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- Author or Editor: A. Öztürk x
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Abstract
The increased interest in the climatology of solar radiation dictates a need for a distribution to fit daily solar radiation totals which tend to have negatively-skewed probability distributions. Even daily mean solar radiation for weekly periods tends to have non-normal distributions. The generalized lambda distribution, which includes a wide variety of curve shapes, is discussed for fitting these data. The underlying probability distribution is a generalization of the lambda distribution from three to four parameters. Using the weekly averages of daily solar radiation totals for each of 12 weeks during the growing season and daily totals for the week 5-11 July at West Lafayette, Indiana, it is shown that the generalized lambda distribution model fits the data well. Some results concerning percentiles and quantiles, parameter estimates, and goodness-of-fit tests are also discussed.
Abstract
The increased interest in the climatology of solar radiation dictates a need for a distribution to fit daily solar radiation totals which tend to have negatively-skewed probability distributions. Even daily mean solar radiation for weekly periods tends to have non-normal distributions. The generalized lambda distribution, which includes a wide variety of curve shapes, is discussed for fitting these data. The underlying probability distribution is a generalization of the lambda distribution from three to four parameters. Using the weekly averages of daily solar radiation totals for each of 12 weeks during the growing season and daily totals for the week 5-11 July at West Lafayette, Indiana, it is shown that the generalized lambda distribution model fits the data well. Some results concerning percentiles and quantiles, parameter estimates, and goodness-of-fit tests are also discussed.
Abstract
Two questions motivated this study: 1) Will meteorological droughts become more frequent and severe during the twenty-first century? 2) Given the projected global temperature rise, to what extent does the inclusion of temperature (in addition to precipitation) in drought indicators play a role in future meteorological droughts? To answer, we analyzed the changes in drought frequency, severity, and historically undocumented extreme droughts over 1981–2100, using the standardized precipitation index (SPI; including precipitation only) and standardized precipitation-evapotranspiration index (SPEI; indirectly including temperature), and under two representative concentration pathways (RCP4.5 and RCP8.5). As input data, we employed 103 high-resolution (0.44°) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), based on a combination of 16 global circulation models (GCMs) and 20 regional circulation models (RCMs). This is the first study on global drought projections including RCMs based on such a large ensemble of RCMs. Based on precipitation only, ~15% of the global land is likely to experience more frequent and severe droughts during 2071–2100 versus 1981–2010 for both scenarios. This increase is larger (~47% under RCP4.5, ~49% under RCP8.5) when precipitation and temperature are used. Both SPI and SPEI project more frequent and severe droughts, especially under RCP8.5, over southern South America, the Mediterranean region, southern Africa, southeastern China, Japan, and southern Australia. A decrease in drought is projected for high latitudes in Northern Hemisphere and Southeast Asia. If temperature is included, drought characteristics are projected to increase over North America, Amazonia, central Europe and Asia, the Horn of Africa, India, and central Australia; if only precipitation is considered, they are found to decrease over those areas.
Abstract
Two questions motivated this study: 1) Will meteorological droughts become more frequent and severe during the twenty-first century? 2) Given the projected global temperature rise, to what extent does the inclusion of temperature (in addition to precipitation) in drought indicators play a role in future meteorological droughts? To answer, we analyzed the changes in drought frequency, severity, and historically undocumented extreme droughts over 1981–2100, using the standardized precipitation index (SPI; including precipitation only) and standardized precipitation-evapotranspiration index (SPEI; indirectly including temperature), and under two representative concentration pathways (RCP4.5 and RCP8.5). As input data, we employed 103 high-resolution (0.44°) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), based on a combination of 16 global circulation models (GCMs) and 20 regional circulation models (RCMs). This is the first study on global drought projections including RCMs based on such a large ensemble of RCMs. Based on precipitation only, ~15% of the global land is likely to experience more frequent and severe droughts during 2071–2100 versus 1981–2010 for both scenarios. This increase is larger (~47% under RCP4.5, ~49% under RCP8.5) when precipitation and temperature are used. Both SPI and SPEI project more frequent and severe droughts, especially under RCP8.5, over southern South America, the Mediterranean region, southern Africa, southeastern China, Japan, and southern Australia. A decrease in drought is projected for high latitudes in Northern Hemisphere and Southeast Asia. If temperature is included, drought characteristics are projected to increase over North America, Amazonia, central Europe and Asia, the Horn of Africa, India, and central Australia; if only precipitation is considered, they are found to decrease over those areas.
