The effects of climatic changes owing to urbanization, geographical and topographical conditions on FAO Penman-Monteith (FAO P-M) reference evapotranspiration (RET), and energy and aerodynamic terms of RET have been studied. In this study, 56 climatological stations including the Seoul metropolis in South Korea have been selected, and the area of study site was set at 314 km 2 . The climatological station is centrally located in the study area with a 10 km radius. The geographical and topographical characteristics of these sites were examined using GIS analysis. Land use status of the study area was also examined to estimate the extent of urbanization. The study results indicated that the variation of RET rate is closely related to urbanization in most climatological stations. The level of change in RET was higher in areas with higher urbanization rates. As topographical slope of study area increases, RET decreases. Average elevation of the study area also shows the negative correlation with RET. As the wet land area increases, RET decreases. When considering the effect of proximity of the observation station to sea, the closer the observation station is to the sea, the higher the RET. The study results showed that climatic change due to proximity of the observation station to sea had the greatest effect on RET.

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ABSTRACT:The implications of geographical factors (i.e. elevation, freshwater area, urbanization, and proximity to coast) and climatic factors (i.e. air temperature, wind speed, relative humidity, and solar radiation) with regard to drought trend were investigated by analyzing the monthly averaged daily climate data (i.e. precipitation, temperature, wind speed, relative humidity, and solar radiation) recorded from 1973 to 2006 at 53 climatological stations in South Korea. In addition, geographical characteristics were identified by GIS analysis and land cover data were analyzed for these 53 stations. Further, multivariate regression analyses were performed by setting the Standardized Precipitation Index (SPI) trend as the dependent variable and the geographical and climatic factors as the independent variables. The results indicated that, overall, the droughts in South Korea are becoming more severe in spring for the short-and seasonal term; however, the droughts in all seasons are becoming less severe for the long term. The effects of geographical and climatic factors on drought trends are also closely related to seasonality and drought duration for short-, seasonal-, and medium-term droughts, but not for long-term droughts. Therefore, for efficient water resources management for drought preparedness, drought duration and seasonality should also be considered along with geographical and climatic characteristics of a region.

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In this study, monthly and annual aridity indices which are the ratios of precipitation to potential evapotranspiration in Seoul climate measurement station were analyzed for past 50 years (1961～2010), and the ratio of aridity index simulated by climate change scenarios (RCP 4.5 and 8.5) for each future period (2011～2040, 2041～2070, 2071～2100) to aridity index for the past period (1971～2000) was analyzed. Furthermore, 5 different potential evapotranspiration equations (FAO P-M, Penman, Makkink, PriestleyTaylor, Hargreaves) were applied to analyze the effect of potential evapotranspiration equation on estimating aridity index and aridity index variation ratio (%). The study results indicate that the monthly precipitation, average temperature and potential evapotranspiration were increased in each future period as compared to past period for both RCP 4.5 and RCP 8.5. Furthermore, winter period showed more significant increase of potential evapotranspiration than summer period, but aridity index showed different patterns as compared with potential evapotranspiration reflecting the influence of precipitation. Therefore, it is necessary to make preparation for the increment of winter evapotranspiration in terms of water resources management. The monthly and annual aridity indices based on future climate change scenarios were greatly different according to potential evapotranspiration equations; however, monthly and annual patterns of aridity index variation ratio (%) in the future period as compared to past period were very similar regardless of applied potential evapotranspiration equation.