Synchronized generation of high-resolution gridded precipitation and temperature fields

Abstract

In this study, synchronized gridded precipitation and temperature generators were developed and evaluated in terms of their ability to reconstruct the spatial structure and other statistical properties of high-resolution CaPA (Canadian Precipitation Analysis) precipitation and GEM (Global Environmental Multiscale Model) temperature products. The precipitation generator is an extension to the gridded multi-site occurrence-amount model. While the multi-site framework is not efficiently applicable to regions with limited precipitation information and sparse observation network, this paper provides the full mathematical description of estimating the model based on high-resolution gridded products. The temperature model, on the other hand, introduces the first gridded hourly generator in the literature in which cyclic temperature components are conditioned using wet and dry day status information. This was achieved using harmonic functions establishing the connection between the simulated daily precipitation occurrence time-series and the moments of the generated temperature data. One of the key features of the proposed gridded generators is the capacity to produce temporally coherent fields of precipitation and temperature; an essential prerequisite for hydrologic modeling applications. The generators were evaluated in terms of their ability to reproduce the standard, interannual, and extreme-value characteristics of observed gridded products. The gridded precipitation model can preserve key statistical and spatial properties of the gridded CaPA observations to an acceptable level, while similar to the original multi-site framework, it falls short to capture long dry spells and the interannual variability of monthly total precipitation. The temperature model, on the other hand, preserves the majority of key features of the gridded GEM temperature observations, including the first two moments of the hourly data and the cumulative frequency of maximum and minimum temperature thresholds. The only notable defect identified is the departure of the interannual variability of the generated maximum and minimum temperatures from those observed.