March of following year.

We analyse the behaviour of daily time series of precipitation and temperature for gages located at -33.5° latitude, -70.5° longitude to -37.7° latitude, -72° longitude. Mean annual precipitation, mean annual temperature, the number of days with precipitation, the number of days with precipitation less or greater than specific values, the mean temperature during rainy days and in extreme events, for each period (base line, near and far ahead future) are determined for each site. Special attention is given to the effect of temperatures on rainy days on the elevation of 0°C isotherm on representative watersheds and to the occurrence of extreme events during the snowmelt period with high elevation of 0°C isotherm.

In general, results show a spatial decay of annual precipitation from north to south from base line to future being greater the falloff for far ahead future. Similarly the number of rainy days decreases in the future and this decay is greater at the northern site than at the southern site. Results for temperature indicate that this variable would rise in the future in Chile for all the sites we analysed; nevertheless the increase is higher at the southern site than at the northern one.