Poster Open Access
Zambrano-Bigiarini, Mauricio; Garreaud, René
Central Chile (30-40°S) has experienced a rainfall decline since the early 80s. Such long-term drying has been accentuated by an intense rainfall deficit from 2010 to date. Moreover, the maximum air temperatures have risen since the late 70s, with warm anomalies between 0.5° and 1°C relative to the past 30 years, resulting in the use of the term megadrougth for the 2010-2015 period.
In this work, we used two drought indices to analyze the contribution of precipitation and temperature on recent droughts, and to improve our understanding about the onset, duration and magnitude thereof. First, the traditional Standardized Precipitation Index (SPI) is used to describe the effect of lack of precipitation on drought conditions. Second, the Standardized Precipitation-Evapotranspiration Index (SPEI), based on a simple climatic water balance (precipitation minus reference evapotranspiration), is used to assess the effect of temperature -throughout changes in evaporation- on drought severity at different time scales. Data from 781 raingauges and 281 temperature stations were analyzed for the period 1981-2015, but only 21 stations with 98% of days with information (or more) were used to compute SPI and SPEI at 12-month scale (SPI-12 and SPEI-12, respectively), as representative of the long-term effects of meteorological droughts on hydrology.
Results reveal that in almost all the analyzed stations both SPI and SPEI are close or below zero since August 2010 onwards, with stations located northern to 32°S recovering in July 2015 due to extreme rainfall events. We note that the SPEI-12 was able to identify drought events even after some above-normal rainfall periods, which was in agreement with reported socioeconomic impacts on agriculture and water supply. Comparison of moving averages of SPI-12 and SPEI-12 during the megadrought against their historical values (1966-2010), for selected stations, reveals two different conditions. In the arid north, the SPI-12 was low but not extraordinary, whilst the SPEI-12 was well beyond the historical distribution, indicating that the increase in temperature have worsened the rainfall deficit by increasing evaporation. In the humid south, we found little difference between SPI-12 and SPEI-12 during the megadrought, but both values were extraordinary in their historical context.