Development of Precise Precipitation Data for Assessing the Potential Impacts of Climate Change

Abstract

In this chapter we introduce the rain-gauge-based grid precipitation data APHRODITE, and show an experimental result of applying the synthetic super-ensemble (SSE) method to winter precipitation over the Middle East. As the change in precipitation according to climate variation is essential, in this study we used the precise observational precipitation as well as the outputs of numerical simulations. The APHRODITE precipitation data is widely used for understanding monsoon variability, various downscaling for impact assessment studies of global warming and validating precipitation estimates from satellites and models. Since the rain-gauge products are more accurate than those of satellites and used as ‘teacher’ data in various situations, APHRODITE is used for the SSE method developed at Florida State University. It is a unique method to combine several model outputs and precise observation data to make the best forecast. We first show the application of SSE to the Middle East area. We used the simulated precipitation of the five coupled general circulation model (CGCM) outputs, which are part of the CMIP5 project. The five models were chosen due to the availability of the APHRODITE model data up to 2007, along with the 10 years of (1997/1998–2006/2007) monthly precipitation (December, January and February) over the Middle East region (20°E–65°E, 15°N–45°N).

For the seasonal climate forecasts, a SSE technique was used and a cross-validation technique was adopted, in which the year to be forecasted was excluded from the calculations for obtaining the regression coefficients. As a result, seasonal forecasts of the Middle East precipitation were considerably improved by the use of APHRODITE rain-gauge-based data. These forecasts are much superior to those from the best model of our suite and ensemble mean. The use of statistical downscaling and SSE for multi-model forecasts of seasonal climate significantly improved precipitation prediction at higher resolution.

These results demonstrate that high-resolution precipitation data from a dense network of rain gauges is essential for improving seasonal rainfall estimation over the Middle Eastern region. However, unfortunately, SSE does not represent the large-scale decreasing trend pattern, except in the eastern part of Turkey and part of Israel.

A. Yatagai, Professor, Hirosaki University, 3 Bunkyocho, Hirosaki, Aomori 036-8561, Japan; e-mail: yatagai@hirosaki-u.ac.jp.

V. Kumar, Researcher, Florida State University, Department of Earth, Ocean and Atmospheric Science, Tallahassee, FL, United States.

T. N. Krishnamurti, Professor Emeritus, Florida State University, Department of Earth, Ocean and Atmospheric Science, Tallahassee, FL, United States.