CCAFS-CMIP5 Delta Method Downscaling database

We apply a downscaling method, called Delta Method, based on thin plate spline spatial interpolation of anomalies (deltas) of original GCM outputs. Anomalies are interpolated between GCM cell centroids and are then applied to a baseline climate given by a high resolution surface (i.e. WorldClim 1.4 , http://www.worldclim.org/). The process consists in the following steps: 1) Calculation of 30-year averages for present day simulations and 4 future periods; (2) calculation of anomalies as the absolute difference between future and present day values in temperatures (minimum and maximum) and proportional differences in total precipitation; (3) interpolation of these anomalies using centroids of GCM cells as points for interpolation; and (4) addition of the interpolated surfaces to the current climates from WorldClim<br>WorldClim and full GCM timeseries are freely available in the internet, whilst all other calculations are carried out by means of Geographic Information Systems (GIS) software. Used formats are NetCDF (for GCM outputs), ESRI-GRID (for WorldClim and final downscaled data), and ESRI-ASCII grids for providing standard and easy-of-use outputs to potential users of the data.<br>CCAFS and its partners have processed this data to provide seamless continuous future climate surfaces. This work is licensed under a Creative Commons Atribution 4.0 International (CC BY 4.0). Users should acknowledge CCAFS as the source used in the creation of any reports, publications, new data sets, derived products, or services resulting from the use of this data set.本研究采用基于原始全球气候模式（Global Circulation Model，GCM）输出结果的距平（Delta差值）薄板样条空间插值的降尺度方法，命名为差值法（Delta Method）。首先在GCM格点质心之间对距平进行插值，随后将其应用于由高分辨率地表气候数据集（即WorldClim 1.4，http://www.worldclim.org/）所定义的基准气候。该流程包含以下步骤：(1) 计算当代模拟时段与4个未来时段的30年气候平均值；(2) 计算气温（最低与最高气温）的绝对差值距平，以及总降水量的比例差值距平；(3) 以GCM格点质心作为插值点，对上述距平进行空间插值；(4) 将插值得到的气候表面叠加至WorldClim提供的当代气候数据集。 WorldClim与完整的GCM时间序列可通过互联网免费获取，其余所有计算均借助地理信息系统（Geographic Information Systems，以下简称GIS）软件完成。本数据集采用的文件格式包括：用于存储GCM输出结果的NetCDF格式、用于存储WorldClim及最终降尺度数据的ESRI-GRID格式，以及用于向潜在数据用户提供标准化、易用型输出的ESRI-ASCII网格格式。 CCAFS及其合作伙伴对本数据进行处理，以生成无缝连续的未来气候表面数据集。本作品采用知识共享署名4.0国际许可协议（Creative Commons Attribution 4.0 International，CC BY 4.0）进行授权。使用本数据集生成的任何报告、出版物、新数据集、衍生产品或服务，均需注明CCAFS为数据来源。