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İstanbul Teknik Üniversitesi (2014)

Bias Correction Of Precipitation Simulated By Regional Climate Model With Different Configurations Over Turkey

BALLI Ceren

Titre : Bias Correction Of Precipitation Simulated By Regional Climate Model With Different Configurations Over Turkey

Bölgesel İklim Modelinin Farklı Konfigürasyonlarıyla Simüle Edilmiş Yağış Verisinin Türkiye Üzerindeki Yanlılık Düzeltmesi

Auteur : BALLI Ceren

Université de soutenance : İstanbul Teknik Üniversitesi

Grade : Master of Science (MS) 2014

Résumé partiel
In this study, 2.5 degree grid size ECMWF ERA40 reanalysis data are downscaled to first 50 km coarse resolution and then 10 km high resolution over Turkey by regional climate model, RegCM4.3. The precipitation field has been simulated for the period 1971 to 2000, while the first 20 years are calibrated and the last 10 years are validated. RegCM is coupled with two different land surface models (LSMs) ; BATS and CLM. Coarse resolution simulations are carried out for BATS and CLM while high-resolution simulations only for BATS. The simulated precipitation climatology of two different land surface models is compared to the CRU TS3.10 data set. Also, 245 station-observations of Turkish Meteorological Service are used to estimate model biases in the precipitation field. Two common bias correction methods, Mean Value (MV) and Quantile Mapping (QM), have been carried out to reduce the bias of the precipitation simulations for monthly, seasonal and yearly bases. The QM method is also applied with two fitted distributions, Gamma (Gamma QM) and the best-fitted cumulative distribution functions (best-fitted QM) and the results are compared with each other. The results of these methods are tested by three quantitative validation measures such as Spearman rank correlation, Root Mean Square Error (RMSE) and Nash-Sutcliffe Efficiency (NSE). Generally, RegCM is good at modeling the general precipitation patterns. Mostly, the positive biases have been obtained over Turkey and the mountainous regions when compared with CRU observations during winter and spring seasons. The dryness of the summer season is very well captured by two configurations of RegCM. Meanwhile, the highest positive bias is estimated in the spring with the amount of 300 mm. However, the autumn season has been simulated drier than the CRU climatology. The precipitation is underestimated for two LSMs (BATS50, CLM50 and BATS10) along the Black Sea and the Mediterranean Sea regions where the mountains run parallel to the coastlines. Throughout the Aegean Sea and inland parts of Turkey, the overestimations have been observed.

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