California Drought- Annual scPDSI 1896 to 2013

We used remotely sensed self calibrating Palmer Drought Severity Index (scPDSI), made available through the Western Regional Climate Center (www.wrcc.dri.edu/wwdt/data/PRISM/scpdsi/). The scPDSI ranges from -5.0 to 5.0. The number shows the magnitude and the sign denotes (+) wetter than average or (-) drier than average conditions for a location based on historical climate and sensitivity to changes in water availability. Absolute values greater than 4 represent extreme conditions and unlike earlier versions of the PDSI, extreme conditions occur based on the history of the location and are not determined relative to a default location. The scPDSI allows more exact comparisons between location and times and is a more accurate index compared to PDSI for extreme events. A detailed description of scPDSI can be found in Wells, N., Goddard, S., & Hayes, M. J. (2004). A self-calibrating Palmer Drought Severity Index. Journal of Climate, 17, 2335–2351.本研究采用了由西部区域气候中心（Western Regional Climate Center）公开发布的基于遥感反演的自校准帕默干旱严重度指数（self-calibrating Palmer Drought Severity Index, scPDSI），数据公开获取地址为www.wrcc.dri.edu/wwdt/data/PRISM/scpdsi/。该scPDSI的取值区间为-5.0至5.0，其数值代表干湿状况的量级，符号则用于表征某站点基于历史气候与水分供应变化敏感性的干湿状况：正号（+）表示该站点气候较历史平均水平更为湿润，负号（-）则表示气候较历史平均水平更为干旱。当scPDSI的绝对值大于4时，代表该站点处于极端干湿状况；与早期版本的帕默干旱严重度指数（Palmer Drought Severity Index, PDSI）不同，本指数的极端状况判定基于站点自身的历史气候序列，而非通过与默认站点的相对比较得出。相较于传统PDSI，scPDSI可实现不同站点与不同时段间更为精准的横向与纵向对比，且在极端气候事件的监测中具备更高的准确性。关于scPDSI的详细技术说明可参见下述文献：Wells N, Goddard S, Hayes M J. A self-calibrating Palmer Drought Severity Index. Journal of Climate, 2004, 17: 2335–2351。