Jin I. Yun

Urban-Effect Correction to Improve Accuracy of Spatially Interpolated Temperature Estimates in Korea

Abstract Gridded temperature data are frequently used to run ecological models at regional scales and are routinely generated by spatially interpolating point observations at synoptic weather stations. If synoptic stations are located in urbanized areas, observed temperature and the interpolated data could be contaminated by the urban heat island effect. Without an appropriate correction, temperature estimates over rural areas or forests might deviate significantly from the actual values. This study was conducted to remove the urban effects embedded in the interpolated surfaces of daily minimum temperature in South Korea, where most weather stations are located in urbanized or industrialized areas. To overcome the spatially discontinuous nature of the population statistics, urban land cover information at a 30 m × 30 m resolution was used along with population data. A population density was calculated by dividing the population of a city by the number of urban pixels falling within the city boundary. Popu...

Using Thermal Time to Simulate Dormancy Depth and Bud-Burst of Vineyards in Korea for the Twentieth Century

Abstract A winter-season warming trend has been observed in eastern Asian countries during the last century. Significant effects on dormancy and the subsequent bud-burst of deciduous fruit trees are expected. However, phenological observations are scant in comparison with long-time climate records in the region. Chill-day accumulation, estimated from daily maximum and minimum temperature, is a reasonable proxy for dormancy depth of temperate-zone fruit trees. A selected chill-day model was parameterized for the Campbell Early grapevine, which is the major cultivar (grown virtually everywhere) in South Korea. To derive model parameters (threshold temperature for chilling and the chilling requirement for breaking dormancy), a controlled-environment experiment using field-sampled twigs of Campbell Early was conducted. The chill-day model to estimate bud-burst dates was adjusted by derived parameters and was applied using 1994–2004 daily temperature data obtained from the automated weather station in the vine...

Distribution of Midday Air Temperature and the Solar Irradiance Over Sloping Surfaces under Cloudless Condition

Automated weather stations were installed at 9 locations with, three different elevations, (i.e., 50m, 100m, and 300m a.s.l.) with different slope and aspect in a small watershed (50km 2 area). Air temperature at 1500 LST and solar radiation accumulated for 1100-1500 LST were collected from January to December 2012. Topography of the study area was defined by a 30 × 30 m digital elevation model (DEM) grid. Accumulated solar irradiance was calculated for each location with the spatially averaged slope and aspect of surrounding circles with 5, 10, 15, 20, 25, and 30 grid cell radii, respectively. The 1500 LST air temperature from clear sky conditions with zero cloud amount was regressed to the 1100-1500 LST solar irradiance at 9 locations. We found the highest coefficient of determination (r 2 = 0.544) at 25 grid cell radius and the temperature variation in this study was explained by Y = 0.8309X + 0.0438, where Y is 1500 LST temperature (in o C) and X is 1100-1500 LST accumulated solar irradiance (in MJ/m 2 ).

Improving Usage of the Korea Meteorological Administration's Digital Forecasts in Agriculture: I. Correction for Local Temperature under the Inversion Condition

An adequate downscaling of the official forecasts of Korea Meteorological Administration (KMA) is a prerequisite to improving the value and utility of agrometeorological information in rural areas, where complex terrain and small farms constitute major features of the landscape. In this study, we suggest a simple correction scheme for scaling down the KMA temperature forecasts from mesoscale (5 km by 5 km) to the local scale (30 m by 30 m) across a rural catchment, especially under temperature inversion conditions. The study area is a rural catchment of 50 km 2 area with complex terrain and located on a southern slope of Mountain Jiri National Park. Temperature forecasts for 0600 LST on 62 days with temperature inversion were selected from the fall 2011-spring 2012 KMA data archive. A geospatial correction scheme which can simulate both cold air drainage and the so-called ‘thermal belt’ was used to derive the site-specific temperature deviation across the study area at a 30 m by 30 m resolution from the original 5 km by 5 km forecast grids. The observed temperature data at 12 validation sites within the study area showed a substantial reduction in forecast error: from ±2 o C to ±1 o C in the mean error range and from 1.9 o C to 1.6 o C in the root mean square error. Improvement was most remarkable at low lying locations showing frequent cold pooling events. Temperature prediction error was less than 2 o C for more than 80% of the observed inversion cases and less than 1 o C for half of the cases. Temperature forecasts corrected by this scheme may accelerate implementation of the freeze and frost early warning service for major fruits growing regions in Korea.

Geographical Shift in Blooming Date of Kiwifruits in Jeju Island by Global Warming

A kiwifruit cultivar `Hayward` has been grown in Jeju Island where the current climate is suitable for growth and development of this crop. Prediction of the geographical shift in the phenology can help the kiwifruits growers to adapt to the local climate change in the future. Two phenology models (i.e., chill-day and DVS) were parameterized to estimate flowering date of kiwifruits `Hayward` based on the data collected from field plots and chamber experiments in the southern coastal and island locations in South Korea. Spatio-temporally independent datasets were used to evaluate performance of the two models in predicting flowering date of `Hayward`. Chill-day model showed better performance than DVS model (2.5 vs. 4.0 days in RMSE). Daily temperature data interpolated at a higher spatial resolution over Jeju Island were used to predict flowering dates of `Hayward` in 2021-2100 under the A1B scenario. According to the model calculation under the future climate condition, the flowering of kiwifruits shall accelerate and the area with poor flowering might increase due to the warmer winter induced insufficient chilling. Optimal land area for growing `Hayward` could increase for a while in the near future (2021-2030), whereas such areas could decrease to one half of the current areas by 2100. The geographic locations suitable for `Hayward` cultivation would migrate from the current coastal area to the elevated mountain area by 250 m.

Improving the Usage of the Korea Meteorological Administration's Digital Forecasts in Agriculture: IV. Estimation of Daily Sunshine Duration and Solar Radiation Based on 'Sky Condition' Product

College of Life Sciences, Kyung Hee University, Yongin 17104, Korea(Received October 13, 2015; Revised November 1, 2015; Accepted November 2, 2015)ABSTRACTInformation on sunshine duration and solar radiation are indispensable to the understanding of cropgrowth and development. Yet, relevant variables are not available in the Korea MeteorologicalAdministrations (KMA) digital forecast. We proposed the methods of estimating sunshine durationand solar radiation based on the ‘sky condition’ of digital forecast products and validated using theobserved data. The sky condition values (1 for clear, 2 for partly cloudy, 3 for cloudy, and 4 forovercast) were collected from 22 weather stations at 3-hourly intervals from August 2013 to July 2015.According to the observed relationship, these data were converted to the corresponding amount ofclouds on the 0 to 10 scale (0 for clear, 4 for partly cloudy, 7 for cloudy, and 10 for overcast). Anequation for the cloud amount–sunshine duration conversion was derived from the 3-year observationdata at three weather stations with the highest clear day sunshine ratio (i.e., Daegwallyeong,Bukgangneung, and Busan). Then, the estimated sunshine hour data were used to run the Angstrom-Prescott model which was parameterized with the long-term KMA observations, resulting in dailysolar radiation for the three weather stations. Comparison of the estimated sunshine duration andsolar radiation with the observed at those three stations showed that the root mean square errorranged from 1.5 to 1.7 hours for sunshine duration and from 2.5 to 3.0 MJ m

Improving usage of the Korea Meteorological Administration`s Digital Forecasts in Agriculture: III. Correction for Advection Effect on Determination of Daily Maximum Temperature Over Sloped Surfaces

The effect of solar irradiance has been used to estimate daily maximum temperature, which make it possible to reduce the error inherent to lapse-rate based elevation difference correction in mountainous terrain. Still, recent observations indicated that the effect of solar radiation would need correction for estimation of daily maximum temperature. It was attempted to examine what would cause the variability of solar irradiance effect in determination of daily maximum temperature under natural field conditions and to suggest improved methods for estimation of the temperature distribution over mountainous regions. Temperature at 1500 and the wind speed for 1100 to 1500 were obtained at 10 validation sites with various topographical features including slope and aspect within a mountainous 50 km 2 catchment for 2012-2013. Lapse-rate corrected temperature estimates on clear days were compared with these observations, which would represent the differential irradiance effect among sloped surfaces. Results indicated a negative correlation between the mean wind speed and the estimation error. A simple scheme was derived from relationship between wind speed and estimation error for daily temperature to correct the effect of solar radiation. This scheme was incorporated into an existing model to estimate daily maximum temperature based on the effect of solar radiation. At 10 validation sites on clear days, estimates of 1500 LST temperature with and without the correction scheme were compared. It was found that a substantial improvement was achieved when the correction scheme was applied in terms of bias correction as well as error size reduction at all sites.

Performance of Angstrom-Prescott Coefficients under Different Time Scales in Estimating Daily Solar Radiation in South Korea

While global solar radiation is an essential input variable in crop models, the observation stations are relatively sparse compared with other meteorological elements. Instead of using measured solar radiation, the Angstrom-Prescott model estimates have been widely used. Monthly data for solar radiation and sunshine duration are a convenient basis for deriving Angstrom-Prescott coefficients (a, b), but it is uncertain whether daily solar radiation could be estimated with a sufficient accuracy by the monthly data - derived coefficients. We derived the Angstrom-Prescott coefficients from the 25 years observed global solar radiation and sunshine duration data at 18 locations across South Korea. In order to figure out any improvements in estimating daily solar radiation by replacing monthly data with daily data, the coefficients (a, b) for each month were derived separately from daily data and monthly data. Local coefficients for eight validation sites were extracted from the spatially interpolated maps of the coefficients and used to estimate daily solar radiation from September 2008 to August 2009 when, pyranometers were operated at the same sites for validation purpose. Comparison with the measured radiation showed a better performance of the daily data - derived coefficients in estimating daily global solar radiation than the monthly data - derived coefficients, showing 9.3% decrease in the root mean square error (RMSE).

Drought Index Development for Agricultural Drought Monitoring in a Catchment

Natinal Institute of Horticultural & Herbal Science, RDA, Jeju 690-150, Korea(Received September 27, 2014; Revised November 7, 2014; Accepted November 9, 2014)ABSTRACTDrought index can be used to implement an early warning system for drought and to operate adrought monitoring service. In this study, an approach was examined to determine agriculturaldrought index (ADI) at high spatial resolution, e.g., 270 m. The value of ADI was calculated based onsoil water balance between supply and demand of water. Water supply is calculated by the cumulativeeffective precipitation with the application of the weight to the precipitation from two months ago.Water demand is derived from the actual evapotranspiration, which was calculated applying a cropcoefficient to the reference evapotranspiration. The amount of surface runoff on a given soil type wasalso used to calculate soil residual moisture. Presence of drought was determined based on theprobability distribution in the given area. In order to assess the reliability of this index, the amount ofresidual moisture, which represents severity of drought, was compared with measurements of soilmoisture at three experimental between July 2012 and December 2013. As a result, the ADI hadgreater correlation with measured soil moisture compared with the standardized precipitation index,which suggested that the ADI would be useful for drought warning services.Key words: Agricultural drought index, Effective precipitation, Evapotranspiration, Runoff, Soilmoisture