Abstract
Abstract. To evaluate satellite rainfall estimates of Tropical Rain Measurement Mission (TRMM) level 3 output (3B42) (TRMM_3B42) over Iran (20°–45° N, 40°–65° E), we compared these data with high-resolution gridded precipitation datasets (0.25°×0.25° latitude/longitude) based on rain gauges (Iran Synoptic gauges Version 0902 (IS0902)). Spatial distribution of mean annual and mean seasonal rainfall in both IS0902 and TRMM_3B42 from 1998 to 2006 shows two main rainfall patterns along the Caspian Sea and over the Zagros Mountains. Scatter plots of annual average rainfall from IS0902 versus TRMM_3B42 for each 0.25°×0.25° grid cell over the entire country (25°–40° N, 45°–60° E), along the Caspian Sea (35°–40° N, 48°–56° E), and over the Zagros Mountains (28°–37° N, 46°–55° E) were derived. For the entire country, the Caspian Sea region, and the Zagros Mountains, TRMM_3B42 underestimates mean annual precipitation by 0.17, 0.39, and 0.15 mm day−1, respectively, and the mean annual rainfall spatial correlation coefficients are 0.77, 0.57, and 0.75, respectively. The mean annual precipitation temporal correlation coefficient for IS0902 and TRMM_3B42 is ~0.8 in the area along the Zagros Mountains, and ~0.6 in the Caspian Sea and desert regions.
Highlights
Global precipitation is a major component of the global water and energy cycle that influences significantly Earth’s climate system, and in is turn affected by climate system variability and change
Javanmard ergy and Water Cycle experiment (GEWEX) of the World Climate Research Programme (WCRP) was formed to improve understanding of seasonal and inter-annual and longerterm variability of the global hydrological cycle, to determine the atmospheric latent heat rates needed for weather and climate prediction models, and to provide an observational precipitation data set for model validation, initialization and other hydrological applications (Gruber and Levizzani, 2008)
Using the 0.25◦×0.25◦ data set of annual rainfall means in IS0902 and Tropical Rain Measurement Mission (TRMM) 3B42 (1998–2006), a scatter plot of IS0902 versus TRMM 3B42 for three regions is presented in Fig. 7a, b and c
Summary
Global precipitation is a major component of the global water and energy cycle that influences significantly Earth’s climate system, and in is turn affected by climate system variability and change. The performance of five satellite-based high-resolution precipitation outputs by comparison against gauge analysis: TRMM (3B42, 3B42RT )(Huffman et al, 2004; Huffman et al, 2007), National Weather Service, USA (NWS), Climate Prediction Center (CPC), Morphing Techniques (CMORPH; Joyce et al, 2004), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN; Sorooshian et al 2000), Naval Research Laboratory (NRL; Turk et al, 2004) They found that all satellite data performed better in depicting precipitation for wet climate regions and wet seasons, but were limited skills in estimating precipitation over central Asian arid and semi-arid regions. Iran is classified generally as arid or semiarid with mean annual rainfall ∼250 mm for the entire country, ranging from 50 mm in the deserts to 1600 mm on the Caspian coast (Fig. 2).
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