Vegetation Health Index (Global - Dekadal - 1 km) - FAO ASIS

The Vegetation Health Index (VHI) illustrates the severity of drought based on the vegetation health and the influence of temperature on plant conditions. The VHI is a composite index and the elementary indicator used to compute the seasonal drought indicators in ASIS: Agricultural Stress Index (ASI), Drought Intensity and Weighted Mean Vegetation Health Index (Mean VHI). If the index is below 40, different levels of vegetation stress, losses of crop and pasture production might be expected; if the index is above 60 (favorable condition) plentiful production might be expected. VHI is very useful for an advanced prediction of crop losses. Phenomenon Mapped: Vegetation Health Index Units: None Time Interval: 10-day Time Extent: 1984-Present Cell Size: 1 km Pixel Type: 32-bit Signed Integer Data Projection: WGS 1984 Mosaic Projection: WGS 1984 Web Mercator Source: Food and Agriculture Organization of the United Nations Update Cycle: 10-days + 3-4 days lag VHI combines both the Vegetation Condition Index (VCI) and the Temperature Condition Index (TCI). The TCI is calculated using a similar equation to the VCI, but relates the current temperature to the long-term maximum and minimum, as it is assumed that higher temperatures tend to cause a deterioration in vegetation conditions. A decrease in the VHI would, for example, indicate relatively poor vegetation conditions and warmer temperatures, signifying stressed vegetation conditions, and over a longer period would be indicative of drought. In ASIS, VHI is computed in two temporal granularities: dekadal and monthly. The dekadal/monthly VHI raster layer published is further updated in the following 5 dekads (improve data precision, remove cloud pixel etc.). Flags of raster file: 251=missing, 252=cloud, 253=snow, 254=sea, 255=background Explore this and related data in this web application More information please visit FAO GIEWS Earth Observation website.植被健康指数（Vegetation Health Index, VHI）基于植被健康状态与温度对植物生长状况的影响，用以表征干旱严重程度。VHI是一类综合指数，同时也是ASIS中计算季节性干旱指标的基础指标，该类季节性干旱指标包括农业胁迫指数（Agricultural Stress Index, ASI）、干旱强度及加权平均植被健康指数（Mean VHI）。当该指数低于40时，可能出现不同等级的植被胁迫、作物与牧草减产情况；当指数高于60时则代表条件适宜，有望实现丰产。VHI可有效用于作物减产的前瞻性预测，实用性极强。 映射现象：植被健康指数 单位：无 时间间隔：10日 时间范围：1984年至今 像元大小：1千米 像素类型：32位有符号整数 数据投影：WGS 1984 镶嵌投影：WGS 1984 Web墨卡托（Web Mercator） 数据来源：联合国粮食及农业组织（Food and Agriculture Organization of the United Nations, FAO） 更新周期：每10日更新，滞后3-4天 VHI同时结合了植被状况指数（Vegetation Condition Index, VCI）与温度状况指数（Temperature Condition Index, TCI）。TCI的计算方程与VCI相似，但将当前温度与长期最高、最低温度进行关联，其假设前提为温度升高往往会导致植被生长状况恶化。例如，VHI降低可表征植被状况相对较差且温度偏高，意味着植被受到胁迫，长期来看则预示着干旱的发生。 在ASIS系统中，VHI以两种时间粒度进行计算：旬度与月度。本次发布的旬度/月度VHI栅格图层会在后续5个旬度内进行更新，以提升数据精度、去除云像元等。 栅格文件标识值如下：251=缺失值，252=云，253=积雪，254=海洋，255=背景值 可通过该Web应用探索此数据集及相关数据。更多信息请访问FAO GIEWS地球观测官网。