Mean Annual Precipitation (mm)

The MAP (mm) characterises the long term quantity of water available to a region for hydrological and agricultural purposes. Under non-irrigated conditions the MAP gives an upper limit to a region's sustainable agricultural potential in regard to biomass production if other factors (e.g. light, temperature, topography, soils) are not limiting. Not only is MAP important as a general statistic in its own right, but it is probably also the one climatic variable best known to hydrologists and agriculturists, and to which they can relate many other things.

Mean annual precipitation was mapped using quality controlled and infilled daily rainfall values from over 9 600 stations each with ≥ 15 years of daily records, applied a Geographically Weighted Regression (GWR) approach with derivatives of altitude, latitude, longitude and slope to generate 1 arc minute (1` x 1` latitude/longitude, 1.7 km x 1.7 km) values of MAP Station residuals between simulated and observed rainfall were then superimposed over the generated surface of rainfall by interpolative techniques, akin to those used by Dent et al. (1989), to adjust the `global` surface to more local conditions.

年平均降水量（Mean Annual Precipitation，MAP，单位：毫米）表征了某一区域可用于水文与农业用途的长期可利用水资源总量。在非灌溉情境下，若光照、温度、地形、土壤等其他因素未构成限制条件，年平均降水量可为区域生物质生产相关的可持续农业潜力设定上限。年平均降水量不仅本身作为通用统计指标具有重要意义，同时或许也是水文与农业领域研究者最为熟知的气候变量，诸多其他研究对象均可与之建立关联。

本数据集的年平均降水量空间制图，基于超过9600个降雨监测站点的日均降水记录时长≥15年的经质量控制与插补的日降雨数据完成；研究采用地理加权回归（Geographically Weighted Regression，GWR）方法，结合海拔、纬度、经度与坡度的衍生变量，生成了分辨率为1弧分（1'×1'经纬度，对应约1.7km×1.7km）的年平均降水量数据。随后，通过参照Dent等人（1989）所采用的插值技术，将模拟降雨与实测降雨的站点残差叠加至生成的降雨表面，以此对"全球"尺度的降雨表面进行本地化校正。