Simulation of seasonal precipitation and raindays over Greece: a statistical downscaling technique based on artificial neural networks (ANNs)

Abstract

Abstract:A statistical downscaling technique based on artificial neural network (ANN) was employed for the estimation of local changes on seasonal (winter, spring) precipitation and raindays for selected stations over Greece. Empirical transfer functions were derived between large-scale predictors from the NCEP/NCAR reanalysis and local rainfall parameters. Two sets of predictors were used: (1) the circulation-based 500 hPa and (2) its combination along with surface specific humidity and raw precipitation data (nonconventional predictor). The simulated time series were evaluated against observational data and the downscaling model was found efficient in generating winter and spring precipitation and raindays. The temporal evolution of the estimated variables was well captured, for both seasons. Generally, the use of the nonconventional predictors are attributed to the improvement of the simulated results. Subsequently, the present day and future changes on precipitation conditions were examined using large-scale data from the atmospheric general circulation model HadAM3P to the statistical model. The downscaled climate change signal for both precipitation and raindays, partly for winter and especially for spring, is similar to the signal from the HadAM3P direct output: a decrease of the parameters is predicted over the study area. However, the amplitude of the changes was different.

Effects of Domain Selection on Singular-Value-Decomposition Based Statistical Downscaling of Monthly Rainfall Accumulation in Southern Taiwan

“…Climate change is one of the reasons and a critical issue not only for climatic research but also for hydrological research (Tolika et al 2007;Labraga 2010). The Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC 2007) points out that possible extreme events of rainfall become more serious under climate change and lead to flood or drought.…”

Classification of circulation types over Eastern mediterranean using a self-organizing map approach

“…The 500 hPa level was chosen because it presents a strong relationship with surface variables (Tolika, Maheras, Vafiadis, Flocas, & Arseni-Papadimitriou, 2007) and at the same time, it strongly affects the weather over an area. Furthermore, anomalies were chosen over absolute geopotential values in order to eliminate the seasonality of the data and to get a clearer image of the atmospheric circulation over the study area (Anagnostopoulou et al, 2009).…”

Principal component analysis of precipitation in Thessaly region (Central Greece)

“…Recently, more objective methods are used and it is concluded that the precipitation regime in Greece can be explained in terms of variability of a small number of circulation type patterns (Maheras and Anagnostopoulou, 2003). Recent studies, which describe rainfall variability in the Greek region in relation to circulation types, have been carried out by (Maheras et al, 2004;Tolika et al, 2007). The relationship between the atmospheric circulation and the environment of a region is considered to be crucial for the understanding of the regional climate and its changes.…”